Updated to a reference to a CPG on testosterone therapy in men with hypogonadism.
The male reproductive system regulates sex differentiation, androgenization, and the hormonal changes that accompany puberty, ultimately leading to spermatogenesis and fertility. Under the control of the pituitary hormones—luteinizing hormone (LH) and follicle-stimulating hormone (FSH)—the Leydig cells of the testes produce testosterone and germ cells are nurtured by Sertoli cells to divide, differentiate, and mature into sperm. During embryonic development, testosterone and dihydrotestosterone (DHT) induce the wolffian duct and virilization of the external genitalia. During puberty, testosterone promotes somatic growth and the development of secondary sex characteristics. In the adult, testosterone is necessary for spermatogenesis, libido and normal sexual function, and maintenance of muscle and bone mass. This chapter focuses on the physiology of the testes and disorders associated with decreased androgen production, which may be caused by gonadotropin deficiency or by primary testis dysfunction. A variety of testosterone formulations now allow more physiologic androgen replacement. Infertility occurs in ~5% of men and is increasingly amenable to treatment by hormone replacement or by using sperm transfer techniques. For further discussion of sexual dysfunction, disorders of the prostate, and testicular cancer, see Chaps. 390, 83, 84, respectively.
DEVELOPMENT AND STRUCTURE OF THE TESTIS
The fetal testis develops from the undifferentiated gonad after expression of a genetic cascade that is initiated by the SRY (sex-related gene on the Y chromosome) (Chap. 383). SRY induces differentiation of Sertoli cells, which surround germ cells and, together with peritubular myoid cells, form testis cords that will later develop into seminiferous tubules. Fetal Leydig cells and endothelial cells migrate into the gonad from the adjacent mesonephros but may also arise from interstitial cells that reside between testis cords. Fetal Leydig cells atrophy after birth and do not contribute to the origin of adult Leydig cells, which originate from undifferentiated progenitor cells that appear in the testis after birth and acquire full steroidogenic function during puberty. Testosterone produced by the fetal Leydig cells supports the growth and differentiation of wolffian duct structures that develop into the epididymis, vas deferens, and seminal vesicles. Testosterone is also converted to DHT (see below), which induces formation of the prostate and the external male genitalia, including the penis, urethra, and scrotum. Testicular descent through the inguinal canal is controlled in part by Leydig cell production of insulin-like factor 3 (INSL3), which acts via a receptor termed Great (G protein–coupled receptor affecting testis descent). Sertoli cells produce müllerian inhibiting substance (MIS), which causes regression of the müllerian structures, including the fallopian tube, uterus, and upper segment of the vagina.
NORMAL MALE PUBERTAL DEVELOPMENT
Puberty commonly refers to the maturation of the reproductive axis and the development of secondary sex characteristics. In addition to reproductive hormones, it requires a coordinated response of multiple hormonal systems including metabolic signals (e.g., leptin), as well as the adrenal and growth hormone (GH) axes (Fig. 384-1). The development of secondary sex characteristics is initiated by adrenarche, which usually occurs between 6 and 8 years of age when the adrenal gland begins to produce greater amounts of androgens from the zona reticularis, the principal site of dehydroepiandrosterone (DHEA) production. The sex maturation process is greatly accelerated by the activation of the hypothalamic-pituitary axis and the production of gonadotropin-releasing hormone (GnRH). The GnRH pulse generator in the hypothalamus is active during fetal life and early infancy, but is restrained until the early stages of puberty by a neuroendocrine brake imposed by the inhibitory actions of glutamate and γ–amino butyric acid (GABA) in the mediobasal hypothalamus, and neuropeptide Y. Although the pathways that initiate reactivation of the GnRH pulse generator at the onset of puberty remain incompletely understood, mounting evidence supports involvement of GPR54, a G protein–coupled receptor that binds an endogenous ligand, kisspeptin. Individuals with mutations of GPR54 fail to enter puberty, and experiments in primates demonstrate that infusion of the ligand is sufficient to induce premature puberty. Kisspeptin signaling plays an important role in mediating the feedback action of sex steroids on gonadotropin secretion and in regulating the tempo of sexual maturation at puberty. Leptin, a hormone produced by adipose cells, plays a permissive role in the resurgence of GnRH secretion at the onset of puberty, as leptin-deficient individuals also fail to enter puberty (Chap. 394). Adipocyte hormone leptin, gut hormone ghrelin, neuropeptide Y, and kisspeptin integrate the signals originating in energy stores and metabolic tissues with mechanisms that control onset of puberty through regulation of GnRH secretion. Energy deficit and excess, and metabolic stress are associated with disturbed reproductive maturation and timing of puberty.
Pubertal events in males. Sexual maturity ratings for genitalia and pubic hair and divided into five stages. (From WA Marshall, JM Tanner: Variations in the pattern of pubertal changes in boys. Arch Dis Child 45:13, 1970.)
The early stages of puberty are characterized by nocturnal surges of LH and FSH. Growth of the testes is usually the first clinical sign of puberty, reflecting an increase in seminiferous tubule volume. Increasing levels of testosterone deepen the voice and stimulate muscle growth. Conversion of testosterone to DHT leads to growth of the external genitalia and pubic hair. DHT also stimulates prostate and facial hair growth and initiates recession of the temporal hairline. The growth spurt occurs at a testicular volume of about 10–12 mL. GH increases early in puberty and is stimulated in part by the rise in gonadal steroids. GH increases the level of insulin-like growth factor 1 (IGF-1), which enhances linear bone growth. The prolonged pubertal exposure to gonadal steroids (mainly estradiol) ultimately induces epiphyseal closure and limits further bone growth.
REGULATION OF TESTICULAR FUNCTION
REGULATION OF THE HYPOTHALAMIC-PITUITARY-TESTIS AXIS IN ADULT MAN
Hypothalamic GnRH regulates the production of the pituitary gonadotropins, LH and FSH (Fig. 384-2). GnRH is released in discrete pulses approximately every 2 h, resulting in corresponding pulses of LH and FSH. These dynamic hormone pulses account in part for the wide variations in LH and testosterone, even within the same individual. LH acts primarily on the Leydig cell to stimulate testosterone synthesis. The regulatory control of androgen synthesis is modulated by dynamic integration of the feedforward elements exerted on the testis by LH and FSH, and the feedback exerted by testosterone and estrogen on both the hypothalamus and the pituitary. FSH acts on the Sertoli cell to regulate spermatogenesis and the production of Sertoli products such as inhibin B, which acts to selectively suppress pituitary FSH. Despite these somewhat distinct Leydig and Sertoli cell–regulated pathways, testis function is integrated at several levels: GnRH regulates both gonadotropins; spermatogenesis requires high levels of testosterone; numerous paracrine interactions between Leydig and Sertoli cells are necessary for normal testis function.
Hypothalamic pituitary gonadotropin axis, structure of testis, seminiferous tubule. E2, 17β-estradiol; DHT, dihydrotestosterone.
THE LEYDIG CELL: ANDROGEN SYNTHESIS
LH binds to its seven transmembrane, G protein–coupled receptor to activate the cyclic AMP pathway. Stimulation of the LH receptor induces steroid acute regulatory (StAR) protein, along with several steroidogenic enzymes involved in androgen synthesis. LH receptor mutations cause Leydig cell hypoplasia or agenesis, underscoring the importance of this pathway for Leydig cell development and function. The rate-limiting process in testosterone synthesis is the transport of intracellular cholesterol by the StAR protein to the inner mitochondrial membrane. Mutations of the StAR protein are associated with Congenital Lipoid Adrenal Hyperplasia, a rare form of congenital adrenal hyperplasia (CAH) characterized by very low adrenal and gonadal steroids. Peripheral benzodiazepine receptor, a mitochondrial cholesterol-binding protein, is also an acute regulator of Leydig cell steroidogenesis. The major enzymatic steps involved in testosterone synthesis are summarized in Fig. 384-3. After cholesterol transport into the mitochondrion, the formation of pregnenolone by CYP11A1 (side chain cleavage enzyme) is a limiting enzymatic step. The 17α-hydroxylase and the 17,20-lyase reactions are catalyzed by a single enzyme, CYP17; posttranslational modification (phosphorylation) of this enzyme and the presence of specific enzyme cofactors, such as cytochrome B, confer 17,20-lyase activity selectively in the testis and zona reticularis of the adrenal gland. Abiraterone is a dual inhibitor of 17 α-hydroxylase and 17,20-lyase activities, which play an important role in androgen synthesis in castration-resistant prostate cancers. Testosterone can be converted to the more potent DHT by a family of steroid 5α-reductase enzymes, or it can be aromatized to estradiol by CYP19 (aromatase). At least two isoforms of steroid 5α-reductase, SRD5A1 and SRD5A2, have been described; all known patients with 5α-reductase deficiency have had mutations in SRD5A2, the predominant form in the prostate and the skin. Finasteride predominantly inhibits SRD5A2, while dutasteride is a dual inhibitor of both SRD5A1 and SRD5A2. DHT can also be derived directly through the backdoor pathway in which 17 α-hydroxyprogesterone is converted through a series of 5 α and 3 α reductions to androsterone and eventually to DHT. Recent reports of mutations in AKR1C2/4 genes in undervirilized 46, XY individuals suggest that the backdoor pathway for DHT formation, which was originally described in the tammar wallaby, is active in the human fetal testis.
The biochemical pathway in the conversion of 27-carbon sterol cholesterol to androgens and estrogens.
Testosterone Transport and Metabolism
In males, 95% of circulating testosterone is derived from testicular production (3–10 mg/d). Direct secretion of testosterone by the adrenal and the peripheral conversion of androstenedione to testosterone collectively account for another 0.5 mg/d of testosterone. Only a small amount of DHT (70 μg/d) is secreted directly by the testis; most circulating DHT is derived from peripheral conversion of testosterone. Most of the daily production of estradiol (~45 μg/d) in men is derived from aromatase-mediated peripheral conversion of testosterone and androstenedione.
Circulating testosterone is bound predominantly to sex hormone–binding globulin (SHBG) and albumin (Fig. 384-4), and to a lesser extent to cortisol binding globulin (CBG), and orosomucoid. SHBG binds testosterone with much greater affinity than albumin, CBP, and orosomucoid. Only 1.0–4.0% of testosterone is unbound. According to the “free hormone” hypothesis, only the unbound fraction is biologically active. The term “bioavailable testosterone” refers to unbound testosterone plus testosterone bound loosely to albumin, and reflects the concept that albumin-bound testosterone can dissociate at the capillary level, especially in tissues with long transit time, such as the liver and the brain. SHBG-bound testosterone also may be internalized through endocytic pits by binding to a protein called megalin. SHBG concentrations are decreased by androgens, obesity, diabetes mellitus, hypothyroidism, nephrotic syndrome, and genetic factors. Conversely, estrogen administration, hyperthyroidism, many chronic inflammatory illnesses, infections such as HIV or hepatitis B and C, aging, and the use of some anticonvulsants are associated with high SHBG concentrations.
Androgen metabolism and actions. SHBG, sex hormone–binding globulin.
Testosterone is metabolized predominantly in the liver, although some degradation occurs in peripheral tissues, particularly the prostate and the skin. In the liver, testosterone is converted by a series of enzymatic steps that involve 5α- and 5β-reductases, 3α- and 3β-hydroxysteroid dehydrogenases, and 17β-hydroxysteroid dehydrogenase into androsterone, etiocholanolone, DHT, and 3-α-androstanediol. These compounds undergo glucuronidation or sulfation before being excreted by the kidneys.
Mechanism of Androgen Action
Testosterone exerts some of its biologic effects by binding to androgen receptor (AR), either directly or after its conversion to DHT by the steroid 5-α reductase. The actions of testosterone on the Wolffian structures, skeletal muscle, erythropoiesis, and bone in men do not require its obligatory conversion to DHT. However, the conversion of testosterone to DHT is necessary for the masculinization of the urogenital sinus and genital tubercle. Aromatization of testosterone to estradiol mediates additional effects of testosterone on the bone resorption, epiphyseal closure, sexual desire, vascular endothelium, and fat. DHT can also be converted in some tissues by 3-keto reductase/3β-hydroxysteroid dehydrogenase enzymes to 5α-androstane-3β,17β-diol, which is a high-affinity ligand and agonist of estrogen receptor ER β.
The AR is structurally related to the nuclear receptors for estrogen, glucocorticoids, and progesterone (Chap. 370). The AR is encoded by a gene on the long arm of the X chromosome and has a molecular mass of about 110 kDa. A polymorphic region in the amino terminus of the receptor, which contains a variable number of glutamine repeats, modifies the transcriptional activity of the receptor. The AR protein is distributed in both the cytoplasm and the nucleus. The ligand binding to the AR induces conformational changes that allow the recruitment and assembly of tissue-specific cofactors, and causes it to translocate into the nucleus, where it binds to specific androgen response elements in the DNA or other transcription factors already bound to DNA. Thus, the AR is a ligand-regulated transcription factor that regulates the expression of androgen-dependent genes in a tissue-specific manner. Some androgen effects, such as those on the smooth muscle, may be mediated by nongenomic AR signal transduction pathways. Testosterone binds to AR with half the affinity of DHT. The DHT-AR complex also has greater thermostability and a slower dissociation rate than the testosterone-AR complex. However, the molecular basis for selective testosterone versus DHT actions remains incompletely explained.
