Disturbed sleep is one of the most common health complaints that physicians encounter. More than one-half of adults in the United States experience at least intermittent sleep disturbance, and only 30% of adult Americans report consistently obtaining a sufficient amount of sleep. The National Academy of Medicine has estimated that 50–70 million Americans suffer from a chronic disorder of sleep and wakefulness, which can adversely affect daytime functioning as well as physical and mental health. A high prevalence of sleep disorders across all cultures is also now increasingly recognized, and these problems are expected to further increase in the years ahead as the global population ages. Over the last 20 years, the field of sleep medicine has emerged as a distinct specialty in response to the impact of sleep disorders and sleep deficiency on overall health. Nonetheless, over 80% of patients with sleep disorders remain undiagnosed and untreated—costing the U.S. economy over $400 billion annually in increased health care costs, lost productivity, accidents and injuries, and leading to the development of workplace-based sleep health education and sleep disorders screening programs designed to address this unmet medical need.
PHYSIOLOGY OF SLEEP AND WAKEFULNESS
Adults need at least 7 h of sleep per night to promote optimal health, although the timing, duration, and internal structure of sleep vary among individuals. In the United States, adults tend to have one consolidated sleep episode each night, although in some cultures sleep may be divided into a mid-afternoon nap and a shortened night sleep. This pattern changes considerably over the life span, as infants and young children sleep considerably more than older people.
The stages of human sleep are defined on the basis of characteristic patterns in the electroencephalogram (EEG), the electrooculogram (EOG—a measure of eye-movement activity), and the surface electromyogram (EMG) measured on the chin, neck, and legs. The continuous recording of these electrophysiologic parameters to define sleep and wakefulness is termed polysomnography.
Polysomnographic profiles define two basic states of sleep: (1) rapid eye movement (REM) sleep and (2) non–rapid eye movement (NREM) sleep. NREM sleep is further subdivided into three stages: N1, N2, and N3, characterized by increasing arousal threshold and slowing of the cortical EEG. REM sleep is characterized by a low-amplitude, mixed-frequency EEG similar to that of NREM stage N1 sleep, and the EOG shows REMs which tend to occur in flurries or bursts. EMG activity is absent in nearly all skeletal muscles except those involved in respiration, reflecting the brainstem-mediated muscle paralysis that is characteristic of REM sleep.
ORGANIZATION OF HUMAN SLEEP
Normal nocturnal sleep in adults displays a consistent organization from night to night (Fig. 27-1). After sleep onset, sleep usually progresses through NREM stages N1–N3 sleep within 45–60 min. NREM stage N3 sleep (also known as slow-wave sleep) predominates in the first third of the night and comprises 15–25% of total nocturnal sleep time in young adults. Sleep deprivation increases the rapidity of sleep onset and both the intensity and amount of slow-wave sleep.
Wake-sleep architecture. Alternating stages of wakefulness, the three stages of non–rapid eye movement sleep (N1–N3), and rapid eye movement (REM) sleep (solid bars) occur over the course of the night for representative young and older adult men. Characteristic features of sleep in older people include reduction of N3 slow-wave sleep, frequent spontaneous awakenings, early sleep onset, and early morning awakening.
The first REM sleep episode usually occurs in the second hour of sleep. NREM and REM sleep alternate through the night with an average period of 90–110 min (the “ultradian” sleep cycle). Overall, in a healthy young adult, REM sleep constitutes 20–25% of total sleep, and NREM stages N1 and N2 constitute 50–60%.
Age has a profound impact on sleep state organization (Fig. 27-1). N3 sleep is most intense and prominent during childhood, decreasing with puberty and across the second and third decades of life. N3 sleep declines during adulthood to the point where it may be completely absent in older adults. The remaining NREM sleep becomes more fragmented, with many more frequent awakenings from NREM sleep. It is the increased frequency of awakenings, rather than a decreased ability to fall back asleep, that accounts for the increased wakefulness during the sleep episode in older people. While REM sleep may account for 50% of total sleep time in infancy, the percentage falls off sharply over the first postnatal year as a mature REM-NREM cycle develops; thereafter, REM sleep occupies about 25% of total sleep time.
Sleep deprivation degrades cognitive performance, particularly on tests that require continual vigilance. Paradoxically, older people are less vulnerable to the neurobehavioral performance impairment induced by acute sleep deprivation than young adults, maintaining their reaction time and sustaining vigilance with fewer lapses of attention. However, it is more difficult for older adults to obtain recovery sleep after staying awake all night, as the ability to sleep during the daytime declines with age.
After sleep deprivation, NREM sleep is generally recovered first, followed by REM sleep. However, because REM sleep tends to be most prominent in the second half of the night, sleep truncation (e.g., by an alarm clock) results in selective REM sleep deprivation. This may increase REM sleep pressure to the point where the first REM sleep may occur much earlier in the nightly sleep episode. Because several disorders (see below) also cause sleep fragmentation, it is important that the patient have sufficient sleep opportunity (at least 8 h per night) for several nights prior to a diagnostic polysomnogram.
There is growing evidence that inadequate sleep in humans is associated with glucose intolerance that may contribute to the development of diabetes, obesity, and the metabolic syndrome, plus impaired immune responses, accelerated atherosclerosis, and increased risk of cardiac disease, cognitive impairment, Alzheimer’s disease, and stroke. For these reasons, the National Academy of Medicine declared sleep deficiency and sleep disorders “an unmet public health problem.”
WAKE AND SLEEP ARE REGULATED BY BRAIN CIRCUITS
Two principal neural systems govern the expression of sleep and wakefulness. The ascending arousal system, illustrated in green in Fig. 27-2, consists of clusters of nerve cells extending from the upper pons to the hypothalamus and basal forebrain that activate the cerebral cortex, thalamus (which is necessary to relay sensory information to the cortex), and other forebrain regions. The ascending arousal neurons use monoamines (norepinephrine, dopamine, serotonin, and histamine), glutamate, or acetylcholine as neurotransmitters to activate their target neurons. Some basal forebrain neurons use GABA to disinhibit cortical inhibitory interneurons, thus promoting arousal. Additional wake-promoting neurons in the hypothalamus use the peptide neurotransmitter orexin (also known as hypocretin, shown in blue) to reinforce activity in the other arousal cell groups.
Relationship of drugs for insomnia with wake-sleep systems. The arousal system in the brain (green) includes monoaminergic, glutamatergic, and cholinergic neurons in the brainstem that activate neurons in the hypothalamus, thalamus, basal forebrain, and cerebral cortex. Orexin neurons (blue) in the hypothalamus, which are lost in narcolepsy, reinforce and stabilize arousal by activating other components of the arousal system. The sleep-promoting system (red) consists of GABAergic neurons in the preoptic area and brainstem that inhibit the components of the arousal system, thus allowing sleep to occur. Drugs used to treat insomnia include those that block the effects of arousal system neurotransmitters (green and blue) and those that enhance the effects of γ-aminobutyric acid (GABA) produced by the sleep system (red).
Damage to the arousal system at the level of the rostral pons and lower midbrain causes coma, indicating that the ascending arousal influence from this level is critical in maintaining wakefulness. Injury to the hypothalamic branch of the arousal system causes profound sleepiness, but usually not coma. Specific loss of the orexin neurons produces the sleep disorder narcolepsy (see below). Damage to the thalamus causes loss of the content of wakefulness, but wake-sleep cycles are largely preserved.
The arousal system is turned off during sleep by inhibitory inputs from cell groups in the sleep-promoting system, shown in Fig. 27-2 in red. These neurons in the preoptic area and pons use γ-aminobutyric acid (GABA) to inhibit the arousal system. Additional neurons in the lateral hypothalamus containing the peptide melanin-concentrating hormone promote REM sleep. Many sleep-promoting neurons are themselves inhibited by inputs from the arousal system. This mutual inhibition between the arousal- and sleep-promoting systems forms a neural circuit akin to what electrical engineers call a “flip-flop switch.” A switch of this type tends to promote rapid transitions between the on (wake) and off (sleep) states, while avoiding intermediate states. The relatively rapid transitions between waking and sleeping states, as seen in the EEG of humans and animals, is consistent with this model.
Neurons in the ventrolateral preoptic nucleus, one of the key sleep-promoting sites, are lost during normal human aging, correlating with reduced ability to maintain sleep (sleep fragmentation). The ventrolateral preoptic neurons are also injured in Alzheimer’s disease, which may in part account for the poor sleep quality in those patients.
