Hirata's Disease: A Case Report.

Insulin Autoimmune Syndrome (IAS), also known as Hirata's disease, is a rare endocrine disorder characterized by recurrent hypoglycemia due to endogenous hyperinsulinemia and the presence of insulin autoantibodies (IAAs). We report a case of IAS successfully treated with corticosteroid therapy. Notably, the definitive diagnosis was established only during the second hospitalization, after multiple recurrent hypoglycemic episodes. The delayed diagnosis reflects the nonspecific presentation and the low initial suspicion for autoimmune hypoglycemia. In the first admission, although insulinoma had been excluded, the patient was discharged without a confirmed diagnosis. This case highlights the importance of early insulin autoantibody testing in patients with unexplained endogenous hyperinsulinemic hypoglycemia to prevent diagnostic delay and unnecessary investigations. Initial evaluation prioritized exclusion of insulinoma, the most common cause of endogenous hyperinsulinemic hypoglycemia, before autoimmune testing was pursued.