Insulin autoimmune syndrome: Three case reports

Insulin autoimmune syndrome (IAS) is a rare endocrine disease characterized by repeated fasting hypoglycemia or episodes of hypoglycemia late after meals, elevated serum insulin, and positivity for insulin autoantibody (IAA) or insulin receptor antibody (IRA). We summarize the clinical manifestations and treatment experiences of 3 patients with IAS.

One patient with >20-year history of type 2 diabetes mellitus had irregular episodes of hypoglycemia 2 years of after treatment with insulin. Another patient with a 6-year history of type 2 diabetes mellitus presented irregular episodes of hypoglycemia after 6 months of treatment with insulin. One patient with a history of Graves' disease showed hypoglycemia after administration of thiamazole.

Serum islet cell antibody (ICA) and glutamic acid decarboxylase antibody (GADA) were negative, while antibody insulin autoantibodies were positive in all the 3 patients. Two patients demonstrated diabetes mellitus after an oral glucose tolerance test, while one had normal glucose tolerance. Furthermore, serum insulin levels significantly elevated and did not matched C peptide levels. No abnormalities were found on enhanced MRI of the pancreas, and all 3 patients were clinically diagnosed with IAS.

In case one, insulin aspart 30 injection was withdrawn after admission. In addition, the patient was prescribed sublingual acarbose 3 times daily. Two weeks after admission, prednisone acetate was administered orally once daily at night. In case 2, insulin aspart 30 injection was withdrawn after admission, the patient was prescribed sublingual acarbose 3 times daily with a meal. Five days after admission, oral prednisone acetate was administered once daily at night. In case 3, oral propylthiouracil was prescribed and thiamazole withdrawn after admission, and the patient consumed an extra meal before sleeping.

At the 3-month follow-up visit, the hypoglycemic episodes had disappeared, serum insulin levels were significantly decreased, and insulin antibody (IA) levels were no longer detectable in all 3 patients.

For those patients with high-insulin hypoglycemia, IAA should be evaluated if serum insulin concentrations are inconsistent with C peptide levels. Therapeutically, a lower dose of glucocorticoids with more appropriate medication timing can be used to achieve good results.