Wave I of early auditory evoked potentials in multiple sclerosis

Early auditory evoked potentials (EAEPs) were recorded in a series of 71 consecutively examined patients suffering from clinically definite or probable multiple sclerosis (MS). Wave I abnormalities, i.e., delayed latency, with or without reduced amplitude, were observed in 15 such patients and were interpreted as due to MS in 8 of them. As EAEP wave I is identical with the potential N1 in electrocochleography and corresponds to activity of the most distal part of the acoustic nerve or the spiral ganglion, it is concluded that the peripheral part of the acoustic nerve is involved in about 10% of MS patients. In two cases normalization of initially delayed wave I latencies were demonstrated during follow-up recording. The pattern of a late wave I but normal hearing in 3 patients is interpreted in terms of a desynchronized compound nerve activity with fully preserved conductivity, segmental demyelination of a considerable number of acoustic nerve fibres being the most likely cause.