RF19 | PSUN368 Surviving Insulinoma: Severe Insulin Resistance in the Face of Endogenous Hyperinsulinemia

INTRODUCTION: Insulinoma is a rare pancreatic neuroendocrine tumor (PNET) accounting for 1-2% of pancreatic neoplasms. Usually benign, even small tumors can cause significant morbidity due to hypoglycemia. Surgical resection is preferable choice of treatment, but diagnosis is usually delayed and localization can be evasive. We present a case of insulinoma in a patient who battled his symptoms with high carbohydrate intake leading to massive weight gain associated with severe insulin resistance. CASE: A 70 year old male presented to the ED after being found unconscious in his home. Blood glucose was 34 mg/dl after missing a meal. He had a remote history of diabetes mellitus, which gradually resolved. Five years ago, he began experiencing sweats, tremors, headaches and confusion early in the morning or when fasting that improved with eating. He was hospitalized four years ago due to hypoglycemia where he was suspected to have endogenous hyperinsulinemia. CT abdomen at that time was unremarkable. Possibility of insulinoma was raised, but patient did not pursue further investigations. In the last 4 years, he avoided severe hypoglycemic events with frequents meals, but had gained more than 50 lbs with resultant BMI of 51 kg/m2. While admitted, he underwent a 72h fasting test showed glucose 42 mg/dl, insulin level was 84.8 IU/L (range <3), proinsulin was 105.7 (pmol/l) and C-peptide was 4.83 ng/ml (ref <0.2). EUS revealed 7 mm×4 mm mass in pancreatic body. FNAB confirmed well differentiated PNET, grade 1. CT abdomen remained unrevealing. He was started on weight based diazoxide therapy with resolution of hypoglycemic events and persistent hyperglycemia, which required high dose insulin therapy and improved with significant decrease in diazoxide dose. Hospitalization was complicated by hypoxic hypercarbic respiratory failure due to obesity hypoventilation syndrome, COVID19 infection and new onset rapid atrial fibrillation. Patient was deemed not to be a surgical candidate due to multiple comorbidities and his medical management was switched to octreotide with low dose insulin therapy, which patient tolerated well. CONCLUSION: Diagnosis of insulinoma can be significantly delayed in cases with mild or slowly progressive course of the disease. We suggest that progressive development of severe insulin resistance in patients with baseline obesity and insulin resistance-driven DM2 can mask endogenous hyperinsulinemia for extended period of time. This gives a false sense of slower progression or even resolution of symptomatology, as well as diversion to alternative diagnoses, like postprandial hypoglycemia. We also argue that "resolution" of diabetes with significant weight gain, especially when associated with increased calorie intake through frequent meals and symptomatology suggestive of hypoglycemia should be a red flag for workup towards possible insulinoma, akin to suspecting adrenal insufficiency in diabetic patients with an unexplained decrease in insulin requirements. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m., Sunday, June 12, 2022 1:00 p.m. - 1:05 p.m.