Thyroid Disorders

(Goiter; Graves' Disease; Hashimotos Disease; Hyperthyroidism; Hypothyroidism; Myxedema)

The thyroid, a butterfly-shaped gland that rests over the windpipe at the base of the neck, produces hormones that regulate metabolism and many other body processes. Both an overproduction (hyperthyroidism) or an underproduction (hypothyroidism) of these hormones can have a profound effect on almost all body functions.

The thyroid is regulated by the pituitary, a gland in the brain that produces thyroid-stimulating hormone, or TSH. A rise in TSH levels signals the thyroid to extract iodide from the bloodstream, convert it to iodine, and create the hormones known as thyroxine (T4) and triiodothyronine (T3). (The numbers refer to how many iodine molecules each hormone contains.)

The thyroid gland appears to be the only tissue in the body that uses iodine. Although the thyroid needs only a very small amount to create the T3 and T4 hormones, an iodine deficiency can cause a goiter, an overgrowth of thyroid tissue produced as the gland enlarges itself to increase its ability to extract and process iodine. Goiters have become increasingly rare in the United States, thanks to the widespread use of iodized salt and the consumption of iodine-rich seafood.

An estimated 10 million Americans have some sort of thyroid disorder, with women outnumbering men five to one. Some of the disorders are triggered by hormones and by pregnancy; they may also be a response to excessive stress, to a disturbance in the immune system, and to occupational hazards, especially exposure to radiation and certain industrial chemicals.

Thyroid disorders can occur at any age, but are sometimes hard to detect because their symptoms are easily ascribed to other conditions, especially in older people. These disorders fall into two main categories: hyperthyroidism, in which the gland produces excessive hormones; and hypothyroidism, which is characterized by too little.

Approximately 2 million Americans have some form of hyperthyroidism, which tends to run in families. The most common type is Graves' disease, one of many autoimmune disorders in which the body's defense system attacks its own tissues. Antibodies in the blood stimulate an overproduction of the thyroid hormones, which in tum speed up metabolism.

A person with Graves' disease feels on edge all the time; other symptoms include weight loss (even with an increased appetite), nervousness, irritability, insomnia, fatigue, muscle weakness, hand tremors, undue heat intolerance, excessive sweating, and frequent, loose stools. The heart rate speeds up, causing palpitations and potentially dangerous cardiac arrhythmias. An increase in bulk of the muscular tissue behind the eyes causes the eyeballs to bulge, and in some cases, to become inflamed.

Hyperthyroidism may be caused by excessive production of TSH because of a pituitary tumor, an inflammation of the thyroid gland (thyroiditis), or development of thyroid nodules. Less commonly, abuse of thyroid pills to control weight is responsible.

An acute form of hyperthyroidism, thyroid storm, may be triggered by a severe infection, surgery, pregnancy, or the sudden withdrawal of antithyroid medications. This condition is indicated by a rapid rise in body temperature, a fast heartbeat, and mental changes that may lead to delirium and coma. Thyroid storm is always a life-threatening emergency calling for medical attention.

Hypothyroidism (thyroid deficiency), also known as myxedema, affects about 5 million Americans. Babies born with such a deficiency are at great risk for developing cretinism, a devastating form of mental retardation and abnormal growth, unless treatment begins within the first few weeks of life. Consequently, all babies born in hospitals in the United States are tested for thyroid deficiency.

An autoimmune disorder called Hashimotos disease is the most common form of hypothyroidism. Named for the Japanese doctor who first described it, the disease is characterized by chronic inflammation of the thyroid, causing it to enlarge and impairing its ability to produce hormones. The cause is unknown, but there appears to be a hereditary disposition to develop it and it is more prevalent in women than men.

Hypothyroidism can sometimes result from treatment for hyperthyroidism. Secondary hypothyroidism is attributed to failure of the pituitary gland to produce the essential supply of thyroid-stimulating hormone.

