Polymorphic lymphoproliferative disorder arising in a rheumatoid arthritis patient, presenting as fibrin-associated large B-cell lymphoma-like lesions in aortic and mitral valves.

We herein report a case of methotrexate-associated lymphoproliferative disorder (MTX-LPD) showing fibrin-associated large B-cell lymphoma-like heart valve lesions, and Epstein-Barr virus (EBV)-positive mucocutaneous ulcer-like cutaneous and oral mucosal lesions. MTX-LPD is a critical complication that can occur in RA patients who are treated with MTX. EBV also plays a defining or important role in LPDs. Among the sites of MTX-LPD, 40-50% occur in extranodal sites, including the gastrointestinal tract, skin, liver, lung, and kidney. There are few reports of MTX-LPDs involving the heart valves, and to the best of our knowledge, this is the first case to be reported in the English literature. The possibility of EBV-positive LPD should be considered in RA patients, even in patients with an atypical site, as in this case.