Insulin autoimmune syndrome as a cause of hypoglycemia--report of four cases.

Insulin autoimmune syndrome is a syndrome consisting of fasting hypoglycemia, hyperinsulinemia and detectable insulin-binding antibodies in patients who have never been exposed to exogenous insulin. Four cases who developed symptoms of hypoglycemic attack with self-limited duration and spontaneous remission were collected in our hospital from 1984 to 1988. The elevated serum total and free insulin and C-peptide levels, as well as the titer of insulin autoantibodies, decreased gradually; but insulin autoantibodies were still present in the serum for more than six months after the initial episodes of hypoglycemia. Three of four patients had Graves' disease and developed the syndrome after methimazole treatment. The fourth one had a history of hemorrhagic cystitis and denied history of specific drug exposure. The cause or stimulus for insulin autoantibody formation is still unknown, but drugs containing a sulfhydryl group like methimazole may play a role in the development of the syndrome. Extremely high insulin antibodies in patients with fasting hypoglycemia along with elevated serum levels of insulin and C-peptide suggest a diagnosis of insulin autoimmune syndrome and usually exclude the possibility of insulinoma or factitious hypoglycemia.