Challenge of coexisting type 2 diabetes mellitus and insulinoma: a case report

Background Insulinomas are rare clinical entities, but concurrent diabetes mellitus is even more uncommon, and the combination is easily missed. Recurrent hypoglycemia could be misconstrued as improved glycemic control. We present an unusual patient with type 2 diabetes and neuroglycopenia, with apparent improved glycemic control due to an insulinoma. Case presentation A 54-year-old mixed ancestry man with a positive family history of type 2 diabetes mellitus was diagnosed with type 2 diabetes mellitus and hypertension 8 years prior to admission. He presented with episodes of abnormal behavior and hypoglycemia. Inappropriately high insulin and C-peptide concentrations were identified at the time of hypoglycemia. Despite poor adherence to his diabetic treatment, he had no target organ damage relating to diabetes, and his hemoglobin A1c (HbA1c) was 5.3%. A diagnosis of insulinoma was made, and he was started on diazoxide, with endoscopic ultrasound revealing a possible lesion in the pancreatic tail measuring 12 mm × 12 mm. A fine-needle aspiration biopsy could not be performed due to overlying splenic arteries and the risk of vascular perforation. An intraoperative ultrasound confirmed a 15 mm × 10 mm tumor in the pancreatic tail, necessitating a partial pancreatectomy and splenectomy, which were curative. A well-differentiated intermediate grade 2 pancreatic neuroendocrine tumor producing insulin was confirmed on histopathology. Conclusions Recurrent, progressive hypoglycemia and improved glycemic control in a diabetic, without an alternative explanation, may suggest an insulinoma. Insulinomas that exist with type 1 diabetes mellitus, particularly malignant insulinomas, must have escaped autoimmune attack through lack of autoantigen expression. Computed tomography on its own may be insufficiently sensitive for diagnosis of insulinomas, whereas endoscopic and intraoperative ultrasonography may improve the identification of the culprit lesion.