Systemic Autoimmune Rheumatic Diseases (SARDs)
All of the studies on associations between PM2.5 air pollution exposure and the development of SARDs (systemic lupus erythematosus, Sjögren’s syndrome, scleroderma, polymyositis, dermatomyositis or undifferentiated connective tissue disease) come from Canada. Population-based administrative data from two provinces, Alberta and Quebec, were used in one study, and significant associations found. In Quebec residents, the adjusted OR for being a case of SARDs was increased by PM2.5 levels (OR 1.05 per µg/m3, 95%CI 1.05–1.06). In Alberta, First Nations populations were particularly susceptible, with an adjusted OR of 1.38 (95%CI 1.14–1.68) per µg/m3.28 In the city of Calgary, the odds of being a SARDs case increased with PM2.5 levels (OR 1.10 per µg/m3, 95%CI 1.01–1.22), again with First Nations being at increased risk compared to non-First Nations residents, although an association with NO2 could not be clearly detected.29
Vasculitis & Juvenile Dermatomyositis
In a U.K. study, no evidence for spatial clustering, PM10 exposure and ANCA-associated vasculitis was found.30 Similarly, in a North American study, no link between PM2.5 and Kawasaki disease was found, after controlling for time trends, seasonality, month and weekday.31
Using multivariate analysis controlling for smoking, occupational exposure, home distance to sources of inhaled pollutants, seasonality and traffic exposure, a Brazilian study showed a significant association between CO exposure in the third trimester and the subsequent development of juvenile dermatomyositis (OR 12.2, 95%CI 1.3–116.0).32
Effect of Air Pollution on Disease Activity in Established Rheumatic Disease
Data are sparse on this topic. Canadian data have shown that SLE disease activity is influenced by exposure to PM2.5. Hourly PM2.5 concentrations were taken from fixed-site stations, and levels were averaged over 24 hours for the day preceding clinical review. Higher exposure was associated with levels of anti-dsDNA antibodies (adjusted OR 1.34, 95%CI 1.02–1.77).33
A Brazilian study demonstrated a delayed association between SO2 exposure and hospital admissions due to pediatric rheumatic diseases. There was an increase in the number of admissions by 1.98% (95%CI 0.25–3.69), and the maximum effect was noted 16 days after the exposure.34
Knowledge Gaps
At this time, there is no definitive association determined for any air pollutant in any rheumatic disease. More data are needed to elucidate the progression from pollution-related immune stimulation, the formation of antibodies and the ultimate progression to clinically apparent disease, as well as the effect of air pollution on disease phenotype, prognosis and activity. Another outstanding issue that needs to be addressed by future research is the potential for differential toxicity between source types.
