A 56-year-old man with Nelson's syndrome after bilateral adrenalectomy for Cushing's disease presents with worsening headache and bitemporal hemianopia. MRI shows an enlarging pituitary macroadenoma. The pathophysiology responsible for this pituitary enlargement is:
- A Loss of cortisol-mediated negative feedback causing corticotroph hyperplasia and tumour growth ✓
- B Paradoxical GH hypersecretion after adrenalectomy
- C Radiation-induced secondary pituitary neoplasm
- D TSH-secreting adenoma developing after thyroid failure
Correct answer: A. Loss of cortisol-mediated negative feedback causing corticotroph hyperplasia and tumour growth
Explanation
Nelson's syndrome occurs after bilateral adrenalectomy for Cushing's disease when the pre-existing ACTH-secreting corticotroph adenoma expands rapidly. Removal of both adrenal glands eliminates cortisol, which normally exerts negative feedback on the pituitary corticotrophs; without this brake, the residual adenoma grows aggressively and secretes very high levels of ACTH and pro-opiomelanocortin-derived peptides causing hyperpigmentation. The other options do not explain this specific post-adrenalectomy syndrome.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.