THE SEMINIFEROUS TUBULES: SPERMATOGENESIS
The seminiferous tubules are convoluted, closed loops with both ends emptying into the rete testis, a network of progressively larger efferent ducts that ultimately form the epididymis (Fig. 384-2). The seminiferous tubules total about 600 m in length and comprise about two-thirds of testis volume. The walls of the tubules are formed by polarized Sertoli cells that are apposed to peritubular myoid cells. Tight junctions between Sertoli cells create the blood-testis barrier. Germ cells comprise the majority of the seminiferous epithelium (~60%) and are intimately embedded within the cytoplasmic extensions of the Sertoli cells, which function as “nurse cells.” Germ cells progress through characteristic stages of mitotic and meiotic divisions. A pool of type A spermatogonia serve as stem cells capable of self-renewal. Primary spermatocytes are derived from type B spermatogonia and undergo meiosis before progressing to spermatids that undergo spermiogenesis (a differentiation process involving chromatin condensation, acquisition of an acrosome, elongation of cytoplasm, and formation of a tail) and are released from Sertoli cells as mature spermatozoa. The complete differentiation process into mature sperm requires 74 days. Peristaltic-type action by peritubular myoid cells transports sperm into the efferent ducts. The spermatozoa spend an additional 21 days in the epididymis, where they undergo further maturation and capacitation. The normal adult testes produce >100 million sperm per day.
Naturally occurring mutations in FSHβ or in the FSH receptor confirm an important, but not essential, role for this pathway in spermatogenesis. Females with mutations in FSHβ or the FSH receptor are hypogonadal and infertile because ovarian follicles do not mature; males with these mutations exhibit variable degrees of reduced spermatogenesis, presumably because of impaired Sertoli cell function. Because Sertoli cells produce inhibin B, an inhibitor of FSH, seminiferous tubule damage (e.g., by radiation) causes a selective increase of FSH. Testosterone reaches very high concentrations locally in the testis and is essential for spermatogenesis. The cooperative actions of FSH and testosterone are important in the progression of meiosis and spermiation. FSH and testosterone regulate germ cell survival via the intrinsic and the extrinsic apoptotic mechanisms. FSH may also play an important role in supporting spermatogonia. Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25), a testis-specific gonadotropin/androgen-regulated RNA helicase, is present in germ cells and Leydig cells and may be an important factor in the paracrine regulation of germ cell development. Several cytokines and growth factors are also involved in the regulation of spermatogenesis by paracrine and autocrine mechanisms. A number of knockout mouse models exhibit impaired germ cell development or spermatogenesis, presaging possible mutations associated with male infertility.
The human Y chromosome contains a small pseudoautosomal region that can recombine with homologous regions of the X chromosome. Most of the Y chromosome does not recombine with the X chromosome and is referred to as the male-specific region of the Y (MSY). The MSY contains 156 transcription units that encode for 26 proteins, including nine families of Y-specific multicopy genes; many of these Y-specific genes are also testis-specific and necessary for spermatogenesis. Microdeletions in several nonoverlapping subregions of the Y chromosome—AZFa, AZFb, AZFc and AZFd, which contain many spermatogenic genes (e.g., RNA-binding motif, RBM; deleted in azoospermia, DAZ)—are associated with oligospermia or azoospermia. Approximately 15% of infertile men with azoospermia and about 6% of men with severe oligozoospermia harbor a Y microdeletion. Microdeletions of the AZFa and AZFb subregions are typically associated with Sertoli cell only or maturation arrest histology, azoospermia, and poor prognosis for sperm retrieval. In contrast, AZFc subregion microdeletions are typically associated with oligozoospermia and higher success rates for sperm retrieval. Microdeletion involving the DAZ gene in the AZFc region is one of the commonest Y chromosome microdeletions in infertile men. A partial deletion of the AZFc region called the gr/gr deletion is associated with infertility among Caucasian men in Europe and the Western Pacific region.
TREATMENT Male Factor Infertility
Treatment options for male factor infertility have expanded greatly in recent years. Secondary hypogonadism is highly amenable to treatment with pulsatile GnRH or gonadotropins (see below). Assisted reproductive technologies, such as the in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), have provided new opportunities for patients with primary testicular failure and disorders of sperm transport. Choice of initial treatment options depends on sperm concentration and motility. Expectant management should be attempted initially in men with mild male factor infertility (sperm count of 15–20 × 106/mL and normal motility). Moderate male factor infertility (10–15 x 106/mL and 20–40% motility) should begin with intrauterine insemination alone or in combination with treatment of the female partner with clomiphene or gonadotropins, but it may require IVF with or without ICSI. For men with a severe defect (sperm count of <10 × 106/mL, 10% motility), IVF with ICSI or donor sperm has become the treatment of choice. Yq microdeletions will be transmitted through ICSI from the affected father to his male offspring if sperm carrying Yq microdeletion is used.
CLINICAL AND LABORATORY EVALUATION OF MALE REPRODUCTIVE FUNCTION
HISTORY AND PHYSICAL EXAMINATION
The history should focus on developmental stages such as puberty and growth spurts, as well as androgen-dependent events such as early morning erections, frequency and intensity of sexual thoughts, and frequency of masturbation or intercourse. Although libido and the overall frequency of sexual acts are decreased in androgen-deficient men, young hypogonadal men can achieve erections in response to visual erotic stimuli. Men with acquired androgen deficiency often report decreased energy and low mood.
The physical examination should focus on secondary sex characteristics such as hair growth, gynecomastia, testicular volume, prostate, and height and body proportions. Eunuchoid proportions are defined as an arm span >2 cm greater than height and suggest that androgen deficiency occurred before epiphyseal fusion. Hair growth in the face, axilla, chest, and pubic regions is androgen-dependent; however, changes may not be noticeable unless androgen deficiency is severe and prolonged. Ethnicity also influences the intensity of hair growth (Chap. 387). Testicular volume is best assessed by using a Prader orchidometer. Testes range from 3.5 to 5.5 cm in length, which corresponds to a volume of 12–25 mL. Advanced age does not influence testicular size, although the consistency becomes less firm. Asian men generally have smaller testes than western Europeans, independent of differences in body size. Because of its possible role in infertility, the presence of varicocele should be sought by palpation while the patient is standing; it is more common on the left side. Patients with Klinefelter syndrome have markedly reduced testicular volumes (1–2 mL). In congenital hypogonadotropic hypogonadism, testicular volumes provide a good index for the degree of gonadotropin deficiency and the likelihood of response to therapy.
GONADOTROPIN AND INHIBIN MEASUREMENTS
LH and FSH are measured using two-site immunoradiometric, immunofluorometric, or chemiluminescent assays, which have very low cross-reactivity with other pituitary glycoprotein hormones and human chorionic gonadotropin (hCG) and have sufficient sensitivity to measure the low levels present in patients with hypogonadotropic hypogonadism. In men with a low testosterone level, an LH level can distinguish primary (high LH) versus secondary (low or inappropriately normal LH) hypogonadism. An elevated LH level indicates a primary defect at the testicular level, whereas a low or inappropriately normal LH level suggests a defect at the hypothalamic-pituitary level. LH pulses occur about every 1–3 h in normal men. Thus, gonadotropin levels fluctuate, and samples should be pooled or repeated when results are equivocal. FSH is less pulsatile than LH because it has a longer half-life. Selective increase in FSH suggests damage to the seminiferous tubules. Inhibin B, a Sertoli cell product that suppresses FSH, is reduced with seminiferous tubule damage. Inhibin B is a dimer with α-βB subunits and is measured by two-site immunoassays.
The GnRH test is performed by measuring LH and FSH concentrations at baseline and at 30 and 60 min after intravenous administration of 100 μg of GnRH. A minimally acceptable response is a twofold LH increase and a 50% FSH increase. In the prepubertal period or with severe GnRH deficiency, the gonadotrope may not respond to a single bolus of GnRH because it has not been primed by endogenous hypothalamic GnRH; in these patients, GnRH responsiveness may be restored by chronic, pulsatile GnRH administration. With the availability of sensitive and specific LH assays, GnRH stimulation testing is used rarely.
Total testosterone includes both unbound and protein-bound testosterone and is measured by radioimmunoassays, immunometric assays, or liquid chromatography tandem mass spectrometry (LC-MS/MS). LC-MS/MS involves extraction of serum by organic solvents, separation of testosterone from other steroids by high-performance liquid chromatography and mass spectrometry, and quantitation of unique testosterone fragments by mass spectrometry. LC-MS/MS provides accurate and sensitive measurements of testosterone levels even in the low range and has emerged as the method of choice for testosterone measurement. The use of laboratories that have been certified by the Centers for Disease Control’s Hormone Standardization Program for Testosterone (HoST) can ensure that testosterone measurements are accurate and calibrated to an international standard. A single fasting morning sample provides a good approximation of the average testosterone concentration with the realization that testosterone levels fluctuate in response to pulsatile LH. Testosterone is generally lower in the late afternoon and is reduced by acute illness. The harmonized normal range for total testosterone, measured using LC-MS/MS in nonobese populations of European and American men, 19–39 years, is 264–916 ng/dL. This harmonized reference range can be applied to values from laboratories that are certified by the CDC’s Hormone Standardization Program for Testosterone.
Alterations in SHBG levels due to aging, obesity, diabetes mellitus, hyperthyroidism, some types of medications, chronic illness, or on a congenital basis, can affect total testosterone levels. Heritable factors contribute substantially to the population level variation in testosterone levels and genome wide association studies have revealed polymorphisms in SHBG gene as important contributors to variation in testosterone levels.
Measurement of Unbound Testosterone Levels
Most circulating testosterone is bound to SHBG and to albumin; only 1.0–4% of circulating testosterone is unbound, or “free.” Free testosterone should ideally be measured by equilibrium dialysis under standardized conditions using an accurate and reliable assay for total testosterone. The unbound testosterone concentration also can be calculated from total testosterone, SHBG, and albumin concentrations. Recent research has shown that testosterone binding to SHBG is a multi-step process that involves complex allosteric interactions between the two binding sites within the SHBG dimer; a novel ensemble allosteric model of testosterone’s binding to SHBG dimers provides good estimates of free testosterone concentrations. The previous law-of-mass action equations based on linear models of testosterone binding to SHBG used assumptions that have been shown to be erroneous. Tracer analogue methods are relatively inexpensive and convenient, but they are inaccurate. Bioavailable testosterone refers to unbound testosterone plus testosterone that is loosely bound to albumin; it can be determined by the ammonium sulfate precipitation method. However, the measurements of bioavailable testosterone using the ammonium sulfate precipitation are technically challenging, susceptible to imprecision, and are not recommended.
The hCG stimulation test is performed by administering a single injection of 1500–4000 IU of hCG intramuscularly and measuring testosterone levels at baseline and 24, 48, 72, and 120 h after hCG injection. An alternative regimen involves three injections of 1500 units of hCG on successive days and measuring testosterone levels 24 h after the last dose. An acceptable response to hCG is a doubling of the testosterone concentration in adult men. In prepubertal boys, an increase in testosterone to >150 ng/dL indicates the presence of testicular tissue. No response may indicate an absence of testicular tissue or marked impairment of Leydig cell function. Measurement of MIS, a Sertoli cell product, is also used to detect the presence of testes in prepubertal boys with cryptorchidism.
Semen analysis is the most important step in the evaluation of male infertility. Samples are collected by masturbation following a period of abstinence for 2–3 days. Semen volumes and sperm concentrations vary considerably among fertile men, and several samples may be needed before concluding that the results are abnormal. Analysis should be performed within an hour of collection. Using semen samples from over 4500 men in 14 countries, whose partners had a time-to-pregnancy of <12 months, WHO has generated the following one-sided reference limits for semen parameters: semen volume, 1.5 mL; total sperm number, 39 million per ejaculate; sperm concentration, 15 million per mL; vitality, 58% live; progressive motility, 32%; total (progressive + non-progressive) motility, 40%; morphologically normal forms, 4.0%. Some men with low sperm counts are nevertheless fertile. A variety of tests for sperm function can be performed in specialized laboratories, but these add relatively little to the treatment options.
Testicular biopsy is useful in some patients with oligospermia or azoospermia as an aid in diagnosis and indication for the feasibility of treatment. Using fine-needle aspiration biopsy is performed under local anesthesia to aspirate tissue for histology. Alternatively, open biopsies can be performed under local or general anesthesia when more tissue is required. A normal biopsy in an azoospermic man with a normal FSH level suggests obstruction of the vas deferens, which may be correctable surgically. Biopsies are also used to harvest sperm for ICSI and to classify disorders such as hypospermatogenesis (all stages present but in reduced numbers), germ cell arrest (usually at primary spermatocyte stage), and Sertoli cell–only syndrome (absent germ cells) or hyalinization (sclerosis with absent cellular elements).
Testing for Y Chromosome Microdeletions
Y chromosome microdeletions are detected by extracting DNA from peripheral blood leukocytes and using polymerase chain reaction (PCR) amplification using primers for some 300 sequence-tagged sites on the Y chromosome, followed by gel electrophoresis to determine whether the DNA sequences corresponding to the selected Y chromosome markers are present. However, because these ~300 Y chromosome markers account for only a small fraction of the 23 million base pairs on the Y chromosome, a negative test does not exclude microdeletions in other subregions of the Y chromosome.
DISORDERS OF SEXUAL DIFFERENTIATION
The onset and tempo of puberty varies greatly in the general population and is affected by genetic, nutritional, and environmental factors. Although a substantial fraction of the variance in the timing of puberty is explained by heritable factors, the genes involved remain unknown.
Puberty in boys aged <9 years is considered precocious. Isosexual precocity refers to premature sexual development consistent with phenotypic sex and includes features such as the development of facial hair and phallic growth. Isosexual precocity is divided into gonadotropin-dependent and gonadotropin-independent causes of androgen excess (Table 384-1). Heterosexual precocity refers to the premature development of estrogenic features in boys, such as breast development.
