gigantism, excessive growth in stature, well beyond the average for the individual’s heredity and environmental conditions. Tall stature may result from hereditary, dietary, or other factors. Gigantism is caused by disease or disorder in those parts of the endocrine system that regulate growth and development. Androgen deficiency, for example, delays the closure of end plates, or epiphyses, of the long bones, which usually takes place when full growth is achieved. If the pituitary gland functions normally, producing appropriate amounts of growth hormone, while epiphyseal closure is delayed, the growth period of the bones will be prolonged. Gigantism associated with androgen deficiency is more frequent in men than in women and may be genetic.

Another type of gigantism associated with endocrine disorder is pituitary gigantism, caused by hypersecretion of growth hormone (somatotropin), during childhood or adolescence, prior to epiphyseal closure. Pituitary gigantism is usually associated with a tumour of the pituitary gland. Acromegaly (q.v.), a condition marked by progressive enlargement of skeletal extremities, occurs if growth hormone continues to be produced in large volume after epiphyseal closure. (Signs of acromegaly are occasionally seen in younger patients, prior to closure.) Since most pituitary giants continue to produce growth hormone after they reach adulthood, the two conditions—gigantism and acromegaly—are often concurrent.

In pituitary gigantism, growth is gradual but continuous and consistent; the affected person, with bones in normal proportion, may attain a height of eight feet. Muscles may be well developed but later undergo some atrophy or weakening. The life span of pituitary giants is shorter than normal because of their greater susceptibility to infection and metabolic disorders. Treatment by surgery or irradiation of the pituitary gland curtails further growth, but stature cannot be reduced once gigantism has occurred.

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acromegaly, growth and metabolic disorder characterized by enlargement of the skeletal extremities. It is the result of overproduction of pituitary growth hormone (somatotropin) after maturity, caused by a tumour of the pituitary gland. Acromegaly is often associated with the abnormal growth in stature known as pituitary gigantism (see gigantism).

The onset of acromegaly is gradual. Hands and feet become enlarged; facial features are exaggerated as the jaw lengthens and the nose and forehead grow thicker; the skin thickens; and most internal organs enlarge. Headache, excessive sweating, muscle weakness, and high blood pressure are other manifestations.

Acromegalic subjects may develop congestive heart failure, particularly when blood pressure becomes high. At times, excessive overgrowth of bone and cartilage involves the joints and causes pain. The bones may become thin and porous—a condition known as osteoporosis. Diabetes mellitus appears in 20 to 40 percent of acromegalic subjects because excess growth hormone blocks the action of insulin. If the pituitary tumour enlarges, it can cause visual-field defects, blindness or paralysis of the eye muscles, and can injure the posterior pituitary gland or the hypothalamus. Also, hemorrhage into the tumour can cause sudden loss of vision.

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Acromegaly may be treated by surgical removal of the pituitary tumour or destruction of it by X-ray irradiation or liquid nitrogen. Rarely, the pituitary tumour will cease to secrete growth hormone because of a spontaneous hemorrhage or a blockage of the blood supply. Decreases in acromegalic manifestations and amelioration of diabetes mellitus have followed therapy with female hormones—estrogen or medroxyprogesterone—which reduce the secretion of growth hormone. For those treated by pituitary surgery, irradiation, or other measures and for those who spontaneously develop deficits of gonadal, thyroidal, or adrenocortical hormones, replacement-hormone therapy is necessary.

This article was most recently revised and updated by Kara Rogers.