Hyperthyroidism

SOURCE

Source: Jonklaas J, Kane MP. Thyroid disorders. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146066204. Accessed April 14, 2017.

CONDITION/DISORDER SYNONYMS

• Thyrotoxicosis.

• Overactive thyroid.

DEFINITION

• Clinical and biochemical syndrome resulting from increased thyroid hormone production.

ETIOLOGY

• TSH-secreting pituitary adenomas.

• Graves’ disease.

• Trophoblastic diseases.

• Thyroid autonomy.

• Toxic adenoma.

• Multinodular goiter.

• Subacute thyroiditis.

• Painless thyroiditis.

• Ectopic thyroid tissue.

• Struma ovarii.

• Exogenous thyroid hormone sources.

• Medications.

• Foods.

PATHOPHYSIOLOGY

• Thyrotoxicosis results when tissues exposed to excessive levels of thyroxine (T₄), triiodothyronine (T₃), or both.

• TSH-secreting pituitary tumors release active hormone unresponsive to normal feedback control.

• In Graves’ disease, hyperthyroidism results from action of thyroid-stimulating antibodies (TSAb).

• Autonomous thyroid nodule (toxic adenoma) is thyroid mass whose function is independent of pituitary control.

• In multinodular goiters, follicles with autonomous function generate more thyroid hormone than required.

• Painful subacute thyroiditis often develops after viral illness.

• Painless thyroiditis may have underlying autoimmune cause.

• Amiodarone may induce thyrotoxicosis and may also cause destructive thyroiditis with loss of thyroglobulin and thyroid hormones.

EPIDEMIOLOGY

• In National Health and Nutrition Examination Survey III:

  • 0.7% of those surveyed had subclinical hyperthyroidism and 0.5% had clinically significant hyperthyroidism.

  • Prevalence of suppressed TSH peaked for people aged 20–39, declined in those 40–79, and increased again in those 80 or older.

  • Abnormal TSH levels were more common among women than men.

CLINICAL PRESENTATION

SIGNS AND SYMPTOMS

• Symptoms:

  • Nervousness.

  • Anxiety.

  • Palpitations.

  • Emotional lability.

  • Easy fatigability.

  • Heat intolerance.

  • Weight loss with increased appetite.

  • Increased frequency of bowel movements.

  • Proximal muscle weakness.

  • Scanty or irregular menses in women.

• Signs:

  • Thyroid enlargement.

  • Exophthalmos.

  • Pretibial myxedema.

  • Warm, smooth, moist skin and unusually fine hair.

  • Onycholysis.

  • Lid lag.

  • Resting tachycardia, widened pulse pressure, and systolic ejection murmur.

  • Gynecomastia in men.

  • Fine tremor of protruded tongue and outstretched hands.

  • Hyperactive deep tendon reflexes.

• Thyroid storm:

  • Decompensated thyrotoxicosis.

  • High fever (often above 39.4°C [103°F])

  • Tachycardia.

  • Tachypnea.

  • Dehydration.

  • Delirium.

  • Coma.

  • Nausea.

  • Vomiting.

  • Diarrhea.

DIAGNOSIS

LABORATORY TESTS

• TSH, total T₄, free T₄, T₃ resin uptake, free thyroxine index, 24-hour radioactive iodine uptake (RAIU).

IMAGING

• Thyroid scan shows areas of autonomously functioning thyroid tissue in multinodular goiters.

DIFFERENTIAL DIAGNOSIS

• General anxiety disorder, panic disorder, mania

• Other hypermetabolic states (eg, cancer, pheochromocytoma)

• Hypopituitarism.

• Subclinical hyperthyroidism.

DESIRED OUTCOMES

• Eliminate excess thyroid hormone.

• Minimize symptoms and long-term consequences.

• Provide individualized therapy based on:

  • Disease type and severity.

  • Patient age and sex.

  • Existence of nonthyroid conditions.

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