TABLE 384-1Causes of Precocious or Delayed Puberty in Boys ||Download (.pdf) TABLE 384-1 Causes of Precocious or Delayed Puberty in Boys
Hypothalamic hamartoma or other lesions
CNS tumor or inflammatory state
Congenital adrenal hyperplasia
Activating LH receptor mutation
Androgen producing tumors of the adrenal or the testis
Constitutional delay of growth and puberty
CNS tumors and their treatment (radiotherapy and surgery)
Hypothalamic-pituitary causes of pubertal failure (low gonadotropins)
Congenital disorders (Table 384-2)
Infiltrative disorders, such as hemachromatosis
Gonadal causes of pubertal failure (elevated gonadotropins)
Bilateral undescended testes
Chemotherapy or radiotherapy
Gonadotropin-Dependent Precocious Puberty
This disorder, called central precocious puberty (CPP), is less common in boys than in girls. It is caused by premature activation of the GnRH pulse generator, sometimes because of central nervous system (CNS) lesions such as hypothalamic hamartomas, but it is often idiopathic. CPP is characterized by gonadotropin levels that are inappropriately elevated for age. Because pituitary priming has occurred, GnRH elicits LH and FSH responses typical of those seen in puberty or in adults. MRI should be performed to exclude a mass, structural defect, infection, or inflammatory process. Mutations in kisspeptin, kisspeptin receptor, and MKRN3, an imprinted gene encoding makorin RING-finder protein 3, which is expressed only from the paternally inherited allele, have been associated with CPP. Loss of function mutations in MKRN3 remove the brake that restrains pulsatile GnRH, resulting in precocious puberty.
Gonadotropin-Independent Precocious Puberty
Androgens from the testis or the adrenal are increased but gonadotropins are low. This group of disorders includes hCG-secreting tumors; CAH; sex steroid–producing tumors of the testis, adrenal, and ovary; accidental or deliberate exogenous sex steroid administration; hypothyroidism; and activating mutations of the LH receptor or Gsα subunit.
Familial Male-Limited Precocious Puberty
Also called testotoxicosis, familial male-limited precocious puberty is an autosomal dominant disorder caused by activating mutations in the LH receptor, leading to constitutive stimulation of the cyclic AMP pathway and testosterone production. Clinical features include premature androgenization in boys, growth acceleration in early childhood, and advanced bone age followed by premature epiphyseal fusion. Testosterone is elevated, and LH is suppressed. Treatment options include inhibitors of testosterone synthesis (e.g., ketoconazole, medroxyprogesterone acetate), AR antagonists (e.g., flutamide and bicalutamide), and aromatase inhibitors (e.g., anastrozole).
This is a sporadic disorder caused by somatic (postzygotic) activating mutations in the Gsα subunit that links G protein–coupled receptors to intracellular signaling pathways (Chap. 405). The mutations impair the guanosine triphosphatase activity of the Gsα protein, leading to constitutive activation of adenylyl cyclase. Like activating LH receptor mutations, this stimulates testosterone production and causes gonadotropin-independent precocious puberty. In addition to sexual precocity, affected individuals may have autonomy in the adrenals, pituitary, and thyroid glands. Café au lait spots are characteristic skin lesions that reflect the onset of the somatic mutations in melanocytes during embryonic development. Polyostotic fibrous dysplasia is caused by activation of the parathyroid hormone receptor pathway in bone. Treatment is similar to that in patients with activating LH receptor mutations. Bisphosphonates have been used to treat bone lesions.
CONGENITAL ADRENAL HYPERPLASIA
Boys with CAH who are not well controlled with glucocorticoid suppression of adrenocorticotropic hormone (ACTH) can develop premature virilization because of excessive androgen production by the adrenal gland (Chaps. 379 and 383). LH is low, and the testes are small. Adrenal rests may develop within the testis of poorly controlled patients with CAH because of chronic ACTH stimulation; adrenal rests do not require surgical removal and regress with effective glucocorticoid therapy. Some children with CAH may develop gonadotropin-dependent precocious puberty with early maturation of the hypothalamic-pituitary-gonadal axis, elevated gonadotropins, and testicular growth.
Heterosexual Sexual Precocity
Breast enlargement in prepubertal boys can result from familial aromatase excess, estrogen-producing tumors in the adrenal gland, Sertoli cell tumors in the testis, marijuana smoking, or exogenous estrogens or androgens. Occasionally, germ cell tumors that secrete hCG can be associated with breast enlargement due to excessive stimulation of estrogen production (see “Gynecomastia,” below).
APPROACH TO THE PATIENT Precocious Puberty
After verification of precocious development, serum testosterone, LH and FSH levels should be measured to determine whether gonadotropins are increased in relation to chronologic age (gonadotropin-dependent) or whether sex steroid secretion is occurring independent of LH and FSH (gonadotropin-independent). In children with gonadotropin-dependent precocious puberty, CNS lesions should be excluded by history, neurologic examination, and MRI scan of the head. If organic causes are not found, one is left with the diagnosis of idiopathic central precocity. Patients with high testosterone but suppressed LH concentrations have gonadotropin-independent sexual precocity; in these patients, DHEA sulfate (DHEAS) and 17α-hydroxyprogesterone should be measured. High levels of testosterone and 17α-hydroxyprogesterone suggest the possibility of CAH due to 21α-hydroxylase or 11β-hydroxylase deficiency. If testosterone and DHEAS are elevated, adrenal tumors should be excluded by obtaining a CT scan of the adrenal glands. Patients with elevated testosterone but without increased 17α-hydroxyprogesterone or DHEAS should undergo careful evaluation of the testis by palpation and ultrasound to exclude a Leydig cell neoplasm. Activating mutations of the LH receptor should be considered in children with gonadotropin-independent precocious puberty in whom CAH, androgen abuse, and adrenal and testicular neoplasms have been excluded.
TREATMENT Precocious Puberty
In patients with a known cause (e.g., a CNS lesion or a testicular tumor), therapy should be directed towards the underlying disorder. In patients with idiopathic CPP, long-acting GnRH analogues can be used to suppress gonadotropins and decrease testosterone, halt early pubertal development, delay accelerated bone maturation, prevent early epiphyseal closure, promote final height gain, and mitigate the psychosocial consequences of early pubertal development without causing osteoporosis. The treatment is most effective for increasing final adult height if it is initiated before age 6. Puberty resumes after discontinuation of the GnRH analogue. Counseling is an important aspect of the overall treatment strategy.
In children with gonadotropin-independent precocious puberty, inhibitors of steroidogenesis, such as ketoconazole, AR antagonists, and aromatase inhibitors have been used empirically. Long-term treatment with spironolactone (a weak androgen antagonist) and ketoconazole has been reported to normalize growth rate and bone maturation and to improve predicted height in small, nonrandomized trials in boys with familial male-limited precocious puberty. Aromatase inhibitors, such as testolactone and letrozole, have been used as adjuncts to antiandrogen therapy for children with familial male-limited precocious puberty, CAH, and McCune-Albright syndrome. More potent novel inhibitors of testosterone synthesis, such as abiraterone, have not been evaluated in boys with gonadotropin-independent precocious puberty.
Puberty is delayed in boys if it has not ensued by age 14, an age that is 2–2.5 standard deviations above the mean for healthy children. Delayed puberty is more common in boys than in girls. There are four main categories of delayed puberty: (1) constitutional delay of growth and puberty (~60% of cases); (2) functional hypogonadotropic hypogonadism caused by systemic illness or malnutrition (~20% of cases); (3) hypogonadotropic hypogonadism caused by genetic or acquired defects in the hypothalamic-pituitary region (~10% of cases); and (4) hypergonadotropic hypogonadism secondary to primary gonadal failure (~15% of cases) (Table 384-1). The constitutional delay of growth and puberty clusters in families displays an autosomal dominant pattern of inheritance, and has been linked in some families with a locus on pericentromeric region of chromosome 2. Functional hypogonadotropic hypogonadism is more common in girls than in boys. Permanent causes of hypogonadotropic or hypergonadotropic hypogonadism are identified in <25% of boys with delayed puberty.
APPROACH TO THE PATIENT Delayed Puberty
History of systemic illness, eating disorders, excessive exercise, social and psychological problems, and abnormal patterns of linear growth during childhood should be verified. Boys with pubertal delay may have accompanying emotional and physical immaturity relative to their peers, which can be a source of anxiety. Physical examination should focus on height; arm span; weight; visual fields; and secondary sex characteristics, including hair growth, testicular volume, phallic size, and scrotal reddening and thinning. Testicular size >2.5 cm generally indicates that the child has entered puberty.
The main diagnostic challenge is to distinguish those with constitutional delay, who will progress through puberty at a later age, from those with an underlying pathologic process. Constitutional delay should be suspected when there is a family history and when there are delayed bone age and short stature. Pituitary priming by pulsatile GnRH is required before LH and FSH are synthesized and secreted normally. Thus, blunted responses to exogenous GnRH can be seen in patients with constitutional delay, GnRH deficiency, or pituitary disorders. On the other hand, low-normal basal gonadotropin levels or a normal response to exogenous GnRH is consistent with an early stage of puberty, which is often heralded by nocturnal GnRH secretion. Thus, constitutional delay is a diagnosis of exclusion that requires ongoing evaluation until the onset of puberty and the growth spurt.
TREATMENT Delayed Puberty
If therapy is considered appropriate, it can begin with 25–50 mg testosterone enanthate or testosterone cypionate every 2 weeks, or by using a 2.5-mg testosterone patch or 25-mg testosterone gel. Because aromatization of testosterone to estrogen is obligatory for mediating androgen effects on epiphyseal fusion, concomitant treatment with aromatase inhibitors may allow attainment of greater final adult height. Testosterone treatment should be interrupted after 6 months to determine if endogenous LH and FSH secretion have ensued. Other causes of delayed puberty should be considered when there are associated clinical features or when boys do not enter puberty spontaneously after a year of observation or treatment.
Reassurance without hormonal treatment is appropriate for many individuals with presumed constitutional delay of puberty. However, the impact of delayed growth and pubertal progression on a child’s social relationships and school performance should be weighed. The boys with constitutional delay of puberty are less likely to achieve their full genetic height potential and have reduced total body bone mass as adults, mainly due to narrow limb bones and vertebrae as a result of impaired periosteal expansion during puberty. Furthermore, the time of onset of puberty is negatively associated with bone mineral content and density in boys at skeletal maturity. Judicious use of androgen therapy in carefully selected boys with constitutional delay can induce pubertal induction and progression, and promote short-term growth without compromising final height, and when administered with an aromatase inhibitor, it may improve final height.
DISORDERS OF THE MALE REPRODUCTIVE AXIS DURING ADULTHOOD
Because LH and FSH are trophic hormones for the testes, impaired secretion of these pituitary gonadotropins results in secondary hypogonadism, which is characterized by low testosterone in the setting of low or inappropriately normal LH and FSH. Those with the most severe gonadotropin deficiency have complete absence of pubertal development, sexual infantilism, and, in some cases, hypospadias and undescended testes. Patients with partial gonadotropin deficiency have delayed or arrested sex development. The 24-h LH secretory profiles are heterogeneous in patients with hypogonadotropic hypogonadism, reflecting variable abnormalities of LH pulse frequency or amplitude. In severe cases, basal LH is low and there are no LH pulses. A smaller subset of patients has low-amplitude LH pulses or markedly reduced pulse frequency. Occasionally, only sleep-entrained LH pulses occur, reminiscent of the pattern seen in the early stages of puberty. Hypogonadotropic hypogonadism can be classified into congenital and acquired disorders. Congenital disorders most commonly involve GnRH deficiency, which leads to gonadotropin deficiency. Acquired disorders are much more common than congenital disorders and may result from a variety of sellar mass lesions or infiltrative diseases of the hypothalamus or pituitary, or due to the effects of drugs, nutritional or psychiatric disorders, or systemic diseases.
Congenital Disorders Associated with Gonadotropin Deficiency
Congenital hypogonadotropic hypogonadism is a heterogeneous group of disorders characterized by decreased gonadotropin secretion and testicular dysfunction either due to impaired function of the GnRH pulse generator or the gonadotrope. The disorders characterized by GnRH deficiency represent a family of oligogenic disorders whose phenotype spans a wide spectrum. Some individuals with GnRH deficiency may suffer from complete absence of pubertal development, while others may manifest varying degrees of gonadotropin deficiency and pubertal delay, and a subset that carries the same mutations as their affected family members may even have normal reproductive function. In ~10% of men with idiopathic hypogonadotropic hypogonadism (IHH), reversal of gonadotropin deficiency may occur in adult life after sex steroid therapy. Also, a small fraction of men with IHH may present with androgen deficiency and infertility in adult life after having gone through apparently normal pubertal development. Nutritional, emotional, or metabolic stress may unmask gonadotropin deficiency and reproductive dysfunction (e.g., hypothalamic amenorrhea) in some patients who harbor mutations in the candidate genes but who previously had normal reproductive function. The clinical phenotype may include isolated anosmia or hyposmia. Oligogenicity, and gene-gene and gene-environment interactions may contribute to variations in clinical phenotype.
Mutations in a number of genes involved in the development and migration of GnRH neurons, or in the regulation of GnRH secretion have been linked to GnRH deficiency, although the genetic defect remains elusive in nearly two thirds of cases. Familial hypogonadotropic hypogonadism can be transmitted as an X-linked (20%), autosomal recessive (30%), or autosomal dominant (50%) trait. Some individuals with IHH have sporadic mutations in the same genes that cause inherited forms of the disorder. The genetic defects associated with GnRH deficiency can ben conveniently classified as anosmic (Kallmann syndrome) or normosmic (Table 384-2), although the occurrence of both anosmic and normosmic forms of GnRH deficiency in the same families suggests commonality of pathophysiologic mechanisms. Kallmann syndrome, the anosmic form of GnRH deficiency, can result from mutations in one or more genes associated with olfactory bulb morphogenesis and the migration of GnRH neurons from their origin in the region of the olfactory placode, along the scaffold established by the olfactory nerves, through the cribriform plate into their final location into the pre-optic region of the hypothalamus. Thus, mutations in KAL1, genes involved in fibroblast growth factor (FGF) signaling (FGF8, FGFR1, FGF17, IL17RD, DUSP6, SPRY4, and FLRT3), NELF, genes involved in PROK signaling (PROK2 and PROK2R), WDR11, SEMA3, HS6ST1, CHD7, and FEZF1 have been described in patients with Kallmann syndrome. An X-linked form of IHH is caused by mutations in the KAL1 gene, which encodes anosmin, a protein that mediates the migration of neural progenitors of the olfactory bulb and GnRH-producing neurons. These individuals have GnRH deficiency and variable combinations of anosmia or hyposmia, renal defects, and neurologic abnormalities including mirror movements. Proteins such as those involved in FGF and prokineticin signaling, and KAL1, which account for the great majority of Kallmann syndrome cases, interact with heparin sulfate glycosominoglycan compounds within the extracellular matrix in promoting GnRH neuronal migration. Mutations in the FGFR1 gene cause an autosomal dominant form of hypogonadotropic hypogonadism that clinically resembles Kallmann syndrome; mutations in its putative ligand, the FGF8 gene product have also been associated with IHH. Craniofacial tissues and olfactory ensheathing cells also play important roles in neurogenesis and migration of the GnRH neurons, and additional proteins that regulate these cell types may also be involved in the pathogenesis of Kallmann syndrome. The co-occurrence of tooth anomalies, cleft palate, craniofacial anomalies, pigmentation, and other neurological defects in patients with Kallmann Syndrome suggest that the syndrome may be a part of the spectrum of neurocristopathies.
