FRI362 A Rare Case Of Coexisting Pancreatic Neuroendocrine Tumor And Nesidioblastosis

Disclosure: N. Mon: None. L.K. Tanwani: None. B. Martin: None. C. Scoggins: None. S.L. Mokshagundam: None. Introduction: Nesidioblastosis is a rare cause of endogenous hyperinsulinemic hypoglycemia in adult population. Pancreatic neuroendocrine tumors (NET) are also uncommon among pancreatic tumors. We report a case of a young man who presented with documented Whipple triad and was initially found to have pancreatic cyst. Further evaluation revealed concomitant pancreatic NET and adult nesidioblastosis. Case Report: A 36-year-old Caucasian male with history of anxiety, bipolar, and seizure disorder presented with witnessed seizures and was found to have blood glucose (BG) < 20 mg/dl. He reported recurrent hypoglycemia for 3 years with recent 4-5 ER visits for hypoglycemic seizures. Only medications he was taking were keppra and clonazepam. Physical exam was unremarkable. He was evaluated in Endocrine Clinic and a 72 Hour fast was performed. During the 72 hours fast his BG dropped to 48 mg/dl after 12 hrs. Insulin 16.1 uIU/mL, C peptide 3.02 ng/mL, Proinsulin 60.1 pmol/L, beta-hydroxybutyrate 0.08 mmol/l. BG increased to 116 mg/dl in 30 minutes after 1 mg glucagon injection. Other labs results were: 3PM cortisol 6.6 (7.0-25.0ug/dl), albumin 4.4 mg/dl, HbA1c 5.2%, Alcohol < 5ng/dl, negative urine toxicology screen. CT abdomen without contrast showed a 1.3 cm cyst in the tail of pancreas. Endoscopic ultrasonography revealed a round mixed solid and cystic mass (18x17 mm) with well-defined borders identified in the pancreas tail. The remainder of the pancreas was unremarkable. FNA of the cyst reported findings consistent with a well-differentiated neuroendocrine tumor. He underwent robotic enucleation of distal pancreatic lesion. Postoperative period was uneventful until 2 weeks after procedure when he again started having neuroglycopenic symptoms with lowest BG of 50 mg/dl in the fasting state. He was initiated on diazoxide 50 mg 3 times daily and then 100mg 3 times daily. He continued to have hypoglycemic episodes. Prednisone 10 mg was added at bedtime while waiting for surgery. He underwent distal 80 % pancreatectomy and splenectomy. Hypoglycemia resolved after the surgery. The final pathology was a well-differentiated NET WHO grade I with background neuroendocrine cell hyperplasia/nesidioblastosis. Conclusion: Endogenous hyperinsulinemic hypoglycemia is a rare disorder with nesidioblastosis being the important cause in children and insulinoma in adults, representing a spectrum of pathologic beta cell proliferation. There are very few reports of coexistence of both conditions in adults. Our patient also had an unusual type of insulinoma as it was cystic. The simultaneous occurrence of the two lesions offers significant challenges in diagnosis and management. The mainstay of treatment is surgical resection of insulinoma with localization of insulin hypersecretion; however, how much to remove in nesidioblastosis is still unclear. Presentation: Friday, June 16, 2023