title: Concussion guidelines step 1: systematic review of prevalent indicators.
abstract: BACKGROUND
  Currently, there is no evidence-based definition for concussion that is being uniformly applied in clinical and research settings.
  
  
  OBJECTIVE
  To conduct a systematic review of the highest-quality literature about concussion and to assemble evidence about the prevalence and associations of key indicators of concussion. The goal was to establish an evidence-based foundation from which to derive, in future work, a definition, diagnostic criteria, and prognostic indicators for concussion.
  
  
  METHODS
  Key questions were developed, and an electronic literature search from 1980 to 2012 was conducted to acquire evidence about the prevalence of and associations among signs, symptoms, and neurologic and cognitive deficits in samples of individuals exposed to potential concussive events. Included studies were assessed for potential for bias and confound and rated as high, medium, or low potential for bias and confound. Those rated as high were excluded from the analysis. Studies were further triaged on the basis of whether the definition of a case of concussion was exclusive or inclusive; only those with wide, inclusive case definitions were used in the analysis. Finally, only studies reporting data collected at fixed time points were used. For a study to be included in the conclusions, it was required that the presence of any particular sign, symptom, or deficit be reported in at least 2 independent samples.
  
  
  RESULTS
  From 5437 abstracts, 1362 full-text publications were reviewed, of which 231 studies were included in the final library. Twenty-six met all criteria required to be used in the analysis, and of those, 11 independent samples from 8 publications directly contributed data to conclusions. Prevalent and consistent indicators of concussion are (1) observed and documented disorientation or confusion immediately after the event, (2) impaired balance within 1 day after injury, (3) slower reaction time within 2 days after injury, and/or (4) impaired verbal learning and memory within 2 days after injury.
  
  
  CONCLUSIONS
  The results of this systematic review identify the consistent and prevalent indicators of concussion and their associations, derived from the strongest evidence in the published literature. The product is an evidence-based foundation from which to develop diagnostic criteria and prognostic indicators.
authors.affiliation: *Department of Medical Informatics and Clinical Epidemiology and ‖Center for Spoken Language Understanding, Oregon Health & Science University, Portland, Oregon; ‡Brain Trauma Foundation, New York, New York; §Department of Neurosurgery, Stanford University School of Medicine, Stanford, California; ¶Department of Emergency Medicine and; ‡‡Departments of Psychiatry and Neurology, Icahn School of Medicine at Mount Sinai, New York, New York #Department of Psychology, Portland State University, Portland, Oregon; **US Army Combat Casualty Care Research Program, US Army Medical Research and Materiel Command, Fort Detrick, Maryland.
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mesh_terms: D001924:Brain Concussion / Q000175:diagnosis*; D019317:Evidence-Based Medicine; D006801:Humans; D010808:Physical Examination; D017410:Practice Guidelines as Topic