A Case of Non-diabetic Hypoglycemia in the Elderly: Insulin Autoimmune Syndrome

Insulin autoimmune syndrome (IAS), also known as Hirata syndrome, is a rare cause of spontaneous hyperinsulinemic hypoglycemia, most commonly reported in Asian populations, characterized by the presence of insulin autoantibodies in individuals without prior exposure to exogenous insulin. We report the case of a 71-year-old woman who presented with recurrent postprandial hypoglycemic episodes associated with neuroglycopenic symptoms. There was no history of insulin use, oral hypoglycemic agents, or exposure to drugs known to precipitate IAS. Biochemical evaluation demonstrated marked hyperinsulinemia (>1000 µIU/mL), elevated C-peptide levels, an insulin-to-C-peptide ratio >1, and positive insulin autoantibodies, confirming the diagnosis. Anti-thyroid peroxidase antibodies were elevated with normal thyroid function, suggesting an underlying autoimmune predisposition. She was treated with corticosteroids and dietary modification, resulting in complete resolution without recurrence. Steroids were tapered and discontinued over three months with sustained remission. IAS should be considered in cases of non-diabetic hypoglycemia, and early diagnosis with appropriate management can prevent complications.