Duration of posttraumatic amnesia and the Glasgow Coma Scale as measures of severity and their relationship to cognitive outcome following closed head injury

The Glasgow Coma Scale (GCS) and duration of posttraumatic amnesia (PTA) are the most commonly used clinical instruments for determining severity and predicting outcome in closed head injury (CHI). Many investigations have attempted to determine the relationship between head injury severity and cognitive outcome, as measured by neuropsychological assessment performance, but found mixed results with respect to utility of prediction. The present study proposed that a major reason for these mixed results was other investigations' inclusion of individuals with conditions known to detrimentally affect neuropsychological test performance (i.e., history of alcoholism, drug abuse, psychiatric history, or previous neurologic insult) into their closed head injury sample. This investigation directly examined this hypothesis by adding an additional comparison group, a closed head injury-clean group (CHI-C), and comparing this groups' performance against a closed head injury not-clean group (CHI-NC). The effects of combining the CHI-C and CHI-NC groups into one closed head injury combined (CHI-Comb) group, as previous studies have done, was also examined.

Fifty-one consecutive patients (N = 51) underwent neuropsychological assessment following brain injury. Participants were included if they had exited PTA, demonstrated uncompromised upper extremity use, displayed adequate verbal communication, and were judged capable of completing full Wechsler Adult Intelligence Scale-Revised (WAIS-R), Wechsler Memory Scale, Controlled Oral Word Association Test, Stroop, and Trail Making Tests.

Separating the CHI individuals into the CHI-C and CHI-NC groups, and use of a logarithmic transformation, resulted in better prediction from severity measures to post-injury cognitive performance than observed in previous investigations. Moreover, despite the increased power of adding the CHI-C and CHI-NC groups into one CHIComb group, this combination obscured findings as predicted. Duration of PTA was a more reliable injury severity predictor than the GCS. Combining both measures in a prediction equation did not improve prediction. This investigation did not find the unique effects of closed head injury above that of other brain insults. Although the CHI-C and CHI-NC groups did not significantly differ on PTA duration and GCS severity level, the use of a pre-morbid PIQ estimate showed the CHI-NC group to have a greater post-injury PIQ loss than the CHI-C group. Furthermore, the mean VIQ/PIQ discrepancy was significantly larger for the CHI-NC group as compared to the CHI-C group. In conclusion, these findings as well as others from this investigation were discussed in terms of cognitive reserve theory.