Obinutuzumab-induced acute thrombocytopenia and leukopenia in ANCA-associated glomerulonephritis: case report and literature review.

Obinutuzumab is a humanized type II anti-CD20 monoclonal antibody with enhanced antibody-dependent cellular cytotoxicity. It is widely used in B-cell malignancies and is increasingly being explored in autoimmune diseases such as lupus nephritis. The main adverse effects include infusion reactions and cytopenias. Among these, obinutuzumab-induced acute thrombocytopenia (OIAT) is a rare but potentially life-threatening complication. However, OIAT has been reported almost exclusively in patients with hematologic malignancies; data in autoimmune diseases remain limited. We report a 55-year-old male with anti-neutrophil cytoplasmic antibody-associated glomerulonephritis who developed acute severe thrombocytopenia and leukopenia shortly after the second dose of obinutuzumab, which was given due to rituximab intolerance. His platelet count (PLT) dropped from 121 × 109/L to 2.5 × 109/L, and white blood cell count (WBC) fell to 0.6 × 109/L; the nadir occurred on day 3 after readmission. WBC recovered within one week, whereas PLT recovery took 45 days. To our knowledge, this is the first reported case of obinutuzumab-induced acute bicytopenia in an autoimmune disease setting. This case highlights the need for heightened awareness of hematologic toxicity when using obinutuzumab in patients with autoimmune diseases, and suggests that a rapid decline in PLT, even when still within the normal range, may serve as an early warning sign.