Hyperglucagonemia of insulin autoimmune syndrome induced by methimazole in a patient with Graves' disease

A 47-year-old man with Graves' disease suffered from a feeling of hunger and sweating in the night, polyarthralgia and fever one month after the start of treatment with methimazole. The above symptoms were ascribed to the side effects of methimazole; insulin autoimmune syndrome and lupus-like syndrome. The change in the antithyroid drug to propylthiouracil caused an amelioration of the symptoms. In addition to an anti-insulin antibody with a high binding capacity, hyperglucagonemia (260pg/ml with a plasma glucose level of 61mg/dl) was observed, which returned to normal in parallel with the decrease in the insulin binding capacity of the plasma one month after beginning the treatment with propylthyouracil. A normal decrease in the plasma glucagon level due to exogenous insulin (2mU/kg/min) was observed with the euglycemic clamp. However, the plasma glucagon level was not suppressed by the oral glucose loading and elicited a poor response to the arginine infusion. Taking previous reports into account, this basal hyperglucagonemia seems to be a characteristic finding in the insulin autoimmune syndrome, while a sluggish response of glucagon to oral glucose or arginine infusion might be ascribed to hyperthyroidism.This is the first case report concerning a kinetical study of the glucagon secretion in insulin autoimmune syndrome with Graves' disease.