Study objectives: Patients with rheumatoid arthritis (RA) have a high prevalence of pulmonary function test (PFT) abnormality, but the long-term significance of this is unknown. We performed a longitudinal study of pulmonary function in asymptomatic, nonsmoking patients with active RA requiring disease-modifying drugs. We looked for temporal change in lung function and characteristics that would predict subsequent development of PFT abnormality or respiratory symptoms.
Methods: In 1990, 52 patients (44 women; age range, 29 to 78 years; median, 56 years) underwent clinical assessment (drug history, RA severity, immunologic, and inflammatory markers) and PFTs (spirometry, body plethysmography, gas transfer). PFT results were expressed as standardized residuals (SRs). Thirty-eight patients were reassessed in 2000. A self-administered questionnaire was used to identify respiratory symptoms.
Results: The prevalence of pulmonary function abnormality was higher than expected compared with a reference population, but there was no significant increase in number over 10 years (8.7% in 1990 and 8.8% in 2000). When assessed by group means and compared with reference values, reduced diffusing capacity of the lung for carbon monoxide (Dlco) and increased ratio of residual volume (RV) to total lung capacity (TLC) [RV/TLC] were the only abnormalities to develop over the study period (mean Dlco in 2000, − 0.47 SR; 95% confidence interval [CI], – 0.91 to – 0.01; RV/TLC, 0.49 SR; 95% CI, 0.13 to 0.84). However, rates of change of pulmonary function variables were not significantly different from zero. Logistic regression did not identify any meaningful relationship between disease characteristics and PFT abnormality.
Conclusions: Asymptomatic patients with RA have a higher prevalence of PFT abnormality than expected, but these do not increase in number over time. We did not identify any patient or disease-specific characteristic that could predict the development of respiratory disease in patients with RA. Analysis using percentage of predicted values, rather than SRs, is misleading as it exaggerates the extent of abnormality present. Abnormal lung function is a common and probably benign finding in nonsmoking, asymptomatic patients with RA.