Influence of the stimulation frequency on the morphology of auditory evoked potentials in multiple sclerosis

The Rate-linked modifications observed in the Auditory Brainstem Responses (A.B.R.) in normal subjects are now well known. On the other hand they are a subject of controversy among groups studying multiple sclerosis (M.S.). 49 patients were observed in parallel studies in Milan and Creteil. The A.B.R. obtained for slow stimulus rates (11-21 Hz) were compared to fast ones (51 Hz). The A.B.R. were not significantly modified in 32% of the cases (deterioration: 21%, improvement: 11%). The variations don't seem to depend on the kind of curves involved. This phenomena can be explained by a frequency linked block of conduction of the pathological fibres, either partial or total. These data seem to be specific to demyelinating diseases. A research project is being conducted to study their specificity.