Abstracts

RATIONALE: Equivalent current dipole analysis can be used to visualize the source of epileptic discharges three-dimensionally in children with focal epilepsies. A prolonged video-EEG is necessary in children with intractable epilepsy to define the ictal onset zone. There are often multiple foci recognized from the interictal spike zone and the ictal onset zone. We studied the dipole localizations of these interictal discharges to evaluate and compare epileptic foci with other neuroimaging studies.
METHODS: We studied 18 pediatric patients with intractable epilepsy, who underwent prolonged video-EEGs (19 scalp electrodes, sampling rate 200 Hz). We performed EEG dipole analysis of interictal epileptiform discharges using single moving dipole modeling. We compared EEG dipoles with the interictal spike zone, ictal onset zone detected by video EEG, MRI, PET, SPECT and MEG.
RESULTS: In 4 of 18 patients, a cluster of dipoles was localized to one region corresponding to interictal spike zone, ictal onset zone and neuroimaging data.
In 6 of 18 patients, dipoles and interictal spike zones were localized diffusely in one hemisphere. Two of the 6 patients had the ictal onset zone in one region whereas the other four patients had unlocalized hemispheric onset. Four of the 6 patients had diffuse hemispheric MRI lesions. These lesions consisted of cortical dysplasia in 2 patients, porencephalic cyst in one patient and diffuse hemispheric atrophy in another. MEG spike sources were concordant to MRI lesions in these four patients. The PET showed hemispheric hypometabolism in one patient and diffuse hypermetabolism in another. One of the 6 patients had right occipital tumor and MEG spike sources were localized anterior to the tumor. In the remaining one patient, MRI and PET were normal.
In 3 of 18 patients, dipoles, interictal spike zones and ictal onset zones were localized to the bilateral homologous regions. MRIs were normal in all 3 patients and neither MEG nor PET could lateralize the epileptic region.
In the remaining 5 of 18 patients, dipoles were localized to two or more regions in both hemispheres, which were concordant with multi-focal interictal spike zones. Four patients had diffuse hemispheric ictal onset whereas one patient had bilateral independent onset. One patient with left parieto-occipital cortical dysplasia had consistent lateralization among the ictal onset zone, MRI, PET and MEG, whereas the other four had inconsistent localization.
CONCLUSIONS: EEG dipole analysis from focal or hemispheric interictal epileptiform discharges can localize the zone of epileptogenesis. EEG dipole analysis from multi-focal interictal discharges can predict inconsistent epileptic foci in other neuroimaging studies. Higher spatio-temporal resolution is necessary to evaluate the homologous epileptic discharges to define the primary epileptic focus.
[Supported by: KATANO Award from Kansai Medical University, Osaka, Japan]