Incidence and mortality of interstitial lung disease in rheumatoid arthritis - A population-based study

Objective. Interstitial lung disease (ILD) has been recognized as an important comorbidity in rheumatoid arthritis (RA). We undertook the current study to assess incidence, predictors, and mortality of RA-associated ILD. Methods. We examined a population-based incidence cohort of patients with RA and a matched cohort of individuals without RA. All subjects were followed up longitudinally. The lifetime risk of ILD was estimated. Cox proportional hazards models were used to compare the incidence of ILD between cohorts, to investigate predictors, and to explore the impact of ILD on survival. Results. Patients with RA (n = 582) and subjects without RA (n = 603) were followed up for a mean of 16.4 and 19.3 years, respectively. The lifetime risk of developing ILD was 7.7% for RA patients and 0.9% for non-RA subjects. This difference translated into a hazard ratio (HR) of 8.96 (95% confidence interval [95% CI] 4.02-19.94). The risk of developing ILD was higher in RA patients who were older at the time of disease onset, in male patients, and in individuals with more severe RA. The risk of death for RA patients with ILD was 3 times higher than in RA patients without ILD (HR 2.86 [95% CI 1.98-4.12]). Median survival after ILD diagnosis was only 2.6 years. ILD contributed ∼13% to the excess mortality of RA patients when compared with the general population. Conclusion. Our results emphasize the increased risk of ILD in patients with RA. The devastating impact of ILD on survival provides evidence that development of better strategies for the treatment of ILD could significantly lower the excess mortality among individuals with RA.