Thyroid Disease

Thyroid disease is an impairment in the normal functioning of the thyroid, an important gland located below the chin at the base of tbe neck. A major function of the thyroid is to regulate metabolism, the biochemical 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 cither 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 (hypothyroidism). 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 Graves' disease, an autoimmune disease, 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 in people of any age, but the highest incidence 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 eyeballs protrude (bulge outward).

Less commonly, hyperthyroidism results from a form of thyroiditis (thy-roid-EYE-tus), an 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 disease. 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 puffiness 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 rare 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 have hypothyroidism show slowing of growth and delayed sexual maturation.