P3. Significance of intracranial EEG parameters in prediction of seizure freedom

Abstract

Introduction. In patients with focal drug-resistant epilepsy (DRE), intracranial electroencephalography (iEEG) with subdural electrodes (SDE) is used to delineate the seizure onset zone (SOZ) and to distinguish eloquent cortex areals, if non-invasive diagnostics did not yield conclusive results. Previous studies have shown ambiguous findings on the significance of iEEG parameters with respect to prediction of seizure freedom after resective epilepsy surgery. Most studies focused on subgroups of patients, such as those with frontal or temporal lobe epilepsy, or on some iEEG parameters, only. To that end, we comprehensively analyzed the significance of several iEEG parameters in one set of consecutive patients with DRE. Methods. All patients who had undergone invasive monitoring with SDE between 2005 and 2015 at our tertiary epilepsy center were included in this study 1 . We retrospectively analyzed iEEG parameters including seizure onset pattern (SOP), size of SOZ, latency to EEG seizure propagation and latency from clinical to EEG seizure onset. Furthermore, we assessed associations with post-operative seizure freedom, histopathology und brain region of SOZ. Results. Eighty-one patients (34 female) with 324 seizures were assessed. Low-voltage fast activity (LVFA, 37%) and sharp activity < 13 Hz (30%) were the most frequent SOPs. Focal SOZ (≤2 cm) was the only iEEG parameter independently associated with 1-year post-operative seizure freedom (OR 4.1, 95% CI 1.433–11.679). While no SOP was linked to specific histopathologies, LVFA was associated with temporal neocortical SOZ ( p < 0.01). Median latencies to EEG seizure propagation were significantly longer ( p < 0.001) in seizures originating from temporo-mesial SOZ (median 16.0 s) compared with temporo-neocortical (median 8.0 s) and frontal seizure onset (median 5.5 s). Also, latencies from clinical to EEG seizure onset were significantly longer ( p < 0.001) in seizures from temporo-mesial SOZ (median −20.0 s) compared with temporo-neocortical (median −12.0 s) and frontal seizure onset (median −6.0 s). Discussion. A focal EEG seizure onset but no specific SOP predicted seizure freedom after surgery. Also, different SOPs could be generated by the same histopathology and vice versa, putting clinical significance of SOPs into question. LVFA was associated with temporal neocortical seizure onset, possibly indicating a close-by seizure generator. Longer latencies until seizure spread and clinical signs or symptoms in seizures originating from temporo-mesial SOZ may be explained by inhibitory circuits in the hippocampus. Reference 1. Steinbart D, Steinbrenner M, Oltmanns F, Holtkamp M. Prediction of seizure freedom after epilepsy surgery – critical reappraisal of significance of intracranial EEG parameters. Clin Neurophysiol. 2020;131(11):2682-2690. doi:https://doi.org/10.1016/j.clinph.2020.08.018