Ectopic Adrenocorticotropic Hormone Syndrome Secondary to Pulmonary Neuroendocrine Tumor: Medical Stabilization Enables Serial Imaging and Localization

Background: Ectopic adrenocorticotropic (ACTH) syndrome accounts for 15-20% of Cushing syndrome cases with unique diagnostic challenges.Tumor localization remains difficult, with approximately 20% of cases having occult sources despite extensive imaging.This report describes a patient whose initially occult tumor was successfully localized through serial imaging enabled by medical stabilization, resulting in curative surgical resection.Case Presentation: 39-year-old woman presented with progressive weight gain, new-onset hypertension, hypokalemia, proximal muscle weakness, and cushingoid features.Laboratory evaluation demonstrated severe hypercortisolism with markedly elevated ACTH levels, and inferior petrosal sinus sampling (IPSS) confirmed the diagnosis of ectopic ACTH syndrome.Despite comprehensive imaging-including cross-sectional studies, 68Ga-DOTATATE PET/CT and FDG PET/CT -the ectopic source remained elusive.Medical therapy with ketoconazole and metyrapone achieved rapid biochemical control.An 8 mm lingular pulmonary nodule, non-avid on both DOTATATE and FDG PET but identified on the CT portion of FDG PET/CT, was surgically resected, resulting in complete biochemical cure.Discussion: This case highlights medical stabilization's critical role when tumor localization is initially unsuccessful, enabling serial anatomic imaging that identified an 8mm pulmonary carcinoid initially obscured by atelectasis and non-avid on functional imaging.Small, welldifferentiated neuroendocrine tumors can cause severe hypercortisolism yet remain undetectable on DOTATATE and FDG PET.J o u r n a l P r e -p r o o f Conclusion: This case demonstrates that medical stabilization achieves rapid biochemical control, providing time for serial anatomic imaging to localize occult ectopic ACTH sources.A small pulmonary carcinoid initially obscured by atelectasis and non-avid on functional imaging was identified through repeat CT comparison, enabling curative resection and avoiding bilateral adrenalectomy.