SAT171 An Unusual Presentation Of Insulinoma With Postprandial Hypoglycemia

Disclosure: J.G. Melendez-Rivera: None. F.H. Morgan: None. A. Aneja: None. Background: Insulinomas are rare neuroendocrine tumors of the pancreas with an incidence of four cases per million individuals per year. The most common presentation of insulinoma is fasting hypoglycemia with associated neuroglycopenic symptoms. Postprandial hypoglycemia has been previously reported, usually in combination with fasting hypoglycemia. Exclusive postprandial hypoglycemia is estimated to occur in 6% of insulinomas. Clinical Case: A 61-year-old woman presented with episodes of postprandial blurry vision, diaphoresis, nausea, and dizziness occurring for the last 18 months that have become more frequent. The patient reported blood glucose measurements in the 35 - 40 mg/dL range at the time of symptoms. Fasting blood glucose levels remained consistently in the 70 - 90 mg/dL range. These symptoms were originally sporadic but progressively became more common to the point that they were occurring daily after meals, and she gained 20 pounds due to increased food intake. BMI was 36.28. Her physical exam was unremarkable. Fasting labs revealed a glucose of 82mg/dl and C-peptide of 2.8ng/ml with normal cortisol. After a short trial of a reactive hypoglycemia diet, the patient had no improvement in symptoms, and was admitted for a 72-hour fast. She developed hypoglycemia with a glucose of 42mg/dl within four hours of starting her inpatient fast. At the time of hypoglycemia, insulin and C-peptide were inappropriately normal (insulin 15.9 mIU/mL and C-peptide 2.57 ng/mL) with an elevated proinsulin (42.3 pmol/L). An MRI abdomen with and without IV contrast showed a 16 mm hypervascular mass in the head of the pancreas. She subsequently underwent endoscopic ultrasonography with fine needle aspiration showing findings consistent with a well-differentiated pancreatic neuroendocrine tumor. Ga-68 DOTATATE PET CT revealed increased DOTATATE avidity in the pancreatic head mass compatible with neuroendocrine tumor but no evidence of metastatic disease. She underwent surgical resection of the tumor with resolution of symptoms. Conclusion: The absence of fasting hypoglycemia does not rule out pancreatic neuroendocrine tumors. While rare, exclusive postprandial hypoglycemia can be seen in these types of tumors, especially proinsulin-secreting tumors. This case illustrates the importance of considering insulinoma during the evaluation of postprandial hypoglycemia in the absence of fasting hypoglycemia and persistent hypoglycemia despite dietary modifications. Presentation: Saturday, June 17, 2023