Transitions between NREM and REM sleep appear to be governed by a similar switch in the brainstem. GABAergic REM-Off neurons have been identified in the lower midbrain that inhibit REM-On neurons in the upper pons. The REM-On group contains both GABAergic neurons that inhibit the REM-Off group (thus satisfying the conditions for a REM sleep flip-flop switch) as well as glutamatergic neurons that project widely in the central nervous system (CNS) to cause the key phenomena associated with REM sleep. REM-On neurons that project to the medulla and spinal cord activate inhibitory (GABA and glycine-containing) interneurons, which in turn hyperpolarize the motor neurons, producing the paralysis of REM sleep. REM-On neurons that project to the forebrain may be important in producing dreams.
The REM sleep switch receives cholinergic input, which favors transitions to REM sleep, and monoaminergic (norepinephrine and serotonin) input that prevents REM sleep. As a result, drugs that increase monoamine tone (e.g., serotonin or norepinephrine reuptake inhibitors) tend to reduce the amount of REM sleep. Damage to the neurons that promote REM sleep paralysis can produce REM sleep behavior disorder, a condition in which patients act out their dreams (see below).
SLEEP-WAKE CYCLES ARE DRIVEN BY HOMEOSTATIC, ALLOSTATIC, AND CIRCADIAN INPUTS
The gradual increase in sleep drive with prolonged wakefulness, followed by deeper slow-wave sleep and prolonged sleep episodes, demonstrates that there is a homeostatic mechanism that regulates sleep. The neurochemistry of sleep homeostasis is only partially understood, but with prolonged wakefulness, adenosine levels rise in parts of the brain. Adenosine may act through A1 receptors to directly inhibit many arousal-promoting brain regions. In addition, adenosine promotes sleep through A2a receptors; blockade of these receptors by caffeine is one of the chief ways in which people fight sleepiness. Other humoral factors, such as prostaglandin D2, have also been implicated in this process. Both adenosine and prostaglandin D2 activate the sleep-promoting neurons in the ventrolateral preoptic nucleus.
Allostasis is the physiologic response to a challenge such as physical danger or psychological threat that cannot be managed by homeostatic mechanisms. These stress responses can severely impact the need for and ability to sleep. For example, insomnia is very common in patients with anxiety and other psychiatric disorders. Stress-induced insomnia is even more common, affecting most people at some time in their lives. Positron emission tomography (PET) studies in patients with chronic insomnia show hyperactivation of components of the ascending arousal system, as well as their targets in the limbic system in the forebrain (e.g., cingulate cortex and amygdala). The limbic areas are not only targets for the arousal system, but they also send excitatory outputs back to the arousal system, which contributes to a vicious cycle of anxiety about insomnia that makes it more difficult to sleep. Approaches to treating insomnia may employ drugs that either inhibit the output of the ascending arousal system (green and blue in Fig. 27-2) or potentiate the output of the sleep-promoting system (red in Fig. 27-2). However, behavioral approaches (cognitive behavioral therapy [CBT] and sleep hygiene) that may reduce forebrain limbic activity at bedtime are often the best long term treatment.
Sleep is also regulated by a strong circadian timing signal, driven by the suprachiasmatic nuclei (SCN) of the hypothalamus, as described below. The SCN sends outputs to key sites in the hypothalamus, which impose 24-h rhythms on a wide range of behaviors and body systems, including the wake-sleep cycle.
PHYSIOLOGY OF CIRCADIAN RHYTHMICITY
The wake-sleep cycle is the most evident of many 24-h rhythms in humans. Prominent daily variations also occur in endocrine, thermoregulatory, cardiac, pulmonary, renal, immune, gastrointestinal, and neurobehavioral functions. At the molecular level, endogenous circadian rhythmicity is driven by self-sustaining transcriptional/translational feedback loops. In evaluating daily rhythms in humans, it is important to distinguish between diurnal components passively evoked by periodic environmental or behavioral changes (e.g., the increase in blood pressure and heart rate that occurs upon assumption of the upright posture) and circadian rhythms actively driven by an endogenous oscillatory process (e.g., the circadian variations in adrenal cortisol and pineal melatonin secretion that persist across a variety of environmental and behavioral conditions).
While it is now recognized that most cells in the body have circadian clocks that regulate diverse physiologic processes, most of these disparate clocks when placed in isolation in a tissue explant are unable to maintain the long-term synchronization with each other that is required to produce useful 24-h rhythms aligned with the external light-dark cycle. The neurons in the SCN are interconnected with one another in such a way as to produce a near-24-h synchronous rhythm of neural activity even in prolonged slice culture. They also receive visual input to synchronize them with the external world and have outputs to transmit that signal to the rest of the body. Bilateral destruction of the SCN results in a loss of most endogenous circadian rhythms including wake-sleep behavior and rhythms in endocrine and metabolic systems. The genetically determined period of this endogenous neural oscillator, which averages ~24.15 h in humans, is normally synchronized to the 24-h period of the environmental light-dark cycle through direct input from intrinsically photosensitive ganglion cells in the retina to the SCN. Humans are exquisitely sensitive to the resetting effects of light, particularly the shorter wavelengths (~460–500 nm) in the blue part of the visible spectrum. Small differences in circadian period contribute to variations in diurnal preference. For example, young adults typically have long intrinsic circadian periods and consequently go to bed late and rise late, whereas others have short periods and go to bed and rise earlier. Changes in homeostatic sleep regulation may underlie age-related changes in sleep-wake timing.
The timing and internal architecture of sleep are directly coupled to the output of the endogenous circadian pacemaker. Paradoxically, the endogenous circadian rhythm for wake propensity peaks just before the habitual bedtime, whereas that of sleep propensity peaks near the habitual wake time. These rhythms are thus timed to oppose the rise of sleep tendency throughout the usual waking day and the decline of sleep propensity during the habitual sleep episode, respectively. Misalignment of the endogenous circadian pacemaker with the desired wake-sleep cycle can, therefore, induce insomnia, decrease alertness, and impair performance, posing health problems for night-shift workers and airline travelers.
BEHAVIORAL AND PHYSIOLOGIC CORRELATES OF SLEEP STATES AND STAGES
Polysomnographic staging of sleep correlates with behavioral changes during specific states and stages. During the transitional state (stage N1) between wakefulness and deeper sleep, individuals may respond to faint auditory or visual signals. Formation of short-term memories is inhibited at the onset of NREM stage N1 sleep, which may explain why individuals aroused from that transitional sleep stage frequently lack situational awareness. After sleep deprivation, such transitions may intrude upon behavioral wakefulness notwithstanding attempts to remain continuously awake (see “Shift-Work Disorder,” below).
Subjects woken from REM sleep recall vivid dream imagery >80% of the time, especially later in the night. Less vivid imagery may also be reported after NREM sleep interruptions. Certain disorders may occur during specific sleep stages and are described below under “Parasomnias.” These include sleepwalking, night terrors, and enuresis (bed wetting), which occur most commonly in children during deep (N3) NREM sleep, and REM sleep behavior disorder, which occurs mainly among older men who fail to maintain full paralysis during REM sleep, and often call out, thrash around, or even act out fragments of dreams.
All major physiologic systems are influenced by sleep. Blood pressure and heart rate decrease during NREM sleep, particularly during N3 sleep. During REM sleep, bursts of eye movements are associated with large variations in both blood pressure and heart rate mediated by the autonomic nervous system. Cardiac dysrhythmias may occur selectively during REM sleep. Respiratory function also changes. In comparison to relaxed wakefulness, respiratory rate becomes slower but more regular during NREM sleep (especially N3 sleep) and becomes irregular during bursts of eye movements in REM sleep. Decreases in minute ventilation during NREM sleep are out of proportion to the decrease in metabolic rate, resulting in a slightly higher PCO2.
Within the brain itself, neurotransmission is supported by ion gradients across the cell membranes of neurons and astrocytes. These ion flows are accompanied by increases in intracellular volume, so that during wake, there is very little extracellular space in the brain. During sleep, intracellular volume is reduced, resulting in increased extracellular space, which has higher calcium and lower potassium concentrations, supporting hyperpolarization and reduced firing of neurons. This expansion of the extracellular space during sleep increases diffusion of substances that accumulate extracellularly, like β-amyloid peptide, enhancing their clearance from the brain via cerebrospinal fluid flow. Recent evidence suggests that lack of adequate sleep may contribute to extracellular accumulation of β-amyloid peptide, a key step in the pathogenesis of Alzheimer’s disease.
Endocrine function also varies with sleep. N3 sleep is associated with secretion of growth hormone in men, while sleep in general is associated with augmented secretion of prolactin in both men and women. Sleep has a complex effect on the secretion of luteinizing hormone (LH): during puberty, sleep is associated with increased LH secretion, whereas sleep in postpubertal women inhibits LH secretion in the early follicular phase of the menstrual cycle. Sleep onset (and probably N3 sleep) is associated with inhibition of thyroid-stimulating hormone and of the adrenocorticotropic hormone–cortisol axis, an effect that is superimposed on the prominent circadian rhythms in the two systems.
