Clinico-electroencephalographic variants in pharmacoresistant mesial temporal lobe epilepsy

Introduction. Focal epilepsy secondary to mesial temporal sclerosis (MTS) is one of the main causes of refractory epilepsy. It is typically associated with frontotemporal discharges in the electroencephalogram (EEG), a characteristic image in the magnetic resonance scan and a probability of post-operative remission above 70%. Aims. To identify different patterns of ictal propagation in surface EEG recordings in patients with refractory epilepsy and MTS, and to analyse their relation with the post-operative outcome. Patients and methods. We conducted a retrospective review of the medical records of patients with refractory epilepsy secondary to MTS evaluated in the Epilepsy Surgery Programme of the Hospital de Clinicas, Montevideo (n = 30). The propagation of ictal rhythms was analysed in time windows of three seconds, and propagation maps were produced for each seizure. Results. Six patterns were identified: ipsilateral temporal (type 1; 37%), bilateral frontotemporal with (type 2A; 22%) or without (type 2B; 17%) extension to suprasylvian regions, alternating temporal (type 3; 13%), unilateral suprasylvian (type 4; 7%) and bilateral at onset (type 5; 3%). The type 1 pattern was associated with classic clinical features and a favourable post-operative outcome. The clinical variants were associated with extratemporal EEG propagation. Patients with reflex seizures continued with post-operative seizures. Overall, no unambiguous relation was found between the ictal EEG pattern and the post-operative outcome. Conclusions. The ictal EEG pattern does not allow for a surgical prognosis in patients with epilepsy secondary to MTS. The history of reflex seizures in these patients may be a red flag suggesting a less favourable surgical outcome.