Central auditory tests and auditory nerve-brainstem evoked responses in multiple sclerosis.

In 43 multiple sclerosis (MS) patients and an equal number of age- and sex-matched normal controls, auditory nerve-brainstem evoked responses (ABR), audiometric tests, central auditory tests (CAT) and clinical-neurological examinations were conducted. The CAT included rapid alternating speech perception, masking level differences to tones and to words and lateralization based on interaural time and intensity differences. The results in the MS group on the ABR and each of the CAT differed significantly from those in the control group. The ABR results and the lateralization test results were each abnormal in 50% of the MS patients. The ABR, CAT and clinical examination results were all mutually correlated. These findings are probably related to the fact that the demyelination in MS induces a decrease in impulse velocity, to temporal dispersion and to desynchrony of impulses in groups of affected axons and to the fact that the ABR and the CAT tests chosen are dependent on synchronous impulse firing and on the precise timing of the arrival of impulses from each ear at some brain centre. These tests may therefore contribute to neurological and to audiological diagnosis.