Electroencephalographic correlates of myoclonusCorrelats electroencephalographiques des myoclonies

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Abstract

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.

Résumé

Afin de dépasser diverses contradictions des études polygraphiques conventionnelles sur les relations entre myoclonies et EEG, l'EEG qui précéde et qui suit la secousse myoclonique a été moyenné simultanément par le programme CNV. L'étude porte sur 7 malades présentant diverses sortes de myoclonies. Les enregistrements polygraphiques conventionnels montrent des activités EEG paroxystiques diverses chez 4 malades, mais aucune de ces activités paroxystiques n'était temporellement liée à la myoclonie sauf dans un cas. Comme résultat de la technique du moyennage décrite ici, deux malades avec ataxie cérébelleuse, et myoclonie intentionnelle ont montré des pointes ou des pointes-ondes EEG liées aux myoclonies au niveau des régions centrales ou centropariétales contralatérales. Ces pointes liées aux myoclonies précèdent la myoclonie de 10–17 msec, suggérant la présence d'un foyer de décharge au niveau de structures cérébrales profondes plutôt qu'au niveau du cortex cérébral dans ces cas. Deux autres malades l'un avec myoclonie de repos et l'autre avec myoclonie posturale ont montré des ondes lentes liées à la myoclonie sur l'hémisphère contralatéral. Cette méthode de moyennage des enregistrements polygraphiques non décrite jusqu'ici pourra être utile dans la détection des corrélats EEG d'une myoclonie survenant spontanément.

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    Citation Excerpt :

    Each jerk corresponds to a discharge of a small group of cortical motoneurons, somatotopically connected to a group of contiguous muscles. A cortical potential, time-locked to the myoclonic potential, and localized on the contralateral sensorimotor region, may be demonstrated by EEG, magnetoencephalogram, or jerk-locked averaging (Shibasaki and Kuroiwa, 1975; Hallett et al., 1979; Shibasaki et al., 1991; Mima et al., 1998). Facilitation of interhemispheric and intrahemispheric spread of CM activity through transcallosal or cortico-cortical pathways seems to play a major role in producing generalized or bilateral myoclonus (Brown et al., 1991a).

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