Peptide Receptor Radionuclide Therapy–Induced Hypercortisolemic Crisis in Ectopic Cushing Syndrome

A woman in her fourth decade of life with metastatic ectopic Cushing syndrome due to a thymic neuroendocrine tumor developed an acute adrenocorticotropin (ACTH)-mediated hypercortisolemic crisis 5 days after initiating lutetium-177-labeled DOTA-[Tyr³]-octreotate (¹⁷⁷Lu-DOTATATE) peptide receptor radionuclide therapy (PRRT). She presented with hypertension, rapid weight gain (8 kg in a week), psychosis, and biochemical evidence of severe hypercortisolism: serum cortisol: 141 µg/dL (SI: 3889.7 nmol/L) (reference range, 5-25 µg/dL [SI: 137.9-689.7 nmol/L]), plasma ACTH greater than 2000 pg/mL (SI >440.4 pmol/L) (reference range, 10-60 pg/mL [SI: 2.2-13.3 pmol/L]), potassium: 3.4 mEq/L (reference range, 3.5-5.0 mEq/L). Low-dose intravenous etomidate (0.02 mg/kg/h) was administered as a bridge to bilateral adrenalectomy. On etomidate infusion, she developed clinical evidence of adrenal insufficiency (hypotension) despite persistently high cortisol levels (25 µg/dL [SI: 689.7 nmol/L]) on chemiluminescence assay due to steroid precursor accumulation and assay interference, necessitating liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for accurate diagnosis. Post adrenalectomy, the patient tolerated subsequent PRRT cycles. This case highlights PRRT-induced ACTH-mediated hypercortisolemic crisis treated with etomidate infusion for acute cortisol control and the need for LC-MS/MS for accurate biochemical monitoring.