The pineal hormone melatonin is secreted predominantly at night in both day- and night-active species, reflecting the direct modulation of pineal activity by the SCN via the sympathetic nervous system which innervates the pineal gland. Melatonin secretion does not require sleep, but melatonin secretion is inhibited by ambient light, an effect mediated by the neural connection from the retina to the pineal gland via the SCN. Sleep efficiency is highest when sleep coincides with endogenous melatonin secretion. When endogenous melatonin levels are low, such as during the biological day or at the desired bedtime in patients with delayed sleep-wake phase disorder (DSWPD), administration of exogenous melatonin can hasten sleep onset and increase sleep efficiency, but it does not increase sleep efficiency if administered when endogenous melatonin levels are elevated. This may explain why melatonin is often ineffective in the treatment of patients with primary insomnia. On the other hand, patients with sympathetic denervation of the pineal gland, such as occurs in cervical spinal cord injury or in patients with Parkinson’s disease, often have low melatonin levels, and administration of melatonin (3 mg 30 min before bedtime) may help them sleep.
Sleep is accompanied by alterations of thermoregulatory function. NREM sleep is associated with an increase in the firing of warm-responsive neurons in the preoptic area and a fall in body temperature; conversely, skin warming without increasing core body temperature has been found to increase NREM sleep. REM sleep is associated with reduced thermoregulatory responsiveness.
DISORDERS OF SLEEP AND WAKEFULNESS
APPROACH TO THE PATIENT Sleep Disorders
Patients may seek help from a physician because of: (1) sleepiness or tiredness during the day; (2) difficulty initiating or maintaining sleep at night (insomnia); or (3) unusual behaviors during sleep itself (parasomnias).
Obtaining a careful history is essential. In particular, the duration, severity, and consistency of the symptoms are important, along with the patient’s estimate of the consequences of the sleep disorder on waking function. Information from a bed partner or family member is often helpful because some patients may be unaware of symptoms such as heavy snoring or may underreport symptoms such as falling asleep at work or while driving. Physicians should inquire about when the patient typically goes to bed, when they fall asleep and wake up, whether they awaken during sleep, whether they feel rested in the morning, and whether they nap during the day. Depending on the primary complaint, it may be useful to ask about snoring, witnessed apneas, restless sensations in the legs, movements during sleep, depression, anxiety, and behaviors around the sleep episode. The physical examination may provide evidence of a small airway, large tonsils, or a neurologic or medical disorder that contributes to the main complaint.
It is important to remember that, rarely, seizures may occur exclusively during sleep, mimicking a primary sleep disorder; such sleep-related seizures typically occur during episodes of NREM sleep and may take the form of generalized tonic-clonic movements (sometimes with urinary incontinence or tongue biting) or stereotyped movements in partial complex epilepsy (Chap. 418).
It is often helpful for the patient to complete a daily sleep log for 1–2 weeks to define the timing and amounts of sleep. When relevant, the log can also include information on levels of alertness, work times, and drug and alcohol use, including caffeine and hypnotics.
Polysomnography is necessary for the diagnosis of several disorders such as sleep apnea, narcolepsy, and periodic limb movement disorder (PLMD). A conventional polysomnogram performed in a clinical sleep laboratory allows measurement of sleep stages, respiratory effort and airflow, oxygen saturation, limb movements, heart rhythm, and additional parameters. A home sleep test usually focuses on just respiratory measures and is helpful in patients with a moderate to high likelihood of having obstructive sleep apnea. The multiple sleep latency test (MSLT) is used to measure a patient’s propensity to sleep during the day and can provide crucial evidence for diagnosing narcolepsy and some other causes of sleepiness. The maintenance of wakefulness test is used to measure a patient’s ability to sustain wakefulness during the daytime and can provide important evidence for evaluating the efficacy of therapies for improving sleepiness in conditions such as narcolepsy and obstructive sleep apnea.
EVALUATION OF DAYTIME SLEEPINESS
Up to 25% of the adult population has persistent daytime sleepiness that impairs an individual’s ability to perform optimally in school, at work, while driving, and in other conditions that require alertness. Sleepy students often have trouble staying alert and performing well in school, and sleepy adults struggle to stay awake and focused on their work. More than half of Americans have fallen asleep while driving. An estimated 1.2 million motor vehicle crashes per year are due to drowsy drivers, causing about 20% of all serious crash injuries and deaths. One needn’t fall asleep to have an accident, as the inattention and slowed responses of drowsy drivers are a major contributor. Twenty-four hours of continuous wakefulness impairs reaction time as much as a blood alcohol concentration of 0.10 g/dL (which is legally drunk in all 50 states).
Identifying and quantifying sleepiness can be challenging. First, patients may describe themselves as “sleepy,” “fatigued,” or “tired,” and the meanings of these words may differ between patients. For clinical purposes, it is best to use the term “sleepiness” to describe a propensity to fall asleep; whereas “fatigue” is best used to describe a feeling of low physical or mental energy but without a tendency to actually sleep. Sleepiness is usually most evident when the patient is sedentary, whereas fatigue may interfere with more active pursuits. Sleepiness generally occurs with disorders that reduce the quality or quantity of sleep or that interfere with the neural mechanisms of arousal, whereas fatigue is more common in inflammatory disorders such as cancer, multiple sclerosis (Chap. 436), fibromyalgia (Chap. 366), chronic fatigue syndrome (Chap. 442), or endocrine deficiencies such as hypothyroidism (Chap. 376) or Addison’s disease (Chap. 379). Second, sleepiness can affect judgment in a manner analogous to ethanol, such that patients may have limited insight into the condition and the extent of their functional impairment. Finally, patients may be reluctant to admit that sleepiness is a problem because they may have become unfamiliar with feeling fully alert and because sleepiness is sometimes viewed pejoratively as reflecting poor motivation or bad sleep habits.
Table 27-1 outlines the diagnostic and therapeutic approach to the patient with a complaint of excessive daytime sleepiness.
TABLE 27-1Evaluation of the Patient with Excessive Daytime Sleepiness ||Download (.pdf) TABLE 27-1 Evaluation of the Patient with Excessive Daytime Sleepiness
|Findings on History and Physical Examination ||Diagnostic Evaluation ||Diagnosis ||Therapy |
|Difficulty waking in the morning, rebound sleep on weekends and vacations with improvement in sleepiness ||Sleep log ||Insufficient sleep ||Sleep education and behavioral modification to increase amount of sleep |
|Obesity, snoring, hypertension ||Polysomnogram or home sleep test ||Obstructive sleep apnea (Chap. 291) ||Continuous positive airway pressure; upper airway surgery (e.g., uvulopalatopharyngoplasty); dental appliance; weight loss |
|Cataplexy, hypnogogic hallucinations, sleep paralysis ||Polysomnogram and multiple sleep latency test ||Narcolepsy ||Stimulants (e.g., modafinil, methylphenidate); REM sleep-suppressing antidepressants (e.g., venlafaxine); sodium oxybate |
|Restless legs, kicking movements during sleep ||Assessment for predisposing medical conditions (e.g., iron deficiency or renal failure) ||Restless legs syndrome with or without periodic limb movements ||Treatment of predisposing condition; dopamine agonists (e.g., pramipexole, ropinirole); gabapentin; opiates |
|Sedating medications, stimulant withdrawal, head trauma, systemic inflammation, Parkinson’s disease and other neurodegenerative disorders, hypothyroidism, encephalopathy ||Thorough medical history and examination including detailed neurologic examination ||Sleepiness due to a drug or medical condition ||Change medications, treat underlying condition, consider stimulants |
To determine the extent and impact of sleepiness on daytime function, it is helpful to ask patients about the occurrence of sleep episodes during normal waking hours, both intentional and unintentional. Specific areas to be addressed include the occurrence of inadvertent sleep episodes while driving or in other safety-related settings, sleepiness while at work or school (and the relationship of sleepiness to work and school performance), and the effect of sleepiness on social and family life. Standardized questionnaires such as the Epworth Sleepiness Scale are often used clinically to measure sleepiness.
Eliciting a history of daytime sleepiness is usually adequate, but objective quantification is sometimes necessary. The MSLT measures a patient’s propensity to sleep under quiet conditions. An overnight polysomnogram should precede the MSLT to establish that the patient has had an adequate amount of good-quality nighttime sleep. The MSLT consists of five 20-min nap opportunities every 2 h across the day. The patient is instructed to try to fall asleep, and the major endpoints are the average latency to sleep and the occurrence of REM sleep during the naps. An average sleep latency across the naps of <8 min is considered objective evidence of excessive daytime sleepiness. REM sleep normally occurs only during the nighttime sleep episode, and the occurrence of REM sleep in two or more of the MSLT naps provides support for the diagnosis of narcolepsy.
