Spontaneous Hypoglycemia with Insulin Autoimmunity in Graves' Disease

A patient with Graves' disease developed spontaneous hypoglycemia after treatment for 3 weeks with methimazole. The hypoglycemic attacks lasted for 4 days and disappeared spontaneously. Although the patient had never received exogenous insulin, significant insulin-binding antibodies were found in the serum, and a huge amount of immunoreactive insulin (23 100 to 35 280 μU/ml) was extracted from the serum obtained during the hypoglycemic attacks. One year after the episode of hypoglycemia, insulin-binding antibodies and elevated serum immunoreactive insulin were still present in the patient. The autoimmune concept might provide the most plausible explanation for the combination of Graves' disease and spontaneous hypoglycemia in this case.