Exogenous Insulin Antibody Syndrome: A Rare Cause of Extreme Insulin Resistance Treated With High-dose Corticosteroids

Exogenous insulin antibody syndrome is a rare condition characterized by extreme insulin resistance caused by antibodies that neutralize the action of insulin. An 80-year-old woman with type 1 diabetes mellitus was transferred to an Australian quaternary hospital with refractory hyperglycemia and diabetic ketoacidosis despite receiving >300 units of insulin daily. Laboratory testing revealed a very high insulin antibody titer of 6758 U/mL (6758 kU/L)(<0.4 U/mL; <0.4 kU/L). Plasmapheresis was considered but was not pursued because of hemodynamic instability, multiple comorbidities and frailty. Treatment with high-dose methylprednisolone at 1 mg/kg for 5 days and 500 mg of mycophenolate mofetil twice daily, followed by a tapering regimen of prednisone, resulted in a significant improvement in extreme insulin resistance. The total daily dose of insulin after treatment returned to a baseline of approximately 70 units and insulin antibody titers were reduced by 8-fold. Remission was maintained for more than 2 years until the patient died of an aggressive squamous cell carcinoma of the buccal mucosa.