What causes acromegaly?

Acromegaly is caused by the prolonged overproduction of growth hormone (GH) in adults, which in turn leads the liver to release excess insulin-like growth factor-1 (IGF-1).¹²

Primary Causes

• Pituitary Adenoma: In over 90% to 98% of cases, the condition is caused by a benign (noncancerous) tumor on the anterior pituitary gland—known as a somatotroph or GH-secreting adenoma. These tumor cells secrete excessive amounts of growth hormone.¹²³
• Ectopic Tumors (Rare): Very rarely, tumors located outside the pituitary gland—such as in the lungs, pancreas, or hypothalamus—can cause acromegaly by secreting GH or growth hormone-releasing hormone (GHRH), which stimulates the pituitary to make extra GH.¹²
• Genetic Syndromes (Rare): Inherited genetic conditions can occasionally predispose individuals to pituitary tumors, including Multiple Endocrine Neoplasia type 1 (MEN1), McCune-Albright syndrome, Carney complex, and familial acromegaly.¹

You can learn more about symptoms, screening, and diagnostic paths through the NHS Acromegaly Guide or the Mayo Clinic Acromegaly Overview.¹²Are you asking out of general curiosity, or are you or someone you know experiencing symptoms or trying to understand a recent diagnosis?

Acromegaly is caused by the body producing too much growth hormone (GH) during adulthood, long after the growth plates in the bones have closed.

The primary causes and mechanisms behind this excess hormone production include:

• Pituitary Adenomas (Most Common): In the vast majority of cases (over 95%), acromegaly is caused by a benign (non-cancerous) tumour called an adenoma located on the pituitary gland (a small gland at the base of the brain). These tumour cells secrete excessive amounts of growth hormone into the bloodstream.¹
• Ectopic Tumours (Rare): Sometimes, the excess growth hormone is triggered by non-pituitary tumours located in other parts of the body, such as the lungs, pancreas, or adrenal glands. These tumours may secrete growth hormone-releasing hormone (GHRH) or GH itself, signalling the pituitary gland to overproduce.
• Genetic Factors (Rare): While most cases are sporadic (not inherited from parents), a small percentage of acromegaly cases are linked to inherited genetic syndromes that predispose individuals to pituitary tumours. Examples include:
  • Multiple Endocrine Neoplasia type 1 (MEN1)
  • Carney complex
  • Familial isolated pituitary adenomas (FIPA) ¹

Detailed clinical information and overview notes can be explored directly via the NHS Acromegaly Guide.

Would you like to know more about the common symptoms to look out for, or how acromegaly is diagnosed and treated?

Acromegaly is caused by excessive production of growth hormone (GH), usually due to a benign tumour of the pituitary gland.

1. The main cause: Pituitary adenoma

In approximately 95% of cases, acromegaly is caused by a growth hormone-secreting pituitary adenoma (a non-cancerous tumour in the pituitary gland, located at the base of the brain).

The tumour produces too much growth hormone, which stimulates the liver to produce excess insulin-like growth factor 1 (IGF-1).

IGF-1 is responsible for many of the physical changes associated with acromegaly.

2. What happens in the body?

The process is:

1. A pituitary tumour develops.
2. The tumour releases excessive growth hormone.
3. The liver produces excessive IGF-1.
4. IGF-1 stimulates abnormal growth of bones and soft tissues.
5. Characteristic features of acromegaly develop.

3. Less common causes

Rarely, excess growth hormone can result from:

• Tumours in other parts of the body producing growth hormone-releasing hormone (GHRH).
• Rare pancreatic, lung or other neuroendocrine tumours producing GHRH.
• Ectopic production of growth hormone, which is extremely rare.

4. What changes does it cause?

Common features include:

• Enlarged hands and feet.
• Enlarged jaw (prognathism).
• Larger nose, lips and tongue.
• Coarse facial features.
• Increased sweating and oily skin.
• Joint pain.
• Headaches and visual disturbances.
• Enlargement of internal organs, including the heart.

5. Why does it develop in adulthood?

The timing is important:

6. How is acromegaly diagnosed?

The main investigations are:

• IGF-1 blood test: Usually elevated.
• Oral glucose tolerance test (OGTT): Growth hormone fails to suppress normally after glucose is given.
• Pituitary MRI: Identifies a possible pituitary adenoma.

Key point: Acromegaly is usually caused by a benign growth hormone-secreting pituitary tumour, resulting in increased IGF-1 and excessive growth of bones and soft tissues in adults.