Pneumocystis jiroveci pneumonia associated with low-dose methotrexate treatment for rheumatoid arthritis: report of two cases and review of the literature.

Low-dose methotrexate (MTX) therapy is widely used for rheumatoid arthritis (RA) because of its favorable efficacy and toxicity profile. Although Pneumocystis jiroveci pneumonia (PCP) is most often seen in severely immunosuppressed patients, PCP complicating low-dose MTX therapy for RA has been reported to sometimes occur. We herein report two cases of patients who developed PCP during treatment with low-dose MTX, and discuss the importance of prophylaxis for this opportunistic infection.