The most common cause of acromegaly is excessive growth hormone producing and secreting pituitary tumor. Acromegaly can also result due to other less common tumors such as tumor of pancreas, lungs, and adrenal glands which also secrete excess growth hormone.

This is the commonest cause of acromegaly and accounts for more than 90% of cases of acromegaly. Pituitary adenoma is a benign tumor of pituitary gland. Pituitary adenomas produce excess growth hormone and as they expand in size (due to growth of tumor), they may compress surrounding brain tissues, such as optic nerve and visual disturbances. Increasing size of tumor may also lead to headache, which is seen in many acromegaly patients. The growing (expanding) pituitary adenoma can also compress the normal pituitary tissue and lead to reduced production and secretion of pituitary hormones such as testosterone, which can cause impotence in men and changes in menstruation and breast discharge in women.

Some patients (especially young adults diagnosed with acromegaly), tend to have aggressive tumors which grow very fast and invade and compress surrounding brain tissues, whereas some patients have slowly growing tumors and symptoms may take many years to develop.

Pituitary adenomas are not genetically inherited and arise due to spot mutation and spontaneously. Mutation occurs in the genes which controls the transmission of chemical signals within pituitary cells.

Other tumors causing acromegaly:

There are tumors, other than pituitary adenomas, which can secrete growth hormone and cause acromegaly, e.g. tumors of lungs, pancreas and adrenal glands. Sometimes these tumors produce growth hormone themselves, but in general these tumors produce Growth Hormone Releasing Hormone (GHRH), which stimulate pituitary gland to produce and secrete more growth hormone. Estimation of blood GHRH can establish case of acromegaly and removal of the tumor secreting GHRH can bring down growth hormone level to normal and improve symptoms of acromegaly.