Frontal inhibitory spike component associated with epileptic negative myoclonus

The aim of this study was to characterize paroxysmal EEG activities associated with epileptic negative myoclonus (ENM) in an epileptic patient presenting with ENM. ENM was predominant in the right upper limb and was correlated to a spike in the left central region. Spikes associated with ENM (SaENM) and spikes unrelated to ENM (SuENM) were identified by the temporal relation between the left central spike and the EMG silent period in the right wrist extensor. SaENM showed a significantly longer duration than SuENM (128 +/- 27 msec versus 92 +/- 21 msec, respectively; P < 0.01). SaENM and SuENM were submitted to spike averaging and topographic mapping. Spike averaging was performed averaging the EEG 640 msec before and after the peak of the spike. Both averaged SaENM and SuENM consisted of a negative spike with highest amplitude at C3 and similar topographic characteristics. The discriminant feature between the two types of spikes was the presence, in averaged SaENM, of a second smaller negative spike, 40 msec after the peak of the spike at C3, whose maxima were distributed over the left frontal region. We labeled this second spike as ENM-related component. We conclude that, in our patient, ENM was associated with a frontal cortical potential suggesting the involvement of frontal areas in the generation of negative myoclonus.