DIPOLE SOURCE ANALYSIS MAY DIFFERENTIATE BENIGN FOCAL EPILEPSY OF CHILDHOOD WITH OCCIPITAL PAROXYSMS FROM SYMPTOMATIC OCCIPITAL LOBE EPILEPSY

The aim of the study was to distinguish Benign Focal Epilepsy of Child hood with Occipital Paroxysms (BEOP) from its symptomatic counterpart on the basis of the location of the sources of the interictal EEG spik es. Patients were classified into two groups: idiopathic BEOP and symp tomatic occipital lobe epilepsy. Source analysis of the averaged occip ital spikes was performed using a homogeneously conducting sphere as t he volume conductor model. Results showed a statistically significant difference in the eccentricity, i.e., the distance of the occipital sp ike focus from the centre of the head. The dipole sources of the occip ital spikes in the BEOP group were found to be located more superficia lly than in the symptomatic group, corresponding in six of the nine ca ses with a source position estimated to be within the cortical layer j ust below the skull. The eccentricity of the symptomatic occipital spi kes suggests a location deeper than the cortical layer. The results we re validated in two patients from the symptomatic group. In one patien t the estimated deeper dipole source location corresponded with a deep er location of spike activity observed during ECoG; in the other patie nt's ECoG, spike activity was observed superficially but over an exten ded area. The discrepancy between estimated and real location may be e xplained by the method of dipole source analysis used. It is concluded that the finding of a superficial dipole source location of the occip ital spikes provides an indication for the diagnosis BEOP (sensitivity : 67%; specificity: 74%).