Brittany Krzyzanowski1, Susan Nielson2, Brad Racette1
1Barrow Neurological Institute, 2Neurology, Washington University School of Medicine
Objective:
To identify the national geographic patterns of Parkinson disease (PD) and test for nationwide and region-specific associations with PM2.5.
Background:
Numerous studies suggest that environmental exposures play a critical role in PD pathogenesis. Large population-based discovery studies have the potential to identify novel PD risk factors. Medicare is the only population-based national healthcare system in the U.S. making it ideal for nationwide geographic studies of PD risk factors.
Design/Methods:
We conducted a population-based geographic study of 22,546,965 Medicare beneficiaries and identified 83,674 with incident PD in 2009. Beneficiaries were geocoded to county and zip+4 of residence in the contiguous U.S. We used a multimethod approach that included R-INLA to create age, sex, race, smoking, and healthcare utilization adjusted relative risk (RR) for county-level regression and geographical analyses with PM2.5 as the exposure of interest. To supplement these findings, we performed an individual-level case-control analysis using logistic regression to verify county-level PM2.5 results.
Results:
We identified a PD hot spot in the Mississippi-Ohio River Valley and found a nationwide association between incident PD and average annual PM2.5, whereby the RR for PD increased by 25% (95% CI 23%, 26%) when comparing the lowest to the highest quartile of PM2.5. The strongest association between PM2.5 and PD was found in the Rocky Mountain Region. PM2.5 was also associated with PD in the Mississippi-Ohio river valley where the association was weaker, due to an apparent ceiling effect at ~12 to 19μg/m3 of PM2.5. Individual-level results confirmed that PD increased by 25% (95% CI 20%, 29%) when comparing the lowest to the highest decile of PM2.5.
Conclusions:
Using state-of-the-art geospatial analytical techniques, we identified a nationwide association between PD and PM2.5, which varied in strength by region. A deeper investigation into the specific subfractions of PM2.5 may provide insight into regional variability in the PM2.5-PD association.