title: The prevalence of undiagnosed concussions in athletes.
abstract: OBJECTIVE
  Previous studies suggest athletes underreport concussions. We sought to determine whether athletes in our clinics have sustained previous concussions that went undiagnosed.
  
  
  METHODS
  Multicentered cross sectional study.
  
  
  METHODS
  Two sport concussion clinics.
  
  
  METHODS
  Patients diagnosed with sport-related concussions or concussions with injury mechanisms and forces similar to those observed in sports were included.
  
  
  METHODS
  The proportion of patients who answered "yes" to the following question were defined as having a previously undiagnosed concussion: "Have you ever sustained a blow to the head which was NOT diagnosed as a concussion but was followed by one or more of the signs and symptoms listed in the Post Concussion Symptom Scale?"
  
  
  RESULTS
  Of the 486 patients included in the final analysis, 148 (30.5%) patients reported a previously undiagnosed concussion. Athletes reporting previously undiagnosed concussions had a higher mean Post Concussion Symptom Scale (PCSS) score (33 vs 25; P < 0.004) and were more likely to have lost consciousness (31% vs 22%; P = 0.038) with their current injury than athletes without previously undiagnosed concussions.
  
  
  CONCLUSIONS
  Nearly one-third of athletes have sustained previously undiagnosed concussions, defined as a blow to the head followed by the signs and symptoms included in the PCSS. Furthermore, these previously undiagnosed concussions are associated with higher PCSS scores and higher loss of consciousness rates when future concussions occur.
  
  
  CONCLUSIONS
  Many athletes have sustained previous blows to the head that result in the signs and symptoms of concussion but have not been diagnosed with a concussion. These injuries are associated with increased rates of loss of consciousness and higher symptom scale scores with future concussions.
authors.affiliation: Sports Concussion Clinic, Division of Sports Medicine, Department of Orthopaedics, Boston Children's Hospital, Boston, Massachusetts 02115, USA. concussion.sportsmed@childrens.harvard.edu
authors.forename: William P
authors.initials: WP
authors.lastname: Meehan
authors.forename: Rebekah C
authors.initials: RC
authors.lastname: Mannix
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Brien
authors.forename: Michael W
authors.initials: MW
authors.lastname: Collins
mesh_terms: D000293:Adolescent; D056352:Athletes / Q000706:statistics & numerical data*; D001900:Boston / Q000453:epidemiology; D001924:Brain Concussion / Q000175:diagnosis / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D057210:Delayed Diagnosis; D005260:Female; D006801:Humans; D008297:Male; D010414:Pennsylvania / Q000453:epidemiology