Pulmonary function trajectories in rheumatoid arthritis-associated interstitial lung disease

<bold>Background:</bold> Interstitial lung disease (ILD) is a serious complication to rheumatoid arthritis (RA). The aim of this study was to compare pulmonary function trajectories in RA-ILD focusing on the impact of corticosteroid therapy and radiographic pattern. <bold>Methods:</bold> Patients with RA-ILD diagnosed between 2004 and 2018 were included retrospectively. We used a multiple regression model with linear time and random coefficients for intercept and slope to assess forced vital capacity (FVC) and diffusion capacity of the lung for carbon monoxide (DLco), allowing the description of individual linear patterns as well as differences at a group level. <bold>Results:</bold> We included 101 patients (mean age 68.2 years, 46% male, 53% usual interstitial pneumonia (UIP)). FVC and DLco were lower among treated patients (79% vs. 95% predicted, p>0.001 and 48% vs 58% predicted, p=0.002). The change in FVC per 30 days was -0.10 (CI95% -0.18; -0.04) in the treated group and -0.13 (CI95%-0.19; -0.07) in the untreated group. The between-group difference was insignificant (−0.03, CI95% -0.12;0.06, p=0.571). For DLco, the change per 30 days in the treated group was -0.10 (CI95% -0.15; -0.04) and -0.10 (CI95% -0.14; -0.05) in the untreated group with insignificant between-group difference (0.0007, CI95% -0.07; 0.07, p=0.985). Inclusion of UIP or non-UIP pattern in the model did not change the results. <bold>Conclusion:</bold> The rate of pulmonary function decline was similar for patients who underwent corticosteroid therapy compared with untreated patients, although treated patients had significantly lower pulmonary function. This may indicate a limited disease modifying effect of corticosteroids in RA-ILD, but further studies are needed.