PSUN374 Casting a Wide NET: A Case Report of Recurrent Hypoglycemia and 'Malignant' Insulinoma
Authors: Villarreal Marcos , Ferriter Kevin , Ahle Daniel , Desai Viraj , Kumar Pratima 
Published: November 2022

Abstract

Introduction
Insulinomas are rare neuroendocrine tumors, with an incidence of 4 cases per one million patient-years. Malignant insulinomas are even rarer, with a paucity of data for specific treatment modalities. Surgery, the mainstay of treatment, needs to be determined by the disease extent prior to resection. Here, we describe a patient who presented to a Federally Qualified Health Center with a diagnosis of hypoglycemia and the barriers related to the evaluation and treatment of his insulinoma.

Case Presentation
A 40-year-old Hispanic man with no past medical history presented to the clinic with an 8-year history of syncopal episodes. Continuous glucose monitoring revealed nocturnal hypoglycemia with BG &lt;50 mg/dL, but he discontinued its use due to frequent low blood glucose alerts.
Physical exam was notable for central obesity and acanthosis nigricans. Labs showed a fasting glucose of 63 mg/dL, proinsulin 419.9 (&lt;18.8 pmol/L), insulin 11.3 (&lt;19.6 uIU/ml), C-peptide 2.24 (0.80-3.85 ng/mL), A1C 4.3%, and negative urine sulfonylurea screen. A diagnosis of insulinoma was suspected and he was started on acarbose.
CT abdomen showed a centrally calcified, peripherally enhancing 24 mm lesion in the pancreatic head. 68Ga-DOTATATE PET/CT scan was recommended for further evaluation but was denied by his insurance. Biopsy of the mass using endoscopic ultrasound (EUS) was positive for neuroendocrine tumor with metastasis to a peripancreatic lymph node. Given the concern for metastatic insulinoma, he underwent a pancreaticoduodenectomy. Surgical pathology confirmed the diagnosis of insulinoma but without evidence of tumor in the lymph nodes. The most likely explanation for the tumor cells previously noted in the lymph node was the passage of the needle through the tumor during biopsy. The postoperative course was complicated by hyperglycemia requiring insulin infusion and a pancreatic fistula. The patient was followed in clinic where his repeat proinsulin level was normal. He had resolution of his hypoglycemic episodes, his fistula healed, and he is back at work.

Discussion
Our case reinforces the need for an accurate diagnosis and localization of neuroendocrine tumors prior to surgical intervention. A preoperative 68Ga-DOTATATE PET/CT would have demonstrated an absence of tumor outside the pancreatic mass and prompted a less invasive surgical approach. Because of insurance denial, the EUS biopsy findings suggesting metastatic insulinoma could not be confirmed and he underwent a pancreaticoduodenectomy.
Patients with metastatic insulinoma are at risk for recurrence of hypoglycemia in the postoperative period. Persistence of postoperative hyperglycemia suggests either new-onset diabetes due to insulin deficiency or resistance and suppression of residual endogenous insulin secretion as a result of insulinoma-induced chronic hyperinsulinemia. Decreases in insulin requirements post-operatively can be explained by recovery of remnant pancreatic insulin production after alleviation of chronic suppression, and reduction in insulin resistance induced by surgery.
Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.