TABLE 384-2Causes of Congenital Hypogonadotropic Hypogonadism ||Download (.pdf) TABLE 384-2 Causes of Congenital Hypogonadotropic Hypogonadism
|Gene ||Locus ||Inheritance ||Associated Features |
|A. Hypogonadotropic Hypogonadism due to GnRH Deficiency |
|A1. GnRH Deficiency Associated with Hyposmia or Anosmia |
|KAL1 ||Xp22 ||X-linked ||Anosmia, renal agenesis, synkinesia, cleft lip/palate, oculomotor/visuospatial defects, gut malformations |
|NELF ||9q34.3 ||AR ||Anosmia, hypogonadotropic hypogonadism |
|FGF8 ||10q24 ||AR ||Anosmia (some patients may be normosmic), skeletal abnormalities |
|FGFR1 ||8p11-p12 ||AD ||Anosmia, cleft lip/palate, synkinesia, syndactyly |
|PROK2 ||3p21 ||AR ||Anosmia/ sleep dysregulation |
|PROK2R ||20p12.3 ||AR ||Variable |
|CHD7 ||8q12.1 || ||Anosmia, other features of CHARGE syndrome |
|FEZ1 ||8p22 ||AR ||Anosmia, olfactory bulb aplasia |
|WDR11 ||10q26 ||AD ||Anosmia |
|SOX10 ||22q13 || ||Deafness |
|SEMA3A ||7q21 || ||Anosmia; some persons with mutations are normal |
|HS6ST1 ||2q14 ||complex ||Anosmia |
|A2. GnRH Deficiency with Normal Sense of Smell |
|GNRHR ||4q21 ||AR ||None |
|GnRH1 ||8p21 ||AR ||None |
|KISS1R ||19p13 ||AR ||None |
|TAC3 ||12q13 ||AR ||Microphallus, cryptorchidism, reversal of GnRH deficiency |
|TAC3R ||4q25 ||AR ||Microphallus, cryptorchidism, reversal of GnRH deficiency |
|LEPR ||1p31 ||AR ||Obesity |
|LEP ||7q31 ||AR ||Obesity |
|B. Hypogonadotropic Hypogonadism not due to GnRH Deficiency |
|PC1 ||5q15-21 ||AR ||Obesity, diabetes mellitus, ACTH deficiency |
|HESX1 ||3p21 || |
Septooptic dysplasia, CPHD
Isolated GH insufficiency
|LHX3 ||9q34 ||AR ||CPHD (ACTH spared), cervical spine rigidity |
|PROP1 ||5q35 ||AR ||CPHD (ACTH usually spared) |
|FSHβ ||11p13 ||AR ||↑ LH |
|LHβ ||19q13 ||AR ||↑ FSH |
|SF1 (NR5A1) ||9p33 ||AD/AR ||Primary adrenal failure, XY sex reversal |
Normosmic GnRH deficiency results from defects in pulsatile GnRH secretion, its regulation, or its action on the gonadotrope and has been associated with mutations in GnRHR, GNRH1, KISS1R, TAC3, TACR3, NROB1 (DAX1). Some mutations, such as those in PROK2, PROKR2, and CHD7 have been associated with both anosmic as well as normosmic form of IHH. GnRH receptor mutations, the most frequent identifiable cause of normosmic IHH, account for ~40% of autosomal recessive and 10% of sporadic cases of hypogonadotropic hypogonadism. These patients have decreased LH response to exogenous GnRH. Some receptor mutations alter GnRH binding affinity, allowing apparently normal responses to pharmacologic doses of exogenous GnRH, whereas other mutations may alter signal transduction downstream of hormone binding. Mutations of the GnRH1 gene have also been reported in patients with hypogonadotropic hypogonadism, although they are rare. G protein–coupled receptor KISS1R (GPR54) and its cognate ligand, kisspeptin (KISS1), are important regulators of sexual maturation in primates. Recessive mutations in GPR54 cause gonadotropin deficiency without anosmia. Patients retain responsiveness to exogenous GnRH, suggesting an abnormality in the neural pathways controlling GnRH release. The genes encoding neurokinin B (TAC3), which is involved in preferential activation of GnRH release in early development, and its receptor (TAC3R) have been implicated in some families with normosmic IHH. X-linked hypogonadotropic hypogonadism also occurs in adrenal hypoplasia congenita, a disorder caused by mutations in the DAX1 gene, which encodes a nuclear receptor in the adrenal gland and reproductive axis. Adrenal hypoplasia congenita is characterized by absent development of the adult zone of the adrenal cortex, leading to neonatal adrenal insufficiency. Puberty usually does not occur or is arrested, reflecting variable degrees of gonadotropin deficiency. Although sexual differentiation is normal, some patients have testicular dysgenesis and impaired spermatogenesis despite gonadotropin replacement. Less commonly, adrenal hypoplasia congenita, sex reversal, and hypogonadotropic hypogonadism can be caused by mutations of steroidogenic factor 1 (SF1). Rarely, recessive mutations in the LHβ or FSHβ genes have been described in patients with selective deficiencies of these gonadotropins.
A number of homeodomain transcription factors are involved in the development and differentiation of the specialized hormone-producing cells within the pituitary gland (Table 384-2). Patients with mutations of PROP1 have combined pituitary hormone deficiency that includes GH, prolactin (PRL) thyroid-stimulating hormone (TSH), LH, and FSH, but not ACTH. LHX3 mutations cause combined pituitary hormone deficiency in association with cervical spine rigidity. HESX1 mutations cause septooptic dysplasia and combined pituitary hormone deficiency. Mutations of ARNT1, inherited as an autosomal recessive disorder, are associated with diabetes insipidus, ACTH deficiency, GH, LH, FSH deficiency, anterior pituitary hypoplasia, hypoplastic frontal and temporal lobes, thin corpus callosum, prominent forehead, and retrognathia. Patients with SOX2 mutations can have gonadotropin deficiency, variable deficiencies of TSH and ACTH, pituitary hypoplasia, microphthalmia, and intellectual disability.
Prader-Willi syndrome is characterized by obesity, hypotonic musculature, mental retardation, hypogonadism, short stature, and small hands and feet. Prader-Willi syndrome is a genomic imprinting disorder caused by deletions of the proximal portion of paternally derived chromosome 15q11-15q13 region, which contains a bipartite imprinting center; uniparental disomy of the maternal alleles; or mutations of the genes/loci involved in imprinting (Chap. 456). Laurence-Moon syndrome is an autosomal recessive disorder characterized by obesity, hypogonadism, mental retardation, polydactyly, and retinitis pigmentosa. Recessive mutations of leptin, or its receptor, cause severe obesity and pubertal arrest, apparently because of hypothalamic GnRH deficiency (Chap. 394).
Acquired Hypogonadotropic Disorders
SEVERE ILLNESS, STRESS, MALNUTRITION, AND EXERCISE
These may cause reversible gonadotropin deficiency. Although gonadotropin deficiency and reproductive dysfunction are well documented in these conditions in women, men exhibit similar but less-pronounced responses. Unlike women, most male runners and other endurance athletes have normal gonadotropin and sex steroid levels, despite low body fat and frequent intensive exercise. Testosterone levels fall at the onset of illness and recover during recuperation. The magnitude of gonadotropin suppression generally correlates with the severity of illness. Although hypogonadotropic hypogonadism is the most common cause of androgen deficiency in patients with acute illness, some have elevated levels of LH and FSH, which suggest primary gonadal dysfunction. The pathophysiology of reproductive dysfunction during acute illness is unknown but likely involves a combination of cytokine and/or glucocorticoid effects. There is a high frequency of low testosterone levels in patients with chronic illnesses such as HIV infection, end-stage renal disease, chronic obstructive lung disease, and many types of cancer and in patients receiving glucocorticoids. About 20% of HIV-infected men with low testosterone levels have elevated LH and FSH levels; these patients presumably have primary testicular dysfunction. The remaining 80% have either normal or low LH and FSH levels; these men have a central hypothalamic-pituitary defect or a dual defect involving both the testis and the hypothalamic-pituitary centers. Muscle wasting is common in chronic diseases associated with hypogonadism, which also leads to debility, poor quality of life, and adverse outcome of disease. There is great interest in exploring strategies that can reverse androgen deficiency or attenuate the sarcopenia associated with chronic illness.
Men using opioids for relief of cancer or noncancerous pain or because of addiction often have suppressed testosterone and LH levels and high prevalence of sexual dysfunction and osteoporosis; the degree of suppression is dose-related and particularly severe with long acting opioids such as methadone. Opioids suppress GnRH secretion and alter the sensitivity to feedback inhibition by gonadal steroids. Men who are heavy users of marijuana have decreased testosterone secretion and sperm production. The mechanism of marijuana-induced hypogonadism is decreased GnRH secretion. Gynecomastia observed in marijuana users can also be caused by plant estrogens in crude preparations. Androgen deprivation therapy in men with prostate cancer has been associated with increased risk of bone fractures, diabetes mellitus, cardiovascular events, fatigue, sexual dysfunction, tender gynecomastia, and poor quality of life.
In men with mild to moderate obesity, SHBG levels decrease in proportion to the degree of obesity, resulting in lower total testosterone levels. However, free testosterone levels usually remain within the normal range. SHBG production in the liver is inhibited by hepatic lipids, and by TNF-α and interleukin-1, but it is not affected by insulin. Thus, the low SHBG levels seen in obesity and diabetes are likely the result of low grade inflammation and the increased amount of hepatic lipids rather than high insulin levels. Estradiol levels are higher in obese men compared to healthy, nonobese controls, because of aromatization of testosterone to estradiol in adipose tissue. Weight loss is associated with reversal of these abnormalities including an increase in total and free testosterone levels and a decrease in estradiol levels. A subset of obese men with moderate to severe obesity may have a defect in the hypothalamic-pituitary axis as suggested by low free testosterone in the absence of elevated gonadotropins. Weight gain in adult men can accelerate the rate of age-related decline in testosterone levels.
(See also Chap. 373) Elevated PRL levels are associated with hypogonadotropic hypogonadism. PRL inhibits hypothalamic GnRH secretion either directly or through modulation of tuberoinfundibular dopaminergic pathways. A PRL-secreting tumor may also destroy the surrounding gonadotropes by invasion or compression of the pituitary stalk. Treatment with dopamine agonists reverses gonadotropin deficiency, although there may be a delay relative to PRL suppression.
Neoplastic and nonneoplastic lesions in the hypothalamus or pituitary can directly or indirectly affect gonadotrope function. In adults, pituitary adenomas constitute the largest category of space-occupying lesions affecting gonadotropin and other pituitary hormone production. Pituitary adenomas that extend into the suprasellar region can impair GnRH secretion and mildly increase PRL secretion (usually <50 μg/L) because of impaired tonic inhibition by dopaminergic pathways. These tumors that cause hyperprolactinemia by stalk compression should be distinguished from prolactinomas, which typically are associated with higher PRL levels. The presence of diabetes insipidus suggests the possibility of a craniopharyngioma, infiltrative disorder, or other hypothalamic lesions (Chap. 374).
(See also Chap. 407) Both the pituitary and testis can be affected by excessive iron deposition. However, the pituitary defect is the predominant lesion in most patients with hemochromatosis and hypogonadism. The diagnosis of hemochromatosis is suggested by the association of characteristic skin discoloration, hepatic enlargement or dysfunction, diabetes mellitus, arthritis, cardiac conduction defects, and hypogonadism.
PRIMARY TESTICULAR CAUSES OF HYPOGONADISM
Common causes of primary testicular dysfunction include Klinefelter syndrome, uncorrected cryptorchidism, cancer chemotherapy, radiation to the testes, trauma, torsion, infectious orchitis, HIV infection, anorchia syndrome, and myotonic dystrophy. Primary testicular disorders may be associated with impaired spermatogenesis, decreased androgen production, or both. See Chap. 383 for disorders of testis development, androgen synthesis, and androgen action.
(See also Chap. 383) Klinefelter syndrome is the most common chromosomal disorder associated with testicular dysfunction and male infertility. It occurs in about 1 in 600 live-born males. Azoospermia is the rule in men with Klinefelter syndrome who have the 47,XXY karyotype; however, men with mosaicism may have germ cells, especially at a younger age. The clinical phenotype of Klinefelter syndrome can be variable, possibly because of mosaicism, polymorphisms in AR gene, the parental origin of the X chromosome, X-linked copy number variations, gene-dosage effects in conjunction with X chromosome inactivation, variable testosterone levels, or other genetic factors. Testicular histology shows hyalinization of seminiferous tubules and absence of spermatogenesis. Although their function is impaired, the number of Leydig cells appears to increase. Testosterone is decreased and estradiol is increased, leading to clinical features of undervirilization and gynecomastia. Men with Klinefelter syndrome are at increased risk of systemic lupus erythematosus, Sjögren’s syndrome, breast cancer, diabetes mellitus, osteoporosis, non-Hodgkin’s lymphoma, and some types of lung cancer, and reduced risk of prostate cancer. Periodic mammography for breast cancer surveillance is recommended for men with Klinefelter syndrome. Fertility can be achieved by intracytoplasmic injection of sperm retrieved surgically from the testes of men with Klinefelter syndrome, including some men with nonmosaic form of Klinefelter syndrome. The karyotypes 48,XXXY and 49,XXXXY are associated with a more severe phenotype, increased risk of congenital malformations, and lower intelligence than 47,XXY individuals.
