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

Source localization methods were applied to interictal spikes from scalp EEGs and correlated with metabolic (PET scan) data in eight patients suffering from drug-resistant temporal lobe epilepsy (TLE). Dipolar sources, [18F]fluorodeoxyglucose (18FDG)-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, five patients; lateral and polar neocortex, three patients). Six patients showed a unilateral interictal decrease in glucose uptake, as measured with 18FDG-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 the presence of preferential epileptogenic networks inside the hypometabolic temporal lobe. Fusion of bioelectric, metabolic and anatomical data proves to be a convenient 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 18FDG-PET data might be useful, as a complement to ictal electro-clinical data, in the presurgical evaluation of such patients.