For the safety of the individual and the general public, physicians have a responsibility to help manage issues around driving in patients with sleepiness. Legal reporting requirements vary from state to state, but at a minimum, physicians should inform sleepy patients about their increased risk of having an accident and advise such patients not to drive a motor vehicle until the sleepiness has been treated effectively. This discussion is especially important for commercial drivers, and it should be documented in the patient’s medical record.
Insufficient sleep is probably the most common cause of excessive daytime sleepiness. The average adult needs 7.5–8 h of sleep, but on weeknights, the average U.S. adult gets only 6.75 h of sleep. Only 30% of the U.S. adult population reports consistently obtaining sufficient sleep. Insufficient sleep is especially common among shift workers, individuals working multiple jobs, and people in lower socioeconomic groups. Most teenagers need ≥9 h of sleep, but many fail to get enough sleep because of circadian phase delay, plus social pressures to stay up late coupled with early school start times. Late evening light exposure, television viewing, video-gaming, social media, texting, and smartphone use often delay bedtimes despite the fixed, early wake times required for work or school. As is typical with any disorder that causes sleepiness, individuals with chronically insufficient sleep may feel inattentive, irritable, unmotivated, and depressed, and have difficulty with school, work, and driving. Individuals differ in their optimal amount of sleep, and it can be helpful to ask how much sleep the patient obtains on a quiet vacation when he or she can sleep without restrictions. Some patients may think that a short amount of sleep is normal or advantageous, and they may not appreciate their biological need for more sleep, especially if coffee and other stimulants mask the sleepiness. A 2-week sleep log documenting the timing of sleep and daily level of alertness is diagnostically useful and provides helpful feedback for the patient. Extending sleep to the optimal amount on a regular basis can resolve the sleepiness and other symptoms. As with any lifestyle change, extending sleep requires commitment and adjustments, but the improvements in daytime alertness make this change worthwhile.
Respiratory dysfunction during sleep is a common, serious cause of excessive daytime sleepiness as well as of disturbed nocturnal sleep. At least 24% of middle-aged men and 9% of middle-aged women in the United States have a reduction or cessation of breathing dozens or more times each night during sleep, with 9% of men and 4% of women doing so more than a hundred times per night. These episodes may be due to an occlusion of the airway (obstructive sleep apnea), absence of respiratory effort (central sleep apnea), or a combination of these factors. Failure to recognize and treat these conditions appropriately may lead to impairment of daytime alertness, increased risk of sleep-related motor vehicle crashes, depression, hypertension, myocardial infarction, diabetes, stroke, and increased mortality. Sleep apnea is particularly prevalent in overweight men and in the elderly, yet it is estimated to go undiagnosed in most affected individuals. This is unfortunate because several effective treatments are available. Readers are referred to Chap. 291 for a comprehensive review of the diagnosis and treatment of patients with sleep apnea.
Narcolepsy is characterized by difficulty sustaining wakefulness, poor regulation of REM sleep, and disturbed nocturnal sleep. All patients with narcolepsy have excessive daytime sleepiness. This sleepiness is usually moderate to severe, and in contrast to patients with disrupted sleep (e.g., sleep apnea), people with narcolepsy usually feel well rested upon awakening and then feel tired throughout much of the day. In addition, they often experience symptoms related to an intrusion of REM sleep characteristics. REM sleep is characterized by dreaming and muscle paralysis, and people with narcolepsy can have: (1) sudden muscle weakness without a loss of consciousness, which is usually triggered by strong emotions (cataplexy; Video 27-1); (2) dream-like hallucinations at sleep onset (hypnagogic hallucinations) or upon awakening (hypnopompic hallucinations); and (3) muscle paralysis upon awakening (sleep paralysis). With severe cataplexy, an individual may be laughing at a joke and then suddenly collapse to the ground, immobile but awake for 1–2 min. With milder episodes, patients may have partial weakness of the face or neck. Narcolepsy is one of the more common causes of chronic sleepiness and affects about 1 in 2000 people in the United States. Narcolepsy typically begins between age 10 and 20; once established, the disease persists for life.
Video 027-1: Classic Cataplexy
A typical episode of severe cataplexy. The patient is joking and then falls to the ground with an abrupt loss of muscle tone. The electromyogram recordings (four lower traces on the right) show reductions in muscle activity during the period of paralysis. The electroencephalogram (top two traces) shows wakefulness throughout the episode. (Video courtesy of Giuseppe Plazzi, University of Bologna.)
Narcolepsy is caused by loss of the hypothalamic neurons that produce the orexin neuropeptides (also known as hypocretins). Research in mice and dogs first demonstrated that a loss of orexin signaling due to null mutations of either the orexin neuropeptides or one of the orexin receptors causes sleepiness and cataplexy nearly identical to that seen in people with narcolepsy. Although genetic mutations rarely cause human narcolepsy, researchers soon discovered that patients with narcolepsy with cataplexy (now called type 1 narcolepsy) have very low or undetectable levels of orexins in their cerebrospinal fluid, and autopsy studies showed a nearly complete loss of the orexin-producing neurons in the hypothalamus. The orexins normally promote long episodes of wakefulness and suppress REM sleep, and thus, loss of orexin signaling results in frequent intrusions of sleep during the usual waking episode, with REM sleep and fragments of REM sleep at any time of day (Fig. 27-3). Patients with narcolepsy but no cataplexy (type 2 narcolepsy) usually have normal orexin levels and may have other yet uncharacterized causes of their excessive daytime sleepiness.
Polysomnographic recordings of a healthy individual and a patient with narcolepsy. The healthy individual has a long period or NREM sleep before entering REM sleep, but the individual with narcolepsy enters rapid eye movement (REM) sleep quickly at night and has moderately fragmented sleep. During the day, the healthy subject stays awake from 8:00 AM until midnight, but the patient with narcolepsy dozes off frequently, with many daytime naps that include REM sleep.
Extensive evidence suggests that an autoimmune process likely causes this selective loss of the orexin-producing neurons. Certain human leukocyte antigens (HLAs) can increase the risk of autoimmune disorders (Chap. 343), and narcolepsy has the strongest known HLA association. HLA DQB1*06:02 is found in >90% of people with type 1 narcolepsy, whereas it occurs in only 12–25% of the general population. Researchers now hypothesize that in people with DQB1*06:02, an immune response against influenza, Streptococcus, or other infections may also damage the orexin-producing neurons through a process of molecular mimicry. This mechanism may account for the eight- to twelvefold increase in new cases of narcolepsy among children in Europe who received a particular brand of H1N1 influenza A vaccine (Pandemrix). Traumatic brain injury can also damage orexin-containing neurons, inducing type 2 narcolepsy.
On rare occasions, narcolepsy can occur with neurologic disorders such as tumors or strokes that directly damage the orexin-producing neurons in the hypothalamus or their projections.
Narcolepsy is most commonly diagnosed by the history of chronic sleepiness plus cataplexy or other symptoms. Many disorders can cause feelings of weakness, but with true cataplexy, patients will describe definite functional weakness (e.g., slurred speech, dropping a cup, slumping into a chair) that has consistent emotional triggers such as heartfelt mirth when laughing at a great joke, happy surprise at unexpectedly seeing a friend, or intense anger. Cataplexy occurs in about half of all narcolepsy patients and is diagnostically very helpful because it occurs in almost no other disorder. In contrast, occasional hypnagogic hallucinations and sleep paralysis occur in about 20% of the general population, and these symptoms are not as diagnostically specific.
When narcolepsy is suspected, the diagnosis should be firmly established with a polysomnogram followed the next day by an MSLT. The polysomnogram helps rule out other possible causes of sleepiness such as sleep apnea and establishes that the patient was not sleep deprived the night before, and the MSLT provides essential, objective evidence of sleepiness plus REM sleep dysregulation. Across the five naps of the MSLT, most patients with narcolepsy will fall asleep in <8 min on average, and they will have episodes of REM sleep in at least two of the naps. Abnormal regulation of REM sleep is also manifested by the appearance of REM sleep within 15 min of sleep onset at night, which is rare in healthy individuals sleeping at their habitual bedtime. Stimulants should be stopped 1 week before the MSLT and antidepressants should be stopped 3 weeks prior, because these medications can affect the MSLT. In addition, patients should be encouraged to obtain a fully adequate amount of sleep each night for the week prior to the test to eliminate any effects of insufficient sleep.
