HEARING-LOSS IN MULTIPLE-SCLEROSIS - LOCALIZATION OF THE AUDITORY PATHWAY LESION ACCORDING TO ELECTROCOCHLEOGRAPHIC FINDINGS

Multiple sclerosis is known to affect the myelin of the auditory pathw ay resulting in acute hearing loss. Two cases of sudden deafness due t o multiple sclerosis have been evaluated by conventional audiometry, b rainstem auditory evoked response audiometry and transtympanic electro cochleography. The abnormalities of the compound action potential in b oth patients (enhanced latency, abnormal adaptation using fast stimulu s rate) and the normal receptor potentials (cochlear microphonic, summ ating potential), as well as the absence of brainstem responses sugges t a disturbance of synchronization at the level of the first auditory neurone. The electrocochleography provides valuable information for th e topodiagnosis of this and other neural hearing losses, especially in the absence of reliable brainstem responses.