Abnormalities of the auditory evoked potentials in patients with multiple sclerosis

Fifteen components of the auditory evoked potential can be recorded within 300 ms of a click stimulus and these can be classified by latency in early (0-8 ms), middle (8-60 ms) and late (greater than 60 ms) components. Follwing a click stimulus of high intensity these components have been studied in 45 normal subjects and in 88 patients with definite multiple sclerosis. Component V, thought to arise from brain-stem structures, was the most consistently abnormal in patients and there was a correlation between the abnormalities and clinical evidence of a brain-stem lesion. Thus in 79 per cent of patients with definite evidence of a brain-stem lesion and in 51 per cent of those without clinical signs related to the brain-stem, component V was abnormal. Abnormalities were also detected for components Pa, Nb and P1 of the middle components, and in 12 per cent of these the early components were normal. The late components were normal in all but 3 patients. Evidence is presented to show that pairs of click stimuli, 5 ms apart, presented at a fast stimulus rate, stress the auditory system in normal subjects. Using this technique abnormalities of component V in patients became more marked and the proportion of abnormalities detected was increased. The contribution of the reflex muscle responses to the click to the middle components of the auditory evoked potential has also been studied. It is concluded that components Pa, Nb and P1 are independent of these reflexes.