The treatment of narcolepsy is symptomatic. Most patients with narcolepsy feel more alert after sleep, and they should be encouraged to get adequate sleep each night and to take a 15- to 20-min nap in the afternoon. This nap may be sufficient for some patients with mild narcolepsy, but most also require treatment with wake-promoting medications. Modafinil is used quite often because it has fewer side effects than amphetamines and a relatively long half-life; for most patients, 200–400 mg each morning is very effective. Methylphenidate (10–20 mg bid) or dextroamphetamine (10 mg bid) are often effective, but sympathomimetic side effects, anxiety, and the potential for abuse can be concerns. These medications are available in slow-release formulations, extending their duration of action and allowing easier dosing. Sodium oxybate (gamma hydroxybutyrate) is given twice each night and is often very valuable in improving alertness, but it can produce excessive sedation, nausea, and confusion.
Cataplexy is usually much improved with antidepressants that increase noradrenergic or serotonergic tone because these neurotransmitters strongly suppress REM sleep and cataplexy. Venlafaxine (37.5–150 mg each morning) and fluoxetine (10–40 mg each morning) are often quite effective. The tricyclic antidepressants, such as protriptyline (10–40 mg/d) or clomipramine (25–50 mg/d) are potent suppressors of cataplexy, but their anticholinergic effects, including sedation and dry mouth, make them less attractive.1 Sodium oxybate, given at bedtime and 3–4 h later, is also very helpful in reducing cataplexy.
Insomnia is the complaint of poor sleep and usually presents as difficulty initiating or maintaining sleep. People with insomnia are dissatisfied with their sleep and feel that it impairs their ability to function well in work, school, and social situations. Affected individuals often experience fatigue, decreased mood, irritability, malaise, and cognitive impairment.
Chronic insomnia, lasting >3 months, occurs in about 10% of adults and is more common in women, older adults, people of lower socioeconomic status, and individuals with medical, psychiatric, and substance abuse disorders. Acute or short-term insomnia affects over 30% of adults and is often precipitated by stressful life events such as a major illness or loss, change of occupation, medications, and substance abuse. If the acute insomnia triggers maladaptive behaviors such as increased nocturnal light exposure, frequently checking the clock, or attempting to sleep more by napping, it can lead to chronic insomnia.
Most insomnia begins in adulthood, but many patients may be predisposed and report easily disturbed sleep predating the insomnia, suggesting that their sleep is lighter than usual. Clinical studies and animal models indicate that insomnia is associated with activation during sleep of brain areas normally active only during wakefulness. The polysomnogram is rarely used in the evaluation of insomnia, as it typically confirms the patient’s subjective report of long latency to sleep and numerous awakenings but usually adds little new information. Many patients with insomnia have increased fast (beta) activity in the EEG during sleep; this fast activity is normally present only during wakefulness, which may explain why some patients report feeling awake for much of the night. The MSLT is rarely used in the evaluation of insomnia because, despite their feelings of low energy, most people with insomnia do not easily fall asleep during the day, and on the MSLT, their average sleep latencies are usually longer than normal.
Many factors can contribute to insomnia, and obtaining a careful history is essential so one can select therapies targeting the underlying factors. The assessment should focus on identifying predisposing, precipitating, and perpetuating factors.
Many patients with insomnia have negative expectations and conditioned arousal that interfere with sleep. These individuals may worry about their insomnia during the day and have increasing anxiety as bedtime approaches if they anticipate a poor night of sleep. While attempting to sleep, they may frequently check the clock, which only heightens anxiety and frustration. They may find it easier to sleep in a new environment rather than their bedroom, as it lacks the negative associations.
Patients with insomnia sometimes develop counterproductive behaviors that contribute to their insomnia. These can include daytime napping that reduces sleep drive at night; an irregular sleep-wake schedule that disrupts their circadian rhythms; use of wake-promoting substances (e.g., caffeine, tobacco) too close to bedtime; engaging in alerting or stressful activities close to bedtime (e.g., arguing with a partner, work-related emailing and texting while in bed, sleeping with a smartphone or tablet at the bedside); and routinely using the bedroom for activities other than sleep or sex (e.g., TV, work), so the bedroom becomes associated with arousing or stressful feelings.
About 80% of patients with psychiatric disorders have sleep complaints, and about half of all chronic insomnia occurs in association with a psychiatric disorder. Depression is classically associated with early morning awakening, but it can also interfere with the onset and maintenance of sleep. Mania and hypomania can disrupt sleep and often are associated with substantial reductions in the total amount of sleep. Anxiety disorders can lead to racing thoughts and rumination that interfere with sleep and can be very problematic if the patient’s mind becomes active midway through the night. Panic attacks can arise from sleep and need to be distinguished from other parasomnias. Insomnia is common in schizophrenia and other psychoses, often resulting in fragmented sleep, less deep NREM sleep, and sometimes reversal of the day-night sleep pattern.
Medications and Drugs of Abuse
A wide variety of psychoactive drugs can interfere with sleep. Caffeine, which has a half-life of 6–9 h, can disrupt sleep for up to 8–14 h, depending on the dose, variations in metabolism, and an individual’s caffeine sensitivity. Insomnia can also result from use of prescription medications too close to bedtime (e.g., antidepressants, stimulants, glucocorticoids, theophylline). Conversely, withdrawal of sedating medications such as alcohol, narcotics, or benzodiazepines can cause insomnia. Alcohol taken just before bed can shorten sleep latency, but it often produces rebound insomnia 2–3 h later as it wears off. This same problem with sleep maintenance can occur with short-acting benzodiazepines such as alprazolam.
A large number of medical conditions disrupt sleep. Pain from rheumatologic disorders or a painful neuropathy commonly disrupts sleep. Some patients may sleep poorly because of respiratory conditions such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, congestive heart failure, or restrictive lung disease, and some of these disorders are worse at night in bed due to circadian variations in airway resistance and postural changes that can result in nocturnal dyspnea. Many women experience poor sleep with the hormonal changes of menopause. Gastroesophageal reflux is also a common cause of difficulty sleeping.
Dementia (Chap. 25) is often associated with poor sleep, probably due to a variety of factors, including napping during the day, altered circadian rhythms, and perhaps a weakened output of the brain’s sleep-promoting mechanisms. In fact, insomnia and nighttime wandering are some of the most common causes for institutionalization of patients with dementia, because they place a larger burden on caregivers. Conversely, in cognitively intact elderly men, fragmented sleep and poor sleep quality are associated with subsequent cognitive decline. Patients with Parkinson’s disease may sleep poorly due to rigidity, dementia, and other factors. Fatal familial insomnia is a very rare neurodegenerative condition caused by mutations in the prion protein gene, and although insomnia is a common early symptom, most patients present with other obvious neurologic signs such dementia, myoclonus, dysarthria, or autonomic dysfunction.
Treatment of insomnia improves quality of life and can promote long-term health. With improved sleep, patients often report less daytime fatigue, improved cognition, and more energy. Treating the insomnia can also improve the comorbid disease. For example, management of insomnia at the time of diagnosis of major depression often improves the response to antidepressants and reduces the risk of relapse. Sleep loss can heighten the perception of pain, so a similar approach is warranted in acute and chronic pain management.
The treatment plan should target all putative contributing factors: establish good sleep hygiene, treat medical disorders, use behavioral therapies for anxiety and negative conditioning, and use pharmacotherapy and/or psychotherapy for psychiatric disorders. Behavioral therapies should be the first-line treatment, followed by judicious use of sleep-promoting medications if needed. TREATMENT OF MEDICAL AND PSYCHIATRIC DISEASE
If the history suggests that a medical or psychiatric disease contributes to the insomnia, then it should be addressed by, for example, treating the pain, improving breathing, and switching or adjusting the timing of medications. IMPROVE SLEEP HYGIENE
Attention should be paid to improving sleep hygiene and avoiding counterproductive, arousing behaviors before bedtime. Patients should establish a regular bedtime and wake time, even on weekends, to help synchronize their circadian rhythms and sleep patterns. The amount of time allocated for sleep should not be more than their actual total amount of sleep. In the 30 min before bedtime, patients should establish a relaxing “wind-down” routine that can include a warm bath, listening to music, meditation, or other relaxation techniques. The bedroom should be off-limits to computers, televisions, radios, smartphones, videogames, and tablets. Once in bed, patients should try to avoid thinking about anything stressful or arousing such as problems with relationships or work. If they cannot fall asleep within 20 min, it often helps to get out of bed and read or listen to relaxing music in dim light as a form of distraction from any anxiety, but artificial light, including light from a television, cell phone, or computer, should be avoided, because light itself suppresses melatonin secretion and is arousing.
Table 27-2 outlines some of the key aspects of good sleep hygiene to improve insomnia. COGNITIVE BEHAVIORAL THERAPY
CBT uses a combination of the techniques above plus additional methods to improve insomnia. A trained therapist may use cognitive psychology techniques to reduce excessive worrying about sleep and to reframe faulty beliefs about the insomnia and its daytime consequences. The therapist may also teach the patient relaxation techniques, such as progressive muscle relaxation or meditation, to reduce autonomic arousal, intrusive thoughts, and anxiety. MEDICATIONS FOR INSOMNIA
If insomnia persists after treatment of these contributing factors, pharmacotherapy is often used on a nightly or intermittent basis. A variety of sedatives can improve sleep.
