Short-term air pollution exposure and emergency department visits for amyotrophic lateral sclerosis: A time-stratified case-crossover analysis

Background: Amyotrophic lateral sclerosis (ALS) is a progressive and devastating neurodegenerative disease, eventually leading to respiratory failure. Although the only currently available therapeutic interventions merely slow the disease progression, few studies have examined risk factors associated with ALS exacerbation and progression. Objective: To investigate the association between exposure to short-term air pollution and acute exacerbation of ALS requiring emergency department (ED) visit. Methods: We identified from the national emergency database of Korea 617 patients who visited EDs in Seoul with ALS as a primary cause during the period 2008-2014. We estimated short-term exposure to particles < 2.5 mu m (PM2.5), particles < 10 mu m (PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O-3), and carbon monoxide (CO). We conducted a conditional logistic regression with a time-stratified case-crossover design to examine the association between ED visits for ALS and short-term exposure to interquartile range (IQR) increase and upper quartile levels of air pollutants on the day of the ED visit, compared to the control days matched to day of the week, month, and year. Results: The risk of ED visits for ALS was significantly associated with an IQR increase of PM2.5 [Odds ratio (OR) = 1.21; 95% confidence interval (CI): 1.08, 1.35], PM10 [OR = 1.13; 95% CI: 1.02, 1.25], SO2 [OR = 1.19; 95% CI: 1.01, 1.41], and CO [OR = 1.19; 95% CI: 1.03, 1.36]. Exposure to the highest quartiles of PM2.5 and PM10 showed higher associations with ED visits for ALS [OR = 1.40; 95% CI: 1.06, 1.85 and OR = 1.33; 95% CI: 1.00, 1.77]. Discussion: We provide new evidence that exposure to short-term air pollution may increase the risk of acute exacerbation of ALS. Further studies are warranted to understand the underlying mechanisms.