RESUMO
BACKGROUND: Type B insulin resistance syndrome is a rare form of diabetes due to the presence of anti-insulin receptor antibodies [1, 2], which causes glycemic decompensation and antidiabetic therapy failure and instead responds to immunosuppressive therapy. CASE REPORT: A 67-year-old patient was admitted to the hospital due to autoimmune hemolytic anemia and glycemic decompensation. We first prescribed subcutaneous basal-bolus insulin and then intravenous insulin without improvement in blood sugar levels (between 300 and 500 mg/dL). Considering the non-response to therapy and the autoimmune diathesis of the patient (hemolytic anemia and mixed connective tissue disease), we suspected an autoimmune etiopathogenesis of glycemic decompensation; we excluded type 1 diabetes mellitus (specific antibodies were negative), and we considered the anti-insulin-antibodies-(-assayed and negative) and anti-insulin receptor antibodies (not assayed due to the lack of a center specialized in this assay in the area). Therefore, we decided to start Rituximab. After 2 weeks from the infusion, the patient improved glycemic compensation, reducing insulin requirement. Further, 2 months after the first infusion, the patient stopped insulin, returning to oral therapy with Metformin. To date, the patient has completed 3 cycles of Rituximab with the benefit of glycemic control (HbA1c 6.7%). CONCLUSION: The brilliant response to Rituximab supports the hypothesis of an autoimmune pathogenesis. The anti-insulin receptor antibodies (in the type B insulin resistance syndrome) affect mostly middle-aged adults, especially women, in the context of other autoimmune diseases. Hence, it is necessary to consider the diagnosis of this rare disease in order to perform timely and effective treatment.