Motor evoked potentials in Wilson's disease: early and late motor responses.

Motor evoked potentials following magnetic stimulation of the motor cortex and the spinal roots were studied in 13 patients with Wilson's disease (WD). The fast-conducting motor pathway function was normal in 9 patients. The cortically-evoked motor responses were absent in patients with cerebral white matter lesion and akinetic rigid syndrome. In addition to the primary or early motor response, late motor response was common in WD and occurred with a latency of 70-90 msec for the upper limb and 90-110 msec for the lower limb. The cause of the late motor response is unknown, but may be an enhanced late response infrequently observed in normal subjects.