Prognostic value of frontal and parietal somatosensory evoked potentials in severe head injury: a long-term follow-up study

We have shown that the combined analysis of the frontal and parietal somatosensory evoked response (SEP) improves the global short-term outcome prediction in severe head injury (SHI) after 3-6 months. In the present study the same patients were reexamined 18 months after trauma and the prognostic value of the combined SEP parameters reassessed, in particular their value of predicting the exact Glasgow Outcome Scale (GOS) class reached (as opposed to a crude good or bad distinction). Frontal (P20/22, N30) and parietal (N20) SEP components were studied in 50 patients within 72 h after the injury and were related to the GOS after 3-6 months and again after 18 months. When both frontal and parietal components were used as predictors, discriminant analysis correctly classified 76% of the patients after 3-6 months and 82% after 18 months. Considering parietal SEP alone, classification was less accurate (74% after 3-6 months, and 68% after 18 months) and misclassifications were more severe. Our results show that (i) a combined analysis of frontal and parietal components of the SEP improves and refines the outcome prediction in SHI, (ii) the predictive power of the combined approach increases with time after trauma, while that of the parietal response alone decreases.