Highly aggressive plasmablastic neoplasms in patients with rheumatoid arthritis treated with methotrexate.

Patients with rheumatoid arthritis occasionally develop lymphoproliferative disorders. Methotrexate-associated lymphoproliferative disorders is a lymphoproliferative disease or lymphoma in patients treated with methotrexate for autoimmune diseases, such as rheumatoid arthritis. Here we report two rare cases of highly aggressive plasmablastic lymphoproliferative disorders in rheumatoid arthritis treated with methotrexate. Case 1 is a 68-year-old female patient with leukemic transformation of malignant lymphoma. She received methotrexate therapy for rheumatoid arthritis for >6 years. The patient showed rapid progressive course and died on the 2nd hospital day. After the death, we diagnosed the patient as plasmablastic lymphoma. Case 2 is an 80-year-old female patient with plasmablastic plasma cell myeloma, with a history of methotrexate treatment for rheumatoid arthritis for >5 years. Although M-protein was decreased by chemotherapy, bone marrow examination revealed the further increase of plasmablastic cells and she died 2 months later. The present cases were difficult to diagnose because proliferation of malignant plasmablasts was hardly predicted because neither lymph node enlargement nor an evident M-protein was observed. Both cases showed aggressive features and extremely poor prognosis. Clinicians should be aware of the underlying malignant plasmablastic proliferation when inexplicable inflammatory findings are observed in inactive rheumatoid arthritis patients.