SUN-320 Insulinomatosis: A Rare Cause of Recurrent Hyperinsulinemic Hypoglycemia

Abstract Background: Hyperglycemic hypoglycemia (HH) is most commonly caused by a single, sporadic insulinoma. Insulinomatosis is a rare cause of HH. The histology is characterized by several tumors and grouping of neuroendocrine cells that produce exclusively insulin. (1) Case report: A 52 year old woman, with no known disease, presented to a tertiary hospital with a 1 year record of several, recurrent hypoglycemic episodes. During one of this episodes the laboratory workout revealed: glucose 26 mg/dL (1.44 mmol/L), insulin 13.4 µU/mL (< 3 µg/dL), C-peptide 2,7 ng/dL (<0,6 ng/dL), negative cetonemia and negative sulfonylurea hypoglycemia panel, which confirmed a HH case. Subsequently she performed abdominal magnetic resonance imaging (MRI) and endoscopic ultrasonography, which were normal, and a pancreatic arteriography with intra-arterial calcium stimulation that revealed a 6.2 insulin gradient in the splenic artery consistent with a higher insulin production in the pancreatic body/tail. Another directed MRI scan revealed a small (1 cm) T2-Hyperintense lesion which was previously unnoted in the pancreatic tail. This lesion was enucleated, with histology showing a insulin positive neuroendocrine tumor. Unexpectedly, enucleation of the lesion did not lead to symptoms remission, and the patient relapsed on hypoglycemic episodes, which were confirmed by a second fasting test. MRI was repeated and showed a new pancreatic tail lesion (1.0 cm). Distal pancreatectomy was performed, and detailed histopathological examination revealed several small (< 0.5cm) tumors along the pancreatic body with positive immunohistochemistry staining for insulin, chromogranin A, synaptophysin and negative for glucagon. After the second surgical procedure, the patient showed symptomatic remission with no further hypoglycemia. Conclusion: We have described a rare case of HH caused by insulinomatosis. Although initial presentation could point out to an insulinoma, the recurrence of hypoglycemia after enucleation of the suspected lesion suggested another etiology. Subsequent surgery and histologic study confirmed the insulinomatosis hypothesis. Its histology is characterized by multiple neuroendocrine tumors producing exclusively insulin, which could comprise the concurrence of different lesions, including macrotumors, microadenomas (<0,5cm), and/or small proliferative insulin-expressing monohormal endocrine cell clusters (IMECCs). This represents a rare cause of HH, and literature is scarce on the management of this condition. It has been described high recurrence of hypoglycemic episodes. The patient is currently being followed in our service with no further hypoglycemic episodes.