Understanding Sports-Related Concussion: Title and subTitle BreakComing Into Focus but Still Fuzzy

A young athlete collides with an opponent. The play ends. The athlete walks from the field of play in an unsteady fashion. The medical staff begins the process of assessment. And the questions begin: Are you OK? What's wrong? How many fingers? What do you remember?"

After the assessment is complete, decisions are made. Initially, the question is, should the athlete be returned to play? Other questions routinely follow: How should the injury be handled? What's likely to occur with the individual in the ensuing hours and days? Can clinicians intercede to speed the process of recovery and rehabilitation? And finally, the most important question: What's the "right" thing to do in this situation?

The above scenario is repeated, in its infinite variations, thousands of times each year^{1 - 2} as athletes sustain sports-induced mild traumatic brain injury (TBI). Controversy has surrounded this topic for a long time. As clinical science begins to embrace the concepts of evidence-based injury management, substantial gaps in the evaluation and treatment of certain mild TBIs have become apparent. In fact, there has been disagreement even as to the definition of concussion until relatively recently.

Concussion management has been a particularly vexing issue, dominated more by opinion than by evidence. Proprietary interests do exist. At least 17 concussion management protocols exist in the medical literature,^{3 - 19} all attempting to categorize and determine the best way to manage mild TBI cases. Clinical scientists have emphasized various approaches, usually based on particular symptom sets, without regard to much more than clinical experience and anecdotal preferences. Since large data sets from rigorous outcome studies have been unavailable, concussion treatment typically has been rather parochial, sometimes using a particular published protocol, many times modifying that protocol to the comfort level of the practitioner involved.²⁰

In this issue of THE JOURNAL, 2 articles^{21 - 22} use data from the National Collegiate Athletic Association tracking system, the largest US data set on concussion, to study the natural history of sports-induced mild TBI. This prospective cohort study of collegiate football players during 3 competitive seasons at 25 colleges resulted in accumulation of data on 196 concussions in 184 players.

The study by Guskiewicz et al²¹ documents an overall rate of incident concussion of 0.81 per 1000 athlete exposures, with higher rates of concussive injury in games than in practices. Guskiewicz et al also suggest that players with a history of previous concussions are more likely to sustain future injury and that previous concussions may be associated with slower recovery. McCrea et al²² examined immediate effects and recovery following sports-related concussion and found that "collegiate football players require several days for recovery of symptoms, cognitive dysfunction, and postural instability after concussion."

While these 2 studies might not surprise sports clinicians because the results are generally consistent with current experience in concussion management, these reports add to the understanding of the natural history of mild TBI. In an evidence-based environment, this is an extremely important initial step. The results of these studies, taken in concert with other large studies, have begun to help define what is relevant and important as well as what is critical in the symptom sets that manifest clinically in athletes with brain injuries.

Yet, despite an expanding evidence base, clinicians and researchers are humbled by how little is truly known about mild TBI. The amazing complexity associated with studying the human brain and especially its response to injury is now beginning to be recognized and appreciated. For instance, Hovda et al²³ and Giza and Hovda²⁴ have provided insights into what occurs immediately following impact to the head. Animal studies suggest that a cascade of physiological events may adversely affect cerebral functioning for days or weeks after concussion.²³ These studies^{23 - 24} have also demonstrated increased neuronal vulnerability for several days after concussion, consistent with the findings of Guskiewicz et al that recovery time is prolonged after subsequent concussions.

Likewise, Collins et al²⁵ and McCrory et al²⁶ have demonstrated how a hypermetabolically challenged central nervous system outwardly works and differs from an unaffected system. Neurocognitive analysis through neuropsychological testing has demonstrated memory, concentration, and executive functioning deficits.^{25 ,27 - 28} In retrospective analysis, Lovell et al²⁹ found that brief loss of consciousness may not be the predictor of poor outcome that most clinicians (and protocol authors) have always assumed. The search for a pathognomonic profile of poor outcome currently centers on amnesia as a more powerful predictive symptom.³⁰

Historically, the problem with research of mild TBI has been the tendency to overgeneralize results. From the information now available, it appears that no other human organ system is quite as variable in its response to external stimuli or insult as the central nervous system. If each individual begins with a uniquely different central nervous system profile, it should be safe to postulate that each person will react differently to a particular insult. Thus, both cognitive and functional losses would be expected to vary based on the extent of the initial insult, the brain areas involved, and inherent variables, such as age and baseline mental status. Each traumatic brain insult is generally different in terms of vector, force, protective equipment used, and ambient conditions. Thus, if the intended outcome is to provide a dependable, practical guideline with universal agreement, it will not happen. Such a goal is foolish and ill conceived.

Although much progress has been made in beginning to understand sports-related mild TBI, several key research questions must be pursued. What are the best predictors of outcome? What are the important variables to consider? How strong are the associations between different factors and outcomes? Is there a clinically relevant and practical solution? And can known strong associations be used to develop clinical equations to help tailor treatment for each individual on an injury-by-injury basis?

The articles by Guskiewicz et al²¹ and McCrea et al²² on the natural history of mild TBI help to provide an opportunity to see where there is agreement and evidence-based consensus on concussion. First, any athlete with a concussion should be removed from competition. Second, no athlete should return to play or practice until he or she is completely asymptomatic at rest and with exertion. Third, any athlete with a prolonged loss of consciousness or evidence of amnesia should not return to play that day. Fourth, careful and repeated assessments by individuals with training and experience in evaluating concussive injuries should be the rule. Fifth, any patient with a concussion whose symptoms evolve downward requires immediate neurologic evaluation and possible hospital admission.

Now is the time to consider sports-induced mild TBI differently. Several collaborative efforts^{31 - 32} have provided an opportunity to move in this direction. Using these suggestions, clinicians caring for athletes and sports medicine researchers need to identify more areas of agreement while continuing research on the substantial knowledge gaps that remain. The picture is coming into focus but still remains a bit fuzzy.