PM10 increases mortality risk in rheumatoid arthritis-associated interstitial lung disease

Abstract

Objectives: The effect of air pollution on the prognosis of rheumatoid arthritis-associated interstitial lung disease (RA-ILD) remains poorly understood. We aimed to evaluate the effect of long-term exposure to particulate matter with an aerodynamic diameter of ≤10 µm (PM₁₀) and nitrogen dioxide (NO₂) on mortality in patients with RA-ILD.

Methods: We included 309 patients (mean age, 61.7 years; male, 44.3%) with RA-ILD. Individual-level long-term exposures to PM₁₀ and NO₂ at their residential addresses were estimated using a national-scale exposure prediction model. The effect of the two air pollutants on mortality was estimated using a Cox-proportional hazards model adjusted for individual-level and area-level characteristics.

Results: The median follow-up period was 4.8 years, and 40.8% of patients died or underwent lung transplantation. The annual average concentrations of PM₁₀ and NO₂ were 56.3 μg/m³ and 22.4 ppb, respectively. When air pollutant levels were stratified by quartiles, no association was observed between air pollutant concentration and mortality in patients with RA-ILD. However, when stratified by two groups (high exposure (top 25th percentile) vs low exposure (bottom 75th percentile)), we observed a significant association between high PM₁₀ exposure and mortality (HR 1.68; 95% CI 1.11 to 2.52; p=0.013) but no association between NO₂ exposure and mortality. In the subgroup analyses, the effect of high PM₁₀ exposure on mortality was significant in patients aged <65 years (HR 1.98; 95% CI 1.02 to 3.85; p=0.045).

Conclusions: Our results indicated that high PM₁₀ exposure may be associated with mortality in patients with RA-ILD.

Keywords: Arthritis; Pulmonary Fibrosis; Rheumatoid Arthritis.

Figure 1

Spatial distribution of air pollutants and the residential addresses of patients with RA-ILD. The map of estimated concentration of PM₁₀ (μg/m³) (A) and NO₂ (ppb) (B) in 2006. The map of the distribution of the residential addresses of patients with RA-ILD (C). RA-ILD, rheumatoid arthritis-associated interstitial lung disease; PM₁₀, particulate matter ≤10 µm; NO₂, nitrogen dioxide.

Figure 2

Comparison of survival probability over time between the high-concentration group (top 25th percentile) and the low-concentration group (bottom 75th percentile) among patients with RA-ILD. (A) The Kaplan-Meier survival curve for PM₁₀. (B) The Kaplan-Meier survival curve for NO₂. RA-ILD, rheumatoid arthritis-associated interstitial lung disease; PM₁₀, particulate matter≤10 µm; NO₂, nitrogen dioxide.

Figure 3

The effect of high (top 25th percentile) air pollutant concentrations on the mortality in patients with RA-ILD. Symbols and error bars represent HRs and 95% CIs, respectively. RA-ILD, rheumatoid arthritis-associated interstitial lung disease; PM₁₀, particulate matter ≤10 µm; NO₂, nitrogen dioxide.

Figure 4

Comparison of the effect of high (top 25th percentile) air pollutant concentrations on mortality in patients with RA-ILD stratified by age^*. * ≥65 years (n=137) versus <65 years (n=172). The forest plot of (A) PM₁₀ and (B) NO₂. Symbols and error bars represent HRs and 95% CIs, respectively. RA-ILD, rheumatoid arthritis-associated interstitial lung disease; PM₁₀, particulate matter ≤10 µm; NO₂, nitrogen dioxide.

Figure 5

Comparison of the effect of high (top 25th percentile) air pollutant concentrations on mortality in patients with RA-ILD stratified by sex^*. *Male (n=137) versus female (n=172). The forest plot of PM₁₀ (A) and NO₂ (B). Symbols and error bars represent HRs and 95% CIs, respectively. RA-ILD, rheumatoid arthritis-associated interstitial lung disease; PM₁₀, particulate matter ≤10 µm; NO₂, nitrogen dioxide.