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 rig ht foot is presented. Rhythmic myoclonic jerks were localized to the 1 st and 2nd toes of the right foot and persisted for 72 h. EEG/video mo nitoring did not show any epileptiform transient in association with m yoclonic jerks. MRI and MRA demonstrated an arterio-venous malformatio n involving the left fronto-parietal parasagittal area. Using the EMG signal from the myoclonic jerk we back-averaged the EEG 640 msec befor e and after the onset of the twitch. A negative-positive deflection wa s observed preceding the myoclonic jerks by 128-188 msec. Voltage topo graphic mapping showed a negative maximum in the left centro-parietal region. A multiple spatio-temporal dipole model was applied to the bac k-averaged deflection preceding the myoclonus. The patient's MRI was u sed to determine the center of the best fitting sphere, and the model was corrected accordingly. The best dipole solution consisted of 3 dip oles localized in the parasagittal frontal cortex, in the location of the motor representation for the foot. The utilization of a combined t echnique of back-averaging from the myoclonus and dipole source locali zation supported the epileptogenic etiology in this case.