The accurate definition of the seizure onset zone (SOZ) is a central problem in drug-resistant epilepsies. Signal processing methods may be used to complement the interpretation of SEEG recordings by quantifying interictal events and SOZ. In this chapter, we will describe some of these methods and focus on insular epilepsies with some detailed case examples.
Introduction Epilepsy surgery is the only curative treatment for patients with drug-resistant focal epilepsy. Stereoelectroencephalography (SEEG) is the gold standard to delineate the seizure-onset zone (SOZ). However, up to 40% of patients are subsequently not operated as no focal non-eloquent SOZ can be identified. The 5-SENSE Score is a 5-point score to predict whether a focal SOZ is likely to be identified by SEEG. This study aims to validate the 5-SENSE Score, improve score performance by incorporating auxiliary diagnostic methods and evaluate its concordance with expert decisions. Methods and analysis Non-interventional, observational, multicentre, prospective study including 200 patients with drug-resistant epilepsy aged ≥15 years undergoing SEEG for identification of a focal SOZ and 200 controls at 22 epilepsy surgery centres worldwide. The primary objective is to assess the diagnostic accuracy and generalisability of the 5-SENSE in predicting focality in SEEG in a prospective cohort. Secondary objectives are to optimise score performance by incorporating auxiliary diagnostic methods and to analyse concordance of the 5-SENSE Score with the expert decisions made in the multidisciplinary team discussion. Ethics and dissemination Prospective multicentre validation of the 5-SENSE score may lead to its implementation into clinical practice to assist clinicians in the difficult decision of whether to proceed with implantation. This study will be conducted in accordance with the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans (2014). We plan to publish the study results in a peer-reviewed full-length original article and present its findings at scientific conferences. Trial registration number NCT06138808 .
Les epilepsies « focales » sont des maladies affectant specifiquement certains reseaux cerebraux. Cette these vise a approfondir, l'investigation de ces reseaux etudiee par des enregistrements intracrâniens (stereoelectroencephalographie - SEEG) dans le cadre de l'evaluation prechirurgicale de l'epilepsie. A cette fin, nous avons applique des methodes d'analyse de signaux en se basant sur des biomarqueurs neurophysiologiques de l'epileptogenicite. Dans le premier travail, nous avons etudie la relation entre le neocortex et l'heterotopie nodulaire, une malformation du developpement cortical. On a demontre que le neocortex ou le neocortex avec la lesion heterotopique, est la structure leader du reseau epileptique et finalement la lesion malformative est tres rarement la region la plus epileptogene. Dans le second travail, nous avons etudie la relation entre le neocortex et d'autres noyaux sous-corticaux, en particulier le thalamus. Nous avons demontre que le degre d'epileptogenicite du thalamus est en correlation directe avec l'extension du reseau epileptique et est associe a un mauvais resultat chirurgical. La troisieme etude a ete effectuee sur des enregistrements intracerebraux et de surface simultanes, SEEG -magnetoencephalographie (MEG). Nous avons pu demontre, par le biais d'une analyse en composantes independantes (ICA) sur la MEG, que les reseaux epileptiques des structures cerebrales profondes peuvent etre recuperes par des enregistrements de surface. Ces resultats confirment que l'analyse quantifiee du signal est un outil puissant pour la comprehension des reseaux epileptiques complexes etudies par les enregistrements intracerebraux et la MEG.
