Sports Injuries

Summer  2000
Volume 11, Number 1

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There is growing concern in sport medicine about the risks of chronic brain dysfunction from repetitive concussions, yet the risk factors have not been clearly identified. Recently, neuropsychological research methodology has been utilized to systematically evaluate the cognitive effects of sport concussions. This line of research has identified objective measures that are sensitive to concussion and has shown that even a single mild concussion produces slowed processing speed and memory difficulties during the first week post-injury. Additionally, these studies raise concern about slow or incomplete recovery following repetitive concussions. This article reviews the major studies of acute and long-term effects of concussion in organized sports and the application of neuropsychological evaluation to sport concussion.

Introduction. Concussion is widely regarded as a "transient post-traumatic impairment of neural function."1 Anecdotal accounts by athletes about their persisting post-concussion symptoms, and the development of dementia pugilistica in former boxers, has raised concern about the risks of more permanent neural impairment resulting from concussions sustained during sport.

Sport medicine personnel are confronted with difficult questions about the risks of playing for athletes with concussion histories, however, risk factors for chronic brain dysfunction from sport concussions have not been clearly identified. Research efforts have been hampered by difficulties with objective measurement of the subtle effects of concussions. Frequently, concussed athletes perform normally on basic neurological examinations and have negative neuro-radiological studies. Neuropsychological research methodology has been recently introduced into sports medicine to systematically examine the effects of concussions. Neuropsychology uses standardized tests to objectively measure cognitive function. This line of research has been able to identify tests that are both sensitive and specific to the effects of concussion and to recovery from concussion. This article will review the major neuropsychological studies of acute and chronic effects of concussion in organized sports and the application of neuropsychological evaluation to the management of the concussed athlete.

Acute Effects of Concussion in Sport. Neuropsychological studies of the acute effects of sport concussion typically utilize a pre-injury test/post-injury retest design. At preseason, athletes complete cognitive tests that are sensitive to the effects of concussion, i.e., attention, speed of processing and memory. They also rate themselves on common concussion symptoms such as headache and dizziness. This information provides a “baseline” for each athlete. When an athlete sustains a concussion, he is retested and then compared against his baseline scores. Serial retesting is frequently conducted at regular intervals to measure recovery from the injury.

Football. The first large scale study of acute concussion in organized sport in the US was conducted by Barth et al.2 Baseline evaluation, including symptom inventory and neuropsychological testing of information processing speed, was performed on 2300 college football players. Post-concussion evaluation was conducted on 183 athletes. The concussed athletes exhibited increased symptoms, particularly headache, and decreased performance on measures of processing speed at 24 hours post injury. The cognitive deficits normalized between 5 to 10 days post injury, but the post concussion symptoms showed a slower course of improvement.

More recently, Collins et al3 conducted preseason symptom and neuropsychological screening of 393 college football players. They found that learning disabilities (LD) or a history of 2 or more concussions independently contributed to lower baseline testing scores. Athletes with both LD and prior concussions performed even worse. Additionally, they found that 16 athletes who sustained concussions during the season exhibited a verbal memory impairment that persisted for at least five 5 days post-injury.

The National Football League (NFL) began conducting concussion research in 1996. The research is a product of the NFL subcommittee on mild traumatic brain injury. Team participation is voluntary and 22 teams are currently participating. Baseline screening includes a concussion history, symptom checklist, and neuropsychological screening.4 The protocol takes approximately 30 minutes to complete and focuses on testing of attention, processing speed, and memory. The baseline data is anonymously submitted to a database. Any athlete who subsequently sustains a concussion is re-evaluated against their baseline data within 24 to 48 hours post injury. Serial re-evaluation occurs until the athlete’s symptoms and test performance normalize. At present, approximately 1500 athletes have completed baseline evaluation and post-concussion data is being prepared for analysis.

Overall, research on collegiate football players suggests that single mild concussions produce acute impairments of processing speed and memory that rapidly improve during the first 5 to 10 days post injury. Athletes with learning disabilities and multiple concussions may be at risk for slower or less complete cognitive recovery. There is no research to date that has analyzed the effects of repeated concussions in a large sample of football players.

Rugby and Australian Rules Football. Maddocks5 evaluated 75 Australian rules football players during the preseason using a speed of processing test and followed 13 players who sustained concussions during the season. He found visuomotor slowing deficits immediately post injury that significantly improved during the week post injury. Several players who were more moderately concussed demonstrated a prolonged recovery period. Hinton-Bayre et al6 conducted preseason baseline testing of processing speed on 54 rugby league players and followed 10 players who sustained concussions during the season. This study also found visuomotor speed impairment that persisted for up to 10 days. Additionally, this study found speed of processing deficits on more complex verbal tasks that persisted for up to 3 weeks post-injury.

