Case 57 - Severe Corticotropin-Dependent Cushing Syndrome From a Pituitary Adenoma

Abstract

Most patients with corticotropin (ACTH)-dependent Cushing syndrome (CS) will have an ACTH-secreting pituitary microadenoma—50% of which are so small that they cannot be seen on magnetic resonance imaging (MRI). 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. However, there is a subset of patients with pituitary-dependent CS who have large pituitary adenomas, and the clinical presentation can overlap with that of ectopic ACTH secretion. Herein we present such a case.