Hypothyroidism is a clinical syndrome resulting from a deficiency of thyroid hormone. Myxedema is the nonpitting edema caused by subcutaneous accumulation of mucopolysaccharides in severe cases of hypothyroidism; the term is sometimes used to describe the entire syndrome of severe hypothyroidism.
Primary hypothyroidism accounts for more than 95% of cases and may be congenital or acquired. Most primary cases are due to Hashimoto thyroiditis (discussed in the following section), “idiopathic” myxedema (thought by many to be end-stage Hashimoto thyroiditis), and iatrogenic causes (131I or surgical treatment of hyperthyroidism). hypothyroidism, caused by hypothalamic or pituitary dysfunction (usually after pituitary surgery), is much less common. As in hyperthyroidism, the female preponderance among adults is significant. Subclinical hypothyroidism is defined as a normal T4 concentration and a slightly elevated TSH level. These patients may or may not have symptoms suggestive of hypothyroidism, and some controversy surrounds whether such patients should be treated.
Clinically, a patient with hypothyroidism presents with signs and symptoms of hypometabolism and accumulation of mucopolysaccharides in the tissues of the body. Many of the symptoms are nonspecific—they include weakness, fatigue, memory loss, dry skin, hair loss, deepening of the voice, weight gain (despite loss of appetite), cold intolerance, arthralgias, constipation, and muscle cramps—and their relationship to thyroid dysfunction may not be recognized for some time. Clinical signs include bradycardia, reduced pulse pressure, myxedema, weight gain, loss of body and scalp hair, and menstrual disorders. In severe cases, personality changes (“myxedema psychosis”) and death (following “myxedema coma”) may occur.
Treatment of hypothyroidism is straightforward, consisting of oral thyroid replacement medication to normalize circulating hormone levels. Levothyroxine is the most commonly used preparation. Serum T4 and TSH levels are monitored at regular intervals to ensure that euthyroidism is maintained.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.