Insulinoma in a Patient with Type 2 Diabetes: A Case Report

ABSTRACT Objective: To describe a case of insulinoma in a patient with pre-existing type 2 diabetes mellitus. Methods: We report a case, with clinical, biochemical, and imaging findings, and give a literature review. Results: The most common causes of recurrent hypoglycemia in a patient with diabetes mellitus are insulin excess and use of insulin secretagogues. If these are completely ruled out, other causes must be considered. The co-existence of diabetes mellitus and insulinoma is very rare, with less than 40 cases reported in the literature. We report the case of a 66-year-old woman with obesity, hypertension, and type 2 diabetes mellitus treated with premixed insulin, who was diagnosed with an insulinoma in the setting of a 6-month history of severe recurrent hypoglycemia that persisted despite discontinuation of insulin therapy. A computed tomography of the abdomen revealed a 14-mm tumor in the pancreatic tail that was removed through laparoscopic distal pancreatectomy. Histopathologic examination confirmed the diagnosis. Postoperatively, the patient had to resume insulin therapy and is now being managed with premixed insulin with a total daily insulin dose of 40 units (0.6 U/kg), without hypoglycemic episodes. Conclusion: Although hypoglycemic agents are the most common cause of hypoglycemia in patients with diabetes, insulinomas may also occur in these patients. This case report stresses the importance of considering this diagnosis in patients with diabetes and recurrent hypoglycemic episodes that persist after antidiabetic treatment adjustment or discontinuation. Abbreviations: DM = diabetes mellitus; HbA1c = glycated hemoglobin; TDID = total daily insulin dose