Cryptorchidism occurs when there is incomplete descent of the testis from the abdominal cavity into the scrotum. About 3% of full-term and 30% of premature male infants have at least one undescended testis at birth, but descent is usually complete by the first few weeks of life. The incidence of cryptorchidism is <1% by 9 months of age. Androgens regulate predominantly the inguinoscrotal descent of the testes through degeneration of the cranio-suspensory ligament and a shortening of the gubernaculums, respectively. Mutations in INSL3 and leucine-rich repeat family of G-protein-coupled receptor 8 (LGR8), which regulate transabdominal portion of testicular descent, have been found in some patients with cryptorchidism.
Cryptorchidism is associated with increased risk of malignancy, infertility, inguinal hernia, and torsion. Unilateral cryptorchidism, even when corrected before puberty, is associated with decreased sperm count, possibly reflecting unrecognized damage to the fully descended testis or other genetic factors. Epidemiologic, clinical, and molecular evidence supports the idea that cryptorchidism, hypospadias, impaired spermatogenesis, and testicular cancer may be causally related to common genetic and environment perturbations, and are components of the testicular dysgenesis syndrome.
Acquired Testicular Defects
Viral orchitis may be caused by the mumps virus, echovirus, lymphocytic choriomeningitis virus, and group B arboviruses. Orchitis occurs in as many as one-fourth of adult men with mumps; the orchitis is unilateral in about two-thirds and bilateral in the remainder. Orchitis usually develops a few days after the onset of parotitis but may precede it. The testis may return to normal size and function or undergo atrophy. Semen analysis returns to normal for three-fourths of men with unilateral involvement but normal for only one-third of men with bilateral orchitis. Trauma, including testicular torsion, can also cause secondary atrophy of the testes. The exposed position of the testes in the scrotum renders them susceptible to both thermal and physical trauma, particularly in men with hazardous occupations.
The testes are sensitive to radiation damage. Doses >200 mGy (20 rad) are associated with increased FSH and LH levels and damage to the spermatogonia. After ~800 mGy (80 rad), oligospermia or azoospermia develops, and higher doses may obliterate the germinal epithelium. Permanent androgen deficiency in adult men is uncommon after therapeutic radiation; however, most boys given direct testicular radiation therapy for acute lymphoblastic leukemia have permanently low testosterone levels. Sperm banking should be considered before patients undergo radiation treatment or chemotherapy.
Drugs interfere with testicular function by several mechanisms, including inhibition of testosterone synthesis (e.g., ketoconazole), blockade of androgen action (e.g., spironolactone), increased estrogen (e.g., marijuana), or direct inhibition of spermatogenesis (e.g., chemotherapy).
Combination chemotherapy for acute leukemia, Hodgkin’s disease, and testicular and other cancers may impair Leydig cell function and cause infertility. The degree of gonadal dysfunction depends on the type of chemotherapeutic agent and the dose and duration of therapy. Because of high response rates and the young age of these men, infertility and androgen deficiency have emerged as important long-term complications of cancer chemotherapy. Cyclophosphamide and combination regimens containing procarbazine are particularly toxic to germ cells. Thus, 90% of men with Hodgkin’s lymphoma receiving MOPP (mechlorethamine, oncovin, procarbazine, prednisone) therapy develop azoospermia or extreme oligozoospermia; newer regimens that do not include procarbazine, such as ABVD (adriamycin, bleomycin, vinblastine, dacarbazine), are less toxic to germ cells.
Alcohol, when consumed in excess for prolonged periods, decreases testosterone, independent of liver disease or malnutrition. Elevated estradiol and decreased testosterone levels may occur in men taking digitalis.
The occupational and recreational history should be carefully evaluated in all men with infertility because of the toxic effects of many chemical agents on spermatogenesis. Known environmental hazards include pesticides (e.g., vinclozolin, dicofol, atrazine), sewage contaminants (e.g., ethinyl estradiol in birth control pills, surfactants such as octylphenol, nonyphenol), plasticizers (e.g., pthalates), flame retardants (PCBs, polybrominated diphenol ethers), industrial pollutants (e.g., heavy metals cadmium and lead, dioxins, polycyclic aromatic hydrocarbons), microwaves and ultrasound. In some populations, sperm density is said to have declined by as much as 40% in the past 50 years. Environmental estrogens or antiandrogens may be partly responsible.
Testicular failure also occurs as a part of polyglandular autoimmune insufficiency (Chap. 381). Sperm antibodies can cause isolated male infertility. In some instances, these antibodies are secondary phenomena resulting from duct obstruction or vasectomy. Granulomatous diseases can affect the testes, and testicular atrophy occurs in 10–20% of men with lepromatous leprosy because of direct tissue invasion by the mycobacteria. The tubules are involved initially, followed by endarteritis and destruction of Leydig cells.
Systemic disease can cause primary testis dysfunction in addition to suppressing gonadotropin production. In cirrhosis, a combined testicular and pituitary abnormality leads to decreased testosterone production independent of the direct toxic effects of ethanol. Impaired hepatic extraction of adrenal androstenedione leads to extraglandular conversion to estrone and estradiol, which partially suppresses LH. Testicular atrophy and gynecomastia are present in approximately one-half of men with cirrhosis. In chronic renal failure, androgen synthesis and sperm production decrease despite elevated gonadotropins. The elevated LH level is due to reduced clearance, but it does not restore normal testosterone production. About one-fourth of men with renal failure have hyperprolactinemia. Improvement in testosterone production with hemodialysis is incomplete, but successful renal transplantation may return testicular function to normal. Testicular atrophy is present in one-third of men with sickle cell anemia. The defect may be at either the testicular or the hypothalamic-pituitary level. Sperm density can decrease temporarily after acute febrile illness in the absence of a change in testosterone production. Infertility in men with celiac disease is associated with a hormonal pattern typical of androgen resistance, namely elevated testosterone and LH levels.
Neurologic diseases associated with altered testicular function include myotonic dystrophy, spinobulbar muscular atrophy, and paraplegia. In myotonic dystrophy, small testes may be associated with impairment of both spermatogenesis and Leydig cell function. Spinobulbar muscular atrophy is caused by an expansion of the glutamine repeat sequences in the amino-terminal region of the AR; this expansion impairs function of the AR, but it is unclear how the alteration is related to the neurologic manifestations. Men with spinobulbar muscular atrophy often have undervirilization and infertility as a late manifestation. Spinal cord injury that causes paraplegia is often associated with low testosterone levels and may cause persistent defects in spermatogenesis; some patients retain the capacity for penile erection and ejaculation.
ANDROGEN INSENSITIVITY SYNDROMES
Mutations in the AR cause resistance to the action of testosterone and DHT. These X-linked mutations are associated with variable degrees of defective male phenotypic development and undervirilization (Chap. 383). Although not technically hormone-insensitivity syndromes, two genetic disorders impair testosterone conversion to active sex steroids. Mutations in the SRD5A2 gene, which encodes 5α-reductase type 2, prevent the conversion of testosterone to DHT, which is necessary for the normal development of the male external genitalia. Mutations in the CYP19 gene, which encodes aromatase, prevent testosterone conversion to estradiol. Males with CYP19 mutations have delayed epiphyseal fusion, tall stature, eunuchoid proportions, visceral adiposity, and osteoporosis, consistent with evidence from an estrogen receptor–deficient individual that these testosterone actions are mediated via estrogen.
Gynecomastia refers to enlargement of the male breast. It is caused by excess estrogen action and is usually the result of an increased estrogen/androgen ratio. True gynecomastia is associated with glandular breast tissue that is >4 cm in diameter and often tender. Glandular tissue enlargement should be distinguished from excess adipose tissue: glandular tissue is firmer and contains fibrous-like cords. Gynecomastia occurs as a normal physiologic phenomenon in the newborn (due to transplacental transfer of maternal and placental estrogens), during puberty (high estrogen to androgen ratio in early stages of puberty), and with aging (increased fat tissue and increased aromatase activity along with the age-related decline in testosterone levels), but it can also result from pathologic conditions associated with androgen deficiency or estrogen excess. The prevalence of gynecomastia increases with age and body mass index (BMI), likely because of increased aromatase activity in adipose tissue. Medications that alter androgen metabolism or action may also cause gynecomastia. The relative risk of breast cancer is increased in men with gynecomastia, although the absolute risk is relatively small.
Any cause of androgen deficiency can lead to gynecomastia, reflecting an increased estrogen/androgen ratio, as estrogen synthesis still occurs by aromatization of residual adrenal and gonadal androgens. Gynecomastia is a characteristic feature of Klinefelter syndrome (Chap. 383). Androgen insensitivity disorders also cause gynecomastia. Excess estrogen production may be caused by tumors, including Sertoli cell tumors in isolation or in association with Peutz-Jegher syndrome or Carney complex. Tumors that produce hCG, including some testicular tumors, stimulate Leydig cell estrogen synthesis. Increased conversion of androgens to estrogens can be a result of increased availability of substrate (androstenedione) for extraglandular estrogen formation (CAH, hyperthyroidism, and most feminizing adrenal tumors) or to diminished catabolism of androstenedione (liver disease) so that estrogen precursors are shunted to aromatase in peripheral sites. Obesity is associated with increased aromatization of androgen precursors to estrogens. Extraglandular aromatase activity can also be increased in tumors of the liver or adrenal gland or rarely as an inherited disorder. Several families with increased peripheral aromatase activity inherited as an autosomal dominant or as an X-linked disorder have been described. In some families with this disorder, an inversion in chromosome 15q21.2-3 causes the CYP19 gene to be activated by the regulatory elements of contiguous genes resulting in excessive estrogen production in the fat and other extragonadal tissues. The familial aromatase excess syndrome due to CYP19 mutation or chromosomal rearrangement is characterized by pre- or peripubertal onset of gynecomastia, advanced bone age, short adult height due to premature epiphyseal closure, and hypogonadotropic hypogonadism. Drugs can cause gynecomastia by acting directly as estrogenic substances (e.g., oral contraceptives, phytoestrogens, digitalis), inhibiting androgen synthesis (e.g., ketoconazole), or action (e.g., spironolactone); for many drugs, such as cimetidine, imatinib, or some antiretroviral drugs for HIV, the precise mechanism is unknown.
Because up to two-thirds of pubertal boys and about half of hospitalized men have palpable glandular tissue that is benign, detailed investigation or intervention is not indicated in all men presenting with gynecomastia (Fig. 384-5). In addition to the extent of gynecomastia, recent onset, rapid growth, tender tissue, and occurrence in a lean subject should prompt more extensive evaluation. This should include a careful drug history, measurement and examination of the testes, assessment of virilization, evaluation of liver function, and hormonal measurements including testosterone, estradiol, and androstenedione, LH, and hCG. A karyotype should be obtained in men with very small testes to exclude Klinefelter syndrome. In spite of extensive evaluation, the etiology is established in fewer than one-half of patients.
Evaluation of gynecomastia. E2, 17β-estradiol; FSH, follicle-stimulating hormones; hCGβ, human chorionic gonadotropin β; LH, luteinizing hormone; T, testosterone.
When the primary cause can be identified and corrected shortly after the onset of gynecomastia, breast enlargement usually subsides over several months. However, if gynecomastia is of long duration, surgery is the most effective therapy. Indications for surgery include severe psychological and/or cosmetic problems, continued growth or tenderness, or suspected malignancy. In patients who have painful gynecomastia and in whom surgery cannot be performed, treatment with antiestrogens such as tamoxifen (20 mg/d) can reduce pain and breast tissue size in over half the patients. Estrogen receptor antagonists, tamoxifen and raloxifen, have been reported in small trials to reduce breast size in men with pubertal gynecomastia, although complete regression of breast enlargement is unusual with the use of estrogen receptor antagonists. Aromatase inhibitors can be effective in the early proliferative phase of the disorder. However, in a randomized trial in men with established gynecomastia, anastrozole proved no more effective than placebo in reducing breast size. Tamoxifen is effective in prevention and treatment of breast enlargement and breast pain in men with prostate cancer who are receiving anti-androgen therapy.
AGING-RELATED CHANGES IN MALE REPRODUCTIVE FUNCTION
A number of cross-sectional and longitudinal studies (e.g., The Baltimore Longitudinal Study of Aging, the Framingham Heart Study, the Massachusetts Male Aging Study, and the European Male Aging Study [EMAS]) have established that testosterone concentrations decrease with advancing age. This age-related decline starts in the third decade of life and progresses slowly; the rate of decline in testosterone concentrations is greater in obese men, in men with chronic illness, and in those taking medications. Because SHBG concentrations are higher in older men than in younger men, free or bioavailable testosterone concentrations decline with aging to a greater extent than total testosterone concentrations. The age-related decline in testosterone is due to defects at all levels of the hypothalamic-pituitary-testicular axis: pulsatile GnRH secretion is attenuated, LH response to GnRH is reduced, and testicular response to LH is impaired. However, the gradual rise of LH with aging suggests that testis dysfunction is the main cause of declining androgen levels. The term andropause has been used to denote age-related decline in testosterone concentrations; this term is a misnomer because there is no discrete time when testosterone concentrations decline abruptly.
