Clinical Studies
Immediate Neurocognitive Effects of Concussion

COMMENTS

McCrea et al. report on the immediate neurocognitive effects of concussion. The authors are careful to specify the definition of concussion and that this definition does not require a definable loss of consciousness (LOC). This point is important because the lack of a stringent definition has confused research comparisons during the past 20 years. Not surprisingly, the authors found that individuals with LOC were more severely impaired on the Standardized Assessment of Concussion (SAC) instrument (1) than those without LOC, but evidence of significant impairment in neurocognitive ability was still noted in patients with traumatic brain injuries who did not have evidence of either LOC or posttraumatic amnesia (PTA). Of course, care must be taken not to conclude that individuals with minor head injuries according to the definition used in this study will be left with significant residua. The vast majority, as shown in this study, recover quickly. Questions that should be the basis for further research relate to the ability to identify those patients who do not recover as quickly and for whom early supportive interventions might improve outcome. The authors have made a good start on building a solid foundation for research into this major public health problem, and they have performed their work carefully.

Lawrence F. Marshall
San Diego, California

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1. McCrea M, Randolph C, Kelly JP: The Standardized Assessment of Concussion (SAC): Manual for Administration, Scoring and Interpretation. Waukesha, CNS, Inc., 2000, Ed 2.

This limited prospective study by McCrea et al. focuses on the immediate, detectable neurocognitive manifestations of mild traumatic brain injuries in a total of 2385 varsity football players from 30 high schools and 15 colleges. It examines the application of the relatively new SAC (1), which athletic trainers administer on the sideline of the field immediately after the concussive event.

Although many schools participated in this study, only 91 of the individuals studied experienced minor head injuries. Overall, the project was well designed, but my criticisms of the study’s methodology are as follows. No physicians or specialists were involved in the examination of the injured athletes; instead, athletic trainers administered and interpreted the test results. Individuals with only mild concussion and having no PTA or LOC (84%) were predominant in the study. In the athletes with LOC (7.7%), none experienced LOC for longer than 1 minute. Thus, the individuals in this population had a very mild form of athletic head injury. The definition of concussion used in the study is subject to scrutiny and debate, because some disagreement prevails about which classification system is the most accurate or would be applicable in such a study. The authors’ follow-up was not as originally expected: only one-third of the participants complied with the designed reassessment at three time points in the postconcussion period. In addition, no radiological examination, formal neurological examination, or other ancillary correlation with the results of the SAC was performed.

However, the authors’ conclusions seem to validate not only that progressive seriousness of concussion is demonstrated in neuropsychological performance in the immediate postinjury phase but also that increasing levels of concussion result in continued diminution in test performance. The authors confirm the impression that PTA and LOC represent increasingly severe concussion severity. I await the publication of further studies that validate these findings in a larger group of athletes with more serious forms of mild traumatic brain injury and that compare the results of formal neuropsychological, neuroimaging, or postural stability testing. In addition, it would be of interest to ultimately determine whether a modified SAC instrument would be advantageous in assessing all forms of mild traumatic brain injury in the general patient population.

Julian E. Bailes
Morgantown, West Virginia

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1. McCrea M, Randolph C, Kelly JP: The Standardized Assessment of Concussion (SAC): Manual for Administration, Scoring and Interpretation. Waukesha, CNS, Inc., 2000, Ed 2.

This report describes an important study of the use of a new, brief cognitive screening measure, the SAC (1). The SAC was administered to a total of 2385 football players before the football season and to 91 of the players immediately after injury and at 15 minutes, 48 hours, and 90 days after injury. Immediately after concussion, the players’ SAC scores were below preseason baseline, even among those players without PTA or LOC. Players without LOC or PTA were the least impaired, and those with LOC were the most severely impaired as measured using the SAC.

Within 2 days after injury, "nearly all subjects, with or without LOC and PTA, demonstrated full recovery with the SAC." Indeed, by 48 hours postinjury, there was a significant increase in SAC score as compared with baseline. Figure 2 suggests that this improvement over baseline increased further at 90 days postinjury. This significant improvement over baseline suggests that learning and practice effects may have inflated the players’ scores. Practice effects are important because they can mask continued cognitive difficulties and make improvement in performance difficult to interpret. This problem could have been avoided if a noninjured control group had been used to quantify the effects of learning and other sources of variability. In addition, the results from the SAC need to be compared with more extensive neuropsychological assessment to determine the extent to which the SAC is capable of identifying more subtle cognitive impairments. Fortunately, the authors report that additional studies are under way to address these issues.

Carol A. McCleary
Neuropsychologist
Los Angeles, California

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1. McCrea M, Randolph C, Kelly JP: The Standardized Assessment of Concussion (SAC): Manual for Administration, Scoring and Interpretation. Waukesha, CNS, Inc., 2000, Ed 2.

The authors’ findings of PTA and brief LOC associated with increased severity of concussion as determined by abnormal neurocognitive scores on the SAC (5) immediately and 15 minutes after injury are consistent with data reported by Erlanger et al. (2) using a more detailed neuropsychological battery, the Concussion Resolution Index (HeadMinder, Inc., New York, NY). Several studies, including one published in Neurosurgery (4), have documented that there is no relationship between LOC and abnormality detected on neuropsychological testing at 48 hours after injury, raising concern with regard to brief LOC as a severity marker for concussion (2, 3; MR Lovell, MW Collins, GL Iverson, M Field, J Maroon, RCCantu, submitted for publication). More recently, two large, unrelated prospective studies of concussion found the presence of PTA correlates best with abnormal neuropsychological testing at 48 hours as well as with the duration and the number of other postconcussion signs and symptoms. These findings have led to new evidence-based grading of concussion severity that places more weight on PTA as a potential predictor of subsequent impairment (1). That the results of testing using the SAC instrument did not demonstrate abnormality at 48 hours after injury may reflect decreased sensitivity of the SAC as compared with a much more detailed, computer-generated neuropsychological test that includes reaction times.

Robert C. Cantu
Concord, Massachusetts

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1. Cantu RC: Posttraumatic retrograde and anterograde amnesia: Pathophysiology and implications in grading and safe return to play. J Athletic Training 36:244–248, 2001.
2. Erlanger D, Saliba E, Barth J, Almquist J, Webright W, Freeman J: Monitoring resolution of postconcussion symptoms in athletes: Preliminary results of a web-based neuropsychological test protocol. J Athletic Training 36:280–287, 2001.
3. Lovell MR, Iverson GL, Collins MW, McKeag D, Maroon JC: Does loss of consciousness predict neuropsychological decrements after concussion? Clin J Sport Med 9:193–198, 1999.
4. Maroon JC, Lovell MR, Norwig J, Podell K, Powell JW, Hartl R:Cerebral concussion in athletes: Evaluation and neuropsychological testing. Neurosurgery 47:659–672, 2000.
5. McCrea M, Randolph C, Kelly JP: The Standardized Assessment of Concussion (SAC): Manual for Administration, Scoring and Interpretation. Waukesha, CNS, Inc., 2000, Ed 2.