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Thyroid Disease By Nancy C. Greep, MD

The thyroid is a gland located in the neck just below the Adam's apple. Its main secretion is thyroid hormone-often referred to as T4 because it contains 4 molecules of iodine. Thyroid hormone is important for normal growth (of a fetus or child) and cellular metabolism.

The thyroid gland is stimulated to secrete thyroid hormone by thyroid stimulating hormone (TSH), a hormone secreted by the pituitary gland. When the bloodstream level of T4 is too low, the pituitary increases its secretion of TSH so that the thyroid gland is stimulated to make and secrete more thyroid hormone. Conversely, if the blood level of T4 is too high, TSH decreases. When T4 interacts with body tissues, it is converted to a more active hormone by the removal of one iodine molecule, and hence is called T3.

There are two categories of thyroid disease-functional and structural. Functional disorders of the thyroid include hypothyroidism (insufficient thyroid hormone) and hyperthyroidism (too much thyroid hormone).

Common causes of hypothyroidism in the USA include Hashimoto's disease (in which the body's immune system attacks and destroys its own thyroid gland), as well as prior treatment with drugs, radioactive iodine or surgery for thyroid disease. Worldwide, the most common cause of hypothyroidism is iodine deficiency but this is uncommon in the USA. Symptoms of hypothyroidism include feeling tired, cold, achy, having dry skin and hair, constipation, and modest weight gain. The diagnosis is confirmed by blood tests for thyroid function (a low T4 and, assuming the pituitary is functioning normally, a high TSH). The preferred treatment is with pure thyroid hormone (T4)-as opposed to mixtures of T3 and T4 or desiccated thyroid extracts. It is not necessary to take T3 because the body will convert as much T4 to T3 as it needs. During pregnancy, it is important to monitor thyroid tests in women with thyroid disease because their requirement for thyroid hormone may increase.

Hyperthyroidism may be caused by Grave's disease, an overactive thyroid nodule, a transient inflammation of the thyroid gland ("thyroiditis"), or taking too much thyroid hormone. In Grave's disease, the body makes an antibody which interacts with the thyroid gland and causes it to secrete thyroid hormones. A few per cent of people with Grave's disease (especially those who smoke) may develop bulging of one or both eyes. Symptoms of hyperthyroidism include palpitations, weight loss in spite of increased appetite, feeling hot, excess sweating, tremulousness, palpitations, insomnia, frequent stools, and muscular weakness. Hyperthyroidism is confirmed by blood tests (a high T4 and, assuming the pituitary is functioning normally, a low TSH). Treatments for hyperthyroidism include medications, radioactive iodine (which is preferentially concentrated in the thyroid gland and thus damages thyroid cells), and surgery. During pregnancy, women with hyperthyroidism can be safely treated with anti-thyroid drugs as long as their doses are carefully monitored.

Structural diseases of the thyroid include generalized enlargement (goiter), and focal nodules or cysts. Nodules are found by ultrasound in about half or normal people and most are benign. Thyroid function in patients with structural abnormalities of the thyroid gland can be normal, low, or high. If a structural abnormality of the thyroid gland is suspected, it can be further investigated with an ultrasound or radioactive iodine scan of the thyroid. If nodules appear suspicious on these studies, a fine needle aspiration biopsy can be performed. Only about 5% of biopsies will show a definite cancer, and another 10% may require a surgical biopsy for a definitive diagnosis.

The most common forms of thyroid cancer grow slowly and do not spread to distant sites until the disease is quite advanced. Consequently, the prognosis for most patients is very good. Treatments include surgery, radioactive iodine, and thyroid hormone therapy. Lifelong follow-up is recommended to minimize recurrence and detect it early if it does occur.

For a referral to Dr. Nancy Greep, or another specialist visit http://www.stjohnswomens.org or call 1-800-STJOHNS.

Further information about thyroid disease can be found on the web site for the American Thyroid Association (www.thyroid.org).