“The Unusual Suspect” - Insulin Autoimmune Syndrome, an Extremely Rare Cause of Hypoglycemia

Background: Insulin autoimmune syndrome (IAS), also called Hirata syndrome, is a rare diagnosis which is characterized by hypoglycemia, normal or elevated fasting insulin level, and elevated anti-insulin antibody titers. Clinical Case: 45-year-old nondiabetic Caucasian female presented to the emergency department (ED) with chief complaint of near-syncope. She reported difficulty concentrating and feeling faint roughly 1 hour after consuming breakfast. Upon ED arrival, fingerstick glucose (FSG) was 47 mg/dL. Her symptoms resolved with ingestion of orange juice and repeat blood glucose (BG) 15 minutes later was 120 mg/dL. She reported similar symptoms in the last 5 years happening “every few months” without a predictable pattern; twice with witnessed loss of consciousness. Workup for syncope in the past included normal neurologic, cardiac, and tilt-table testing. She had no prior low FSG/BG recorded, no personal history of bariatric surgery or family history of diabetes mellitus and no access to antihyperglycemic medications. Past medical history included ulcerative colitis and medications included sulfasalazine and multivitamins. Pertinent review of systems was negative for weight loss, nausea, and diarrhea. Vital signs were within normal limits. Physical exam was unremarkable. Height was 165 cm, weight 67.8 kg and body mass index 24.9 kg/m2. Blood draw after overnight fast revealed BG of 78 mg/dL, C-peptide 0.7 ng/mL (ref range 0.8–3.5), insulin 10 µIU/mL (3–19), proinsulin