Changes in epileptogenicity biomarkers after stereotactic thermocoagulation

Abstract

Objective 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. Methods 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. Results 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). Significance 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.

In pursuit of the epileptogenic zone in focal epilepsy: A dynamical network biomarker approach

“…CT-scan/MRI data co-registration was performed, to check the anatomical location of each contact along the electrode’s trajectory, using the open-source software GARDEL ((Medina Villalon et al, 2018). For each patient, clinicians associated to each bipolar channel a ROI tagged as EZ, PZ or non-identified (NI), based on the Epileptogenicity Index method (Bartolomei et al, 2008), full details on the data acquisition and EZ designation by clinicians are provided in (Bartolomei et al, 2008; Contento et al, 2021). Time intervals of the order of one to 20 seconds around the clinicians specified seizure onset time were analyzed.…”

Changes in local and network brain activity after stereotactic thermocoagulation in patients with drug‐resistant epilepsy

“…Channels were labeled as either thermocoagulated (TC) or not (non-TC) and as either involved (INV) or noninvolved (non-INV) in the epileptogenic network. 7 Involved channels included channels in the epileptogenic zone and in the propagation zone (as defined by clinicians during the SEEG clinical investigation). The remaining channels were labeled as noninvolved.…”

“…Recent studies have shown that RF-TC induces changes in the rates of epileptic spikes and high-frequency oscillations that are related to the clinical outcome of the procedure. 6,7 It is now established that epilepsy is a network disease, affecting spread brain areas rather than a focal region. [8][9][10] Russo and colleagues 11 recently demonstrated that thermocoagulation-induced focal lesions lead to an increase of slow wave activity (delta band range, 0.5 Hz to 4 Hz) both in the perilesional area and in the regions connected to that area.…”

“…According to a recent meta‐analysis including accounts for 162 patients, about 67% of subjects show a >50% decrease in seizure frequency after RF‐TC, which lasts for >12 months in 48% of them. Recent studies have shown that RF‐TC induces changes in the rates of epileptic spikes and high‐frequency oscillations that are related to the clinical outcome of the procedure 6,7 …”

“…We thus sought to evaluate, by means of SEEG recordings before and after RF‐TC, whether a variation of the functional brain network properties induced by this procedure exists and, in such case, whether it is related to the clinical outcome. To this end, we assessed local (spectral power) and network (FC) changes in electrical brain activity for a period closely following RF‐TC in a retrospective cohort of patients who underwent SEEG investigation 7 and compared the findings between the clinical responders and nonresponders.…”