Authors :
Presenting Author: Puneet Jain, MD,DM – The Hospital For Sick Children
Ayako Ochi, Neurophysiologist – The Hospital For Sick Children; Hiroshi Otsubo, Neurophysiologist – The Hospital For Sick Children; Rohit Sharma, Manager, Neurophysiology – Hospital for Sick Children; Shelly Weiss, Professor – The Hospital For Sick Children; Elizabeth Donner, Professor – Hospital for Sick Children
Rationale:
Recent evidence in adults has demonstrated that stimulation-induced seizures (SIS) can identify ictal onset zone as reliably as spontaneous seizures do. Further, the occurrence of SIS predicted a more favourable seizure outcome after surgery. This study aimed to explore the effectiveness of low frequency stimulation in provoking SIS in children with drug-resistant epilepsy undergoing stereo-EEG (SEEG) evaluations.Methods:
This retrospective study enrolled children aged two to eighteen years of age with drug-resistant focal epilepsy who underwent SEEG evaluation between January 2018 and June 2023. Consecutive children who underwent extra-operative direct electrical cortical stimulation for seizure induction were included. All children underwent detailed phase one non-invasive presurgical evaluations. SEEG was done in selected patients to delineate epileptogenic zone, guide boundaries for resection or map the eloquent cortex. Direct electrical cortical stimulation (DCES) for seizure induction was only performed in children who did not have spontaneous seizures or who showed wide apparent ictal onset zone on SEEG with spontaneous seizures, to possibly identify “critical” electrodes for seizure generation within a wider epileptic network. Bipolar electrical stimulation was performed and the stimulation parameters consisted of biphase square waveforms at frequency of 1 Hz, pulse width one millisecond, and train duration 20 seconds. The currents were gradually increased from 1 mA to a maximum of 3 mA. The stimulations were repeated every 30 to 60 seconds once the EEG activity returned to baseline on SEEG.
Results:
Fourteen patients were included (57.1% girls). The mean age at seizure onset and duration of epilepsy were 3.9 and 8.2 years, respectively. Nine patients (64.3%) had daily seizures and had failed a median of 5 anti-seizure medications. Six (42.9%) had significant neurological co-morbidities. MRI brain showed a lesion/possible lesion in all except one. Two patients had Tuberous Sclerosis complex, two had pathogenic variant in GATOR1 complex genes and one had
SLC6A1 related epilepsy. SEEG coverage was unilateral in 10 (six over right hemisphere) and bilateral in four patients. A mean of 13.2 ten- or fourteen-contact electrodes were used. All had spontaneous seizures before DCES except one. DCES was perfomed after a median of five days. SIS were seen in four patients (28.6%) and all were habitual seizures. The ictal onset zones included: orbitofrontal (1), anterior (1) and middle (1) insula, and anterior cingulate (1). Only orbitofrontal electrode had inter-ictal ripples ( >80 Hz); rest of the electrodes had no interictal HFOs. Regions provoking SIS were ablated in three patients; one had class 1 outcome and other two had class 5 outcomes.
Conclusions:
Low frequency stimulation was well tolerated in children and provoked habitual SIS in 28.6% of patients. The results from the electrical stimulation for seizure induction need to be interpreted along with ictal SEEG data from spontaneous seizures (if obtained), interictal data and the presurgical evaluation/hypothesis.
Funding: None