Five patients with partial epilepsy of diverse etiology insidiously de
veloped action-activated jerks. The disorder was limited to one arm in
two patients and to the legs in another, and was multifocal in the re
maining two. Each jerk was related to an EMG silent period lasting 100
to 400 msec, causing a lapse followed by resumption of posture. Simul
taneous 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 occur
red. The three patients who were able to cooperate during neurologic e
valuation also exhibited motor neglect in the most affected body segme
nt and decreased awareness of the disorder. In three patients, the phe
nomenon 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 neuropsycholo
gical abnormalities. This disabling movement disorder can be classifie
d as ''epileptic negative myoclonus'' and may result from focal-discha
rge-related transient disruption of cortical function in the sensorimo
tor cortex.