Epileptic negative myoclonus and brief asymmetric tonic seizures. A supplementary sensorimotor area involvement for both negative and positive motor phenomena.

Epileptic negative myoclonus (ENM) is an epileptic motor dysfunction characterised by brief lapses of postural tone provoked by paroxysmal cortical discharges. We report the electrophysiological and video-polygraphic findings in a patient presenting with the unusual association of ENM and brief asymmetric tonic-postural seizures of cryptogenetic origin. Focal EMG silent periods in the left deltoid muscle (mean duration 81.2 +/- 16.4 ms), time-locked with vertex spikes were present. The time lag between spikes and ENM was 33.1 +/- 4.6 ms. We suggest the involvement of mesial frontal areas in the genesis of both negative and positive motor phenomena.