Insulin autoimmune syndrome (Hirata Disease): An updated review of epidemiology, pathophysiology, clinical features, diagnosis, and management.

BACKGROUND: Insulin autoimmune syndrome (IAS), or Hirata disease, is a rare but clinically compelling cause of hyperinsulinemic hypoglycemia in individuals without prior insulin exposure. Antibody-mediated sequestration of insulin followed by delayed dissociation produces marked glycemic variability, often mimicking insulinoma or factitious hypoglycemia. Increasing global recognition has linked IAS to medications, nutritional supplements, and autoimmune conditions. OBJECTIVE: This review summarizes current evidence on the epidemiology, immunogenetic susceptibility, pathophysiology, clinical presentation, diagnostic evaluation, and management of IAS, with emphasis on mechanisms that explain glycemic variability and practical strategies for accurate diagnosis. METHODS: A structured narrative review was conducted using major biomedical databases to identify publications describing IAS, insulin autoantibodies, or antibody-mediated hypoglycemia. Case reports, case series, mechanistic studies, and reviews were included. Evidence was synthesized to highlight consistent clinical patterns, immunologic mechanisms, and management approaches. RESULTS: IAS is driven by high-capacity, low-affinity insulin autoantibodies that bind endogenous insulin after meals and release it unpredictably, producing postprandial hyperglycemia followed by delayed hypoglycemia. HLA-DR4-related alleles, particularly DRB1×0406, increase susceptibility, while sulfhydryl-containing medications and alpha-lipoic acid are common triggers. Diagnostic challenges arise from immunoassay interference, disproportionately elevated insulin levels, and negative imaging for insulinoma. Most cases improve with withdrawal of triggering agents, dietary modification, and supportive care; persistent hypoglycemia may require glucocorticoids, acarbose, diazoxide, or antibody-directed therapies. CONCLUSION: IAS is an underrecognized immune-mediated cause of hyperinsulinemic hypoglycemia. Early consideration of IAS in patients with discordant insulin-C-peptide results or recent exposure to high-risk medications can prevent unnecessary imaging and guide effective, mechanism-based treatment.