Hypoglycemia and transient diabetes mellitus in an insulin autoimmune syndrome

A 53-year-old Caucasian woman presented with repeated episodes of hypoglycemia. Self-monitored blood glucose levels during the attacks were between 40 and 60 mg/dl (2.2-3.3 mmol/l). An oral glucose tolerance test performed over 210 minutes showed normal baseline glucose levels, markedly elevated levels of serum insulin and slightly elevated C-peptide concentrations. During the test, a marked increase of insulin and a normal increment of C-peptide were observed. The tentative diagnosis of an insulinoma was raised and a 72 h fasting test performed, throughout which the insulin-glucose-ratio was pathologically elevated, whereas C-peptide levels were only slightly elevated. Strongly positive levels of insulin antibodies led to the diagnosis of an insulin autoimmune syndrome. This syndrome is caused by IgG-insulin-complexes with prolonged plasma half-life in the presence of reduced insulin action. The therapy consisted of fractionated meals to avoid hyperinsulinism and following hypoglycemic episodes. After four months a spontaneous clinical remission was observed. The autoimmune insulin syndrome is a rare cause of recurrent, spontaneous hypoglycemia in Europe in non diabetic patients. Its prognosis is good as there is a high rate of spontaneous clinical remission in up to 80 % of patients.