Authors :
Presenting Author: Petr Klimes, PhD – Institute of Scientific Instruments of the CAS, Brno, Czech Republic
Petr Nejedly, Msc – St. Anne's university hospital Brno, Czech Republic
Valentina Hrtonova, Msc – Institute of Scientific Instruments of the CAS, Brno, Czech Republic
Barbora Matouskova, Msc – Institute of Scientific Instruments of the CAS, Brno, Czech Republic
Jan Cimbalnik, PhD – International Clinical Research Center, St. Anne’s University Hospital, Brno, Czech Republic
Vojtech Travnicek, Msc – Institute of Scientific Instruments of the CAS, Brno, Czech Republic
Martin Pail, MD, PhD – Institute of Scientific Instruments of the CAS, Brno, Czech Republic
Jeffery Hall, MD – Montreal Neurological Hospital, McGill University, Montreal, Quebec, Canada
Raluca Pana, MD – McGill University
Pavel Jurak, PhD – Institute of Scientific Instruments of the CAS, Brno, Czech Republic
Milan Brázdil, MD, PhD – 1st Department of Neurology, Faculty of Medicine, Masaryk University and St. Anne´s University Hospital, Brno, Czech Republic – member of ERN EpiCARE
Birgit Frauscher, MD, PhD – Department of Neurology, Duke University School of Medicine, Durham, NC, USA
Rationale: In epilepsy surgery, the epileptogenic zone (EZ) refers to the brain area indispensable for seizure generation. The gold standard for EZ identification is the seizure onset zone (SOZ) - the region where first electroencephalographic (EEG) changes are seen at the time of seizure onset. Recent studies suggest that incomplete resection of the SOZ is not associated with post-surgical outcomes (Klimes et al. Epilepsia 2019; Gascoigne et al. Epilepsia 2024). However, these studies define a good post-surgical outcome as ILAE 1-2 or Engel IA-D. Whether this result holds for completely seizure-free patients is unclear. Furthermore, interictal markers, which offer a promising alternative, are not well described in the context of SOZ localization, resection, and post-surgical outcomes.
Methods: We analyzed stereo-EEG (SEEG) recordings from 50 patients recorded at Montreal Neurological Institute (Canada) and St. Anne’s University Hospital Brno (Czechia). The SOZ was identified visually by board-certified epileptologists. Within each patient, a proportion of resected SOZ contacts was calculated and tested against the different thresholds of a good post-surgical outcome, defined as Engel IA (completely seizure-free) or Engel IA-D (good outcome). Furthermore, 30 minutes of SEEG recorded during non-rapid eye movement was used to train a logistic regression model based on the following interictal markers of the EZ: interictal epileptiform discharges, relative entropy, and spectral power in the beta band (Klimes et al. Epilepsia 2024). Similarly to the SOZ, a proportion of resected predicted contacts was calculated. Statistical differences were tested using the Mann-Whitney U test and Cliff's delta effect size.
Results: There was no statistically significant difference in the proportion of resected SOZ contacts between good post-surgical outcome patients (defined as Engel IA-D, N=25, median [IQR] 0.888 [0.5]) and poor outcome patients (defined as Engel II-IV, N=25, median [IQR] 0.571 [0.604]), p=0.11, small effect size 0.26. Interictal markers showed similar trends with median [IQR] 0.307 [0.446] for good outcome patients and median [IQR] 0.2 [0.298] for poor outcome patients, p=0.058, small effect size 0.31. When the good post-surgical outcome was defined as Engel IA, there was a significant difference in the proportion of resected SOZ contacts between seizure-free (N=18, median [IQR] 1.0 [0.421]) and poor (N=32, median [IQR] 0.531 [0.619]) outcome patients, p=0.009, medium effect size 0.44. Interictal markers showed similar trends with median [IQR] 0.406 [0.401] for seizure-free patients and 0.211 [0.237] for poor outcome patients, p=0.011, medium effect size 0.44.
Conclusions: Larger proportions of resected SEEG contacts, identified as EZ, are associated with improved seizure-free outcomes. Interictal markers derived from 30 minutes of SEEG recording achieve similar results as the evaluation of the SOZ. Smaller proportions of resected contacts identified by the machine learning algorithm suggest a higher sensitivity of interictal markers to the EZ.
Funding:
Ministry of Health of the Czech Republic, project NU22-08-00278; Czech Science Foundation, project 22-28784S.