A patient with a corticotroph adenoma (Cushing's disease) undergoes bilateral adrenalectomy. Post-operatively, the tumor enlarges and produces excessive MSH along with ACTH, causing hyperpigmentation. This phenomenon is called Nelson's syndrome. The shared precursor molecule for both ACTH and MSH is:

• A Proopiocorticotropin (POCT)
• B Pro-opiomelanocortin (POMC) ✓
• C Corticotropin-releasing hormone (CRH)
• D Big ACTH (31 kDa precursor specific to the corticotroph)

Explanation

Pro-opiomelanocortin (POMC) is the 241-amino acid precursor polypeptide produced by corticotroph cells of the anterior pituitary. Post-translational cleavage of POMC yields ACTH (39 amino acids) and beta-lipotropin; further cleavage of ACTH yields alpha-MSH and CLIP (corticotropin-like intermediate lobe peptide). In Nelson's syndrome, removal of the adrenal glands eliminates cortisol feedback, causing the residual (now uninhibited) corticotroph adenoma to proliferate and produce massive amounts of POMC-derived peptides including MSH, causing severe skin hyperpigmentation.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.