Dipole source localization in a case of epilepsia partialis continua without premyoclonic EEG spikes

A 72-year-old woman with epilepsia partialis continua (EPC) of the right foot is presented. Rhythmic myoclonic jerks were localized to the 1st and 2nd toes of the right foot and persisted for 72 h. EEG/video monitoring did not show any epileptiform transient in association with myoclonic jerks. MRI and MRA demonstrated an arterio-venous malformation involving the left fronto-parietal parasagittal area. Using the EMG signal from the myoclonic jerk we back-averaged the EEG 640 msec before and after the onset of the twitch. A negative-positive deflection was observed preceding the myoclonic jerks by 128-188 msec. Voltage topographic mapping showed a negative maximum in the left centro-parietal region. A multiple spatio-temporal dipole model was applied to the back-averaged deflection preceding the myoclonus. The patient's MRI was used to determine the center of the best fitting sphere, and the model was corrected accordingly. The best dipole solution consisted of 3 dipoles localized in the parasagittal frontal cortex, in the location of the motor representation for the foot. The utilization of a combined technique of back-averaging from the myoclonus and dipole source localization supported the epileptogenic etiology in this case.