Antibodies to the insulin receptor are insulinomimetic in vitro, although they generally induce insulin resistance in vivo. We report the novel case of a patient who presented with fasting hypoglycemia as the sole manifestation of autoantibodies to the insulin receptor. Prednisone therapy (120 mg per day) produced a rise in fasting glucose to more than 100 mg per deciliter (6 mmol per liter) within 48 hours, although there was no detectable change in the titer of antireceptor antibodies. After 10 weeks of therapy, the titer of antireceptor antibodies had fallen approximately 100-fold, and prednisone could be discontinued without recurrence of hypoglycemia.

This case demonstrates that antireceptor antibodies must be considered in the differential diagnosis of hypoglycemia, especially in patients with other manifestations of autoimmunity. (N Engl J Med. 1982; 307:1422–6.)