[Clinico-electroencephalographic variants in pharmacoresistant mesial temporal lobe epilepsy]

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%.

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.

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.

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.

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.