Asymptomatic Hirata syndrome with thionamide use – An underdiagnosed entity

ABSTRACT Hirata syndrome or autoimmune hypoglycemia is a rare cause of hypoglycemia. Patients usually present multiple episodes of postprandial hypoglycemia, usually associated with neuroglycopenic symptoms. This condition has been previously described with multiple drugs such as methimazole or carbimazole in patients of Graves’ disease. We report the case of a 41-year-old woman who was diagnosed with Graves’ disease and was on remission for 3 years on methimazole therapy and was incidentally detected to have persistently low postprandial blood glucose levels on routine evaluation. She denied any symptoms that are typical of hypoglycemia. The anti-insulin antibody came out to be positive. In the absence of fasting hypoglycemia and weight gain; no prior history of diabetes, exogenous insulin, or oral antidiabetic drug use; and a long history of methimazole intake, she was diagnosed to be a case of Hirata syndrome. The culprit drug, methimazole, was stopped, and she underwent radioactive iodine ablation. The incidental detection of Hirata syndrome in a patient on methimazole therapy without symptoms of hypoglycemia raises the possibility that the incidence of Hirata syndrome reported is just the tip of the iceberg, with many asymptomatic cases remaining unidentified, particularly for patients on thionamide therapy.