A Rare Cyclic Cushing Syndrome Mystery Illustrates Diagnostic Principles

Pheochromocytomas predominantly produce catecholamines, and rarely also produce ACTH, causing Cushing syndrome (CS). Cyclic CS, an uncommon presentation of hypercortisolism, poses a diagnostic challenge. We report a 71-year-old woman who developed cyclic ectopic ACTH secretion from a pheochromocytoma. Previous evaluations showed intermittent elevations in cortisol and ACTH levels, normal pituitary magnetic resonance imaging, and an adrenal nodule. On admission, she was hypertensive and had cushingoid features. Bilateral inferior petrosal sinus sampling with desmopressin stimulation and an 8-mg dexamethasone suppression test suggested ectopic ACTH secretion, but ACTH increased during the peripheral desmopressin stimulation test. Plasma normetanephrines were about 2-fold above the upper reference limit.