FRI359 Postprandial Hypoglycemia With Elevated Pro-insulin As A Rare Presentation Of Insulinoma

Disclosure: S. Kalik: None. S. Dehghani: None. J. Zaidan: None. Background: Insulinoma, a neuroendocrine neoplasm, typically presents with fasting hypoglycemia with abnormally elevated insulin levels but can infrequently present with post-prandial hypoglycemia with elevated pro-insulin levels. Clinical Case: A 49-year-old non-diabetic male, presented with a 3-year history of episodes of blurry vision, sweating, and palpitations associated with low finger stick glucose (45-70mg/dL). Episodes primarily occurred 2-3 hours post-meals particularly after eating a high carbohydrate meal. Symptoms improved after taking glucose tabs consistent with Whipple’s triad. He denied fasting hypoglycemia symptoms. Patient had symptoms at the office 2 hours after eating breakfast and Lab work done at that time showed glucose <35 of mg/dL (70-99 mg/dL), inappropriately high-normal c-peptide level of 3.57 ng/mL (0.81-3.85 ng/mL), elevated pro-insulin level of 12.8 pmol/L (<8.0 pmol/L), and a high insulin level of 29.8 uIU/mL (3-25.0 uIU/mL). Insulin antibodies and Sulfonylurea screen were negative. Review of old imaging revealed unremarkable pancreas on Ct scan done three years ago and a month prior to presentation. Given persistent symptoms and lab results Patient underwent an endoscopic ultrasonography with advanced gastroenterology which showed a 14.2 x 11mm hypoechoic, well circumscribed, regularly shaped and homogenous mass at the pancreatic head that was sampled using fine needle biopsy. Pathology confirmed pancreatic neuroendocrine neoplasm, low grade, consistent with insulinoma. Patient went for MRI of abdomen and pelvis which confirmed a 1.4 x 1.2cm slightly T2 hyperintense, hyper-enhancing lesion in the uncinate process suspicious for islet cell tumor. In addition, a 0.6cm liver lesion was identified although not clearly characterized but small metastatic lesion could not be excluded. PET/CT scan did not reveal any metastatic lesions except the focal uptake at the pancreatic uncinate process. Patient was evaluated by surgery and underwent a successful Whipple procedure for resection of the insulinoma. Discussion: 20% of all insulinomas are misdiagnosed with a seizure disorder or psychiatric disorder before an insulinoma is recognized. This case highlights the fact that insulinoma can be present as post prandial hypoglycemia and the superior imaging modality of EUS and MRI for localizing and identifying smaller functional insulinomas. Conclusion: Insulinoma can present as postprandial hypoglycemia with elevated pro-insulin levels. If high clinical and biochemical suspicion for insulinoma, patient should be evaluated with EUS or MRI even in the setting of a negative CT due to higher diagnostic specificity for insulinoma. Presentation: Friday, June 16, 2023