Insulin Autoimmune Syndrome (Hirata's Disease) Caused by Methimazole in a 47-Year-Old Man

Insulin autoimmune syndrome (IAS), or Hirata's disease, is a rare disease characterized by episodes of hypoglycemia with elevated levels of insulin secondary to high concentrations of insulin autoantibodies. The use of methimazole is a risk factor for the development of Hirata's disease. We report a case of a 47-year-old man being treated for thyroid storm initially with methimazole and other agents. Medical management was stopped, as the patient was refractory to treatment. Ultimately, the patient underwent plasmapheresis and thyroidectomy. While the patient was initially noted to have hyperglycemia during his hospital stay, requiring a regular insulin drip, he subsequently developed hypoglycemia even after cessation of insulin therapy. Lab work was positive for insulin autoantibodies, and the patient was diagnosed with IAS. IAS should be considered in patients with hypoglycemia who have been exposed to specific agents.