Severe Fasting Hypoglycemia Mimicking Insulinoma in Three Patients With Insulin Autoimmune Syndrome

Insulin autoimmune syndrome (IAS) is a rare cause of hypoglycemia characterized by the presence of insulin autoantibodies (IAA) in patients without prior exposure to exogenous insulin. Differential diagnosis with other causes of hypoglycemia may be complex. We report three IAS cases with severe fasting hypoglycemia, referred to our Unit for the diagnostic workup of insulinoma. All three patients (two women and a man, age 66, 44, and 50 years) had history of severe fasting hypoglycemia leading to loss of consciousness along with weight gain. Both insulin and C-peptide were high, but their levels varied greatly among patients, ranging from 24 to 1500 μU/ml (n.v.