Rheumatoid arthritis associated interstitial lung disease: Trends in epidemiology and mortality in Ontario from 2000 to 2018.

Background: The epidemiology and mortality of rheumatoid arthritis related interstitial lung disease (RA-ILD) have not been described in Canada. Our aim was to describe recent trends in RA-ILD prevalence, incidence, and mortality in Ontario, Canada.

Methods: This was a retrospective population-based study using repeated cross-sections from 2000 to 2018. We estimated annual age- and sex-standardized rates for RA-ILD prevalence, incidence and mortality.

Results: Among 184,400 RA patients identified between 2000 and 2018, 5722 (3.1%) were diagnosed with RA-ILD. Most RA-ILD patients were women (63.9%) and ≥60 years old (76.9%) at the time of RA-ILD diagnosis. RA-ILD incidence rose from 1.6 (95% confidence interval (CI) 1.3-2.0) to 3.3 (95% CI 3.0-3.6) per 1000 RA patients (204% relative increase, p < 0.0001) during this time. RA-ILD incidence increased in both sexes and all age groups over time. The cumulative prevalence of RA-ILD increased from 8.4 (95% CI 7.6-9.2) to 21.1 (95% CI 20.3-21.8) per 1000 RA patients (250% relative increase, p < 0.0001), increasing in both sexes and all age groups. All-cause and RA-ILD related mortality declined in patients with RA-ILD over time [55.1% relative reduction, (p < 0.0001) and 70.9% relative reduction, (p < 0.0001), respectively]. In RA-ILD patients, RA-ILD contributed to the cause of death in approximately 29% of cases. Men and older patients had higher all-cause and RA-ILD related mortality.

Conclusion: In a large, diverse Canadian population, the incidence and prevalence of RA-ILD are increasing. RA-ILD related mortality is declining, but remains an important cause of death in this population.