Goiter

Definition

Goiter refers to any visible enlargement of the thyroid gland.

Description

The thyroid gland sits astride the trachea (windpipe) and is shaped like a butterfly. It makes thyroxin, a hormone that regulates the metabolic activity of the body, rather like the gas pedal on a car. Too much thyroxin increases the metabolism, causing weight loss, temperature elevation, nervousness, and irritability. Too little thyroxin slows the metabolism down, deepens the voice, causes weight gain and water retention, and retards growth and mental development in children. Both conditions also alter hair and skin growth, bowel function, and menstrual flow.

Curiously, the thyroid gland is often enlarged whether it is making too much hormone, too little, or sometimes even when it is functioning normally. The thyroid is controlled by the pituitary gland, which secretes thyroid stimulating hormone (TSH) in response to the amount of thyroxin it finds in the blood. TSH increases the amount of thyroxin secreted by the thyroid and also causes the thyroid gland to grow.

• Hyperthyroid goiter--If the amount of stimulating hormone is excessive, the thyroid will both enlarge and secrete too much thyroxin. The result--hyperthyroidism with a goiter. Graves' disease is the most common form of this disorder.
• Euthyroid goiter--The thyroid is the only organ in the body to use iodine. If dietary iodine is slightly inadequate, too little thyroxin will be secreted, and the pituitary will sense the deficiency and produce more TSH. The thyroid gland will enlarge enough to make sufficient thyroxin.
• Hypothyroid goiter--If dietary iodine is severely reduced, even an enlarged gland will not be able to make enough thyroxin. The gland will keep growing under the influence of TSH, but it may never be able to make enough thyroxin.

Causes & symptoms

Excess TSH (or similar hormones), cysts, and tumors will enlarge the thyroid gland. Of these, TSH enlarges the entire gland while cysts and tumors enlarge only a part of it.

The only symptom from a goiter is the large swelling just above the breast bone. Rarely, it may constrict the trachea (windpipe) or esophagus and cause difficulty breathing or swallowing. The rest of the symptoms come from thyroxin or the lack of it.

Diagnosis

The size, shape, and texture of the thyroid gland help the physician determine the cause. A battery of blood tests are required to verify the specific thyroid disease. Functional imaging studies using radioactive iodine determine how active the gland is and what it looks like.

Treatment

Goiters of all types will regress with treatment of the underlying condition. Dietary iodine may be all that is needed. However, if an iodine deficient thyroid that has grown in size to accommodate its deficiency is suddenly supplied an adequate amount of iodine, it could suddenly make large amounts of thyroxin and cause a thyroid storm, the equivalent of racing your car motor at top speed.

Hyperthyroidism can be treated with medications, therapeutic doses of radioactive iodine, or surgical reduction. Surgery is much less common now than it used to be because of progress in drugs and radiotherapy.

Prognosis

Although goiters diminish in size, the thyroid may not return to normal. Sometimes thyroid function does not return after treatment, but thyroxin is easy to take as a pill.

Prevention

Euthyroid goiter and hypothyroid goiter are common around the world because many regions have inadequate dietary iodine, including some places in the United States. International relief groups are providing iodized salt to many of these populations. Because mental retardation is a common result of hypothyroidism in children, this is an extremely important project.

Key Terms

Cyst

A liquid-filled structure developing abnormally in the body.

Euthyroid

Having the right amount of thyroxin stimulation.

Hyperthyroid

Having too much thyroxin stimulation.

Hypothyroid

Having too little thyroxin stimulation.

Pituitary gland

The master gland, located in the middle of the head, that controls most of the other glandss by secreting stimulating hormones.

Radiotherapy

The use of ionizing radiation, either as x rays or radioactive isotopes, to treat disease.

Thyroxin

The hormone secreted by the thyroid gland.

Further Reading

For Your Information

Books

• Bennett, J. Claude and Fred Plum, ed. Cecil Textbook of Medicine. Philadelphia: W. B. Saunders, 1996, pp.1241-1242.
• Gregerman, Robert I. "Thyroid disorders" In Principles of Ambulatory Medicine. Edited by L. Randol Barker, et al. Baltimore: Williams & Wilkins, 1995, pp.1039-41.
• Isselbacher, Kurt, et al., ed. Harrison's Principles of Internal Medicine. New York: McGraw-Hill, 1997, pp.1938-1940.
• Tierney, Lawrence M., ed. Current Medical Diagnosis and Treatment Stamford, CT: Appleton & Lange, 1998, pp.1046-1047.

  Organizations

• International Council for the Control of Iodine Deficiency Disorders. http://www.tulane.edu/~icec/icciddhome.htm.
• The Micronutrient Initiative (c/o International Development Research Centre). 250 Albert Street, Ottawa, Ontario, Canada K1G 3H9. (613) 236-6163, ext. 2050. mi@idrc.ca. http://www.idrc.ca/mi/index.html.

Gale Encyclopedia of Medicine. Gale Research, 1999.