Acromegaly pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Elsaiey, MBBCH [2]

Overview

Acromegaly pathogenesis depends mainly on the excessive secretion of the growth hormone from the pituitary gland. Pituitary somatotroph cell adenoma leads to hyper-secretion of the growth hormone. Insulin-like growth factor 1 (IGF-1) inhibits the secretion of growth hormone in two ways: IGF-1 inhibits directly the somatotroph cells or stimulates secretion the somatostatin that inhibits the GH secretion, IGF-1 is also responsible for the acral features of the acromegaly. The IGF-1 causes the rapid increase in the hand and feet size, forehead protrusion, and jaw prominence. A genetic mutation in the alpha subunit of the guanine nucleotide stimulatory protein leads to increase synthesis of cAMP which increases the secretion of growth hormone. Acromegaly is associated with multiple endocrine neoplasia 1 (MEN-1), Carney complex, McCune-Albright syndrome, paraganglioma, and Pheochromocytoma.

Pathophysiology

Acromegaly is believed to be caused by growth hormone (GH) secreting pituitary adenomas either microadenomas or macroadenomas. The pituitary adenoma leads to hypersecretion of the growth hormone from the somatotroph cells.[1][2][3]

Normal Physiology

Pathogenesis

Genetics

  • The development of acromegaly has been associated also with microduplications on chromosome Xq26.3 which is a location for G protein coupled receptor 101 gene (GPCR101).
  • Microduplication of the chromosome Xq26.3 will be associated with mutations of the GPCR101 protein which leads to increase of the growth hormone secretion.[4]

Associated Conditions

Gross pathology

Gross pathology of acromegaly shows pituitary gland adenoma in most of the cases. Findings include the following:

  • Microprolactinomas (<10mm size) are usually found in the lateral wing of the pituitary gland. They are most often surrounded by well defined pseudocapsules composed of reticulin.
  • Macroprolactinomas (>10mm size) differ substantially in size and behavior. Some cause sellar expansion while others invade the base of the skull.
  • About 50% of all prolactinoma grossly invade surrounding structures.

Microscopic pathology

  • Pituitary microadenomas are defined as adenomas less than 10 mm in size.
  • Most frequently diagnosed as a result of investigating hormonal imbalance.
  • They are confined to the sella and have no scope to produce mass effect related symptoms.

References

  1. Dineen R, Stewart PM, Sherlock M (2016). "Acromegaly". QJM. doi:10.1093/qjmed/hcw004. PMID 26873451.
  2. Landis CA, Masters SB, Spada A, Pace AM, Bourne HR, Vallar L (1989). "GTPase inhibiting mutations activate the alpha chain of Gs and stimulate adenylyl cyclase in human pituitary tumours". Nature. 340 (6236): 692–6. doi:10.1038/340692a0. PMID 2549426.
  3. Melmed S (2009). "Acromegaly pathogenesis and treatment". J Clin Invest. 119 (11): 3189–202. doi:10.1172/JCI39375. PMC 2769196. PMID 19884662.
  4. Trivellin G, Daly AF, Faucz FR, Yuan B, Rostomyan L, Larco DO; et al. (2014). "Gigantism and acromegaly due to Xq26 microduplications and GPR101 mutation". N Engl J Med. 371 (25): 2363–74. doi:10.1056/NEJMoa1408028. PMC 4291174. PMID 25470569.
  5. Hannah-Shmouni F, Trivellin G, Stratakis CA (2016). "Genetics of gigantism and acromegaly". Growth Horm IGF Res. 30-31: 37–41. doi:10.1016/j.ghir.2016.08.002. PMC 5154831. PMID 27657986.
  6. 6.0 6.1 https://en.wikipedia.org/wiki/Pituitary_adenoma#/media/File:Pituitary_adenoma_%281%29_GH_production.jpg



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