The human body uses certain hormones to drive growth. If these hormones become unbalanced, such as in the case of the disease known as acromegaly, then the body grows abnormally. The causes of acromegaly are cancerous in nature, but most are benign and not intrinsically life threatening. Usually, the cancers affect the gland that produces an essential growth hormone, but a cancer in another part of the body may also be one of the causes of acromegaly.
Acromegaly is characterized by abnormal growth of bone and cartilage. It occurs in adults, although a similar disease in children results in a condition called gigantism. A patient's first signs commonly include enlargement of the feet and hands, and the name acromegaly in fact is derived from the words for extremities and enlargement in Greek. As the disease progresses, the natural bone structure of the person's face alters, making the jaw and brow bone protrude and the nose larger. Other symptoms of acromegaly include arthritis, carpal tunnel syndrome, and achy joints.
Four different hormones are involved in the bone and cartilage growth process. Growth hormone (GH) is an important one, which is produced by the pituitary gland in the brain. A tumor in this gland can stimulate overproduction of GH and therefore the abnormal overgrowth of bone and cartilage of acromegaly. According to the National Institutes of Health (NIH) in the U.S., more than 95 percent of acromegaly patients suffer from a benign tumor of this gland. The majority of these tumors arise spontaneously, where one pituitary cell turns cancerous through mutation and begins multiplying.
In rare cases where the causes of acromegaly do not involve a pituitary gland tumor, other parts of the body are affected. Sometimes, the tumor directly produces GH. Most often, the tumors do not produce GH but instead cause an overproduction of another hormone called Growth Hormone-Releasing Hormone (GHRH). GHRH encourages the pituitary gland to produce GH, therefore becoming one of the causes of acromegaly.
GH is therefore centrally involved in all acromegaly cases. Its production is controlled by GHRH levels, and it then travels through the blood to the liver. The liver cells sense the GH and release another hormone called insulin-like growth factor I (IGF-I).
IGF-I is the hormone that acts directly on the body to produce the excess growth. When IGF-I gets to a sufficiently high level, a healthy pituitary gland senses the IGF-I and reduces its production of GH appropriately. The reduced GH concentration lowers the IGF-I levels, and the growth ceases.
Another hormone involved in the regulation of GH is somatostatin. Somatostatin blocks the pituitary from producing GH. In healthy people, the interaction among these four hormones and the controlling effect they have on each other is finely tuned, but in acromegalic patients, this system is out of balance. According to the NIH, small benign tumors of the pituitary gland are actually quite common, and up to 17 percent of the population of the U.S. have them but show no symptoms of growth disorder.