Antihistamines, such as diphenhydramine, are the primary active ingredient in most over-the-counter sleep aids. These may be of benefit when used intermittently, but can produce tolerance and anticholinergic side effects such as dry mouth and constipation, which limit their use, particularly in the elderly.
Benzodiazepine receptor agonists (BzRAs) are an effective and well-tolerated class of medications for insomnia. BzRAs bind to the GABAA receptor and potentiate the postsynaptic response to GABA. GABAA receptors are found throughout the brain, and BzRAs may globally reduce neural activity and may enhance the activity of specific sleep-promoting GABAergic pathways. Classic BzRAs include lorazepam, triazolam, and clonazepam, whereas newer agents such as zolpidem and zaleplon have more selective affinity for the α1 subunit of the GABAA receptor.
Specific BzRAs are often chosen based on the desired duration of action. The most commonly prescribed agents in this family are zaleplon (5–20 mg), with a half-life of 1–2 h; zolpidem (5–10 mg) and triazolam (0.125–0.25 mg), with half-lives of 2–4 h; eszopiclone (1–3 mg), with a half-life of 5–8 h; and temazepam (15–30 mg), with a half-life of 8–20 h. Generally, side effects are minimal when the dose is kept low and the serum concentration is minimized during the waking hours (by using the shortest-acting effective agent). For chronic insomnia, intermittent use is recommended, unless the consequences of untreated insomnia outweigh concerns regarding chronic use.
The heterocyclic antidepressants (trazodone, amitriptyline,2 and doxepin) are the most commonly prescribed alternatives to BzRAs due to their lack of abuse potential and lower cost. Trazodone (25–100 mg) is used more commonly than the tricyclic antidepressants, because it has a much shorter half-life (5–9 h) and less anticholinergic activity.
The orexin receptor antagonist suvorexant (10–20 mg) can also improve insomnia by blocking the wake-promoting effects of the orexin neuropeptides. It has a long half-life and can produce morning sedation, and as it reduces orexin signaling, it can rarely produce hypnagogic hallucinations and sleep paralysis (see narcolepsy section above). A dual orexin receptor antagonist daridorexant, also improved sleep outcomes in two randomized phase 3 trials.
Medications for insomnia are now among the most commonly prescribed medications, but they should be used cautiously. All sedatives increase the risk of injurious falls and confusion in the elderly, and therefore if needed, these medications should be used at the lowest effective dose. Morning sedation can interfere with driving and judgment, and when selecting a medication, one should consider the duration of action. Benzodiazepines carry a risk of addiction and abuse, especially in patients with a history of alcohol or sedative abuse. In patients with depression, all sedatives can worsen the depression. Like alcohol, some sleep-promoting medications can worsen sleep apnea. Sedatives can also produce complex behaviors during sleep, such as sleep walking and sleep eating, although this seems more likely at higher doses.
TABLE 27-2Methods to Improve Sleep Hygiene in Insomnia Patients ||Download (.pdf) TABLE 27-2 Methods to Improve Sleep Hygiene in Insomnia Patients
|Helpful Behaviors ||Behaviors to Avoid |
Use the bed only for sleep and sex
Avoid behaviors that interfere with sleep physiology, including:
Make quality sleep a priority
Go to bed and get up at the same time each day
Ensure a restful environment (comfortable bed, bedroom quiet and dark)
In the 2–3 h before bedtime, avoid:
Smoking or alcohol
Develop a consistent bedtime routine. For example:
Prepare for sleep with 20–30 min of relaxation (e.g., soft music, meditation, yoga, pleasant reading)
Take a warm bath
When trying to fall asleep, avoid:
Patients with restless legs syndrome (RLS) report an irresistible urge to move the legs. Many patients report a creepy-crawly or unpleasant deep ache within the thighs or calves, and those with more severe RLS may have discomfort in the arms as well. For most patients with RLS, these dysesthesias and restlessness are much worse in the evening and first half of the night. The symptoms appear with inactivity and can make sitting still in an airplane or when watching a movie a miserable experience. The sensations are temporarily relieved by movement, stretching, or massage. This nocturnal discomfort usually interferes with sleep, and patients may report daytime sleepiness as a consequence. RLS is very common, affecting 5–10% of adults and is more common in women and older adults.
A variety of factors can cause RLS. Iron deficiency is the most common treatable cause, and iron replacement should be considered if the ferritin level is <75 ng/mL. RLS can also occur with peripheral neuropathies and uremia and can be worsened by pregnancy, caffeine, alcohol, antidepressants, lithium, neuroleptics, and antihistamines. Genetic factors contribute to RLS, and polymorphisms in a variety of genes (BTBD9, MEIS1, MAP2K5/LBXCOR, and PTPRD) have been linked to RLS, although as yet, the mechanism through which they cause RLS remains unknown. Roughly one-third of patients (particularly those with an early age of onset) have multiple affected family members.
RLS is treated by addressing the underlying cause such as iron deficiency if present. Otherwise, treatment is symptomatic, and dopamine agonists or alpha-2-delta calcium channel ligands are used most frequently. Agonists of dopamine D2/3 receptors such as pramipexole (0.25–0.5 mg q7PM) or ropinirole (0.5–4 mg q7PM) are usually quite effective, but about 25% of patients taking dopamine agonists develop augmentation, a worsening of RLS such that symptoms begin earlier in the day and can spread to other body regions. Other possible side effects of dopamine agonists include nausea, morning sedation, and increases in rewarding behavior such as gambling and sex. Alpha-2-delta calcium channel ligands such as gabapentin (300–600 mg q7PM) and pregabalin (150–450 mg q7PM) can also be quite effective; these do not cause augmentation and they can be especially helpful in patients with concomitant pain, neuropathy or anxiety. Opioids and benzodiazepines may also be of therapeutic value. Most patients with restless legs also experience PLMD, although the reverse is not the case.
PERIODIC LIMB MOVEMENT DISORDER
PLMD involves rhythmic twitches of the legs that disrupt sleep. The movements resemble a triple flexion reflex with extensions of the great toe and dorsiflexion of the foot for 0.5–5.0 s, which recur every 20–40 s during NREM sleep, in episodes lasting from minutes to hours. PLMD is diagnosed by a polysomnogram that includes recordings of the anterior tibialis and sometimes other muscles. The EEG shows that the movements of PLMD frequently cause brief arousals that disrupt sleep and can cause insomnia and daytime sleepiness. PLMD can be caused by the same factors that cause RLS (see above), and the frequency of leg movements improves with the same medications as used for RLS, including dopamine agonists. Recent genetic studies identified polymorphisms associated with both RLS and PLMD, suggesting that they may have a common pathophysiology.
Parasomnias are abnormal behaviors or experiences that arise from or occur during sleep. A variety of parasomnias can occur during NREM sleep, from brief confusional arousals to sleepwalking and night terrors. The presenting complaint is usually related to the behavior itself, but the parasomnias can disturb sleep continuity or lead to mild impairments in daytime alertness. Two main parasomnias occur in REM sleep: REM sleep behavior disorder (RBD) and nightmares.
Patients affected by this disorder carry out automatic motor activities that range from simple to complex. Individuals may walk, urinate inappropriately, eat, exit the house, or drive a car with minimal awareness. It may be difficult to arouse the patient to wakefulness, and occasional individuals may respond to attempted awakening with agitation or violence. In general it is safest to lead the patient back to bed, at which point he or she will often fall back asleep. Sleepwalking arises from NREM stage N3 sleep, usually in the first few hours of the night, and the EEG initially shows the slow cortical activity of deep NREM sleep even when the patient is moving about. Sleepwalking is most common in children and adolescents, when deep NREM sleep is most abundant. About 15% of children have occasional sleepwalking, and it persists in about 1% of adults. Episodes are usually isolated but may be recurrent in 1–6% of patients. The cause is unknown, although it has a familial basis in roughly one-third of cases. Sleepwalking can be worsened by insufficient sleep, which subsequently causes an increase in deep NREM sleep; alcohol; and stress. These should be addressed if present. Small studies have shown some efficacy of antidepressants and benzodiazepines; relaxation techniques and hypnosis can also be helpful. Patients and their families should improve home safety (e.g., replace glass doors, remove low tables to avoid tripping) to minimize the chance of injury if sleepwalking occurs.
This disorder occurs primarily in young children during the first few hours of sleep during NREM stage N3 sleep. The child often sits up during sleep and screams, exhibiting autonomic arousal with sweating, tachycardia, large pupils, and hyperventilation. The individual may be difficult to arouse and rarely recalls the episode on awakening in the morning. Treatment usually consists of reassuring the parents that the condition is self-limited and benign, and like sleepwalking, it may improve by avoiding insufficient sleep.
