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ABSTRACT
Objectives: Traumatic brain injury (TBI) increased risk of Parkinson disease (PD) in many but not all epidemiologic studies, giving rise to speculations about modifying factors. A recent animal study suggested that the combination of TBI with subthreshold paraquat exposure increases dopaminergic neurodegeneration. The objective of our study was to investigate PD risk due to both TBI and paraquat exposure in humans.
Methods: From 2001 to 2011, we enrolled 357 incident idiopathic PD cases and 754 population controls in central California. Study participants were asked to report all head injuries with loss of consciousness for >5 minutes. Paraquat exposure was assessed via a validated geographic information system (GIS) based on records of pesticide applications to agricultural crops in California since 1974. This GIS tool assesses ambient pesticide exposure within 500 m of residences and workplaces.
Results: In logistic regression analyses, we observed a 2-fold increase in risk of PD for subjects who reported a TBI (adjusted odds ratio [AOR] 2.00, 95% confidence interval [CI] 1.28–3.14) and a weaker association for paraquat exposures (AOR 1.36, 95% CI 1.02–1.81). However, the risk of developing PD was 3-fold higher (AOR 3.01, 95% CI 1.51–6.01) in study participants with a TBI and exposure to paraquat than those exposed to neither risk factor.
Conclusions: While TBI and paraquat exposure each increase the risk of PD moderately, exposure to both factors almost tripled PD risk. These environmental factors seem to act together to increase PD risk in a more than additive manner.
Glossary
- AOR=
- adjusted odds ratio;
- CI=
- confidence interval;
- GIS=
- geographic information system;
- OR=
- odds ratio;
- PD=
- Parkinson disease;
- RERI=
- relative excess risk due to interaction;
- RR=
- relative risk;
- TBI=
- traumatic brain injury
Footnotes
Study funding: This work was supported by the National Institute of Environmental Health Science (grant numbers R01ES010544 and U54ES012078) and the National Institute of Neurological Disorders and Stroke (grant number P50NS038367); in addition, initial pilot funding was provided from NIH P30ES007048 and a pilot grant by the American Parkinson Disease Association.
Go to Neurology.org for full disclosures. Disclosures deemed relevant by the authors, if any, are provided at the end of this article.
- Received April 22, 2012.
- Accepted July 26, 2012.
- © 2012 American Academy of Neurology
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