Do You Have an Underactive Thyroid?

Thyroid hormones are responsible for controlling metabolism. Hypothyroidism or “underactive thyroid” is a very common disease–affecting over five million Americans and as many as ten percent of women–in which the thyroid gland fails to produce enough thyroid hormone.

Most commonly, hypothyroidism is caused either by inflammation of the thyroid gland or as a consequence of other medical treatments. Hashimoto’s thyroiditis is the most common form of hypothyroidism in the United States. It is an autoimmune disorder in which the thyroid gland is spontaneously destroyed by the body’s own immune system. Blood tests for antibodies directed against the thyroid gland can be helpful in diagnosing this form of hypothyroidism. Hashimoto’s thyroiditis is usually permanent but occasionally goes into remission. It is five to eight times more common in women than in men, may be associated with a goiter or swelling in the neck, and frequently develops after age 50.

Hypothyroidism can also occur as a result of other medical treatments that destroy some of the thyroid gland. People with an overactive thyroid gland (hyperthyroidism) or cancer of the thyroid gland may have part or all of the thyroid gland destroyed either by surgery or by treatment with radioactive iodine. Patients with cancer in the head and neck often undergo radiation therapy of the neck and may lose thyroid function. A few drugs–including lithium and amiodarone– can also lead to hypothyroidism and patients taking these drugs should have their thyroid function monitored periodically. Rarely, a small tumor in the pituitary or hypothalamus areas of the brain can cause hypothyroidism through a deficiency in the hormones that control the thyroid gland itself.

Hypothyroidism often appears with a constellation of vague symptoms. Early in the course of the disease, people may complain of fatigue, weakness, unintentional weight gain or difficulty losing weight, dry hair or skin, hair loss, cold intolerance, muscle cramps, constipation, and depression. If the disease is undiagnosed for a while, abnormal menstrual cycles, slow speech, puffy face, and hoarseness may develop. The thyroid gland can become enlarged, forming a “goiter” or large swelling in the neck. Some people have no symptoms at all.

A simple blood test can be used to diagnose hypothyroidism. TSH is a hormone produced by the pituitary gland–a very small gland in the brain–which controls how much thyroid hormone the thyroid produces. When the pituitary gland senses a low level of thyroid hormones, TSH increases in an effort to increase thyroid production by the thyroid gland. As a result, blood tests in most forms of hypothyroidism usually show a high TSH level and a low level of thyroid hormones.

Because the symptoms of hypothyroidism are so vague, not everyone who has the disease will complain to their doctor. Many people with these complaints might incorrectly attribute them to stress, aging, or depression. As a result, many associations including the American Thyroid Association and the American Association of Clinical Endocrinologists recommend measuring TSH in all women beginning at age 35 and every five years thereafter. The recommendations for screening men are not as clear.

Treatment of hypothyroidism is fairly simple and generally consists of taking one pill per day to replace the missing thyroid hormones. Your doctor will need to monitor your blood levels of TSH and thyroid hormones to make sure that you are taking the right dose of thyroid hormone replacement medication.

Dr. McMahon, a graduate of Yale University and the University of Pittsburgh School of Medicine, is board certified in Internal Medicine. She is a member of the American College of Physicians and the Allegheny County and Pennsylvania Medical Societies. She is in solo practice in the North Hills of Pittsburgh.