High click stimulus repetition rate in the auditory evoked potentials in multiple sclerosis patients with normal MRI....

The purpose of this study was to evaluate whether auditory brainstem responses (ABR) in multiple sclerosis (MS) patients were qualitatively different from a normal population.

This study analysed 69 subjects, separated into two groups; a control group composed of 20 females and 20 males; and an MS group composed of 20 females and 9 males. The controls had no history of neurological or otorhinolaryngological disorders. All MS patients presented a normal magnetic resonance imaging of the brainstem. A definite diagnosis of MS was given according to Poser's criteria for MS research protocols (1983). The following parameters were used in the study of the ABR of each subject: 2000 clicks of 100 ms at 60 dB equivalent peak of sou nd pressure level (pe SPL) above the psycho-acoustic threshold, obtained with the subject's response to clicks. Both ears were initially stimulated at 11 clicks/s, and then with clicks of same intensity, but with a progressive increase of the stimulus rate to 31, 51, 61 and 71 clicks/s. The analysis of variance with independent factors and repeated measures was used in the statistical analysis of the comparison between group results.

The absolute latency of wave III was statistically greater, with a stimulus rate of 51 and 61 clicks/s, in the MS group. The males in the MS group presented a statistically greater absolute latency of wave V with the use of 51 and 61 clicks/s. With stimulus rates above 30 clicks/s, the absolute latency of wave V was also greater for MS females. There were statistically significant differences in the interpeak interval I - III of the control group compared to the MS group, for stimulus rates of 51 and 61 clicks/s, in females and for the stimulus rate of 61 clicks/s in males. This interval was higher in the MS group with these stimulus rates.

The results suggest the inclusion of stimulus rates of 51 and 61 clicks/s in the ABR tests of subjects with clinical suspicion of demyelinating diseases like MS.