Authors :
First Author: Ana Suller Marti, MD, MSc, PhD – Western University
Presenting Author: Jorge G Burneo, – Western University
ahdyie Ahmadi, BA – Western University; Nasim Mortazavi, PhD Candidate – Western University; Greydon Gilmore, PhD – Western University; Jorge Burneo, MD – Western University; Jonathan Lau, MD, PhD – Western University; David Steven, MD – Western University; Michelle Jones, MD – Western University; Keith MacDougall, MD – Western University; Julio martinez-Trujillo, MD, PhD – Western University; ana Suller Marti, MD, PhD – Western University
Rationale:
More than 15 million patients with epilepsy suffer from drug-resistant epilepsy (DRE). In these cases, a successful surgical outcome entails the removal or disconnection of the seizure onset zone (SOZ), which is the brain region(s) responsible for seizure initiation. In this regard, finding robust biomarkers of epileptogenicity will help clinicians to accurately localize the SOZ. In focal epilepsies, interictal epileptiform discharges (IEDs) are paroxysmal events observed in both the SOZ and outside the SOZ.
To identify the SOZ and map the eloquent cortex, extraoperative cortical stimulation (ECS) is used during phase II of presurgical investigation. We evaluated the impact of ECS on interictal epileptiform discharges to find biomarkers of epileptogenicity to accurately delimitate the SOZ.
Methods:
In this study, intracranial signals were recorded from five DRE patients implanted with depth electrodes with stereo-electroencephalography (SEEG) for presurgical evaluation. Bipolar and high frequency (50 Hz) ECS was performed with a pulse width of 300 µs and current spanning 1–6 mA. After preprocessing the intracranial recordings, IEDs (spikes, spike-waves, and polyspikes) were automatically detected and their frequency and morphology were compared before and after stimulation. We analyzed IEDs’ changes in channels that generate seizures, after discharges (AD), and ones that had less epileptic activity (normal).
Results:
The number and synchrony of IEDs significantly increased in channels in which ECS triggered seizures (Wilcoxon signed-rank test, p < 0.05). The spike amplitudes showed varying changes, ranging from subtle to significant, including both increases and decreases, across patients. In the detected spike waves, the amplitude of waves increased significantly. However, no significant changes in IEDs’ characteristics were observed in channels with AD or the contacts that had no electrographic changes after the ECS.