Pneumocystis carinii pneumonia associated with low dose methotrexate treatment for rheumatoid arthritis.

Since 1983 there have been several reports on Pneumocystis carinii pneumonia (PCP), complicating low dose methotrexate (MTX) therapy for rheumatoid arthritis (RA). Two additional cases of this opportunistic infection are reported and a review of the literature on the complication is presented. It is concluded that PCP is a serious complication of low dose MTX therapy for RA and should always be ruled out when a patient presents with pulmonary symptoms. Several factors may play a role in the occurrence of this opportunistic infection, but the exact mechanism has not yet been elucidated.