[Osteonecrosis developing after rituximab-containing chemotherapy for Waldenström macroglobulinemia].

A 71-year-old woman presented with fever, weight loss, and anemia because of recurrent Waldenström macroglobulinemia (WM) with cryoglobulinemia. Treatment with five cycles of doxorubicin, vincristine, cyclophosphamide, and prednisolone (CHOP) therapy was initiated, which resulted in insufficient improvement in anemia. Hence, a combination of rituximab and CHOP therapy was subsequently initiated. The patient complained of lumbago and lower leg pain on day 4 of the chemoimmunotherapy. X-ray findings for the affected sites were unremarkable, and the patient's symptoms gradually and spontaneously subsided. Rituximab monotherapy was then administered, which resulted in the deterioration of her symptoms. Magnetic resonance imaging revealed osteonecrosis of the bilateral distal ends of the femur, and proximal and distal ends of the tibia. This is the first case of lower leg osteonecrosis complicating chemoimmunotherapy for WM. Osteonecrosis may be an unusual adverse effect of rituximab therapy for WM. Tumor lysis by rituximab may have contributed to the pathogenesis of this complication. MRI assessment should be considered when WM patients complain of bone pain following rituximab-containing chemotherapy.