Several epidemiologic studies, such as the Framingham Heart Study, the EMAS, and the Study of Osteoporotic Fractures in Men (MrOS) that used mass spectrometry for measuring testosterone levels have reported ~10% prevalence of low testosterone levels in middle-aged and older men; the prevalence of unequivocally low testosterone and sexual symptoms in men aged 40–70 years in the EMAS was 2.1%, and increased with age from 0.1% for men aged 40–49 years of age to 5.1% for those aged 70–79 years. The age-related decline in testosterone should be distinguished from classical hypogonadism due to diseases of the testes, the pituitary, and the hypothalamus. Low total and bioavailable testosterone concentrations have been associated with decreased appendicular skeletal muscle mass and strength, decreased self-reported physical function, higher visceral fat mass, insulin resistance, and increased risk of coronary artery disease and mortality. An analysis of signs and symptoms in older men in the EMAS revealed a syndromic association of sexual symptoms with total testosterone levels below 320 ng/dL and free testosterone levels below 64 pg/mL in community-dwelling older men.
A series of placebo-controlled testosterone trials have provided important information about the efficacy of testosterone in improving outcomes in older men. Testosterone replacement in older men, aged ≥65, with sexual symptoms improved sexual activity, sexual desire, and erectile function more than placebo. Testosterone replacement did not improve fatigue or cognitive function, and had only a small effect on mood and mobility. Among older men with low testosterone and age-associated memory impairment, testosterone replacement did not improve memory or other measures of cognition relative to placebo. Testosterone replacement was associated with significantly greater increase in vertebral as well as femoral volumetric bone mineral density and estimated bone strength relative to placebo. Testosterone replacement was associated with a greater increase in hemoglobin levels and corrected anemia in a greater proportion of men who had unexplained anemia of aging. Testosterone administration was associated with a significantly greater increase in coronary artery noncalcified plaque volume, as measured by coronary artery computerized tomography angiography. Neither the testosterone trials nor a randomized trial of the effects of testosterone on atherosclerosis progression in aging men (TEAAM Trial) with low or low normal testosterone levels found significant differences between testosterone and placebo arms in the rates of change in either the coronary artery calcium scores or the common carotid artery intima-media thickness. Neither of the trials were long enough or large enough to determine the effects of testosterone replacement therapy on prostate or major adverse cardiovascular events. In systematic reviews of randomized controlled trials, testosterone therapy of healthy older men with low or low-normal testosterone levels was associated with greater increments in lean body mass, grip strength, and self-reported physical function than that associated with placebo. Testosterone therapy has not been shown to improve clinical depression, fracture risk, progression to dementia, progression from prediabetes to diabetes, or response to phosphodiesterase inhibitors in older men.
The long-term risks of testosterone therapy remain largely unknown. While there is no evidence that testosterone causes prostate cancer, there is concern that testosterone therapy might cause subclinical prostate cancers to grow. Testosterone therapy is associated with increased risk of detection of prostate events.
The data relating cardiovascular disease (CVD) and venous thromboembolic (VTE) risk with the use of testosterone supplementation in men with low testosterone levels and hypogonadal symptoms are few and inconclusive. The relationship of testosterone and cardiovascular events in cross-sectional and prospective cohort studies has been inconsistent. A small number of epidemiologic studies have reported an inverse relationship between testosterone concentrations and common carotid artery intima-media thickness. Low testosterone level has been associated with increased risk of all-cause mortality, especially cardiovascular mortality. It is possible that testosterone is a marker of health; older men with multiple co-morbid conditions who are at increased risk of death may have low testosterone levels as a result of comorbid conditions.
Most meta-analyses have not shown a statistically significant association between testosterone and cardiovascular events, major adverse cardiovascular events, or deaths. No adequately powered randomized trials have been conducted to determine the effects of testosterone replacement in major adverse cardiovascular events. Thus, there are insufficient data to establish a causal link between testosterone therapy and CV events.
Population screening of all older men for low testosterone levels is not recommended, and testing should be restricted to men who have symptoms or signs attributable to androgen deficiency. Testosterone therapy is not recommended for all older men with low testosterone levels. In older men with significant symptoms of androgen deficiency who have unequivocally low testosterone levels, testosterone therapy may be considered on an individualized basis and should be instituted after careful discussion of the risks and benefits (see “Testosterone Replacement,” below).
Testicular morphology, semen production, and fertility are maintained up to a very old age in men. Although concern has been expressed about age-related increases in germ cell mutations and impairment of DNA repair mechanisms, there is no clear evidence that the frequency of chromosomal aneuploidy is increased in the sperm of older men. However, the incidence of autosomal dominant diseases, such as achondroplasia, polyposis coli, Marfan syndrome, and Apert syndrome, increases in the offspring of men who are advanced in age, consistent with transmission of sporadic missense mutations. Advanced paternal age may be associated with increased rates of de novo mutations, which may contribute to an increased risk of neurodevelopmental diseases such as schizophrenia and autism. The somatic mutations in male germ cells that enhance the proliferation of germ cells could lead to within-testis expansion of mutant clonal lines, thus favoring the propagation of germ cells carrying these pathogenic mutations, and increasing the risk of mutations in the offspring of older fathers (the “selfish spermatogonial selection” hypothesis).
APPROACH TO THE PATIENT Androgen Deficiency
Hypogonadism is often characterized by decreased sex drive, reduced frequency of sexual activity, inability to maintain erections, reduced beard growth, loss of muscle mass, decreased testicular size, and gynecomastia. Erectile dysfunction and androgen deficiency are two distinct clinical disorders that can co-exist in middle-aged and older men. Less than 10% of patients with erectile dysfunction have testosterone deficiency. Thus, it is useful to evaluate men presenting with erectile dysfunction for androgen deficiency. Except when extreme, these clinical features of androgen deficiency may be difficult to distinguish from changes that occur with normal aging. Moreover, androgen deficiency may develop gradually. When symptoms or clinical features suggest possible androgen deficiency, the laboratory evaluation is initiated by the measurement of total testosterone, preferably in the morning using a reliable assay, such as liquid chromatography tandem mass spectrometry (LC-MS/MS) that has been calibrated to an international testosterone standard (Fig. 384-6). A consistently low total testosterone level <264 ng/dL measured by an LC-MS/MS assay in a Centers for Disease Control (CDC)—certified laboratory, in association with symptoms, is evidence of testosterone deficiency. An early-morning testosterone level >400 ng/dL makes the diagnosis of androgen deficiency unlikely. In men with testosterone levels between 200 and 400 ng/dL, the total testosterone level should be repeated and a free testosterone level should be measured. In older men and in patients with other clinical states that are associated with alterations in SHBG levels, a direct measurement of free testosterone level by equilibrium dialysis can be useful in unmasking testosterone deficiency.
When androgen deficiency has been confirmed by the consistently low testosterone concentrations, LH should be measured to classify the patient as having primary (high LH) or secondary (low or inappropriately normal LH) hypogonadism. An elevated LH level indicates that the defect is at the testicular level. Common causes of primary testicular failure include Klinefelter syndrome, HIV infection, uncorrected cryptorchidism, cancer chemotherapeutic agents, radiation, surgical orchiectomy, or prior infectious orchitis. Unless causes of primary testicular failure are known, a karyotype should be performed in men with low testosterone and elevated LH to diagnose Klinefelter syndrome. Men who have a low testosterone but “inappropriately normal” or low LH levels have secondary hypogonadism; their defect resides at the hypothalamic-pituitary level. Common causes of acquired secondary hypogonadism include space-occupying lesions of the sella, hyperprolactinemia, chronic illness, hemochromatosis, excessive exercise, and the use of anabolic-androgenic steroids, opiates, marijuana, glucocorticoids, and alcohol. Measurement of PRL and MRI scan of the hypothalamic-pituitary region can help exclude the presence of a space-occupying lesion. Patients in whom known causes of hypogonadotropic hypogonadism have been excluded are classified as having IHH. It is not unusual for congenital causes of hypogonadotropic hypogonadism, such as Kallmann syndrome, to be diagnosed in young adults.
Evaluation of hypogonadism. GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; T, testosterone.
TREATMENT Androgen Deficiency GONADOTROPINS
Gonadotropin therapy is used to establish or restore fertility in patients with gonadotropin deficiency of any cause. Several gonadotropin preparations are available. Human menopausal gonadotropin (hMG; purified from the urine of postmenopausal women) contains 75 IU FSH and 75 IU LH per vial. hCG (purified from the urine of pregnant women) has little FSH activity and resembles LH in its ability to stimulate testosterone production by Leydig cells. Recombinant LH is also available. Treatment is usually begun with hCG alone, and hMG is added later to promote the FSH-dependent stages of spermatid development. Recombinant human FSH (hFSH) is available and is indistinguishable from purified urinary hFSH in its biologic activity and pharmacokinetics in vitro and in vivo, although the mature β subunit of recombinant hFSH has seven fewer amino acids. Recombinant hFSH is available in ampoules containing 75 IU (~7.5 μg FSH), which accounts for >99% of protein content. Once spermatogenesis is restored using combined FSH and LH therapy, hCG alone is often sufficient to maintain spermatogenesis.
Although a variety of treatment regimens are used, 1000 IU of hCG or recombinant human LH (rhLH) administered intramuscularly three times weekly is a reasonable starting dose. Testosterone levels should be measured 6–8 weeks later and 48–72 h after the hCG or rhLH injection; the hCG/rhLH dose should be adjusted to achieve testosterone levels in the mid-normal range. Sperm counts should be monitored on a monthly basis. It may take several months for spermatogenesis to be restored; therefore, it is important to forewarn patients about the potential length and expense of the treatment and to provide conservative estimates of success rates. If testosterone levels are in the mid-normal range but the sperm concentrations are low after 6 months of therapy with hCG alone, FSH should be added. This can be done by using hMG, highly purified urinary hFSH, or recombinant hFSH. The selection of FSH dose is empirical. A common practice is to start with the addition of 75 IU FSH three times each week in conjunction with the hCG/rhLH injections. If sperm densities are still low after 3 months of combined treatment, the FSH dose should be increased to 150 IU. Occasionally, it may take ≥18–24 months for spermatogenesis to be restored.
The two best predictors of success using gonadotropin therapy in hypogonadotropic men are testicular volume at presentation and time of onset of gonadotropin deficiency. In general, men with testicular volumes >8 mL have better response rates than those who have testicular volumes <4 mL. Patients who become hypogonadotropic after puberty experience higher success rates than those who have never undergone pubertal changes. Spermatogenesis can usually be reinitiated by hCG alone, with high rates of success for men with postpubertal onset of hypogonadotropism. The presence of a primary testicular abnormality, such as cryptorchidism, will attenuate testicular response to gonadotropin therapy. Prior androgen therapy does not preclude subsequent response to gonadotropin therapy, although some studies suggest that it may attenuate response to subsequent gonadotropin therapy. TESTOSTERONE REPLACEMENT
Androgen therapy is indicated to restore testosterone levels to normal to correct features of androgen deficiency in men with organic hypogonadism due to known diseases of the testes, pituitary, and the hypothalamus. Testosterone replacement induces secondary sex characteristics, improves libido and overall sexual activity; increases lean muscle mass, hemoglobin and hematocrit, and bone mineral density, and decreases fat mass. The benefits of testosterone replacement therapy have only been proven in men who have documented symptomatic androgen deficiency, as demonstrated by testosterone levels that are well below the lower limit of normal.
Testosterone is available in a variety of formulations with distinct pharmacokinetics (Table 384-3). Testosterone serves as a prohormone and is converted to 17β-estradiol by aromatase and to 5α-dihydrotestosterone by steroid 5α-reductase. Therefore, when evaluating testosterone formulations, it is important to consider whether the formulation being used can achieve physiologic estradiol and DHT concentrations, in addition to normal testosterone concentrations. The current recommendation is to restore testosterone levels to the mid-normal range. Oral Derivatives of Testosterone
Testosterone is well-absorbed after oral administration but is quickly degraded during the first pass through the liver. Therefore, it is difficult to achieve sustained blood levels of testosterone after oral administration of crystalline testosterone. 17α-Alkylated derivatives of testosterone (e.g., 17α-methyl testosterone, oxandrolone, fluoxymesterone) are relatively resistant to hepatic degradation and can be administered orally; however, because of the potential for hepatotoxicity, including cholestatic jaundice, peliosis, and hepatoma, these formulations should not be used for testosterone replacement. Hereditary angioedema due to C1 esterase deficiency is the only exception to this general recommendation; in this condition, oral 17α-alkylated androgens are useful because they stimulate hepatic synthesis of the C1 esterase inhibitor. Injectable Forms of Testosterone
The esterification of testosterone at the 17β-hydroxy position makes the molecule hydrophobic and extends its duration of action. The slow release of testosterone ester from an oily depot in the muscle accounts for its extended duration of action. The longer the side chain, the greater the hydrophobicity of the ester and longer the duration of action. Thus, testosterone enanthate, cypionate, and undecanoate with longer side chains have longer duration of action than testosterone propionate. Within 24 h after intramuscular administration of 200 mg testosterone enanthate or cypionate, testosterone levels rise into the high-normal or supraphysiologic range and then gradually decline into the hypogonadal range over the next 2 weeks. A bimonthly regimen of testosterone enanthate or cypionate therefore results in peaks and troughs in testosterone levels that may be accompanied by changes in a patient’s mood, sexual desire, and energy level; weekly administration of testosterone enanthate or cypionate can reduce these variations in testosterone levels during the dosing interval. The kinetics of testosterone enanthate and cypionate are similar. Estradiol and DHT levels are normal if testosterone replacement is physiologic.
