Epileptic negative myoclonus.

Five patients with partial epilepsy of diverse etiology insidiously developed action-activated jerks. The disorder was limited to one arm in two patients and to the legs in another, and was multifocal in the remaining two. Each jerk was related to an EMG silent period lasting 100 to 400 msec, causing a lapse followed by resumption of posture. Simultaneous EEG-EMG recording showed each postural lapse to be time-locked with a sharp or spike and slow-wave transient over the contralateral sensorimotor cortex, where almost continuous paroxysmal activity occurred. The three patients who were able to cooperate during neurologic evaluation also exhibited motor neglect in the most affected body segment and decreased awareness of the disorder. In three patients, the phenomenon was medically resistant, and in two of them it was continuous and could be defined as epilepsia partialis continua. In the other two, medical treatment induced remission of EEG, motor, and neuropsychological abnormalities. This disabling movement disorder can be classified as "epileptic negative myoclonus" and may result from focal-discharge-related transient disruption of cortical function in the sensorimotor cortex.