The Prevalence of Undiagnosed Concussions in Athletes

William P. Meehan, III, MD; Rebekah C. Mannix, MD, MPH; Michael J. O'Brien, MD; Michael W. Collins, PhD


Clin J Sport Med. 2013;23(5):339-342. 

In This Article

Abstract and Introduction


Objective: Previous studies suggest athletes underreport concussions. We sought to determine whether athletes in our clinics have sustained previous concussions that went undiagnosed.

Design: Multicentered cross sectional study.

Setting: Two sport concussion clinics.

Patients: Patients diagnosed with sport-related concussions or concussions with injury mechanisms and forces similar to those observed in sports were included.

Main Outcome Measures: 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.

Clinical Relevance: 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.


Previous studies have suggested that athletes often neglect to report their concussions to medical personnel. In a 2004 study published by McCrea et al,[1] less than half of US high school football players (47.3%) sustaining a concussion reported their symptoms. The authors defined a concussion as "a blow to the head followed by a variety of symptoms that may include any of the following: headache, dizziness, loss of balance, blurred vision, 'seeing stars,' feeling in a fog or slowed down, memory problems, poor concentration, nausea or throwing up."[1]

In 2005, a study by LaBotz et al[2] found that only 17% of collegiate athletes reported sustaining a concussion, although 48% reported sustaining a head injury that was followed by the signs and symptoms of concussion. Williamson and Goodman[3] found similar results in amateur hockey; both retrospective surveying of players and diagnosing concussions by direct observation of players revealed substantially higher incidence rates than those officially reported. In a survey of all college athletes attending the University of Akron between 1995 and 2001, Kaut et al[4] reported that 32% of collegiate athletes had suffered a direct blow to the head resulting in dizziness, but only 20% of the athletes had been diagnosed with a concussion.

Recently, there has been an effort to reach a consensus on the definition of concussion. Specifically, the Third International Conference on Concussion in Sport defined concussion as:

Concussion is defined as a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces. Several common features that incorporate clinical, pathological, and biomechanical injury constructs that may be used in defining the nature of a concussive head injury include

Concussion may be caused by a direct blow to the head, face, neck, or elsewhere on the body with an "impulsive" force transmitted to the head.

Concussion typically results in the rapid onset of short-lived impairment of neurological function that resolves spontaneously.

Concussion may result in neuropathologic changes, but the acute clinical symptoms largely reflect a functional disturbance rather than a structural injury.

Concussion results in a graded set of clinical symptoms that may or may not involve loss of consciousness. Resolution of the clinical and cognitive symptoms typically follows a sequential course; however, it is important to note that in a small percentage of cases, postconcussive symptoms may be prolonged.

No abnormality on standard structural neuroimaging studies is seen in concussion.

We sought to determine whether athletes cared for in our clinics have sustained previously undiagnosed concussions.