Thyroid Diseases

Hypothyroidism is the result of inadequate thyroid hormone production. Myxedema is hypothyroidism that occurs during adult life. The onset of symptoms is usually mild and vague. Patients develop slowness in motion, speech, and mental processes. They often develop more lethargic, sedentary habits, have decreased appetites, gain weight, are constipated, cannot tolerate cold, become weak, and fatigue easily. The body temperature may be subnormal, the skin becomes dry, coarse, and thickened; and the face appears puffy. Patients often have decreased blood pressure, heart rate, elevated cholesterol levels and develop anemia. These patients have an increased susceptibility to infection and are sensitive to small doses of sedative-hypnotics, anesthetics, and narcotics. Myxedema may be caused by excessive use of antithyroid drugs used to treat hyperthyroidism, radiation exposure, thyroid surgery, acute viral thyroiditis, or chronic thyroiditis.

Congenital hypothyroidism occurs when a child is born without a thyroid gland or one that is hypoactive. The historic name of this disease is cretinism. Fortunately, this disorder is becoming rare because most states require diagnostic testing of the newborn for hypothyroidism.

Although the symptoms of hypothyroidism in both infants and adults are for the most part classical, the final diagnosis is usually not made until diagnostic tests have been completed. These tests include determining serum levels of circulating T₃ and T₄ hormones. If the levels are low, the patient is considered to be hypothyroid. Further diagnostic testing is required to determine the cause of thyroid hypofunction.

Hyperthyroidism is caused by excess production of thyroid hormones. Disorders that may cause hyperactivity of the thyroid gland are Graves’ disease, nodular goiter, thyroiditis, thyroid carcinoma, overdoses of thyroid hormones, and tumors of the pituitary gland.

The clinical manifestations of hyperthyroidism are rapid bounding pulse (even during sleep), cardiac enlargement, palpitations, and dysrhythmias. Patients are nervous and easily agitated. They develop tremors, a low-grade fever, and weight loss, despite an increased appetite. Hyperactive reflexes and insomnia are also usually present. Patients are intolerant of heat, the skin is warm, flushed, and moist, with increased sweating, and edema of the tissues around the eyeballs produces characteristic eye changes, including exophthalmos. Patients develop amenorrhea, dyspnea with minor exertion, hoarse, rapid speech, and an increased susceptibility to infection. Elevated circulating thyroid hormone levels easily diagnose hyperthyroidism. Further diagnostic studies are required to determine the cause of hyperthyroidism.

Excessive formation of thyroid hormones and their secretion into the circulatory system causes hyperthyroidism, also known as thyrotoxicosis. Symptoms include increased metabolic rate, increased pulse rate (to perhaps 140 beats/min), increased body temperature, restlessness, nervousness, anxiety, sweating, muscle weakness and tremors, and a sensation of feeling too warm. This condition is treated with antithyroid drugs or surgical removal of the thyroid gland.

Treatment of Thyroid Diseases

The primary goal of therapy for hyperthyroidism and hypothyroidism is to return the patient to a normal thyroid (euthyroid) state. Hypothyroidism can be treated successfully by replacement of thyroid hormones (see monographs on individual agents). After therapy is initiated, the dosage of thyroid hormone is adjusted until serum levels of the thyroid hormones are within the normal range.

Three types of treatment can be used to reduce the hyperthyroid state—subtotal thyroidectomy, radioactive iodine, and antithyroid medications. Until treatment is under way, the patient requires nutritional and psychological support.

Drug Therapy for Thyroid Diseases

There are two general classes of drugs used to treat thyroid disorders: (1) those used to replace thyroid hormones in patients whose thyroid glandular function is inadequate to meet metabolic requirements (hypothyroidism); and (2) antithyroid agents used to suppress synthesis of thyroid hormones (hyperthyroidism). Thyroid hormone replacements available are levothyroxine (T₄), liothyronine (T₃), liotrix, and thyroid, USP. Antithyroid drugs interfere with the formation or release of the hormones produced by the thyroid gland. Antithyroid agents include radioactive iodine, propylthiouracil, and methimazole.