8036 A Rare Case of Cushing’s Syndrome Caused by a Pulmonary Carcinoid Tumor

Abstract Disclosure: A.C. Tep: None. F.M. Wolf: None. Introduction: The most common causes of ectopic ACTH (adrenocorticotropic hormone) syndrome include bronchial carcinoid tumors and other neuroendocrine tumors. Ectopic ACTH syndrome (EAS) can be difficult to diagnose. Differentiating Cushing’s disease and EAS is difficult, as ACTH-secreting tumors are often small and easily missed on imaging. Case Presentation: A 32-year-old male with a history of hypothyroidism presented with a 6-month history of facial rounding. He also noticed a dorsocervical fat pad, muscle weakness in the extremities, easy bruising, and elevated blood pressure progressing over the same period. A 24-hour urine free cortisol was elevated to 1797 mcg. Two salivary cortisol tests performed 1 hour after the patient’s usual bedtime had values of 4.4 ug/dl and 1.000 ug/dl. Both the urine and salivary cortisol results were exceedingly high. ACTH was elevated (150 pg/ml). An MRI of the pituitary gland was normal without evidence of an adenoma. Frequently, ACTH-secreting pituitary adenomas are small enough that they are missed on MRI; however, given our patient’s rapid clinical presentation, additional imaging was performed to identify an ectopic source. A CT Chest/Abdomen/Pelvis showed a 1.2 cm nodule in the right middle lobe of the lung. The right middle lobe was resected, and pathology revealed a carcinoid tumor. His cortisol levels slowly decreased postoperatively and eventually normalized. At his one-month post-operative visit, his symptoms were all improving but not yet resolved. Discussion: This patient was found to have Cushing's syndrome due to ectopic ACTH production from a pulmonary carcinoid tumor. The patient demonstrated clinical improvement after resection of the tumor. Pulmonary carcinoid tumors are rare neuroendocrine epithelial tumors that account for 2-5% of all lung tumors. The annual incidence of these tumors is 2.3-2.8 cases per million people. Endogenous Cushing's syndrome is either ACTH-dependent or ACTH-independent. In ACTH-dependent Cushing's syndrome, the ACTH can either be from the pituitary or an ectopic source. Once ACTH-dependent disease is confirmed, a pituitary MRI is performed to evaluate for an ACTH-secreting pituitary adenoma; this is called Cushing’s disease. Some patients undergo inferior petrosal sinus sampling to confirm the source is central and to determine laterality before transsphenoidal resection of the adenoma. If the source of ACTH is not from the pituitary, obtaining a CT or MRI of the chest and abdomen locates tumors in most patients. At times a functional study, such as an octreotide or PET-DOTATE scan, is done to confirm the diagnosis before proceeding with surgical resection to avoid unnecessary removal of an incidental tumor. Ectopic ACTH production often causes a more rapid progression of Cushingoid features, which can be a clue to the diagnosis of this condition. Presentation: 6/1/2024