Research on concussed rugby players has yielded results similar to American football players. For a single mild concussion, visual processing speed deficits are evident immediately after injury and significantly improve during the first week post injury. Rugby research also suggests that complex processing speed recovers slower and that more moderately injured players recover slower.

Hockey. No formal neuropsychological studies of the effects of concussion in hockey players have been published. Since 1997, however, the National Hockey League (NHL) has conducted a league wide concussion research project. The project consists of preseason baseline screening for every athlete, including concussion history, concussion symptom checklist, and neuropsychological testing of attention, speed of processing, and memory.7 Players sustaining concussions are re-evaluated within 24 to 48 hours after a concussion and are serially re-evaluated every 5 to 7 days until symptoms and test scores normalize. Approximately 1500 NHL players have completed baseline testing. The post concussion data is being prepared for analysis.

Chronic Effects of Concussion in Sport. The effects of repetitive subconcussive and concussive blows to the head on the development of chronic brain dysfunction have been examined for several sports. Two primary research methodologies have been used: 1) a matched control design that compares high and low risk athletes’ performance on specific symptom inventories and cognitive tests to low risk athletes and 2) a single group design that analyzes relationships between the athlete’s performance on cognitive tests and potential mediating factors, such as length of exposure to the sport and injury history.

Boxing. Boxing is unique as a sport, since the primary goal is to deliver a concussive blow to an opponent, ie, knock him out. Athletes participating in boxing sustain repetitive subconcussive blows during the course of their career, and many sustain concussive blows. The risk of chronic brain dysfunction (dementia pugilistica) from boxing has long been recognized, but the sport remains popular. At the amateur level, research that has compared boxers with matched controls has produced mixed results. McLatchie et al8 compared 20 amateur boxers to an equal number of orthopedic control patients and found impairments on measures of attention, reaction time, and memory. Kemp et al9 compared 41 amateur boxers to 27 non-boxing controls and found impairments on reaction time and pattern recognition. In contrast, other studies have failed to detect significant differences between boxers and controls on measures of cognitive abilities.10 Stewart et al11 evaluated 484 boxers at baseline and prospectively re-evaluated 393 of them 2 years later. At baseline, they found significant correlations between the total number of bouts fought prior to baseline and the boxers performance on memory and visual perceptual testing. They did not find any significant relationships between boxing exposure and cognitive changes during the 2 year follow-up period, and hypothesized that there may be a longer latency period before cognitive deficits become manifest.

At the professional level, Ryan12 estimated that 9% to 25% of boxers eventually become “punch drunk.” Multiple risk factors have been identified for the development of dementia pugilistica, including retirement at a later age, longer careers, greater number of bouts, poor performance, being a “slugger,” being able to “take a punch,” and history of KO and TKO.13 Studies on the neuropsychological effects of professional boxing have been fraught with methodological problems that limit their conclusions. It is very difficult to adequately control for the myriad factors that could contribute to cognitive decline in boxers. One recent study that attempted to control for many of the methodological problems was conducted by Jordan et al.14 They tested 42 professional boxers and found strong correlations between the amount of time sparring and impairments on measures of attention and memory. They concluded that exposure to repetitive subconcussive blows, as measured by amount of time sparring, was more strongly associated with cognitive deficits than was age, boxing record (win/loss), length of career, or history of knockout/technical knockout. Overall, the research on boxers suggests a strong relationship between boxing exposure and a decline of cognitive abilities, particularly attention, speed of processing and memory.15 This decline is not only related to concussive injuries, but also to repetitive subconcussive blows.

Soccer. As in any contact sport, soccer players are susceptible to concussions. They also sustain repetitive subconcussive blows by heading the ball. Concern has been raised about the potentially detrimental effect of heading the ball as well as concussion in soccer. Several studies have been conducted at both the amateur and professional level with mixed results. One study of amateur athletes compared 33 soccer players with 27 matched noncontact athletes and found impaired performance on measures of planning and memory that were correlated to the number of concussions.16 At the professional level, Matser et al17 compared 53 professional soccer players with 27 elite noncontact athletes and found impairments on measures of planning and memory that correlated to the number of concussions and to the frequency of heading. Jordan et al18 compared 25 members of the United States National Soccer Team and 20 age-matched control athletes on MRI and a head injury questionnaire. On MRI, 9 of the soccer players and 6 of the track athletes had positive findings. On the head injury symptom questionnaire, the soccer players with prior concussions reported significantly more symptoms, but there was no correlation between heading and symptoms. They concluded that if there was a risk of chronic dysfunction in soccer players, concussion, rather than heading, was the main factor.