A long-acting testosterone undecanoate in oil, administered at an initial priming dose of 750 mg intramuscularly followed by a second dose of 750 mg 4 weeks later, and then at a maintenance dose of 750 mg every 10 weeks, maintains serum testosterone, estradiol, and DHT in the normal male range and corrects symptoms of androgen deficiency in a majority of treated men. However, its relative drawback is the large injection volume and cough in a small proportion of patients. Transdermal Testosterone Patch
The nongenital testosterone patch, when applied in an appropriate dose, can normalize testosterone, DHT, and estradiol levels 4–12 h after application. Sexual function and well-being are restored in androgen-deficient men treated with the nongenital patch. One 4-mg patch may not be sufficient to increase testosterone into the mid-normal male range in all hypogonadal men; many patients may need two 4-mg patches daily to achieve the targeted testosterone concentrations. The use of testosterone patches may be associated with skin irritation in some individuals. Testosterone Gel
Several transdermal testosterone gels, Androgel, Testim, Fortesta, and Axiron, and some generic versions, when applied topically to the skin in appropriate doses (Table 384-3), can maintain total and free testosterone concentrations in the normal range in hypogonadal men. The current recommendations are to begin with an initial FDA-recommended dose and adjust the dose based on testosterone levels. The advantages of the testosterone gel include the ease of application. A major concern is the potential for inadvertent transfer of the gel to a sexual partner or to children who may come in close contact with the patient. The ratio of DHT to testosterone concentrations is higher in men treated with the testosterone gel than in healthy men. Also, there is considerable intra- and inter-individual variation in serum testosterone levels in men treated with the transdermal gel due to variations in transdermal absorption and plasma clearance of testosterone. Therefore, monitoring of serum testosterone levels and multiple dose adjustments may be required to achieve and maintain testosterone levels in the target range. Buccal Adhesive Testosterone
A buccal testosterone tablet, which adheres to the buccal mucosa and releases testosterone as it is slowly dissolved, has been approved. After twice-daily application of 30-mg tablets, serum testosterone levels are maintained within the normal male range in a majority of treated hypogonadal men. The adverse effects include buccal ulceration and gum problems in a few subjects. The effects of food and brushing on absorption have not been studied in detail.
Pellets of crystalline testosterone can be inserted in the subcutaneous tissue through a small skin incision. Testosterone is released by surface erosion of the implant and absorbed into the systemic circulation, and testosterone levels can be maintained in the normal range for 3–4 months. Potential drawbacks include incising the skin for insertion and removal, and spontaneous extrusions and fibrosis at the site of the implant. Testosterone Formulations Not Available in the United States
Testosterone undecanoate, when administered orally in oleic acid, is absorbed preferentially through the lymphatics into the systemic circulation and is spared the first-pass degradation in the liver. Doses of 40–80 mg orally, two or three times daily, are typically used. However, the clinical responses are variable and suboptimal. DHT-to-testosterone ratios are higher in hypogonadal men treated with oral testosterone undecanoate, as compared to eugonadal men.
An intranasal testosterone gel is now available as a metered dose pump and is administered typically at a starting dose of 11 mg testosterone in the form of 2 pump actuations, one in each nostril three times daily. Formulation-specific adverse effects include rhinorrhea, nasal discomfort, epistaxis, nasopharyngitis, and nasal scab. Novel Androgen Formulations
A number of androgen formulations with better pharmacokinetics or more selective activity profiles are under development. Initial clinical trials have demonstrated the feasibility of administering testosterone by the sublingual, oral, or buccal routes. Long-acting biodegradable microsphere formulations have also been investigated. 7α-Methyl-19-nortestosterone is an androgen that cannot be 5α-reduced; therefore, compared to testosterone, it has relatively greater agonist activity in muscle and gonadotropin suppression but lesser activity on the prostate.
Selective Androgen Receptor Modulators (SARMs) are a class of AR ligands that bind the AR and display tissue-selective actions. A number of nonsteroidal SARMs that act as agonists on the muscle and bone and which spare the prostate to varying degrees have advanced to phase III human trials. Nonsteroidal SARMs do not serve as substrates for either the steroid 5-α reductase or the CYP19aromatase. SARM binding to AR induces specific conformational changes in the AR protein, which then modulates protein-protein interactions between AR and its coregulators, resulting in tissue-specific regulation of gene expression. SARMs that are strong agonists for the muscle, bone, and sexual function, and antagonists for the prostate may be valuable in treating men with prostate cancer, who are receiving androgen deprivation therapy. Pharmacologic Uses of Androgens
Androgens and selective AR modulators are being evaluated as anabolic therapies for functional limitations associated with aging and chronic illness. Testosterone supplementation increases skeletal muscle mass, maximal voluntary strength, and muscle power in healthy men, hypogonadal men, older men with low testosterone levels, HIV-infected men with weight loss, and men receiving glucocorticoids. These anabolic effects of testosterone are related to testosterone dose and circulating concentrations. Systematic reviews have confirmed that testosterone therapy of HIV-infected men with weight loss promotes improvements in body weight, lean body mass, muscle strength, and depression indices, leading to the recommendation that testosterone be considered as an adjunctive therapy in HIV-infected men who are experiencing unexplained weight loss and who have low testosterone levels. It is unknown whether testosterone therapy of older men with functional limitations is safe and effective in improving physical function, vitality, and health-related quality of life, and reducing disability. Concerns about potential adverse effects of testosterone on prostate and cardiovascular event rates have encouraged the development of selective AR modulators that are preferentially anabolic and spare the prostate.
Testosterone administration induces hypertrophy of both type 1 and 2 fibers and increases satellite cell (muscle progenitor cells) and myonuclear number. Androgens promote the differentiation of mesenchymal, multipotent progenitor cells into the myogenic lineage and inhibit their differentiation into the adipogenic lineage. Testosterone binding to AR promotes the association of liganded AR with β-catenin and its translocation into the nucleus where it binds TCF-4 and activates Wnt-target genes, including follistatin, which blocks signaling through the TGFβ pathway, thereby promoting myogenic differentiation of muscle progenitor cells. Testosterone may have additional effects on satellite cell replication and muscle protein synthesis, which may contribute to an increase in skeletal muscle mass.
Other indications for androgen therapy are in selected patients with anemia due to bone marrow failure (an indication largely supplanted by erythropoietin) or for hereditary angioedema. Male Hormonal Contraception Based on Combined Administration of Testosterone and Gonadotropin Inhibitors
Supraphysiologic doses of testosterone (200 mg testosterone enanthate weekly) suppress LH and FSH secretion and induce azoospermia in 50% of Caucasian men and >95% of Chinese men. The WHO-supported multicenter efficacy trials have demonstrated that suppression of spermatogenesis to azoospermia or severe oligozoozspermia (<3 million/mL) by administration of supraphysiologic doses of testosterone enanthate to men results in highly effective contraception. Because of concern about long-term adverse effects of supraphysiologic testosterone doses, regimens that combine other gonadotropin inhibitors, such as GnRH antagonists and progestins with replacement doses of testosterone, have been investigated. Regimens containing an androgen plus a progestin such as depo medroxyprogesterone acetate, etonogestrelm, or norethisterone enanthate have been highly effective in inducing azoospermia or severe oligozoospermia (sperm density <1 million/mL) in nearly 99% of treated men over a 1-year period. The combined regimens of testosterone plus a progestin have been associated with weight gain, acne, mood changes including depressed mood, libido changes, and decreased plasma high-density lipoprotein (HDL) cholesterol and their long-term safety has not been demonstrated. One such trial of a combined regimen of testosterone undecanoate plus norethisterone enanthate was stopped early due to adverse events. Selective AR modulators that are more potent inhibitors of gonadotropins than testosterone and spare the prostate hold promise for their contraceptive potential. Recommended Regimens for Androgen Replacement
Testosterone esters are administered typically at doses of 75–100 mg intramuscularly every week, or 150–200 mg every 2 weeks. Testosterone undecanoate is administered at an initial dose of 750 mg followed 4 weeks later by a second injection of 750 mg and then 750 mg every 10 weeks. Testosterone gels are typically applied over a covered area of skin at initial doses that vary with the formulation. The patients should wash their hands after gel application and keep the area of gel application covered with clothing to minimize the risk of gel transfer to another person. One or two 4-mg nongenital testosterone patches are applied daily over the skin of the back, thigh, or upper arm away from pressure areas. Bioadhesive buccal testosterone tablets at a dose of 30 mg are applied twice daily on the buccal mucosa. Intranasal testosterone is administered as a spray in each nostril 3 times a day (33 mg/day). Establishing Efficacy of Testosterone Replacement Therapy
Because a clinically useful marker of androgen action is not available, correction of symptoms, induction and maintenance of secondary sex characteristics, and restoration of testosterone levels into the mid-normal range remain the goal of therapy. Measurements of LH and FSH are not useful in assessing the adequacy of testosterone replacement. Testosterone should be measured 3 months after initiating therapy to assess adequacy of therapy. There is substantial inter-individual variability in serum testosterone levels, especially with transdermal gels, presumably due to genetic differences in testosterone clearance and substantial variation in transdermal absorption. In patients who are treated with testosterone enanthate or cypionate, testosterone levels should be 350–600 ng/dL 1 week after the injection. If testosterone levels are outside this range, adjustments should be made either in the dose or in the interval between injections. In men on transdermal patch, gel, or buccal testosterone therapy, testosterone levels should be in the mid-normal range (400–750 ng/dL) 4–12 h after application. If testosterone levels are outside this range, the dose should be adjusted. Multiple dose adjustments are often necessary to achieve testosterone levels in the desired therapeutic range.
Restoration of sexual function, induction and maintenance of secondary sex characteristics, well-being, and maintenance of muscle and bone health are important objectives of testosterone replacement therapy. The patient should be asked about sexual desire and activity, the presence of early morning erections, and the ability to achieve and maintain erections adequate for sexual intercourse. The hair growth in response to androgen replacement is variable and depends on ethnicity. Hypogonadal men with prepubertal onset of androgen deficiency who begin testosterone therapy in their late twenties or thirties may find it difficult to adjust to their newly found sexuality and may benefit from counseling. If the patient has a sexual partner, the partner should be included in counseling because of the dramatic physical and sexual changes that occur with androgen treatment. Contraindications for Androgen Administration
Testosterone administration is contraindicated in men with prostate or breast cancer (Table 384-4). Testosterone therapy should not be administered without further urologic evaluation to men with a palpable prostate nodule or induration, or prostate-specific antigen >3 ng/mL, or with severe lower urinary tract symptoms (American Urological Association lower urinary tract symptom score >19). Testosterone replacement should not be administered to men with baseline hematocrit ≥50%, severe untreated obstructive sleep apnea, uncontrolled or poorly controlled congestive heart failure, or to men with myocardial infarction, stroke, or acute coronary syndrome in the preceding 3 months. Monitoring Potential Adverse Experiences
The clinical effectiveness and safety of testosterone replacement therapy should be assessed 3–6 months after initiating testosterone therapy and annually thereafter (Table 384-5). Potential adverse effects include acne, oiliness of skin, erythrocytosis, breast tenderness and enlargement, leg edema, and increased risk of detection of prostate events. In addition, there may be formulation-specific adverse effects such as skin irritation with transdermal patch; risk of gel transfer to a sexual partner with testosterone gels; buccal ulceration and gum problems with buccal testosterone; pain and mood fluctuation with injectable testosterone esters; cough and injection site pain with long-acting testosterone undecanoate; and, nasal irritation, epistaxis, and nasal scab with intranasal formulation. Hemoglobin Levels
Administration of testosterone to androgen-deficient men is typically associated with a ~3% increase in hemoglobin levels, due to increased erythropoiesis, stimulation of erythropoietin, suppression of hepcidin, and increased iron availability for erythropoiesis. The magnitude of hemoglobin increase during testosterone therapy is greater in older men than younger men, and in men who have sleep apnea, a significant smoking history, or chronic obstructive lung disease, or who live at high altitude. The frequency of erythrocytosis is higher in hypogonadal men treated with injectable testosterone esters than in those treated with transdermal formulations, presumably due to the higher testosterone dose delivered by the typical regimens of testosterone esters. Erythrocytosis is the most frequent adverse event reported in testosterone trials in middle-aged and older men and is also the most frequent cause of treatment discontinuation in these trials. If hematocrit rises above 54%, testosterone therapy should be stopped until hematocrit has fallen to <50%. After evaluation of the patient for hypoxia and sleep apnea, testosterone therapy may be reinitiated at a lower dose. Prostate and Serum PSA Levels
Testosterone replacement therapy increases prostate volume to the size seen in age-matched controls but does not increase prostate volume beyond that expected for age. There is no evidence that testosterone therapy causes prostate cancer. However, androgen administration can exacerbate preexisting metastatic prostate cancer. Many older men harbor microscopic foci of cancer in their prostates. It is not known whether long-term testosterone administration will induce these microscopic foci to grow into clinically significant cancers.
PSA levels are lower in testosterone-deficient men and are restored to normal after testosterone replacement. There is considerable test-retest variability in PSA measurements. Increments in PSA levels after testosterone supplementation in androgen-deficient men are generally <0.5 ng/mL, and increments >1.0 ng/mL over a 3–6-month period are unusual. The 90% confidence interval for the change in PSA values in men with benign prostatic hypertrophy, measured 3–6 months apart, is 1.4 ng/mL. Therefore, the Endocrine Society expert panel suggested that an increase in PSA >1.4 ng/mL in any one year after starting testosterone therapy, if confirmed, should lead to urologic evaluation. PSA velocity criterion can be used for patients who have sequential PSA measurements for >2 years; a change of >0.40 ng/mL per year merits closer urologic follow-up. Cardiovascular Risk
As discussed above, there is insufficient evidence to determine whether testosterone replacement therapy increases the risk of major adverse cardiovascular events in hypogonadal men. A large prospective randomized trial is being planned to determine the effects of testosterone replacement therapy on major adverse cardiovascular events in middle-aged and older men with low testosterone levels and symptoms of androgen deficiency. Androgen Abuse by Athletes and Recreational Bodybuilders
The illicit use of androgenic-anabolic steroids (AAS) to enhance athletic performance first surfaced in the 1950s among powerlifters and spread rapidly to other sports, professional as well as high school athletes, and recreational bodybuilders. In the early 1980s, the use of AAS spread beyond the athletic community into the general population, and now, as many as 3 million Americans—most of them men—have likely used these compounds. Most AAS users are not athletes, but rather recreational weightlifters, who use these drugs to look lean and more muscular. The most commonly used AAS include testosterone esters, nandrolone, stanozolol, methandienone, and methenolol. AAS users generally use increasing doses of multiple steroids in a practice known as stacking.