Bedwetting, like sleepwalking and night terrors, is another parasomnia that occurs during sleep in the young. Before age 5 or 6 years, nocturnal enuresis should be considered a normal feature of development. The condition usually improves spontaneously by puberty, persists in 1–3% of adolescents, and is rare in adulthood. Treatment consists of bladder training exercises and behavioral therapy. Symptomatic pharmacotherapy is usually accomplished in adults with desmopressin (0.2 mg qhs), oxybutynin chloride (5 mg qhs), or imipramine (10–25 mg qhs). Important causes of nocturnal enuresis in patients who were previously continent for 6–12 months include urinary tract infections or malformations, cauda equina lesions, emotional disturbances, epilepsy, sleep apnea, and certain medications.
Bruxism is an involuntary, forceful grinding of teeth during sleep that affects 10–20% of the population. The patient is usually unaware of the problem. The typical age of onset is 17–20 years, and spontaneous remission usually occurs by age 40. In many cases, the diagnosis is made during dental examination, damage is minor, and no treatment is indicated. In more severe cases, treatment with a mouth guard is necessary to prevent tooth injury. Stress management, benzodiazepines, and biofeedback can be useful when bruxism is a manifestation of psychological stress.
REM Sleep Behavior Disorder (RBD)
RBD (Video 27-2) is distinct from other parasomnias in that it occurs during REM sleep. The patient or the bed partner usually reports agitated or violent behavior during sleep, and upon awakening, the patient can often report a dream that matches the accompanying movements. During normal REM sleep, nearly all non-respiratory skeletal muscles are paralyzed, but in patients with RBD, dramatic limb movements such as punching or kicking lasting seconds to minutes occur during REM sleep, and it is not uncommon for the patient or the bed partner to be injured.
Video 027-2: REM Sleep Behavior Disorder
Typical aggressive movements in rapid eye movement (REM) sleep behavior disorder. (Video courtesy of Dr. Carlos Schenck, University of Minnesota Medical School.)
The prevalence of RBD increases with age, afflicting about 2% of adults aged >70, and is about twice as common in men. Most already have or will develop a neurodegenerative disorder. Within 12 years of disease onset, half of RBD patients develop a synucleinopathy such as Parkinson’s disease (Chap. 427) or dementia with Lewy bodies (Chap. 426), or occasionally multiple system atrophy (Chap. 432), and over 90% develop a synucleinopathy by 25 years. Misfolded a-synuclein can be detected in the CSF of patients with RBD and is associated with an increased risk of development of these disorders. RBD can occur in patients taking antidepressants, and in some, these medications may unmask this early indicator of neurodegeneration. Synucleinopathies probably cause neuronal loss in brainstem regions that regulate muscle paralysis during REM sleep, and loss of these neurons permits movements to break through during REM sleep. RBD also occurs in about 30% of patients with narcolepsy, but the underlying cause is probably different, as they seem to be at no increased risk of a neurodegenerative disorder.
Many patients with RBD have sustained improvement with clonazepam (0.5–2.0 mg qhs).3 Melatonin at doses up to 9 mg nightly may also prevent attacks.
CIRCADIAN RHYTHM SLEEP DISORDERS
A subset of patients presenting with either insomnia or hypersomnia may have a disorder of sleep timing rather than sleep generation. Disorders of sleep timing can be either organic (i.e., due to an abnormality of circadian pacemaker[s]) or environmental/behavioral (i.e., due to a disruption of environmental synchronizers). Effective therapies aim to entrain the circadian rhythm of sleep propensity to an appropriate phase.
Delayed Sleep-Wake Phase Disorder
DSWPD is characterized by: (1) reported sleep onset and wake times persistently later than desired; (2) actual sleep times at nearly the same clock hours daily; and (3) if conducted at the habitual delayed sleep time, essentially normal sleep on polysomnography (except for delayed sleep onset). Patients with DSWPD exhibit an abnormally delayed endogenous circadian phase, which can be assessed by measuring the onset of secretion of melatonin in either the blood or saliva; this is best done in a dimly lit environment as light suppresses melatonin secretion. Dim-light melatonin onset (DLMO) in DSWPD patients occurs later in the evening than normal, which is about 8:00–9:00 P.M. (i.e., about 1–2 h before habitual bedtime). Patients tend to be young adults. The delayed circadian phase could be due to: (1) an abnormally long, genetically determined intrinsic period of the endogenous circadian pacemaker; (2) reduced phase-advancing capacity of the pacemaker; (3) slower rate of buildup of homeostatic sleep drive during wakefulness; or (4) an irregular prior sleep-wake schedule, characterized by frequent nights when the patient chooses to remain awake while exposed to artificial light well past midnight (for personal, social, school, or work reasons). In most cases, it is difficult to distinguish among these factors, as patients with either a behaviorally induced or biologically driven circadian phase delay may both exhibit a similar circadian phase delay in DLMO, and both factors make it difficult to fall asleep at the desired hour. Late onset of dim-light melatonin secretion can help distinguish DSWD from other forms of sleep-onset insomnia. DSWPD is a chronic condition that can persist for years and may not respond to attempts to reestablish normal bedtime hours. Treatment methods involving phototherapy with blue-enriched light during the morning hours and/or melatonin administration in the evening hours show promise in these patients, although the relapse rate is high.
Advanced Sleep-Wake Phase Disorder
Advanced sleep-wake phase disorder (ASWPD) is the converse of DSWPD. Most commonly, this syndrome occurs in older people, 15% of whom report that they cannot sleep past 5:00 A.M., with twice that number complaining that they wake up too early at least several times per week. Patients with ASWPD are sleepy during the evening hours, even in social settings. Sleep-wake timing in ASWPD patients can interfere with a normal social life. Patients with this circadian rhythm sleep disorder can be distinguished from those who have early wakening due to insomnia because ASWPD patients show early onset of dim-light melatonin secretion.
In addition to age-related ASWPD, an early-onset familial variant of this condition has also been reported. In two families in which ASWPD was inherited in an autosomal dominant pattern, the syndrome was due to missense mutations in a circadian clock component (in the casein kinase binding domain of PER2 in one family, and in casein kinase I delta in the other) that shortens the circadian period. Patients with ASWPD may benefit from bright light and/or blue enriched phototherapy during the evening hours to reset the circadian pacemaker to a later hour.
Non-24-h Sleep-Wake Rhythm Disorder
Non-24-h sleep-wake rhythm disorder (N24SWRD) most commonly occurs when the primary synchronizing input (i.e., the light-dark cycle) from the environment to the circadian pacemaker is lost (as occurs in many blind people with no light perception), and the maximal phase-advancing capacity of the circadian pacemaker in response to non-photic cues cannot accommodate the difference between the 24-h geophysical day and the intrinsic period of the patient’s circadian pacemaker, resulting in loss of entrainment to the 24-h day. The sleep of most blind patients with N24SWRD is restricted to the nighttime hours due to social or occupational demands. Despite this regular sleep-wake schedule, affected patients with N24SWRD are nonetheless unable to maintain a stable phase relationship between the output of the non-entrained circadian pacemaker and the 24-h day. Therefore, most blind patients present with intermittent bouts of insomnia. When the blind patient’s endogenous circadian rhythms are out of phase with the local environment, nighttime insomnia coexists with excessive daytime sleepiness. Conversely, when the endogenous circadian rhythms of those same patients are in phase with the local environment, symptoms remit. The interval between symptomatic phases may last several weeks to several months in blind patients with N24SWRD, depending on the period of the underlying nonentrained rhythm and the 24-h day. Nightly low-dose (0.5 mg) melatonin administration may improve sleep and, in some cases, induce synchronization of the circadian pacemaker. In sighted patients, N24SWRD is usually caused by self-selected exposure to artificial light that inadvertently entrains the circadian pacemaker to a >24-h schedule, and these individuals present with an incremental pattern of successive delays in sleep timing, progressing in and out of phase with local time—a clinical presentation that is seldom seen in blind patients with N24SWRD.
More than 7 million workers in the United States regularly work at night, either on a permanent or rotating schedule. Many more begin the commute to work or school between 4:00 A.M. and 7:00 A.M., requiring them to commute and then work during a time of day that they would otherwise be asleep. In addition, each week, millions of “day” workers and students elect to remain awake at night or awaken very early in the morning to work or study to meet work or school deadlines, drive long distances, compete in sporting events, or participate in recreational activities. Such schedules can result in both sleep loss and misalignment of circadian rhythms with respect to the sleep-wake cycle.
