Acromegaly causes an excessive, long-term increase in the production of growth hormone. Common acromegaly causes include tumors, either pituitary or non-pituitary. In over 90% of patients, a pituitary tumor is the cause. As the tumor expands, it compresses surrounding brain tissues, often leading to the headaches and visual disturbances that are common symptoms of this condition.
Acromegaly is caused by prolonged overproduction of growth hormone (GH) by the pituitary gland. Common acromegaly causes include:
In over 90% of acromegaly patients, the acromegaly cause is a benign tumor of the pituitary gland, called a pituitary adenoma (or growth hormone-secreting adenoma). These pituitary tumors produce excess GH and, as they expand, compress surrounding brain tissues, such as the optic nerves. This expansion of the pituitary adenoma causes the headaches and visual disturbances that are often symptoms of acromegaly. In addition, compression of the surrounding normal pituitary tissue can alter production of other hormones, leading to changes in menstruation and breast discharge in women, and impotence (erectile dysfunction or ED) in men.
There is a marked variation in rates of GH production and the aggressiveness of the tumor. Some adenomas grow slowly, and symptoms of excess GH are often not noticed for many years. Other adenomas grow rapidly and invade surrounding brain areas or the sinuses, which are located near the pituitary. In general, younger patients tend to have more-aggressive tumors.
In a few patients, acromegaly is caused not by pituitary tumors, but by tumors of the pancreas, lungs, and adrenal glands. These tumors also lead to an excess of GH, either because they produce GH themselves or, more frequently, because they produce growth hormone-releasing hormone (GHRH), the hormone that stimulates the pituitary to make GH. In these patients, the excess GHRH can be measured in the blood, and establishes that the cause of the acromegaly is not due to a pituitary defect. When these non-pituitary tumors are surgically removed, GH levels fall and the acromegaly symptoms improve.
In patients with GHRH-producing, non-pituitary tumors, the pituitary may still be enlarged and may be mistaken for a tumor. Therefore, it is important that physicians carefully analyze all "pituitary tumors" removed from patients with acromegaly in order not to overlook the possibility that a tumor elsewhere in the body is causing the disorder.