Proinsulin-Predominant Pancreatic Neuroendocrine Tumor-Induced Hypoglycemia After ROUX-EN-Y Gastric Bypass Surgery

ABSTRACT Objective To present a case of recurrent hypoglycemia following Roux-en-Y gastric bypass (RYGB) surgery whose etiology was determined to be a proinsulin-predominant pancreatic neuroendocrine tumor (a proinsulinoma). Methods A case report along with a brief discussion and review of the pertinent literature is presented. Results The patient is a 62-year-old female who presented with symptomatic hypoglycemia 11 years after RYGB surgery. Initial workup revealed low insulin levels with elevated proinsulin levels. A 72-hour fast confirmed the presence of proinsulin-induced hypoglycemia secondary to a pancreatic neuroendocrine tumor (PNET). She underwent distal pancreatectomy with splenectomy and a PNET tumor was successfully removed with resolution of her symptoms. Conclusion Hypoglycemia after RYGB surgery is a well-established syndrome. While there are several etiologies for this, PNETs (including proinsulinomas) should be considered in the differential diagnosis in this population. Proinsulinomas are an increasingly recognized cause of hypoglycemia. Proinsulin levels must always be included as part of the workup of hypoglycemia in an adult.