Thyroid disorders affect approximately 1 in 200 adults but are more common in women and with advancing age. About 4.6% of people have hypothyroidism, and about 1.2% have hyperthyroidism. Hypothyroidism is much more common than hyperthyroidism, nodular disease, or thyroid cancer. Epidemiologic studies have shown the prevalence of palpable thyroid nodules to be approximately 5% in women and 1% in men living in iodine-sufficient parts of the world. High-resolution ultrasound, however, may detect thyroid nodules in 19–68% of randomly selected people. Nodules are more common in women and the elderly.
Thyroid disease is more common in people who have conditions such as diabetes or other autoimmune diseases (eg, lupus); in those with a family history of thyroid disease or a history of head and neck irradiation; and in patients who use certain medications, including amiodarone and lithium.
Causes of hypothyroidism are outlined in Table 37–1. The most common noniatrogenic condition causing hypothyroidism in the United States is Hashimoto thyroiditis. Other common causes are post–Graves disease, thyroid irradiation, and surgical removal of the thyroid. Hypothyroidism may also occur secondary to hypothalamic or pituitary dysfunction, most commonly in patients who have received intracranial irradiation or surgical removal of a pituitary adenoma. In addition, some patients may have mild elevations of thyroid-stimulating hormone (TSH) despite normal thyroxine levels, a condition termed subclinical hypothyroidism.
Table 37–1.Causes of hypothyroidism. |Favorite Table|Download (.pdf) Table 37–1. Causes of hypothyroidism.
Primary hypothyroidism (95% of cases)
Idiopathic hypothyroidism (probably old Hashimoto thyroiditis)
Late-stage invasive fibrous thyroiditis
Drugs (lithium, interferon)
Infiltrative diseases (sarcoidosis, amyloid, scleroderma, hemochromatosis)
Secondary hypothyroidism (5% of cases)
Pituitary or hypothalamic neoplasms
Pituitary necrosis (Sheehan syndrome)
Patients with hypothyroidism present with a constellation of symptoms that can involve every organ system. Symptoms include lethargy, weight gain, hair loss, dry skin, slowed mentation or forgetfulness, depressed affect, cold intolerance, constipation, hair loss, muscle weakness, abnormal menstrual periods (or infertility), and fluid retention. Because of the range of symptoms seen in hypothyroidism, clinicians must have a high index of suspicion, especially in high-risk populations. In older patients, hypothyroidism can be confused with Alzheimer disease or other conditions that cause dementia. In women, hypothyroidism is often confused with depression.
Physical findings that can occur with hypothyroidism include low blood pressure, bradycardia, nonpitting edema, generalized hair thinning along with hair loss in the outer third of the eyebrows, skin drying, and ...