A 30-year-old woman underwent bilateral adrenalectomy for refractory Cushing disease five years ago. She now has increasing skin pigmentation, headache, and a rising plasma ACTH of 2500 pg/mL. MRI shows an enlarging sellar mass. The underlying mechanism driving this pituitary enlargement is:

• A Rebound hyperplasia of normal corticotrophs after steroid withdrawal
• B Malignant transformation of the original microadenoma into carcinoma
• C Metastatic spread of occult adrenocortical carcinoma remnant tissue
• D Loss of negative feedback by cortisol on a pre-existing corticotroph tumor ✓

Explanation

Nelson syndrome follows bilateral adrenalectomy for Cushing disease: removal of cortisol eliminates negative feedback on a pre-existing ACTH secreting corticotroph tumor, allowing rapid growth, very high ACTH, and hyperpigmentation from POMC-derived melanocyte stimulation. It is benign tumor expansion, not malignant transformation or metastasis, and simple rebound hyperplasia of normal corticotrophs would not form an enlarging sellar mass.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.