A parametric scale for BAEP latencies in multiple sclerosis.
A parametric scale for measuring BAEP latencies is set forth here for use in multiple sclerosis (MS) therapeutic trials and similar longitudinal studies. Derived constants are used to create a synthetic I-V interpeak interval, needed for cases where V (or other waves) are absent. Transitional peaks (peaks on the verge of disappearing) were studied in MS patients and used to determine appropriate values for the weighting constants. The resulting scale or index makes use of latencies to whichever peaks are still present. In theory such a scale is more sensitive to small changes than either a simple ordinal scale of which peaks remain or a parametric scale of I-V interpeak intervals excluding the 25-40% of MS records with absent wave V. To test this synthetic I-V index in practice, we studied it in 100 MS patients entering a therapeutic trial. It was found to correlate appropriately with patients' history, physical examination, and clinical scales at entry into the trial. Parametric statistical analysis of the derived scale was able to show a statistically significant drug effect during the therapeutic trial, whereas 3 other data analysis techniques showed at best a trend that did not quite reach significance.