Abstracts

Rationale: Electrical stimulation is performed for functional mapping in patients with drug resistant focal epilepsy undergoing stereoelectroencephalography (sEEG). Resection of brain regions which include electrode contacts that evoke typical seizures during low or high frequency stimulation may be associated with better postoperative outcomes, but evidence for the utility of stimulation-induced seizures in children is sparse.^1,2,3

Methods: We retrospectively studied patients who underwent sEEG evaluation at Children’s Hospital of Philadelphia (CHOP) from 2018-2022 (n=77, age range 1.5-19 years, median 12 years). A subset underwent high frequency stimulation (n=42) with functional mapping as part of their clinical evaluation, and some (n=23) participated in research-based low frequency stimulation (13 had both). Stimulation consisted of biphasic pulses in bipolar configuration at either 1 Hz, 30 s, 300 to 500 µs pulse width, 2 to 4 mA amplitude (low frequency) or 50 Hz, 3 s, 500 to 1000 µs pulse width,1 to 4 mA amplitude (high frequency). The CHOP institutional review board approved this study. Informed consent was obtained from parents or guardians, and assent was obtained from subjects when applicable.

Results: During high frequency stimulation, 28/42 patients (67%) had seizures, of which 20 (71%) were typical in semiology. During low frequency stimulation, 5/23 patients (22%) had seizures, of which 5 (100%) were typical in semiology. During low frequency stimulation, we observed abnormal responses such as high frequency oscillations, delayed responses, and repetitive responses in addition to the normal early response. Subsequently, patients had surgical resection (n=41), RNS placement (n=19), DBS placement (n=2), VNS implantation (n=6), or no further surgical intervention (n=10). Etiology, based on imaging and histopathology, was focal cortical dysplasia (FCD; n=23), hippocampal abnormalities (n=6), Rasmussen encephalitis (n=4), polymicrogyria (n=1), low-grade tumors (n=3), vascular malformations (n=1), or unknown (n=4). For 33 patients with >12 months follow up, 16 had high frequency, 8 had low frequency, and 12 had no stimulation performed during sEEG. At 12 months, 82% of the 33 patients had a good outcome (Engel class 1 or ILAE class 1-3). For 19 patients with concordant stimulated and spontaneous seizure onsets, all 9 patients who went on to resection had good outcomes. In 8 patients with discordant seizure onset patterns, 2 of 4 who went on to resection had good outcomes.

Conclusions: High and low frequency electrical stimulation during sEEG in pediatric patients yields rates of typical seizure generation which are consistent with findings in adult studies. Therefore, using stimulation to elicit seizures and abnormal responses may provide additional information to inform surgical decision making and improve seizure outcomes in pediatric patients.

References:
1. Cuello-Oderiz C et al. JAMA Neurology. 2019;76(9)
2. Jobst B et al. Epilepsy Currents. 2020;20(4)
3. Trebuchon A et al. J Neurol Neurosurg Psychiatry. 2021;92(1)

Funding: ReConNecT-IT T32 (to CA)