Insulin Autoimmune Syndrome Mimicking Insulinoma: A Challenging Diagnosis.

Introduction: Insulin autoimmune syndrome (IAS) is a rare condition characterized by hypoglycemia due to autoantibodies against endogenous insulin. It is correlated, in approximately 50% of cases, to specific drugs intake. Hypoglycemia occurs typically during the late post-prandial period. Aim(s): We report two cases of IAS patients who came to our attention because of recurrent and severe hypoglycemia. Materials and methods: Case 1: A 29-year-old female, affected by Graves disease and treated with methimazole, was evaluated in 2006 because of recurrent hypoglycemia. Insulinemia was > 1000 µUI/ml. Fasting test was negative as well as abdomen MRI. After total thyroidectomy glycemic and insulin levels normalized. Case 2: A 45-year-old female came to our attention in 2011 because of recurrent post-prandial hypoglycemia. Insulinemia was >1000 µUI/ml. An OGTT revealed late reactive hypoglycemia, while fasting test was normal as well as EUS. Dosing of insulin antibodies was 658 U/ml (<0.4). With an adequate diet and acarbose treatment the symptoms improved. Results: In these two cases, inappropriately high levels of insulin were associated with late post-prandial hypoglycemia, with no evidence of pancreatic lesions and negative fasting tests. Conclusion: In the evaluation of patients with hypoglycemia and inappropriate secretion of insulin, IAS should be considered in the differential diagnosis, especially in patients with late post-prandial hypoglycemia with a history of specific drugs intake and negative imaging. [ABSTRACT FROM AUTHOR]