What causes Acromegaly?
In 98% of all reported cases, Acromegaly is caused by an adenoma (i.e., benign tumor) of the pituitary gland that secretes excessive growth hormone (GH). In extremely rare cases, there is no tumor in the pituitary gland, but another non-pituitary tumor usually located in the chest or abdomen area that produces growth hormone-releasing hormone (GHRH).
The most common type of tumor is a non-cancerous, or benign, tumor in the pituitary gland, known as a pituitary adenoma. The location of this tumor causes the pituitary gland to produce excess growth hormone, leading to abnormal growth.
Pituitary tumors are not genetically inherited from parents. They can appear randomly, due to a small genetic change of one cell within the gland. Over time, this cell will replicate and form a tumor, called an adenoma. Adenomas are not malignant, because they do not spread to other parts of the body, but they may cause problems due to their size and location. As the tumor grows, it can put pressure on surrounding brain tissue. Because the skull is a closed space, this growth can crowd the remaining tissue, leading to headaches and vision problems.
The location of the tumor means that the production of other hormones can also be affected. The impact can be different for men and women, due to the type of hormone affected. Women may find that it affects their menstrual cycle, while some men experience impotence. Around 17 percent of the population are thought to have small pituitary adenomas that do not usually produce excess GH or cause any symptoms. It is only when a larger tumor occurs that the problems arise.
It is also important to note that most pituitary adenomas do not secrete any hormone. However, of the ones that do, growth hormone-secreting adenomas account for a third of cases.
Non-Pituitary Adenoma and Other Causes
In rare cases, a tumor elsewhere in the body, such as the lungs, adrenal glands, or pancreas, can lead to an overproduction of growth hormone, resulting in symptoms of Acromegaly. Non-pituitary tumors found in other areas of the body like the abdomen and chest can also cause Acromegaly in extremely rare cases. The pituitary gland responds to a stimulus to produce GH. For example, some hypothalamic tumors may secrete growth hormone-releasing hormone (GHRH), which tells the body to produce GH.
Sometimes, Acromegaly is due to increased growth hormone production from outside the pituitary gland, such as from neuroendocrine tumors like small cell lung cancer or carcinoid tumors.