title: Head injury at early ages is associated with risk of Parkinson's disease.
abstract: BACKGROUND
  The literature on the effect of head injuries on the risk of PD is inconclusive. Some researchers have hypothesized that studies that have seen an effect are simply capturing injury related to pre-clinical PD. However in animal models brain inflammation, which can be initiated by head trauma, has been shown to produce PD-like effects. Furthermore, animal studies have found that early life inflammation in particular is of relevance for PD pathology.
  
  
  METHODS
  We conducted an unmatched case-control study of 379 neurologist confirmed PD patients and 230 controls from the greater Boston, Massachusetts area with questionnaire data on history of head injury and other covariates. We used multivariable logistic regression to estimate adjusted odds ratios (OR) and their corresponding 95% confidence intervals (CI) for PD.
  
  
  RESULTS
  When we excluded injuries that occurred less than 10 years prior to the diagnosis of PD (in order to avoid reverse causation), we found an increased risk of PD associated with a head injury that resulted in a loss of consciousness, but it did not reach statistical significance (OR = 1.57; 95% CI = 0.89-2.80). We found a significant (p = 0.04) effect of age at first head injury. For every 5 year earlier age at first head injury with loss of consciousness the OR for PD was 1.37 (95% CI: 1.01-1.86).
  
  
  CONCLUSIONS
  Our results suggest that head injury in early life increases the risk of PD.
authors.affiliation: Harvard T.H. Chan School of Public Health, Dept of Environmental Health, 401 Park Dr., Landmark Building, 3rd Floor, Boston MA 02215, USA. Electronic address: kmt691@mail.harvard.edu.
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Taylor
authors.affiliation: Department of Neurology, Boston University Medical Center, 72 East Concord Street, C3, Boston, MA 02118, USA. Electronic address: neuromsh@bu.edu.
authors.forename: Marie-Helene
authors.initials: MH
authors.lastname: Saint-Hilaire
authors.affiliation: Department of Neurology, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA. Electronic address: lsudarsky@partners.com.
authors.forename: Lewis
authors.initials: L
authors.lastname: Sudarsky
authors.affiliation: Beth Israel Deaconess Medical Center and Harvard Medical School, Department of Neurology 330 Brookline Avenue, Boston, MA 02215, USA. Electronic address: dsimon1@bidmc.harvard.edu.
authors.forename: David K
authors.initials: DK
authors.lastname: Simon
authors.affiliation: Harvard Vanguard Medical Associates, 133 Brookline Avenue, Boston, MA 02215, USA. Electronic address: bonnie_hersh@vmed.org.
authors.forename: Bonnie
authors.initials: B
authors.lastname: Hersh
authors.affiliation: VA Boston Healthcare System, Jamaica Plain, 150 South Huntington Avenue, Boston, MA 02130, USA; Boston University Schools of Public Health and Medicine, 715 Albany Street, Boston, MA 02118, USA. Electronic address: david.sparrow@va.gov.
authors.forename: David
authors.initials: D
authors.lastname: Sparrow
authors.affiliation: Departments of Epidemiology, Global Health, and Environmental Health, University of Toronto Dalla Lana School of Public Health, 6th Floor, 155 College Street, Toronto, Ontario, Canada. Electronic address: howard.hu@utoronto.ca.
authors.forename: Howard
authors.initials: H
authors.lastname: Hu
authors.affiliation: Department of Epidemiology and Environmental Health, Harvard TH Chan School of Public Health, 677 Huntington Avenue, Boston, MA 02115, USA. Electronic address: mweissko@hsph.harvard.edu.
authors.forename: Marc G
authors.initials: MG
authors.lastname: Weisskopf
mesh_terms: D000293:Adolescent; D000368:Aged; D016022:Case-Control Studies; D002648:Child; D006259:Craniocerebral Trauma / Q000150:complications* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010300:Parkinson Disease / Q000209:etiology*; D012307:Risk Factors; D011795:Surveys and Questionnaires
keywords: Head injury; Parkinson's disease; Traumatic brain injury