SUN-461 A Diagnostic Conundrum: Cushing syndrome due to Ectopic ACTH. When the Signs Don't Add Up

Abstract Disclosure: P. Pandey: None. S. Parajuli: None. R. Bohra: None. K. Patel: None. A. Omer: None. Introduction: Cushing syndrome due to ectopic ACTH secretion is a rare clinical entity and requires extensive workup which takes time and use of resources. Case Report: A 35-year-old Caucasian male with history of morbid obesity, Type 2 diabetes mellitus, hypertension and sleep apnea presented to endocrinology clinic for management of uncontrolled hyperglycemia. He was screened for Cushing syndrome since he had physical examination findings of central obesity and thick abdominal striae. Three consecutive Saliva cortisol levels measured at 11 PM was mildly elevated associated with non-suppressed AM serum cortisol level after 1mg overnight dexamethasone intake. Serum ACTH level was elevated to 64 pg/ml. Repeat labs showed persistently elevated results and Cushing syndrome diagnosis was confirmed. A high-dose (8 mg) dexamethasone suppression test showed suppressed AM cortisol which suggested pituitary origin of ACTH hypersecretion. Two separate pituitary MRI scans revealed no abnormalities although motion artifact could be involved. The Inferior petrosal sinus sampling showed equivocal increase in cortisol levels, failing to provide definitive evidence of pituitary Cushing disease. Given the possibility of an ectopic source of elevated ACTH, the patient underwent to CT scan of abdomen which revealed a 2.7 cm right adrenal adenoma and intra-abdominal lymphadenopathy. ACTH levels remained elevated, and screening for pheochromocytoma and primary hyperaldosteronism was negative. A FDG-PET study did not reveal any metabolically active lesion. An endoscopic ultrasound revealed a 1.9 cm peri-duodenal lymph node. A biopsy confirmed the presence of a neuroendocrine tumor. A PET-using Gallium 68-Dotatae confirmed suspicious uptake in the proximal duodenum. Due to his morbid obesity associated with body weight over 400 pounds and multiple comorbidities, he was deemed an inappropriate candidate for exploratory surgery and recommended to go to bariatric surgery for weight loss. Meanwhile is being evaluated for specific treatment for hypercorticism including glucocorticoid synthesis inhibitors. DISCUSSION: It took over two years to arrive at a diagnosis for this patient's long-standing condition. This case underscores the fact that not all diagnoses follow the clear-cut patterns often outlined in the literature. As healthcare providers, we must pursue every patient's condition to achieve a definitive diagnosis to improve outcomes. Presentation: Sunday, July 13, 2025