Evoked potentials predict the clinical changes in a multiple sclerosis drug study.

Visual, brainstem auditory, and median nerve somatosensory evoked potential (EP) tests were performed annually during a 3-year, double-blind, placebo-controlled study of azathioprine with or without steroids in chronic progressive MS. Treatment-related visual and somatosensory EP changes became statistically different 1 year before corresponding differences were seen in the Standard Neurological Examination scores. The statistical significance of EP changes was substantially greater than seen for changes in other clinical scales. The degree of significance was increased by using EP latency values, rather than simple criteria for change. EPs are sensitive, objective measurements useful in MS therapeutic trials.