Abstract
Most patients with corticotropin (ACTH)-dependent Cushing syndrome (CS) will have an ACTH-secreting pituitary microadenoma. When the pituitary appears normal on magnetic resonance imaging (MRI), it is important to distinguish between ectopic and pituitary ACTH-dependent CS. Use of inferior petrosal sinus sampling (IPSS) can help localize the source (pituitary versus ectopic) of ACTH secretion. Pituitary-dependent CS is typically associated with mild to moderate CS, and 24-hour urinary free cortisol (UFC) excretion is typically 100–500 mcg and very rarely >1000 mcg. When patients with ACTH-dependent CS present with spontaneous hypokalemia and 24-hour UFC >1000 mcg, the clinician should suspect an ectopic ACTH-secreting tumor. A subset of patients with pituitary-dependent CS who have large pituitary adenomas demonstrate the clinical presentation that overlaps with ectopic ACTH secretion. Here we present a case of severe ACTH-dependent CS in a patient with negative MRI and IPSS, suggesting a pituitary source, who was treated with bilateral adrenal cryoablation.
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