Abstract
Background:
Rheumatoid arthritis (RA) is a systemic autoimmune disease. Rheumatoid arthritis associated interstitial lung disease (RA-ILD) is a serious extra-articular manifestation of RA. Few studies from Aotearoa have examined RA epidemiology and little is known regarding the burden of RA-ILD. The purpose of this research is to determine the incidence and prevalence of RA and RA-ILD in the Canterbury District Health Board (CDHB) catchment area, the clinical characteristics and risk factors for developing RA-ILD, and the long terms outcomes of individuals with RA-ILD.
Methods:
A systematic review and meta-analysis was undertaken to establish what is known regarding duration of survival in RA-ILD. A retrospective cohort study of persons aged 18 years and older in the CDHB catchment area between 1 January 2006 and 31 December 2008 (Period One), and 1 January 2011 to 31 December 2013 (Period Two) was performed. Prevalent and incident cases of RA during these periods were followed until 30 June 2019. Prevalent and incident cases of RA-ILD during this time were identified.
Results:
The results from the systematic review found that median survival from diagnosis of RAILD ranged from 2 to 14 years (n=25 studies). The cumulative percentage of mortality up to >5 to ≤ 10 years was 49.1% (95% CI 40.6, 57.5%), and heterogeneity was high (I2 85.0% 95% CI 76.4,90.5%) (n=14 studies, 1322 individuals). The cohort study identified 1930 individuals with RA across the two time periods, and of these 100 met criteria for RA-ILD prior to the end of the study. The 3-year period prevalence of RA for period One and Two were 419.25 (95% CI 398.01,440.50), and 454.77 (95% CI 433.19,476.36) per 100,000, and for RA-ILD were 10.97 (95% CI 7.53, 14.42) and 14.74 (95% CI 10.84,18.63) per 100,000. Seropositivity for rheumatoid factor, and extra-articular manifestations other than ILD were associated with a statistically significant increased risk of developing RA-ILD in individuals with RA by forward and backward stepwise regression adjusted for age. The median survival following identification of RA-ILD was 6.81 years (95% CI 4.77, 8.85), and the standardised mortality ratio (SMR) was 3.90 (95% CI 2.55, 5.71) compared to the general population of the CDHB catchment area. Extent of lung disease on HRCT was the only characteristic with a statistically significant association with mortality (HR for >20% vs < 20% 4.47, 95% CI 1.67, 11.96). Mortality for individuals with prevalent RA was elevated for Period One (SMR 2.01, 95% CI 1.85, 2.19), and Period Two (SMR 1.87, 95% CI 1.69, 2.06).
Conclusion:
The frequency of RA and RA-ILD in the population of the CDHB catchment area were comparable to studies from other countries. Both RA-ILD and RA were associated with substantial mortality. Further research, ideally on a national level, including greater numbers of individuals from Māori and non-European ethnicities is needed to more comprehensively understand the burden of RA and RA-ILD in Aotearoa. The results support the need to ensure that rheumatology services in Aotearoa are adequately resourced and distributed. Improved strategies for the identification and management of RA-ILD are needed.