Source propagation of interictal spikes in temporal lobe epilepsy - Correlations between spike dipole modelling and [F-18]fluorodeoxyglucose PET data

Source localization methods were applied to interictal spikes from scalp EEGs and correlated with metabolic (PET scan) data bz eight patients suffering from drug-resistant temporal lobe epilepsy (TLE). Dipolar sources, [F-18]fluorodeoxyglucose ((18)FDG)-PET data and anatomical images (MRI) were projected into the same three-dimensional coordinates system. Averaged spikes were adequately modelled by two or three dipolar sources with different onset time of activation but overlapping activity (mean residual variance 3.4+/-2.1%). Although, in all patients, spike modelling demonstrated dipolar sources in both mesial and lateral temporal cortex, dipole propagation was consistent with the early involvement Of only one of these two areas (mesio-temporal, Jive patients; lateral and polar neocortex, three patients). Six patients showed a unilateral interictal decrease in glucose uptake, as measured with (18)FDG-PET in the temporal lobe ipsilateral to the EEG spike focus. Temporal hypometabolism was bilateral in one patient and absent in the remaining case. When projected onto PET-scan slices, the dipolar sources of these patients were always included within the hypometabolic area. However; within the hypometabolic zone, the decrease in glucose uptake was not found to be more pronounced in regions containing dipoles. Therefore the spatio-temporal spread of neuronal hyperactivity underlying interictal spiking suggests he presence of preferential epileptogenic networks inside the hypometabolic temporal lobe. Fusion of bioelectric, metabolic and anatomical data proves to be a conveniens way of summarizing multimodal information from non-invasive investigations in TLE patients entering an epilepsy surgery programme, and suggests that both interictal spike dipole modelling and (18)FDG-PET data might be useful, as a complement to ictal electro-clinical data, in the presurgical evaluation of such patients.