Insulin Autoimmune Syndrome in a Patient with Myasthenia Gravis and Graves' Disease

Abstract

We report a case of insulin autoimmune syndrome with concomitant myasthenia gravis (MG) and Graves' disease. A 27-year-old woman developed an allergic reaction while being treated with thiamazole (MMI) and propylthiouracil during two-week treatment elsewheres in May 2007. Surgery was planned, but the patient was brought to the emergency room late in June 2007 with loss of consciousness due to hypoglycemic attack (24 mg/dl). Fasting blood examination showed abnormally high immunoreactive insulin of 233 mIU/ml and, despite no insulin injection history, a high percentage (89%) of serum-bound ¹²⁵I-insulin. Scatchard analysis showed two serum binding sites. At the high-affinity site, we identified a low Kd of 0.0195×10⁸ M^-1 and a high Bmax of 119×10^-8 M. Human leukocyte antigen was DRB1^*0406. These results yielded, a diagnosis of insulin autoimmune syndrome (ISA) induced by MMI. We subsequently conducted subtotal thyroidectomy for Graves' disease. Although Graves' disease is known to accompany MG, this development of ISA in a patient with both MG and Graves' disease is a rare case.