Electroencephalographic correlates of myoclonus.

In order to overcome various drawbacks of the conventional polygraphic study of a relationship between myoclonus and EEG, the EEG preceding and following the myoclonic jerk was simultaneously averaged by the CNV program. The subjects were 7 patients presenting with myoclonus of various kinds. The conventional polygraphs showed various paroxysmal EEG activities in 4 patients, but none of those paroxysmal activities was temporally related to myoclonus except for one case. As a result of the present averaging technique, 2 patients with cerebellar ataxia with intention myoclonus showed myoclonus-related EEG spikes or spike-and-slow-waves in the contralateral central or centroparietal region. These myoclonus-related spikes preceded the myoclonus by 10-17 msec, suggesting the presence of a discharging focus in the deep cerebral structures, rather than in the cerebral cortex, in these cases. Two other patients, one with resting myoclonus and the other with postural myoclonus, showed myoclonus-related slow waves on the contralateral hemisphere. This previously undescribed method of averaged polygraphic recording will be very useful in detecting an EEG correlate of spontaneously occurring myoclonus.