The circadian timing system usually fails to adapt successfully to the inverted schedules required by overnight work or the phase advance required by early morning (4:00 A.M. to 7:00 A.M.) start times. This leads to a misalignment between the desired work-rest schedule and the output of the pacemaker and to disturbed daytime sleep in most such individuals. Excessive work hours (per day or per week), insufficient time off between consecutive days of work or school, and frequent travel across time zones may be contributing factors. Sleep deficiency, increased length of time awake prior to work, and misalignment of circadian phase produce decreased alertness and performance, increased reaction time, and increased risk of performance lapses, thereby resulting in greater safety hazards among night workers and other sleep-deprived individuals. Sleep disturbance nearly doubles the risk of a fatal work accident. In addition, long-term night shift workers have higher rates of breast, colorectal, and prostate cancer and of cardiac, gastrointestinal, metabolic, and reproductive disorders. The World Health Organization has added night-shift work to its list of probable carcinogens.
Sleep onset begins in local brain regions before gradually sweeping over the entire brain as sensory thresholds rise and consciousness is lost. A sleepy individual struggling to remain awake may attempt to continue performing routine and familiar motor tasks during the transition state between wakefulness and stage N1 sleep, while unable to adequately process sensory input from the environment. Such sleep-related attentional failures typically last only seconds but are known on occasion to persist for longer durations. Motor vehicle operators who fail to heed the warning signs of sleepiness are especially vulnerable to sleep-related accidents, as sleep processes can slow reaction times, induce automatic behavior, and intrude involuntarily upon the waking brain, causing catastrophic consequences—including 6400 fatalities and 50,000 debilitating injuries in the United States annually. For this reason, an expert consensus panel has concluded that individuals who have slept <2 h in the prior 24 h are unfit to drive a motor vehicle. There is a significant increase in the risk of sleep-related, fatal-to-the-driver highway crashes in the early morning and late afternoon hours, coincident with bimodal peaks in the daily rhythm of sleep tendency.
Physicians who work prolonged shifts, especially intermittent overnight shifts, constitute another group of workers at greater risk for accidents and other adverse consequences of lack of sleep and misalignment of the circadian rhythm. Recurrent scheduling of resident physicians to work shifts of ≥24 consecutive hours impairs psychomotor performance to a degree that is comparable to alcohol intoxication, doubles the risk of attentional failures among intensive care unit resident physicians working at night, and significantly increases the risk of serious medical errors in intensive care units, including a fivefold increase in the risk of serious diagnostic mistakes. Some 20% of hospital resident physicians report making a fatigue-related mistake that injured a patient, and 5% admit making a fatigue-related mistake that resulted in the death of a patient. Moreover, working for >24 consecutive hours increases the risk of percutaneous injuries and more than doubles the risk of motor vehicle crashes during the commute home. For these reasons, in 2008, the National Academy of Medicine concluded that the practice of scheduling resident physicians to work for >16 consecutive hours without sleep is hazardous for both resident physicians and their patients.
From 5 to 15% of individuals scheduled to work at night or in the early morning hours have much greater-than-average difficulties remaining awake during night work and sleeping during the day; these individuals are diagnosed with chronic and severe shift-work disorder (SWD). Patients with this disorder have a level of excessive sleepiness during work at night or in the early morning and insomnia during day sleep that the physician judges to be clinically significant; the condition is associated with an increased risk of sleep-related accidents and with some of the illnesses associated with night-shift work. Patients with chronic and severe SWD are profoundly sleepy at work. In fact, their sleep latencies during night work average just 2 min, comparable to mean daytime sleep latency durations of patients with narcolepsy or severe sleep apnea.
TREATMENT Shift-Work Disorder
Caffeine is frequently used by night workers to promote wakefulness. However, it cannot forestall sleep indefinitely, and it does not shield users from sleep-related performance lapses. Postural changes, exercise, and strategic placement of nap opportunities can sometimes temporarily reduce the risk of fatigue-related performance lapses. Properly timed exposure to blue-enriched light or bright white light can directly enhance alertness and facilitate more rapid adaptation to night-shift work.
Modafinil (200 mg) or armodafinil (150 mg) 30–60 min before the start of an 8-h overnight shift is an effective treatment for the excessive sleepiness during night work in patients with SWD. Although treatment with modafinil or armodafinil significantly improves performance and reduces sleep propensity and the risk of lapses of attention during night work, affected patients remain excessively sleepy.
Fatigue risk management programs for night shift workers should promote education about sleep, increase awareness of the hazards associated with sleep deficiency and night work, and screen for common sleep disorders. Work schedules should be designed to minimize: (1) exposure to night work; (2) the frequency of shift rotations; (3) the number of consecutive night shifts; and (4) the duration of night shifts.
Each year, >60 million people fly from one time zone to another, often resulting in excessive daytime sleepiness, sleep-onset insomnia, and frequent arousals from sleep, particularly in the latter half of the night. The syndrome is transient, typically lasting 2–14 d depending on the number of time zones crossed, the direction of travel, and the traveler’s age and phase-shifting capacity. Travelers who spend more time outdoors at their destination reportedly adapt more quickly than those who remain in hotel or seminar rooms, presumably due to brighter (outdoor) light exposure. Avoidance of antecedent sleep loss or napping on the afternoon prior to overnight travel can reduce the difficulties associated with extended wakefulness. Laboratory studies suggest that low doses of melatonin can enhance sleep efficiency, but only if taken when endogenous melatonin concentrations are low (i.e., during the biologic daytime).
In addition to jet lag associated with travel across time zones, many patients report a behavioral pattern that has been termed social jet lag, in which bedtimes and wake times on weekends or days off occur 4–8 h later than during the week. Such recurrent displacement of the timing of the sleep-wake cycle is common in adolescents and young adults and is associated with delayed circadian phase, sleep-onset insomnia, excessive daytime sleepiness, poorer academic performance, and increased risk of both obesity and depressive symptoms.
MEDICAL IMPLICATIONS OF CIRCADIAN RHYTHMICITY
Prominent circadian variations have been reported in the incidence of acute myocardial infarction, sudden cardiac death, and stroke, the leading causes of death in the United States. Platelet aggregability is increased in the early morning hours, coincident with the peak incidence of these cardiovascular events. Recurrent circadian disruption combined with chronic sleep deficiency, such as occurs during night-shift work, is associated with increased plasma glucose concentrations after a meal due to inadequate pancreatic insulin secretion. Night shift workers with elevated fasting glucose have an increased risk of progressing to diabetes. Blood pressure of night workers with sleep apnea is higher than that of day workers. A better understanding of the possible role of circadian rhythmicity in the acute destabilization of a chronic condition such as atherosclerotic disease could improve the understanding of its pathophysiology.
Diagnostic and therapeutic procedures may also be affected by the time of day at which data are collected. Examples include blood pressure, body temperature, the dexamethasone suppression test, and plasma cortisol levels. The timing of chemotherapy administration has been reported to have an effect on the outcome of treatment. In addition, both the toxicity and effectiveness of drugs can vary with time of day. For example, more than a fivefold difference has been observed in mortality rates following administration of toxic agents to experimental animals at different times of day. Anesthetic agents are particularly sensitive to time-of-day effects. Finally, the physician must be aware of the public health risks associated with the ever-increasing demands made by the 24/7 schedules in our round-the-clock society.
John W. Winkelman, MD, PhD and Gary S. Richardson, MD contributed to this chapter in prior editions, and some material from their work has been retained here.
et al: Changes in the composition of brain interstitial ions control the sleep-wake cycle. Science 352:550, 2016.
et al: Sleep and Alzheimer disease pathology—A bidirectional relationship. Nat Rev Neurol 10:115, 2014.
et al: High risk of near-crash driving events following night-shift work. Proc Natl Acad Sci USA 113:176, 2016.
et al: Sleep is related to neuron numbers in the ventrolateral preoptic/intermediate nucleus in older adults with and without Alzheimer’s disease. Brain 137:2847, 2014.
et al: Prevalence of healthy sleep duration among adults—United States, 2014. MMWR Morb Mortal Wkly Rep 65:137, 2016.
et al: The neurobiology, investigation, and treatment of chronic insomnia. Lancet Neurol 14:547, 2015.
et al: Neural circuitry of wakefulness and sleep. Neuron 93:747, 2017.
et al: Circadian entrainment to the natural light-dark cycle across seasons and the weekend. Curr Biol 27:508, 2017.
et al: Sleep drives metabolite clearance from the adult brain. Science 342:373, 2013.
Additional Online References
et al: Detection of α-synuclein in CSF by RT-QuIC in patients with isolated rapid-eye-movement sleep behaviour disorder: A longitudinal observational study. Lancet Neurol 20:203, 2021.
et al: Safety and efficacy of daridorexant in patients with insomnia disorder: Results from two multicentre, randomised, double-blind, placebo-controlled, phase 3 trials. Lancet Neurol 21: 125, 2022.