Development of type 1 diabetes in a patient treated with anti‐interleukin‐6 receptor antibody for rheumatoid arthritis

Interleukin‐6 is a pleiotropic cytokine that plays a pathogenic role in type 1 diabetes. Therefore, anti‐interleukin‐6 receptor antibody, tocilizumab, used for the treatment of rheumatoid arthritis, is considered a candidate for immune intervention in type 1 diabetes. Here, we report the case of a 73‐year‐old woman (HLA‐DR9‐DQ3 homozygote) with well‐controlled rheumatoid arthritis who developed type 1 diabetes while receiving tocilizumab treatment. At 57 years‐of‐age, the patient was diagnosed with rheumatoid arthritis, for which she underwent tocilizumab therapy that enabled complete suppression of her joint inflammation. A total of 17 months after starting tocilizumab therapy, she noticed polydipsia, polyuria, general fatigue and weight reduction (−2 kg/month), and was diagnosed with type 1 diabetes with diabetic ketoacidosis based on an arterial pH of 7.26, serum ketone body of 7,437 μmol/L, blood glucose level of 925 mg/dL, glycated hemoglobin of 13.2% and the presence of anti‐islet autoantibodies. This case report shows valuable insight regarding the effect of anti‐interleukin‐6 receptor antibody therapy on type 1 diabetes prevention.