Development of a novel EEG rating scale for head injury using dichotomous variables.

We developed a new EEG rating scale for electrographic assessment of head injured patients. Phenomena present in posttraumatic EEG were scored as dichotomous variables (present or absent). These phenomena included background activity (alpha, beta, theta, delta), sleep spindles, focal abnormalities, reactivity and variability, epileptiform activity, and specific comatose patterns. Each variable was weighted according to its perceived prognostic value: i.e., normal alpha 10, flat EEG -10, spindles 4, etc. Combinations of possible scores ranged from +23 to -10. Fifty-seven EEGs from different head injured patients were independently and retrospectively analyzed by two investigators. There was a high correlation for intra- (r = 0.95) and inter- (r = 0.85) observer rating using the dichotomous test. When patients with scores over 15 (i.e., with reactive alpha) and patients with scores of -10 (i.e., ECI records) were excluded, the intra-rater and inter-rater correlations were still high (0.81 and 0.76, respectively). There was a high correlation between Glasgow outcome score at discharge and the dichotomous EEG score. This EEG scale scores most major categories of EEG activity, utilizes a multipoint scale for correlation purposes, and allows data to be analyzed in sub-categories (i.e., spindles in coma). The separate weighting score allows for refinement of the scale after data collection (i.e., to fit prospective outcome). We feel that this scale is reproducible and valid, and may be applicable to other patient groups with severely altered EEGs.