Objective High‐frequency oscillations (HFOs) in intracerebral EEG (stereoelectroencephalography; SEEG) are considered as better biomarkers of epileptogenic tissues than spikes. How this can be applied at the patient level remains poorly understood. We investigated how well HFOs and spikes can predict epileptogenic regions with a large spatial sampling at the patient level. Methods We analyzed non‐REM sleep SEEG recordings sampled at 2,048Hz of 30 patients. Ripples (Rs; 80–250Hz), fast ripples (FRs; 250–500Hz), and spikes were automatically detected. Rates of these markers and several combinations—spikes co‐occurring with HFOs or FRs and cross‐rate (Spk⊗HFO)—were compared to a quantified measure of the seizure onset zone (SOZ) by performing a receiver operating characteristic analysis for each patient individually. We used a Wilcoxon signed‐rank test corrected for false‐discovery rate to assess whether a marker was better than the others for predicting the SOZ. Results A total of 2,930 channels was analyzed (median of 100 channels per patient). The HFOs or any of its variants were not statistically better than spikes. Only one feature, the cross‐rate, was better than all the other markers. Moreover, fast ripples, even though very specific, were not delineating all epileptogenic tissues. Interpretation At the patient level, the performance of HFOs is weakened by the presence of strong physiological HFO generators. Fast ripples are not sensitive enough to be the unique biomarker of epileptogenicity. Nevertheless, combining HFOs and spikes using our proposed measure—the cross‐rate—is a better strategy than using only one marker. Ann Neurol 2018;83:84–97
Abstract Objective Hyperkinetic epileptic seizures (HKS) are difficult to characterize and localize according to semiologic features. We propose a multicriteria scale to help visual analysis and report results of cerebral localization. Methods We assessed seizures from 37 patients with HKS, explored with stereoelectroencephalography during presurgical evaluation. We used a multicriteria scale (hyperkinetic seizure scale [HSS]) with 10 semiologic features, scored independently by two neurologists. The item scores were used to group seizures using the k‐means method. Semiologic features were correlated with the seizure onset zone (SOZ) localization (temporal, prefrontal dorsolateral, prefrontal ventromesial, parietal, insular). Results Fifty‐five seizures were analyzed, and each item of the HSS was compared between the two examiners with good interrater agreement (85.3%). Dystonia, integrated behavior, and bilateral or unilateral hyperkinetic movements were statistically significant according to localization. Three clusters were identified according to the HSS and correlated with different patterns of anatomic localization of SOZ. Cluster 1 was characterized clinically by asymmetric hyperkinetic movements associated with marked dystonia and vocalization. It mainly included parietal seizures. Cluster 2 was characterized by bilateral and symmetrical stereotyped hyperkinetic movements without dystonia. It represented half of temporal seizures and one‐third of prefrontal seizures (dorsolateral). Cluster 3 was characterized by seizures with strong emotionality and vocalization with bilateral and symmetrical hyperkinetic movements and integrated behavior. It involved half of temporal seizures and a majority of prefrontal (ventromesial) seizures. Significance We propose a first attempt to quantify clinical patterns of HKS. The HSS may help to predict SOZ localization according to three main groups of hyperkinetic seizures.
Abstract The psychological impact of intracerebral electroencephalography (stereoelectroencephalography [SEEG]) including the thermocoagulation procedure has not yet been clearly studied. We present a case of a patient who, following an SEEG procedure for presurgical evaluation of intractable focal epilepsy, developed severe symptoms of posttraumatic stress disorder. Such an occurrence may be under‐estimated. Perceived traumatic exposure during SEEG and the development of posttraumatic psychological symptoms should be further studied in order to define risk factors and to improve the monitoring and psychological management of patients during their hospitalization. A careful and systematic procedure of prevention and support before, during, and after SEEG could decrease the risk of development or worsening of symptoms of anxiety, depression, and posttraumatic stress disorder.
Stereo-electroencephalography (SEEG)-guided radiofrequency thermocoagulation (RF-TC) aims at modifying epileptogenic networks to reduce seizure frequency. High-frequency oscillations (HFOs), spikes, and cross-rate are quantifiable epileptogenic biomarkers. In this study, we sought to evaluate, using SEEG signals recorded before and after thermocoagulation, whether a variation in these markers is related to the therapeutic effect of this procedure and to the outcome of surgery.Interictal segments of SEEG signals were analyzed in 38 patients during presurgical evaluation. We used an automatized method to quantify the rate of spikes, rate of HFOs, and cross-rate (a measure combining spikes and HFOs) before and after thermocoagulation. We analyzed the differences both at an individual level with a surrogate approach and at a group level with analysis of variance. We then evaluated the correlation between these variations and the clinical response to RF-TC and to subsequent resective surgery.After thermocoagulation, 19 patients showed a clinical improvement. At the individual level, clinically improved patients more frequently had a reduction in spikes and cross-rate in the epileptogenic zone than patients without clinical improvement (p = .002, p = .02). At a group level, there was a greater decrease of HFOs in epileptogenic and thermocoagulated zones in patients with clinical improvement (p < .05) compared to those with no clinical benefit. Eventually, a significant decrease of all the markers after RF-TC was found in patients with a favorable outcome of resective surgery (spikes, p = .026; HFOs, p = .03; cross-rate, p = .03).Quantified changes in the rate of spikes, rate of HFOs, and cross-rate can be observed after thermocoagulation, and the reduction of these markers correlates with a favorable clinical outcome after RF-TC and with successful resective surgery. This may suggest that interictal biomarker modifications after RF-TC can be clinically used to predict the effectiveness of the thermocoagulation procedure and the outcome of resective surgery.
