Evoked potential assessment: utility in prognosis of chronic head injury.

Brainstem auditory evoked potentials (BAEP) and somatosensory evoked potentials (SSEP) were performed on 29 patients an average of 12.4 months after traumatic brain injury (TBI). The study purpose was to predict long-term outcome in chronic TBI patients by using multimodality evoked potentials (MEP), the Rancho Los Amigos Scale (RLAS), and other clinical parameters. Neither the BAEP nor SSEP correlated significantly with the cognitive level on the RLAS at the MEP study approximately one year after TBI (RLAS1). Only 11.7% of RLAS1 could be predicted by the combined study of BAEP and SSEP. BAEP and SSEP obtained about one year after TBI jointly had a 15% predictive power of the long-term follow-up RLAS score obtained 18 months after performance of the MEP (RLAS2). Stepwise regression analysis showed that the best predictive indicator of the status of long-term outcome was RLAS1 which alone can predict 60% of long-term outcome. The predictive value of combinations of RLAS1 and age improved prediction of long-term outcome to 66.8%, and the combination of RLAS1, age, and SSEP further increased the value to 72%. Perhaps the MEPs were relatively insensitive in reflecting the patient's adaptation to fixed neuronal damage since patients can perform higher cognitive function by adaptation through behavioral modification and cognitive retraining despite little structural improvement. This adaptation would result in a discrepancy between MEP and RLAS scores in the late chronic phase.