Are event-related potentials in multiple sclerosis indicative of cognitive impairment? Evoked and event-related potentials, psychometric testing and response speed: a controlled study.

Bimodal event-related potentials (ERPs), together with evoked potentials (EPs), measures of motor speed (tapping test, EMG latencies and reaction times (RT)), and psychometric test results were studied in a group of 30 multiple sclerosis (MS) patients and 19 controls. ERPs have been advocated as objective tests of cognitive function. In the present study ERPs were compared with the results of psychometric tests, which have a proven validity in measuring aspects of cognitive function that are important in daily life. Abnormal EMG, RT and tapping speed confirmed that motor aspects of performance were slowed in the MS group. In contrast, cognitive non-motor variables such as Raven-IQ and MQ were not significantly abnormal. The proportions of abnormal ERP N2 and P3 latencies did not differ between the groups. It is concluded that the slow performance of MS subjects is therefore most likely not due to cognitive speed decrement, but to motor, executive impairments. No significant relationships between ERP latencies and psychometric test results were found. This held even for a subgroup of 5 MS patients with psychometrically established cognitive impairments. Based on these results, we query the relevance of ERPs as subtle indicators of cognitive impairment in MS.