Low-dose methotrexate may cause air trapping in patients with rheumatoid arthritis.

Both rheumatoid arthritis (RA) and methotrexate (MTX) are reported to be associated with the development of pulmonary disease. To determine whether MTX enhanced the risk of developing abnormalities in pulmonary function in patients with RA, we prospectively studied 31 subjects (12 male, 19 female) with the diagnosis of classic RA for an average period of 4.4 yr (range, 1 to 5 yr). Each subject was placed on low-dose weekly MTX (mean 17 mg, range 2.5 to 40) for control of RA symptoms. Other medications included non-steroidal anti-inflammatory agents and prednisone if required for control of arthritis symptoms. No other immunosuppressive therapy was used. Each subject was evaluated by pulmonary function tests (PFT) and chest X-ray initially, and at 1, 2, 3.5, and 5 yr. Chest X-rays obtained initially and at the end of the study period were found to be normal. The percent predicted values for initial PFTs in the study group were within the normal range. From the beginning to the end of the observation period, the following mean changes in lung function were observed: 1.9% increase in TLC, 5.1% increase in residual volume (RV), 1.8% increase in FVC, 0.71% decrease in FEV1, 14.7% improvement in alveolar-arterial oxygen (A-aO2) difference, and a 12.7% increase in single-breath diffusing capacity (DLCO). To determine whether MTX (average dose, weekly dose, or cumulative dose) was significantly related to changes in pulmonary function, we used multivariate techniques to control for the initial measure of lung function while assessing the relationship between MTX and the subsequent measures of lung function.(ABSTRACT TRUNCATED AT 250 WORDS)