SUN-LB058 Metastatic Insulinoma after Bariatric Surgery: A Diagnostic Challenge

Background: Post bariatric hypoglycemia (PBH) is an increasingly recognized complication of bariatric surgery. Onset typically occurs more than 1-year post-op with episodes typically occurring postprandially. In contrast, insulinoma causes fasting and postprandial hypoglycemia and has been described after bariatric surgery, with 9 reported cases. Case: A 69-year-old woman presented to the emergency department after syncope in the setting of hypoglycemia to 39 mg/dL. Medical history was notable for Roux-en-Y gastric bypass 9 years ago. She had been experiencing fatigue in the 8 months prior with episodes of diaphoresis, hunger and mental fogginess that occurred randomly throughout the day and resolved with hard candy. An inpatient supervised fast resulted in Whipple triad with blood glucose 32 mg/dL and insulin 28 uU/mL (N 2.6-24.4) within 3 hrs of starting the test, thus making it difficult to exclude PBH. Therefore, a repeat fast was performed after minimal carbohydrate intake. This test yielded similar results with hypoglycemia occurring within 2.5 hrs. Based on this, medical treatment with octreotide and diazoxide was initiated. CT abdomen showed atrophic pancreas with no mass and an enhancing liver mass suggestive of a hemangioma. However, MRI abdomen revealed a 2.9 cm pancreatic tail mass and 3 hypervascular liver lesions concerning for metastasis. Subsequently, biochemical results from the supervised fast confirmed hyperinsulinemic hypoglycemia likely due to metastatic insulinoma based on imaging studies: C-peptide 4.67 ng/mL (N 0.8-3.85), proinsulin >800 pmol/L (N <=18.8), ß hydroxy butyrate 0.04 mmol/L (N <= 0.28). Pancreatic mass FNA via endoscopic ultrasound was suspicious for neuroendocrine tumor (NET). Liver mass biopsy showed metastatic NET. Hypoglycemia worsened despite continuous IV dextrose infusion and medical therapy necessitating distal pancreatectomy, splenectomy and partial hepatectomy for tumor debulking. Pathology revealed a 1.4 cm grade 2 well- differentiated NET in the pancreatic tail (mitotic rate 1 per 10 hpfs, Ki67 5%) and 2 foci of metastasis in the liver (8 and 0.9 cm). Unfortunately, the patient developed unexplained refractory shock with multiorgan failure post-operatively and passed away after 7 days. Conclusion:To our knowledge, this is the first case reported of malignant insulinoma after bariatric surgery. Malignant metastatic insulinoma is very rare. It causes severe hypoglycemia that can occur in the very early PP period similar to PBH, which could delay diagnosis. Inconclusive initial imaging should not preclude comprehensive workup in severe persistent hypoglycemia. Reference: Mulla, CM et al. Insulinoma After Bariatric Surgery: Diagnostic Dilemma and Therapeutic Approaches. Obes Surg. 2016. 26:874-881 Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.