Thyroid Disease

Thyroid disease is an impairment in the normal functioning of the thyroid, an important gland located at the base of the neck. A major function of the thyroid is to regulate metabolism, the bio-chemical processes in the body. Thyroid disease may speed up or slow down metabolism, producing a wide range of physical and mental symptoms.

What Is the Thyroid?

The thyroid is an H-shaped gland that has two main parts, or lobes, that lie on either side of the trachea (TRAY-key-a) or windpipe. The lobes are connected by a narrow segment called the isthmus. The principal hormone ^* produced by the thyroid is thyroxine. Production of this hormone is in turn controlled by another hormone, called thyroid-stimulating hormone (TSH), secreted by the pituitary gland located at the base of the brain. Thyroxine is released into the bloodstream and controls the rate of metabolism ^* . In children, thyroid hormones are essential for normal growth and development.

What Is Thyroid Disease?

Disorders of the thyroid can cause overproduction of thyroid hormones (hyperthyroidism), or underproduction of thyroid hormones (hypo-thyroidism). Sometimes the thyroid becomes enlarged, a condition known as goiter.

Hyperthyroidism: a revving engine

The most common type of hyperthyroidism, or thyrotoxicosis (thy-ro-tox-i-KO-sis), is called Graves' disease. It is an autoimmune disorder, a disturbance of the immune system. Antibodies stimulate the thyroid to produce excessive quantities of hormone, thereby raising the rate of metabolism. Graves' disease can occur at any age, but the highest incidence of this disorder is in women between 20 and 40 years of age.

Symptoms of Graves' disease include an increased heart rate, nervousness and irritability, tremor, loss of weight, enlarged thyroid gland (goiter), abnormalities of the menstrual periods, sweating and heat intolerance, restless overactivity, and sleeplessness. Sometimes there is also exophthalmos (eks-off-THAL-mus), a condition in which the eye-balls protrude (bulge outward).

Less commonly, hyperthyroidism results from a form of thyroiditis (thyroid-EYE-tus) inflammation of the thyroid caused by a viral infection or by thyroid nodules (lumps or growths) that may produce excess hormones.

Hypothyroidism: a slowing down

Whereas hyperthyroidism abnormally raises the metabolic rate, hypothyroidism slows it down too much. Many of the symptoms of hypothyroidism are thus the reverse of those seen in hyperthyroidism. The most common cause of hypothyroidism is Hashimoto's thyroiditis, which occurs most often in young and middle-aged women.

Hashimoto's thyroiditis, like Graves' disease, is an autoimmune disorder. The immune system damages the thyroid rather than stimulating it, resulting in an underproduction of hormone. Symptoms of Hashimoto's thyroiditis include a slow heart rate, tiredness, muscular weakness, weight gain, abnormal menstrual periods, intolerance of cold, dry skin, hair loss, hoarseness, enlarged thyroid (goiter), and mental dullness. In more severe cases, there may be myxedema (mik-se-DEE-ma), a thickening and puffi-ness of the skin most noticeable in the face.

Less often, hypothyroidism is caused by surgical removal of part or all of the thyroid gland to treat other thyroid conditions, or by insufficient iodine in the diet, which is now a rare occurrence in developed countries.

When hypothyroidism occurs in infancy and is not treated cretinism (KREET-in-izm) results. A child with cretinism has stunted growth and mental deficiency. Older children who become hypothyroid show slowing of growth and delayed sexual maturation.

Goiter

Goiter is not itself a disease. The term simply refers to enlargement of the thyroid, sometimes visible as a swelling in the front of the neck. Enlargement of the thyroid can be a sign of hyperthyroidism or hypothyroidism. It even can occur when thyroid function is normal.

A goiter can be seen in hyperthyroidism of Graves' disease, in which the thyroid enlarges due to stimulation of the gland by the malfunctioning immune system. In hypothyroidism, it enlarges as part of the body's attempt to produce enough hormone to compensate for damage done to it by the disease, or because of inflammation ^* caused by the disease, or both.

Goiter also can occur in parts of the world where there is inadequate iodine in the diet. Found in seafood and most table salt preparations, iodine is an element essential for the formation of thyroid hormones in the body.

Nodules

Distinct swellings or lumps within the thyroid are called nodules. They are most common in women and their incidence increases with age. The large majority of thyroid nodules are benign, but some may be cancerous. They therefore require prompt medical evaluation.

Sometimes the thyroid temporarily enlarges slightly during puberty or pregnancy, without impairing its function or causing any other symptoms.

How Are Thyroid Diseases Diagnosed and Treated?

Diagnosis

To diagnose a suspected thyroid disorder, the doctor will take a medical history and perform a physical examination. Blood samples usually are taken to measure the levels of thyroid hormones and TSH, the pituitary hormone that stimulates the thyroid. The thyroid also may be checked using various scanning techniques. If a thyroid tumor is suspected, a sample of thyroid tissue may be removed for examination.

Treatment

Most thyroid diseases are highly treatable. Hyperthyroidism may be treated with a single dose of radioactive iodine, which destroys over-active thyroid cells. Alternatively, antithyroid medications may be prescribed to suppress formation of thyroid hormones. Surgical removal of most of the thyroid is another treatment. Hypothyroidism is treated with hormone replacement medication, which usually must be continued for life.

A goiter of uncertain cause may disappear on its own, or it may be small and not need treatment. Goiters caused by thyroid disease usually shrink with treatment. Occasionally, surgery is needed for removing a very large goiter. Thyroid disease is not contagious. It often runs in families, and there is no way a person can prevent it. People who live in parts of the world where seafood is scarce and table salt is not iodized, however, need to make sure they take in sufficient amounts of iodine to avoid hypothyroidism and goiter.