The Diagnosis and Management of a Rare ACTH-Producing Neuroendocrine Tumor Causing Cushing’s Syndrome

Abstract A 57-year-old woman presented with a three-month history of worsening lethargy, weight gain, central adiposity, proximal muscle weakness, and hypokalemic hypertension. Initial investigations were consistent with ACTH-dependent Cushing’s Syndrome. 24-hour urine cortisol: 711nmol/day (normal<275), cortisol after 1 mg dexamethasone suppression test 960nmol/L (normal<50)), 2-day dexamethasone suppression cortisol: 575 and ACTH: 19 pmol/L. MRI sella was normal. She required several hospital admissions for worsening proximal muscle weakness and falls. She was started on ketoconazole and spironolactone. Basal insulin was started for dysglycemia. Petrosal vein sampling indicated ectopic ACTH production. CT scan of chest/abdomen/pelvis showed no intrathoracic or intra-abdominal abnormality. Thyroid ultrasound and whole-body octreotide scan showed no abnormalities. A Gallium 68-dotatate PET scan showed focal tracer uptake in the pancreatic tail suspicious for a well-differentiated neuroendocrine tumor (NET). MRI pancreas showed a slightly truncated pancreatic tail with no discrete lesion. We proceeded with Endoscopic Ultrasound (EUS) which revealed an irregular hypoechoic mass in the pancreatic tail. EUS–guided fine-needle biopsy (EUS-FNB) using a 22G SharkCore needle, revealed a neuroendocrine neoplasm staining positively for ACTH. She underwent distal pancreatectomy with pathology showing a 1.4cm well-differentiated NET, staining positive for ACTH with a Ki67 index of 10%. Postoperatively, her ketoconazole, spironolactone, and insulin were discontinued. Her dysglycemia, hypertension and other clinical symptoms gradually improved. Immediately post-operatively, her AM cortisol was 403 and her 24-hour urine cortisol was elevated 959nmol/day. Repeat AM cortisol and 24-hour urine cortisol one-month post-surgery were 392 nmol/L and 72 nmol/day respectively, confirming biochemical remission. Discussion: ACTH-producing pancreatic NETs are rare, accounting for less than 15% of reported cases of EAS. They are often aggressive, with 78.7% of reported cases having distant metastasis at diagnosis (1). They are associated with significant morbidity and mortality. Diagnosis and management can be difficult and require multiple investigations and multidisciplinary team involvement. In our case, we utilized endoscopic ultrasound to ensure a correct preoperative localization. We discuss the systematic approach for diagnosis and the management of an ACTH-producing pancreatic NET. References: 1. Maragliano R, Vanoli A, Albarello L, Milione M, Basturk O, et al. ACTH-secreting pancreatic neoplasms associated with Cushing syndrome: clinicopathologic study of 11 cases and review of the literature. Am J Surg Pathol. 2015 Mar;39(3):374-82. doi: 10.1097/PAS.0000000000000340. PMID: 25353285.

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