Acromegaly

Acromegaly (from Greek akros "high" and megalos "large" - extremities enlargement) is a hormonal disorder that results when the pituitary gland produces excess growth hormone (hGH). Most commonly it is a benign hGH producing tumor derived from a distinct type of cells (somatotrophs) and called pituitary adenoma.

Causes

In over 90 percent of acromegaly patients, the overproduction of GH is

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caused by a benign tumor of the pituitary gland, called an adenoma.

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These tumors produce excess GH and, as they expand, compress surrounding

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brain tissues, such as the optic nerves. This expansion causes the

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headaches and visual disturbances that are often symptoms of acromegaly.

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In addition, compression of the surrounding normal pituitary tissue can

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alter production of other hormones, leading to changes in menstruation

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and breast discharge in women and impotence in men.

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There is a marked variation in rates of GH production and the

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aggressiveness of the tumor. Some adenomas grow slowly and symptoms of

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GH excess are often not noticed for many years. Other adenomas grow

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rapidly and invade surrounding brain areas or the sinuses, which are

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located near the pituitary. In general, younger patients tend to have

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more aggressive tumors.

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Most pituitary tumors arise spontaneously and are not genetically

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inherited. Many pituitary tumors arise from a genetic alteration in a

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single pituitary cell which leads to increased cell division and tumor

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formation. This genetic change, or mutation, is not present at birth,

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but is acquired during life. The mutation occurs in a gene that

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regulates the transmission of chemical signals within pituitary cells;

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it permanently switches on the signal that tells the cell to divide and

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secrete GH. The events within the cell that cause disordered pituitary

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cell growth and GH oversecretion currently are the subject of intensive

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research.

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In a few patients, acromegaly is caused not by pituitary tumors but by

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tumors of the pancreas, lungs, and adrenal glands. These tumors also

Related Topics:
Tumor - Pancreas - Lung - Adrenal gland

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lead to an excess of GH, either because they produce GH themselves or,

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more frequently, because they produce GHRH, the hormone that stimulates

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the pituitary to make GH. In these patients, the excess GHRH can be

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measured in the blood and establishes that the cause of the acromegaly

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is not due to a pituitary defect. When these non-pituitary tumors are

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surgically removed, GH levels fall and the symptoms of acromegaly improve.

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In patients with GHRH-producing, non-pituitary tumors, the pituitary

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still may be enlarged and may be mistaken for a tumor. Therefore, it is

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important that physicians carefully analyze all "pituitary tumors"

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removed from patients with acromegaly in order not to overlook the

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possibility that a tumor elsewhere in the body is causing the disorder.

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