Late-onset Neutropenia after Rituximab Treatment for MPO-ANCA-associated Vasculitis.

An underestimated side effect of rituximab is late-onset neutropenia (R-LON), which often resolves spontaneously and rarely results in a severe infection. We herein report a case of febrile neutropenia due to R-LON in a 91-year-old woman with renal failure who was treated with rituximab to induce remission of myeloperoxidase antineutrophil cytoplasmic antibodies-associated vasculitis. Fifty-four days after the last rituximab administration, the patient was hospitalized for febrile neutropenia due to R-LON, which improved with granulocyte colony-stimulating factor and antibiotics. Although R-LON may resolve spontaneously and remain unnoticed, it can cause severe infections in the elderly and patients with renal failure.