The adverse effects of long-term AAS abuse remain poorly understood. Most of the information about the adverse effects of AAS has emerged from case reports, uncontrolled studies, or from clinical trials that used replacement doses of testosterone. The adverse event data from clinical trials using physiologic replacement doses of testosterone have been extrapolated unjustifiably to AAS users who may administer 10–100 times the replacement doses of testosterone over many years, to support the claim that AAS use is safe. A substantial fraction of androgenic steroid users also use other drugs that are perceived to be muscle-building or performance-enhancing, such as growth hormone; erythropoiesis stimulating agents; insulin; stimulants such as amphetamine, clenbuterol, cocaine, ephedrine, and thyroxine; and drugs perceived to reduce adverse effects such as hCG, aromatase inhibitors, or estrogen antagonists. The adverse events associated with AAS use may be due to AAS themselves, concomitant use of other drugs, high-risk behaviors, and host characteristics that may render these individuals more susceptible to AAS use or to other high risk behaviors.
The high rates of premature mortality and morbidities observed in AAS users are alarming. One Finnish study reported 4.6 times the risk of death among elite power lifters than in age-matched men from the general population. The causes of death among power lifters included suicides, myocardial infarction, and hepatic coma. A retrospective review of patient records in Sweden also reported higher standardized mortality ratios for AAS users than for nonusers. Increased death rates among AAS users include suicide, homicide, and accidents. The median age of death among AAS users—24 years—is even lower than that for heroin or amphetamine users.
Four categories of adverse events associated with AAS abuse are of particular concern: cardiovascular events, psychiatric, prolonged suppression of the hypothalamic-pituitary-testicular axis, and potential neurotoxicity. Numerous reports of premature cardiac death among young AAS users raise concerns about the adverse cardiovascular effects of AAS. High doses of AAS may induce proatherogenic dyslipidemia, accelerate atherogenesis, increase thrombosis risk via effects on clotting factors and platelets, and induce vasospasm through their effects on vascular nitric oxide. Recent studies of AAS users using tissue Doppler and strain imaging, and magnetic resonance imaging have reported diastolic and systolic dysfunction, including significantly lower early and late diastolic tissue velocities, reduced E/A ratio, and reduced peak systolic strain in AAS users than in nonusers. Power athletes using AAS often have short QT intervals but increased QT dispersion, which may predispose them to ventricular arrhythmias. Long-term AAS use may be associated with myocardial hypertrophy and fibrosis. Myocardial tissue of power lifters using AAS has been shown to be infiltrated with fibrous tissue and fat droplets. The finding of AR on myocardial cells suggests that AAS might be directly toxic to myocardial cells. Studies of long-term AAS users using computerized tomography angiography have revealed accelerated atherogenesis.
Unlike replacement doses of testosterone, which are associated with only a small decrease in HDL cholesterol and little or no effect on total cholesterol, LDL cholesterol and triglyceride levels, supraphysiologic doses of testosterone and orally administered, 17-α-alylated, nonaromatizable AAS are associated with marked reductions in HDL cholesterol and increases in LDL cholesterol.
Some AAS users develop hypomanic and manic symptoms (irritability, aggressiveness, reckless behavior, and occasional psychotic symptoms, sometimes associated with violence) during AAS exposure, and major depression (sometimes associated with suicidality) during AAS withdrawal. Users may also be susceptible to other forms of illicit drug use, which may be potentiated or exacerbated by AAS.
Long-term AAS use suppresses LH and FSH secretion and inhibits endogenous testosterone production and spermatogenesis. Men, who have used AAS for more than a few months, experience marked suppression of the hypothalamic-pituitary-testicular (HPT) axis after stopping AAS that may be associated with sexual dysfunction, fatigue, infertility, depressed mood, and even suicidality. In some long-term AAS users, HPT suppression may last more than a year, and in a few individuals, recovery of the HPT axis may be incomplete or may never occur. The symptoms of androgen deficiency caused by androgen withdrawal may cause some men to revert back to using AAS, leading to continued use and AAS dependence. As many as 30% of AAS users develop a syndrome of AAS dependence, characterized by long-term AAS use despite adverse medical and psychiatric effects. AAS withdrawal hypogonadism has emerged as an important cause of androgen deficiency accounting for a substantial fraction of testosterone prescriptions in many men’s health clinics.
Supraphysiologic doses of testosterone may also impair insulin sensitivity. Orally administered androgens also have been associated with insulin resistance and diabetes.
Unsafe injection practices, high-risk behaviors, and increased rates of incarceration render AAS users at increased risk of HIV, and hepatitis B and C. In one survey, nearly 1 in 10 gay men had injected AAS or other substances, and AAS users were more likely to report high-risk unprotected anal sex than other men.
Elevated liver enzymes, cholestatic jaundice, hepatic neoplasms, and peliosis hepatis have been reported with oral, 17-α-alkylated AAS. AAS use may cause muscle hypertrophy without compensatory adaptations in tendons, ligaments, and joints, thus increasing the risk of tendon and joint injuries. Upper extremity tendon ruptures are observed almost exclusively among weightlifters who use AAS. AAS use is associated with acne, baldness, as well as increased body hair.
The suspicion of AAS use should be raised by the increased hemoglobin and hematocrit, suppressed LH and FSH and testosterone levels, low high-density lipoproteins cholesterol, and low testicular volume and sperm density in a person who looks highly muscular. In most AAS users seeking medical attention, direct nonjudgmental questioning is sufficient to uncover AAS use and formal testing for AAS usually is not needed. However, if needed, accredited laboratories use gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry to detect anabolic steroid abuse. In recent years, the availability of high-resolution mass spectrometry and tandem mass spectrometry has further improved the sensitivity of detecting androgen abuse. Illicit testosterone use is detected generally by the application of the measurement of urinary testosterone to epitestosterone ratio and further confirmed by the use of the 13C:12C ratio in testosterone by the use of isotope ratio combustion mass spectrometry. Exogenous testosterone administration increases urinary testosterone glucuronide excretion and consequently the testosterone to epitestosterone ratio. Ratios above 4 suggest exogenous testosterone use but can also reflect genetic variation. Genetic variations in the uridine diphospho-glucuronyl transferase 2B17 (UGT2B17), the major enzyme for testosterone glucuronidation, affect testosterone to epitestosterone ratio. Synthetic testosterone has a lower 13C:12C ratio than endogenously produced testosterone and these differences in 13C:12C ratio can be detected by isotope ratio combustion mass spectrometry, which is used to confirm exogenous testosterone use in individuals with a high testosterone to epitestosterone ratio.
TABLE 384-3Clinical Pharmacology of Some Testosterone Formulations ||Download (.pdf) TABLE 384-3 Clinical Pharmacology of Some Testosterone Formulations
|Formulation ||Regimen ||Pharmacokinetic profile ||DHT and E2 ||Advantages ||Disadvantages |
|T enanthate or cypionate ||150–200 mg IM q 2 wk or 75–100 mg/wk ||After a single IM injection, serum T levels rise into the supraphysiological range, then decline gradually into the low normal or the hypogonadal range by the end of the dosing interval ||DHT and E2 levels rise in proportion to the increase in T levels; T:DHT and T:E2 ratios do not change ||Corrects symptoms of androgen deficiency; relatively inexpensive, if self-administered; flexibility of dosing ||Requires IM injection; peaks and valleys in serum T levels |
|Topical testosterone gels and axillary testosterone solution ||Available in sachets, tubes and pumps ||When used in appropriate doses, these topical formulations restore serum T and E2 levels to the physiological male range ||Serum DHT levels and DHT to T ratio are higher in hypogonadal men treated with the transdermal gels than in healthy eugonadal men ||Corrects symptoms of androgen deficiency, ease of application, good skin tolerability ||Potential of transfer to a female partner or child by direct skin-to-skin contact; skin irritation in a small proportion of treated men; moderately high DHT levels; considerable interindividual and intra-indivudal variation in on-treatment testosterone levels |
|Transdermal testosterone patch ||1 or 2 patches, designed to nominally deliver 4–8 mg T over 24 h applied daily on nonpressure areas ||Restores serum T, DHT, and E2 levels to the physiological male range ||T:DHT and T:E2 levels are in the physiological male range ||Ease of application, corrects symptoms of androgen deficiency ||Serum T levels in some androgen-deficient men may be in the low-normal range; these men may need application of 2 patches daily; skin irritation at the application site occurs frequently in many patients |
|Buccal, bioadhesive, T tablets ||30 mg controlled release, bioadhesive tablets bid ||Absorbed from the buccal mucosa ||Normalizes serum T and DHT levels in hypogonadal men ||Corrects symptoms of androgen deficiency ||Gum-related adverse events in 16% of treated men |
|T pellets ||Several pellets implanted sc; dose and regimen vary with formulation ||Serum T peaks at 1 mo and then is sustained in normal range for 3–4 mo, depending on formulation ||T:DHT and T:E2 ratios do not change ||Corrects symptoms of androgen deficiency ||Requires surgical incision for insertions; pellets may extrude spontaneously |
|17-α-methyl T ||This 17-α-alkylated compound should not be used because of potential for liver toxicity. ||Orally active || || ||Clinical responses are variable; potential for liver toxicity; should not be used for treatment of androgen deficiency |
|Oral T undecanoate* ||40–80 mg po bid or tid with meals ||When administered in oleic acid, T undecanoate is absorbed through the lymphatics, bypassing the portal system; considerable variability in the same individual on different days and among individuals ||High DHT to T ratio ||Convenience of oral administration ||Not approved in the US;variable clinical responses, variable serum T levels, high DHT:T ratio |
|Injectable long-acting T undecanoate in oil1 ||US regimen 750 mg IM, followed by 750 mg at 4 wk, and 750 mg every 10 weeks ||When administered at the recommended dose, serum T levels are maintained in the normal range in a majority of treated men ||DHT and E2 levels rise in proportion to the increase in T levels; T:DHT and T:E2 ratios do not change ||Corrects symptoms of androgen deficiency; requires infrequent administration. ||Requires IM injection of a large volume; cough reported immediately after injection in a small number of men |
|Testosterone- in-adhesive matrix patch* ||2 × 60 cm2 patches delivering ~4.8 mg of T/d ||Restores serum T, DHT and E2 to the physiological range ||T:DHT and T:E2 are in the physiological range. ||Lasts 2 d ||Some skin irritation |
|Intranasal Testosterone ||2 actuations of the metered dose pump (11 mg) applied into the nostrils three times daily ||Restores T into the normal male range ||T:DHT and T:E2 ratio in the physiologic range || ||Requires 3x daily application; nasal irritation, epistaxis, nasophyringitis |
TABLE 384-4Conditions in Which Testosterone Administration Is Associated with an Increased Risk of Adverse Outcomes ||Download (.pdf) TABLE 384-4 Conditions in Which Testosterone Administration Is Associated with an Increased Risk of Adverse Outcomes
|Conditions in which testosterone administration is associated with very high risk of serious adverse outcomes: |
|Metastatic prostate cancer |
|Breast cancer |
|Conditions in which testosterone administration is associated with moderate to high risk of adverse outcomes: |
|Undiagnosed prostate nodule or induration |
|PSA > 3 |
|Erythrocytosis (hematocrit >50%) |
|Severe lower urinary tract symptoms associated with benign prostatic hypertrophy as indicated by American Urological Association/International prostate symptom score >19 |
|Uncontrolled or poorly controlled congestive heart failure |
|Myocardial infarction, stroke, or acute coronary syndrome in the preceding 3 months |
TABLE 384-5Monitoring Men Receiving Testosterone Therapy ||Download (.pdf) TABLE 384-5 Monitoring Men Receiving Testosterone Therapy
Evaluate the patient 3–6 months after treatment initiation and then annually to assess whether symptoms have responded to treatment and whether the patient is suffering from any adverse effects.
Monitor testosterone level 3–6 months after initiation of testosterone therapy:
Check hematocrit at baseline, at 3–6 months, and then annually. If hematocrit is >54%, stop therapy until hematocrit decreases to a safe level; evaluate the patient for hypoxia and sleep apnea; reinitiate therapy with a reduced dose.
Measure bone mineral density of lumbar spine and/or femoral neck after 1–2 yr of testosterone therapy in hypogonadal men with osteoporosis or low trauma fracture, consistent with regional standard of care.
In men aged ≥40 years with baseline PSA >0.6 ng/mL, perform digital rectal examination and check PSA level before initiating treatment, at 3–6 months, and then in accordance with guidelines for prostate cancer screening depending on the age and race of the patient.
Obtain urological consultation if there is:
An increase in serum PSA concentration >1.4 ng/mL within any 12-month period of testosterone treatment.
A PSA velocity of >0.4 ng/mL·yr using the PSA level after 6 months of testosterone administration as the reference (only applicable if PSA data are available for a period exceeding 2 yr).
Detection of a prostatic abnormality on digital rectal examination.
An AUA/ IPSS prostate symptom score of >19 along with an increase in IPSS score of ≥5 points above baseline.
Evaluate formulation-specific adverse effects at each visit:
Buccal testosterone tablets*: Inquire about alterations in taste and examine the gums and oral mucosa for irritation.
Injectable testosterone esters (enanthate, cypionate, and undecanoate): Ask about fluctuations in mood or libido, and rarely cough after injections.
Testosterone patches: Look for skin reaction at the application site.
Testosterone gels: Advise patients to cover the application sites with a shirt and to wash the skin with soap and water before having skin-to-skin contact, because testosterone gels leave a testosterone residue on the skin that can be transferred to a woman or child who might come in close contact. Serum testosterone levels are maintained when the application site is washed 4–6 h after application of the testosterone gel.
Testosterone pellets: Look for signs of infection, fibrosis, or pellet extrusion.
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