Intracranial EEG seizure-offset termination patterns: Relation to outcome of epilepsy surgery in temporal lobe epilepsy

Purpose: Studies using stereo-EEG (SEEG) and electrocorticography (ECoG) should not only identify a patient's epileptogenic zone, but also should provide prognostic information for surgical outcome. In this respect, seizure-offset patterns have so far been the subject of only one study, in which they were shown to be associated with poor outcome when recorded over cortical areas outside the temporal lobe of seizure onset. To clarify whether seizure-offset patterns are reliable in predicting seizure outcome, we studied SEEG/ECoG in a similar group of patients with temporal lobe epilepsy (TLE). Methods: SEEG/ECoG records of 44 patients with refractory TLE were analyzed. The areas of seizure termination were classified as ipsilateral or contralateral (mesial and/or lateral) temporal, (temporal and) frontal, and diffuse/bilateral. Patients were classified with respect to seizure outcome as either seizure-free (UCLA class 1a) or not seizure free (UCLA class 2-4); both groups were correlated with specific seizure-offset categories using Fisher's exact probability test and analysis of variance (ANOVA). Results: Of the 44 patients, the majority (n = 36) had at least part of their seizure offsets in the ipsilateral temporal lobe, whereas 8 patients manifested no seizure offsets in this lobe. Only 9 patients (20%) showed exclusive offsets in the ipsilateral temporal lobe. No statistically significant difference was evident between patients with all seizure offsets in the ipsilateral temporal lobe and those with offsets elsewhere. Similarly, no statistically significant difference was evident between patients with a diffuse seizure offset and those with seizure offsets of a different category. Conclusions: Seizure-offset patterns in SEEG/ECoG are unreliable in predicting seizure outcome after resective activity surgery for TLE.