Patterns of interstitial lung disease and mortality in rheumatoid arthritis

Objective. To characterize a cohort of patients with RA who have interstitial lung disease (ILD) and to assess the utility of previously developed mortality staging systems [gender, age, lung physiology (GAP) and ILD-GAP]. Methods. All patients with RA and ILD seen at the Mayo Clinic from 1998 to 2014 were identified and manually screened for study inclusion. RA disease characteristics and pulmonary findings including high-resolution CT and pulmonary function testing were evaluated. Survival was estimated using Kaplan-Meier methods. GAP and ILD-GAP models were evaluated using c-statistics and standardized incidence ratios. Results. The study included 181 patients with RA-associated ILD (96% Caucasian; 48% females; 37% never-smokers). The mean age at ILD diagnosis was 67.4 years (S.D. 9.9). The median time from RA diagnosis to ILD was 4.9 years (range-10.9-48.1). The median follow-up was 3.1 years (range 0.01-14.8). Age, RA disease duration and low initial diffusing capacity for carbon monoxide were predictive of premature mortality in multivariate modelling. Sex, smoking status, obstructive lung disease, seropositivity and erosive disease were not associated with mortality. The 5-year survival rate was 59.7% (95% CI 51.5, 69.2). Survival did not differ between usual interstitial pneumonia, non-specific interstitial pneumonia and organizing pneumonia (P = 0.42). The GAP model performed well in this cohort for both discrimination and calibration (c-statistic 0.71, standardized incidence ratio 0.97). Conclusion. In this large single-centre cohort of patients with RA-ILD, most patients were seropositive and had a history of smoking. ILD most commonly occurred after the RA diagnosis. Mortality was high and did not differ among the types. The GAP model may be useful in assessing mortality risk.