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Acromegaly is a disease caused by an imbalance of hormones that leads to abnormal growth of bone and cartilage. It is usually caused by benign tumors in the gland that produces growth hormone, but can also be caused by tumors elsewhere in the body. Symptoms include enlargement of the hands and feet, changes in facial bone structure, and joint pain. The disease is controlled by a delicate balance of four hormones, but in acromegalic patients, this balance is disrupted.
The human body uses certain hormones to drive growth. If these hormones get out of balance, as in the disease known as acromegaly, the body grows abnormally. The causes of acromegaly are cancerous in nature, but most are benign and not inherently life-threatening. Usually, tumors affect the gland that produces essential growth hormone, but cancer elsewhere in the body can also be a cause 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 comes from the words for extremity and enlargement in Greek. As the disease progresses, the natural bone structure of the person’s face changes, causing the jaw and brow bone to protrude and the nose to become larger. Other symptoms of acromegaly include arthritis, carpal tunnel syndrome and aching joints.
Four different hormones are involved in the growth process of bones and cartilage. Growth hormone (GH) is important, produced by the pituitary gland in the brain. A tumor in this gland can stimulate the overproduction of GH and thus the abnormal overgrowth of bone and cartilage of acromegaly. According to the National Institutes of Health (NIH) in the United States, more than 95% of patients with acromegaly suffer from a benign tumor of this gland. Most of these tumors arise spontaneously, where a pituitary cell becomes cancerous through mutation and begins to multiply.
In rare cases where the causes of acromegaly do not involve a tumor of the pituitary gland, other parts of the body are affected. Sometimes, the tumor directly produces GH. Most often, 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, thus becoming one of the causes of acromegaly.
GH is therefore centrally involved in all cases of acromegaly. Its production is controlled by GHRH levels and then travels through the blood to the liver. Liver cells sense 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 excess growth. When IGF-I reaches a high enough level, a healthy pituitary gland senses IGF-I and reduces its GH production appropriately. The reduced concentration of GH lowers the levels of IGF-I and growth ceases.
Another hormone involved in GH regulation is somatostatin. Somatostatin prevents the pituitary from producing GH. In healthy people, the interaction between 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 U.S. population has them but shows no growth disorder symptoms.
