Severity of sports-related concussion and neuropsychological test performance

We welcome the comments made by Mandel et al. [1] on our report published in this journal [2]. The reported tests were taken from a larger battery that assessed learning, memory, executive function, and verbal fluency, yet these measures failed to identify concussed athletes. We were impressed by the ability of only three measures to identify concussed players so accurately, but do not recommend them as a concussion battery. The Digit Symbol and Symbol Digit tests measure overlapping but not identical constructs. Our data suggest that 47% of their variance is not shared. These two measures also complement each other in the detection of impairment. [3] Multiple measures of a construct are often used to ensure adequate reliability. It is possible that Mandel et al. are not familiar with the Speed of Comprehension test. Reading skills are indeed comparatively resilient to brain trauma, however the ability to conduct parallel processing of language sense under time pressure is not. The Speed of Comprehension test was the most sensitive of the three measures to the acute effects of concussion, identifying more impaired athletes. [3]

In response to particular concerns over methodology only one physician made the rating of severity for any one player and they were not blind to the player's identity. Multiple raters would have been ideal. Sensitivity (18/21 – 86% concussed athletes impaired) and specificity (17/21 – 81% - controls not impaired) were determined using significant decline on at least one measure. The three impaired athletes with Grade 3 concussions all had a history of multiple concussions with the most recent in the previous year. Two of the three players without a previous history of concussion were still impaired at 10 days. Cognitive impairment was not related to duration of symptoms; at 2 days post-trauma five of the 21 concussed players reported ongoing symptoms, with only three of these symptom-positive players demonstrating impaired test performance. At 10 days, only one of the 10 players with impaired test performance was still reporting symptoms. [3] Athletes with a history of concussion within the last 12 months (n=11) were not more likely to be cognitively impaired than other concussed players (n=10) at 2 days (9/11 vs 9/10) or 10 days (4/11 vs 6/10).

We stated that the percentage of impaired athletes was consistent across grades and systems as concussion grades had little bearing on likelihood of impairment at 2 days. Without dismissing the interpretation concerns raised, we would caution against over-interpretation of patterns when using percentages based on very small samples.

• 92% of AAN Grade 2 concussions (n=13) were impaired, compared to 75% of Grade 1 and 3 concussions (ns=4) at 2 days post-trauma.

• At 10 days post-trauma almost double the percentage of Colorado Grade 2 concussions were impaired compared to Grade 1 concussions, which appears reversed for the AAN and Cantu guidelines. One more impaired Colorado Grade 1 athlete would have de-emphasized this apparent trend.

• Mandel et al. correctly point out the discrepancies between Grade 1 and Grade 2 impairment rates at 10 days within and across systems. The consistency we were eluding too was that players with lesser AAN and Cantu severity ratings were more likely to be impaired at 10 days. Similarly, Colorado Grade 1 and 2 injuries were less likely to recover than Grade 3 injuries.

The statements made were intended to represent a general trend, to which Mandel et al. have noted the exceptions. We certainly do not dismiss their points. However given the size of the report and the small numbers, we were reluctant to discuss such exceptions. We appreciate the positive comments made and look forward to advances leading to a greater understanding of the relationship between concussion severity and neuropsychological status.

References:

1) Mandel S, Maitz EA. Tracey JI, & Gordon JE. Severity of sports -related concussion and neuropsychological test performance (Correspondence). Neurology 2003;61:144.

2) Hinton-Bayre AD & Geffen G. Severity of sports-related concussion and neuropsychological test performance. Neurology 2002;59:1068 -1070.

3) Hinton-Bayre AD, Geffen GM, Geffen LB, McFarland KA and Friis P. Concussion in contact sport: reliable change indices of impairment and recovery. J Clin Exp Neuropsychol. 1999;21:70-86.

EDITOR'S NOTE:

This letter is being published in reply to a letter which the authors were sent but did not receive.

We read with interest the article by Drs Hinto-Bayre and Geffen where they described a brief neuropsychological battery to determine when an athlete can be safely cleared to return to play following a sports-related concussion ("Severity of sports-related concussion and neuropsychological test performance").

However, the battery is limited with respect to the number of cognitive constructs it measures and is somewhat redundant. The Digit Symbol Test and the Symbol Digit Test measure identical neuropsychological constructs. While speed of processing is often compromised following concussion, the Speed of Comprehension Test may be an inadequate measure since the durability of reading skills may reduce the chance of observing impaired processing speed.

There are also methodologic issues. (1) There is no indication that the physicians were blind to each other's ratings. (2) How was test sensitivity (86%) and specificity (81%) determined? (3) Is it possible that the three athletes without previous concussions were grade 3? (4) The authors state that cognitive impairment was unrelated to duration of symptoms or history of concussion in the previous year. How was this determined?

Some interpretations are inconsistent with the data. The authors state, "the percentage of athletes showing deteriorated performance 2 days after trauma was similar across grades, irrespective of system." Yet, for the AAN system, 92% percent of grade 2 concussions were impaired compared to 75% for grades 1 and 3. Similarly, the article states that under Colorado guidelines a comparable number of athletes with grade 1 and 2 concussions were impaired at 10 days. However, the grade 1 rate is 33% and the grade 2 rate is 64%. The authors state, "the percentage of athletes impaired at 10 days post-trauma was consistent across severity classifications." However, by the AAN system, 75 % of the subjects were impaired at grade 1 compared to 33 % at grade 1 for the Colorado system. Further, 27% of the grade 2 subjects were impaired in the Canto system with 54% (for the AAN system) and 64% (for the Colorado system).

The study does yield important findings. A sizeable percentage of Grade 1 athletes show cognitive impairment even 10 days post-trauma. The data also suggest that there may be a tendency to underestimate cognitive effects in cases of mild concussions and overestimate impairment for athletes with greater concussion severity. This article is a good step toward an evidence-based system for concussion ratings and clinical decision-making. However, the true nature of the association between concussion severity and neuropsychological status remains to be established.

References:

1) Hinton-Bayre AD and Geffen G. Severity of sports-related concussion and neuropsychological test performance. Neurology 2002;59:1068 -1070.