Short- and long-latency somatosensory evoked potentials in multiple sclerosis.

Thirty-nine of 52 patients, with definite (29) or probable (23) multiple sclerosis (MS) had unequivocal alterations of somatosensory evoked potentials (SEPs). In 28 patients both short- (up to N18) and long-latency (after N18) components were affected, whereas the abnormality was limited to the long-latency SEPs in the remaining 11 patients. These findings indicate that a substantial number of SEP abnormalities may be overlooked if the test is determined solely on the basis of short-latency components. Furthermore, a questionable change of short-latency SEPs could often be decidedly abnormal by finding extreme asymmetry of long-latency components. The long-latency SEPs are therefore a useful adjunct in evaluating cases of MS, especially if bilateral stimulation is used.