SUN-318 An Interesting Case of "Brain Fog" Leading to an Uncommon Endocrinological Diagnosis

Introduction: Hypoglycemia in the non diabetic is uncommon. A thorough work-up is needed to diagnose inappropriate endogenous hyperinsulinemia and to rule out surreptitious causes. Case presentation: This is a case of a 55-year-old, non-diabetic Caucasian male who presented to the office with what was described by him and his wife as "brain fog" and "spacing out". He was found to have symptomatic hypoglycemia with fasting blood glucose (BG) between 40-50 mg/dL and symptoms such as diaphoresis and confusion, which improved with meals. Further workup showed fasting BG of 48 mg/dl, total plasma insulin of 18.7 IU/mL (2.0-19.6 IU/mL), C-Peptide 2.85 ng/mL (0.8-3.85 ng/mL), negative anti insulin antibody <0.4 U/mL, and elevated proinsulin of 129 pmol/L (<18.8 pmol/L). Screening for sulfonylurea abuse was negative. These laboratory findings were consistent with insulinoma, therefore a CT of the abdomen was done and it revealed a 2.5 x 1.9 cm mass in the tail of the pancreas. Preoperatively, the patient was treated with doxazosin, which led to resolution of hypoglycemia and was later switched to octreotide due to an allergic reaction to the doxazosin. He underwent a laparoscopic distal pancreatectomy, with pathology showing a well differentiated neuroendocrine tumor, confirming the diagnosis of insulinoma. Post-operative laboratory testing showed persistent euglycemia, and the patient was discharged from the hospital for outpatient follow-up. Discussion: Insulinomas have a reported incidence of 4 cases/million/year, and usually presents as a single benign tumor located within the pancreas (1, 2). Insulinomas can produce either insulin or pro-insulin, and both can lead to symptomatic hypoglycemia (1), just as the case with this patient. Due to its rarity, there is often a delay in diagnosis. It can be initially misdiagnosed as a neurologic or psychiatric disorder due to overlapping symptoms. Neuroglycopenia warrants further evaluation, and factitious causes of hypoglycemia need to be ruled out. Our patient was spared from unnecessary diagnostics test and medications because an early diagnosis was made. References: 1. Parbhu SK, Adler DG. Pancreatic neuroendocrine tumors: contemporary diagnosis and management. Hosp Pract (1995). 2016 Aug;44(3):109-19. 2. Murtha TD, Lupsa BC, Majumdar S, Jain D, Salem RR. A Systematic Review of Proinsulin-Secreting Pancreatic Neuroendocrine Tumors. J Gastrointest Surg. 2017;21(8):1335-41.