title: Systematic review of the risk of Parkinson's disease after mild traumatic brain injury: results of the International Collaboration on Mild Traumatic Brain Injury Prognosis.
abstract: OBJECTIVE
  To synthesize the best available evidence on the risk of Parkinson's disease (PD) after mild traumatic brain injury (MTBI).
  
  
  METHODS
  MEDLINE and other databases were searched (1990-2012) with terms including "craniocerebral trauma" and "parkinsonian disorders." Reference lists of eligible articles and relevant systematic reviews and meta-analyses were also searched.
  
  
  METHODS
  Controlled clinical trials, cohort studies, and case-control studies were selected according to predefined criteria. Studies had to have a minimum of 30 concussion cases.
  
  
  METHODS
  Eligible studies were critically appraised using a modification of the Scottish Intercollegiate Guidelines Network criteria. Two reviewers independently reviewed and extracted data from accepted studies into evidence tables.
  
  
  RESULTS
  Evidence was synthesized qualitatively according to modified Scottish Intercollegiate Guidelines Network criteria. Sixty-five studies were eligible and reviewed, and 5 of these with a low risk of bias were accepted as scientifically admissible and form the basis of our findings. Among these admissible studies, the definitions of MTBI were highly heterogeneous. One study found a significant positive association between MTBI and PD (odds ratio, 1.5; 95% confidence interval, 1.4-1.7). The estimated odds ratio decreased with increasing latency between MTBI and PD diagnosis, which suggests reverse causality. The other 4 studies did not find a significant association.
  
  
  CONCLUSIONS
  The best available evidence argues against an important causal association between MTBI and PD. There are few high-quality studies on this topic. Prospective studies of long duration would address the limitations of recall of head injury and the possibility of reverse causation.
authors.affiliation: Morton and Gloria Shulman Movement Disorders Centre, and the Edmond J. Safra Program in Parkinson's Research, Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada. Electronic address: cmarras@uhnresearch.ca.
authors.forename: Connie
authors.initials: C
authors.lastname: Marras
authors.affiliation: Division of Health Care and Outcomes Research, Toronto Western Research Institute, University Health Network, University of Toronto, Toronto, Ontario, Canada; Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Cesar A
authors.initials: CA
authors.lastname: Hincapié
authors.affiliation: Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; Department of Health Sciences, Lakehead University, Thunder Bay, Ontario, Canada; Institute for Work and Health, Toronto, Ontario, Canada; Division of Human Sciences, Northern Ontario School of Medicine, Lakehead University, Thunder Bay, Ontario, Canada.
authors.forename: Vicki L
authors.initials: VL
authors.lastname: Kristman
authors.affiliation: Division of Health Care and Outcomes Research, Toronto Western Research Institute, University Health Network, University of Toronto, Toronto, Ontario, Canada; Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Carol
authors.initials: C
authors.lastname: Cancelliere
authors.affiliation: Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
authors.forename: Sophie
authors.initials: S
authors.lastname: Soklaridis
authors.affiliation: Department of Epidemiology and Biostatistics, Western University, London, Ontario, Canada.
authors.forename: Alvin
authors.initials: A
authors.lastname: Li
authors.affiliation: Department of Clinical Sciences, Rehabilitation Medicine, Karolinska Institutet, Danderyd University Hospital, Stockholm, Sweden.
authors.forename: Jörgen
authors.initials: J
authors.lastname: Borg
authors.affiliation: Department of Clinical Sciences, Rehabilitation Medicine, Karolinska Institutet, Danderyd University Hospital, Stockholm, Sweden.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: af Geijerstam
authors.affiliation: Division of Health Care and Outcomes Research, Toronto Western Research Institute, University Health Network, University of Toronto, Toronto, Ontario, Canada; Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada; Institute of Sports Science and Clinical Biomechanics, Faculty of Health, University of Southern Denmark, Odense, Denmark.
authors.forename: J David
authors.initials: JD
authors.lastname: Cassidy
mesh_terms: D000367:Age Factors; D001930:Brain Injuries / Q000175:diagnosis* / Q000453:epidemiology*; D006801:Humans; D010300:Parkinson Disease / Q000453:epidemiology*; D011379:Prognosis; D012307:Risk Factors; D013997:Time Factors; D015599:Trauma Severity Indices
keywords: Brain concussion; Parkinson's disease; Rehabilitation; Review, systematic