Change in the Character of Insulin Autoantibody Over Time in a Patient of Exogenous Insulin Autoimmune Syndrome

Abstract A 65-year-old female with systemic sclerosis, primary hypothyroidism, and type 2 diabetes mellitus presented with uncontrolled hyperglycemia after starting insulin 1 month prior. Her random blood glucose was >600 mg/dL, necessitating insulin infusion at a high dose (1200–1500 U/day). The possibility of type B insulin resistance versus interference by insulin antibodies (IAs) was kept. Her IAs were marginally high [12.25 U/mL (<12)] and were considered clinically nonsignificant. After 22 days of hospitalization on high doses of insulin and oral hypoglycemic agents, she developed hypoglycemia 5 days postdischarge, followed by an increase in hypoglycemia episodes over the next 2 months. Upon reevaluation, her insulin levels were extremely high (7940 IU/mL), with a high insulin–C-peptide ratio (35.3), and IAs were significantly elevated (152 U/mL). The patient was managed by stopping insulin and starting immunosuppressants, leading to clinical improvement. The case highlights interference with IAs presenting as severe insulin resistance with progression over time to frequent hypoglycemia.