Two types of remote propagation in mesial temporal epilepsy: analysis with scalp ictal EEG

The purpose of this study was to describe the propagation pattern of ictal discharges, particularly remote patterns from a localized onset in patients with mesial temporal epilepsy, and to determine whether this provides additional information to that obtained from prolonged presurgery scalp EEG monitoring. This is a retrospective and analytical study that included a historical open cohort of 18 patients with mesial temporal epilepsy, among whom 56 regionalized-lateralized onset seizures were recorded. These seizures were analyzed as to whether remote propagation occurred and as to their temporal characteristics. Thirty-eight regionalized-lateralized onset seizures did not show remote propagation, whereas 18 did. Two types of remote propagation were identified, one early and one late, depending on whether the remote propagation occurred before or after 10 seconds had elapsed from the onset of the electroencephalographic seizure. When the seizures were compared according to the type of propagation, those with early remote propagation showed a correlation, not statistically significant, with the intractability of the epilepsy (P = 0.0754), toward independent bitemporal interictal discharges (P = 0.1667), and from the MRI perspective, to occur with temporal lesions other than pure mesial sclerosis (P = 0.6329). Early remote propagation seizures were not associated with nonlateralized onset (P = 0.2682). The only patient in our study with switch of lateralization seizures experienced early remote propagation seizures. Patients with late remote propagation seizures and those without remote propagation showed no statistically significant differences with respect to these variables. Ictal recording with scalp EEG allows for differentiating between early and late remote propagation in patients with mesial temporal epilepsy and regionalized-lateralized onset seizures. Early remote propagation probably identifies a subgroup of these patients with greater uni- or bitemporal hyperexcitability.