Acromegaly



Acromegaly is the clinical manifestation of excessive growth hormone (GH). Growth hormone is produced by the anterior pituitary gland. The most common cause is unregulated growth hormone secretion by a pituitary adenoma. This adenoma can be microscopic or can be a significantly sized tumour that causes compression of local structures. Rarely, acromegaly can also be secondary to a cancer, such as lung or pancreatic cancer, that secretes ectopic growth hormone releasing hormone (GHRH) or growth hormone.

The optic chiasm sits just above the pituitary gland. The optic chiasm is the point where the optic nerves coming from the eyes crossover to different sides of the head. A pituitary tumour of sufficient size will start to press on the optic chiasm. Pressure on the optic chiasm will lead to a stereotypical “bitemporal hemianopia” visual field defect. This describes loss of vision on the outer half of both eyes.

Presentation

Space Occupying Lesion

  • Headaches
  • Visual field defect (“bitemporal hemianopia”)

Overgrowth of tissues

  • Prominent forehead and brow (“frontal bossing”)
  • Large nose
  • Large tongue (“macroglossia”)
  • Large hands and feet
  • Large protruding jaw (”prognathism”)
  • Arthritis from imbalanced growth of joints

GH can cause organ dysfunction

  • Hypertrophic heart
  • Hypertension
  • Type 2 diabetes
  • Colorectal cancer

Symptoms suggesting active raised growth hormone

  • Development of new skin tags
  • Profuse sweating

Investigations

A random growth hormone level is not helpful as it will fluctuate, giving false positives and false negatives

  • Insulin-like Growth Factor 1 (IGF-1) is the initial screening test (raised)
  • Oral glucose tolerance test whilst measuring growth hormone (high glucose normally suppresses growth hormone)
  • MRI brain for the pituitary tumour
  • Refer to ophthalmology for formal visual field testing

 

Treatment

Trans-sphenoidal (through the nose and sphenoid bone) surgical removal of the pituitary tumour is the definitive treatment of acromegaly secondary to pituitary adenomas.

Where acromegaly is caused by ectopic hormones from a pancreatic or lung cancer, surgical removal of these cancers is the treatment.

There are medication that can be used to block growth hormone

  • Pegvisomant (GH antagonist given subcutaneously and daily)
  • Somatostatin analogues to block GH release (e.g. ocreotide)
  • Dopamine agonists to block GH release (e.g. bromocriptine)

Somatostatin is known as “growth hormone inhibiting hormone”. It is normally secreted by the brain, gastro-intestinal tract and pancreas in response to complex triggers. One of the functions of somatostatin is to block GH release from the pituitary gland. Dopamine also has an inhibitory effect on GH release, however not as potent as somatostatin.

Last updated December 2018
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