Overall, preliminary evidence suggests that participation in soccer may result in neurocognitive changes, but these studies have methodological problems that limit conclusions. Longitudinal, large-scale research is necessary to answer questions of soccer-related cognitive deficits resulting from heading versus concussive injuries.

Clinical Neuropsychological Evaluation of the Athlete. At present, there are no clear guidelines to indicate when an athlete should be referred for neuropsychological screening as part of a concussion work up. Since research has shown that these tests are sensitive and specific to the effects of sport concussion, neuropsychological evaluation may be useful whenever objective information is needed about the athletes’ neurocognitive status for clinical decision making. Kelly19 recommends neuropsychological evaluation when the athlete has sustained a concussion with loss of consciousness, has confusion that lasts longer than a few minutes, has amnesia that persists beyond the end of the game, has sustained multiple concussions, or has an overt change in behavior.

Traditional neuropsychological assessment typically involves several hours of comprehensive testing across the domains of intelligence, academic performance, attention, learning, memory, abstract reasoning and problem solving, language, visuospatial functions, and sensory and motor skills. These lengthy batteries are clearly not feasible for large-scale athletic programs. Brief sport concussion neuropsychological screening protocols have been developed. The sports concussion screening protocols typically acquire data about concussion history (Table1), orientation, neurobehavioral symptom severity (eg, headache), attention, processing speed, and memory (Table 2). For a single, uncomplicated concussion, a brief neuropsychological screening, conducted within 24 to 48 hours post injury, will be able to provide basic information about the athlete’s symptoms and cognitive functioning. The evaluation, which is conducted by a neuropsychologist, typically requires approximately 30 minutes of testing. The test results are compared to norms appropriate to the athlete’s age. This type of evaluation will provide information about the player’s performance on cognitive tests in comparison to normative peers. If any cognitive deficits are identified, then follow-up testing within 5 to 7 days is useful to monitor recovery and to track any persisting problems. This systematic evaluation of the concussed athlete will help to identify those requiring more extensive neuropsychological and medical evaluation. Symptoms and scores should normalize before the athlete returns to play. Athletes who have sustained multiple concussions, or who have sustained concussions with persisting symptoms, will require more extensive evaluation as part of the medical work-up.

Table 1. Concussion Symptoms Scale

Table 2. Acute Neuropsychological Evaluation Protocols.

While comparing the athlete’s performance on cognitive tests to normative peers is a standard neuropsychological practice and provides useful information about the athlete’s cognitive status, comparing the athlete against his own preconcussion baseline provides the most sensitive method for detecting subtle cognitive changes from concussion. Establishing a preseason baseline is important because athletes vary considerably in their cognitive abilities, making it difficult to discern if any subtle deficits that are identified on post-concussion testing are attributable to the concussion or to other unrelated factors. Preseason baseline screening enables the athlete to act as his own control. Baseline screening is recommended whenever possible and is being used at the high school, college, and professional level.

Conclusion. Neuropsychological studies of acute concussion have demonstrated increased symptoms, slow processing speed, and memory impairments that persist for at least 5 to 10 days and up to 3 weeks post-injury. Additionally, studies of the chronic effects of concussion suggest that repetitive subconcussive and concussive injuries may both independently contribute to persisting symptoms and cognitive decline. These are important considerations for the clinical management of the concussed athlete. Neuropsychological evaluation of athletes provides a systematic approach for monitoring symptoms and cognitive changes associated with concussion in both research and clinical applications. At the research level, large scale longitudinal studies will be important for answering questions about classifying injury severity, determining the effects of repetitive injuries, and identifying risk factors for slow or incomplete recovery from concussive injuries. At the clinical level, brief neuropsychological evaluation provides a sensitive method for measuring the acute and cumulative effects of concussions and is being used with increasing frequency by sports medicine personnel in the management of concussed athletes.
 

Address comments and questions to:

Don Gerber, PsyD
CNI Center for Neurobehavioral Trauma
701 E. Hampden Avenue, Suite 160
Englewood, CO 80113

Elizabeth Kozora, PhD, ABPP/ABCN
National Jewish Medical and Research Center
1400 Jackson Street
Denver, Colorado 80206

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