Evoked potentials in motor system diseases.

We studied pattern-shift visual (PSVEP), brainstem auditory (BAEP), and somatosensory (SEP) evoked potentials in 38 unselected patients with motor system diseases (MSD) (28 sporadic, 10 familial). PSVEPs were normal in all patients, and BAEPs were normal in all except one with clinical hearing loss who had absent waves I and III and prolonged wave V latencies. Median and tibial SEPs revealed definite CNS conduction abnormalities in only 1 of 30 and 1 of 18 patients, respectively. In addition, four patients had peripheral and four had peripheral or central delays on tibial nerve testing. There were no or only small group differences in central conduction SEP, BAEP, and PSVEP values in patients with normal studies compared with controls. This study suggests that central conduction SEP, BAEP, or PSVEP abnormalities can rarely be attributed to MSD and that their presence in patients suspected of having this disorder should prompt a search for an alternative diagnosis.