CUSHING'S DISEASE IN A YOUNG ADULT WITH ADRENAL INCIDENTALOMA: A DIAGNOSTIC ODYSSEY THROUGH BIOCHEMICAL AND RADIOLOGICAL WORKUP

Abstract

Cushing’s disease, resulting from ACTH-dependent hypercortisolism driven by a pituitary corticotroph adenoma, represents a diagnostically challenging endocrine disorder. We report the case of a 29-year-old male who presented with dyspnea and was found to have features of cortisol excess including hypertension, lower lid retraction, hyperpigmented knuckles, and abdominal striae. Biochemical evaluation confirmed autonomous cortisol hypersecretion: elevated baseline cortisol (34.38µg/dL), elevated ACTH (71.6 pg/mL), elevated 24-hour urinary free cortisol (300 µg/day), and failure of suppression on low-dose dexamethasone testing, with paradoxical suppression on high-dose testing (2.7 µg/dL), consistent with a pituitary source. Intriguingly, the MRI pituitary with plain and contrast sequences was reported as normal, raising the possibility of a microadenoma below imaging resolution. CT abdomen demonstrated mild right adrenal thickening (4.5 mm), likely reflecting secondary adrenal hyperplasia. The diagnostic workup was escalated to bilateral inferior petrosal sinus sampling (BIPSS) at a tertiary referral center, establishing the pituitary as the source of excess ACTH. This case underscores the critical role of stepwise biochemical confirmation in Cushing’s disease, the limitations of MRI in detecting microadenomas, and the indispensable value of BIPSS in cases with inconclusive imaging.