The typical symptoms of hypothyroidism -- weight gain, lethargy, fatigue, and constipation -- emerge slowly and initially may be ascribed to other disorders. In time, the skin changes, becoming thicker, dry, and scaly; it may feel cold and clammy, and sweating diminishes. Nails also thicken and grow more slowly. The hair becomes coarse and sparse, and in young women, it may gray prematurely. Speech becomes thick and slow, and the voice turns husky. Younger women experience unusually heavy menstrual flow, older women often feel uncomfortably cold, even in a warm room. Personality changes, memory loss, and other signs of intellectual impairment approaching psychosis (myxedema madness) may be incorrectly diagnosed as a form of senile dementia.

Diagnostic Studies and Procedures

Symptoms and the patients appearance usually raise the suspicion of a thyroid disorder. A doctor will feel the thyroid gland for any nodules or enlargement. A referral may then be made to an endocrinologist for more specific tests to evaluate thyroid function. Various blood tests will be ordered to measure levels of thyroid hormones and antibodies. One of the most sensitive tests for hypothyroidism measures the amount of thyroid-stimulating hormone produced in the pituitary gland.

An ultrasound examination of the thyroid can detect nodules and other abnormalities. Sometimes tests using radioactive iodine -- for example, thyroid scanning -- are ordered. Because they are costly, however, require hospitalization, and expose the patient to radiation, they are not done routinely. Nodules are usually biopsied.

Medical Treatments

In treating hyperthyroidism, the goal is to reduce the production of thyroid hormones, but the method used varies according to the age and general condition of the patient. Propranolol (Inderal), a beta-blocking drug normally used to treat high blood pressure and angina, is the first-choice emergency treatment of thyroid storm, because it slows the heart rate. Alternatively, iodine may be given, especially before surgery.

There are three approaches to treating Graves' disease:

1. Antithyroid drugs. These include methimazole (Tapazole) and propylthiouracil (PTU), which prevent the gland from making hormones. This is the first-choice treameni for pregnant or breast-feeding women.
2. Radioactive iodine. Because the thyroid is very sensitive to radiation, carried directly to it by the iodine, this drug destroys part of the gland, thereby decreasing its hormone-making capacity. It should not be used during pregnancy or breast-feeding due to the risk it poses for the fetus or infant.
3. Surgery. Removal of all or part of the thyroid is advised for hyperthyroid patients who should not receive radioactive iodine and cannot tolerate other antithyroid medications. It is also used to remove a large goiter and thyroid nodules. Following surgery, thyroid replacement drugs are necessary.

Hashimoto's disease and other forms of thyroid deficiency are treated with thyroid pills, preferably such T4 preparations as Synthroid and Levothroid. Even though it is less expensive, T4 made from animal thyroid glands is generally not recommended for use because of variability in products and an increased risk of cardiac arrhythmias.

Alternative Therapies

Naturopathy. Naturopaths recommend that the following foods be eliminated from the diet because they are reputed to stimulate goiter growth; soybeans, peanuts, pine nuts, turnips, cabbage, and mustard greens. In treating thyroid disorders, naturopathic practitioners prefer to use dried natural thyroid hormones rather than synthetic equivalents. However, it is best to follow the recommendations of an endocrinologist who is experienced in treating thyroid problems, and to clear any hormone preparation with this specialist.

Nutrition Therapy. An individual who has lost a great deal of weight before the diagnosis and treatment of Graves' disease may benefit from the guidance of a nutritionist, who can recommend a diet that provides extra calories without excessive fat.

Self-Treatment

People with thyroid disorders need to be especially diligent about taking their medication regularly and having checkups to make sure that the dosage is appropriate. Pregnancy poses a special risk to both mother and fetus. A baby born with thyroid deficiency must receive hormone therapy early to prevent retardation and growth problems.

Other Causes of Thyroid Symptoms

Thyroid cancer can induce enlargement of the gland and imbalance of thyroid hormones. Sometimes lithium, a medication used to treat manic-depression, causes hypothyroidism.