Pulmonary function in rheumatoid arthritis treated with low-dose methotrexate: a longitudinal study.

Lung volumes and gas exchange were investigated prospectively in 96 patients with rheumatoid arthritis selected without regard to pulmonary disorders and treated with i.m. methotrexate (MTX) injections [mean weekly dose 13.0 mg (5th-95th percentile (5-95 PC) 7.6-20.8)]. Individual changes over time during MTX treatment [mean duration 2.9 yr (5-95 PC 0.4-5.3)] were assessed by regression analyses in each individual. Forced vital capacity (FVC) remained stable in the majority of patients [mean annual change +0.8% (5-95 PC -8.1 to +14.0) of calculated normal value]. In addition, transfer factor using the indicator gas CO (TL,CO) was unaltered in most patients [mean annual change -2.1% (5-95 PC -16.2 to +11.8) of predicted value]. However, there were significant decreases in the forced expiratory volume in 1 s (FEV1) before and after inhalation of 0.2 mg salbutamol [mean annual change -0.8% (5-95 PC -8.4 to +3.2) and -1.3% (5-95 PC -7.8 to +3.9) of the FVC measured, respectively]. In addition, there were significant increases in alveolar-arterial Po2 gradients (P(A-a),O2) at rest and after exercise [mean annual change +1.7 mmHg (5-95 PC -5.2 to +12.2) and +1.8 mmHg (5-95 PC -3.5 to 9.0), respectively]. Nevertheless, the amounts were small in view of the reliability of the methods applied and reflect, at least in part, the normal process of ageing. The annual change in FEV1/FVC was negatively correlated with FEV1/FVC at baseline (Rs = -0.46, P < 0.001). The annual change in TL,CO was also negatively correlated with TL,CO at baseline (Rs = -0.31, P = 0.028). No other risk factors for deterioration of lung volumes or gas exchange were found, including mean weekly MTX dose, age, gender, smoking, presence of rheumatoid factor and pulmonary function at baseline. We conclude that MTX has no major effect on pulmonary function in the majority of patients and that there is no evidence that patients with pre-existing pulmonary disease are at increased risk for further deterioration of lung function.