Authors :
Presenting Author: Haruo Yamanaka, MD – Kyoto University Graduate School of Medicine
Kiyohide Usami, MD, PhD – Kyoto University Hospital
Hirofumi Takeyama, MD, PhD – Kyoto University Graduate School of Medicine
Katsuya Kobayashi, MD, PhD – Kyoto University Graduate School of Medicine
Masao Matsuhashi, MD, PhD – Kyoto University Graduate School of Medicine
Takayuki Kikuchi, MD, PhD – Kyoto University Graduate School of Medicine
Yoshiki Arakawa, MD, PhD – Kyoto University Graduate School of Medicine
Akio Ikeda, MD, PhD – Kyoto University Graduate School of Medicine
Riki Matsumoto, MD, PhD – Kyoto University Graduate School of Medicine.
Rationale:
Afterdischarges (ADs) are frequently encountered byproducts of cortical electrical stimulation (ES). ADs consist of repetitive epileptiform discharges, rhythmic waves, or a combination of both, occurring following ES. Despite the epileptiform appearance, the utility of ADs for localizing the seizure onset zone (SOZ) remains controversial, as ES induces ADs in both epileptic and non-epileptic cortices. Notably, ADs often appear in regions remote from the stimulation site, although the underlying mechanisms also remain unclear. Single-pulse ES elicits cortico-cortical evoked potentials (CCEPs), which serve as a measure of effective connectivity between cortical regions. In this study, we investigated whether CCEPs can delineate the network underlying ADs. Furthermore, we hypothesized that ADs occurring outside the CCEP-estimated network may be more likely to originate from the SOZ.Methods:
We recruited eight patients with intractable focal epilepsy (age range: 16–61 years; male/female = 6/2) who underwent subdural electrode implantation for presurgical evaluation at Kyoto University Hospital between 2013 and 2016. Both 50 Hz functional mapping and CCEPs were conducted in these patients. ADs were defined as rhythmic activity or repetitive spikes initiating within 2 seconds after the cessation of 50 Hz ES and lasting for more than 5 seconds. For CCEPs, electrocorticograms were time-locked and averaged across 60 trials of single-pulse electrical stimulation (SPES). N1was defined as a negative peak occurring within 10–50 ms after stimulation, and the N2 as one occurring within 50–200 ms. Those activities were considered as significant only when their amplitudes exceeded 6 standard deviations (SD) above the baseline activity. We investigated the relationship between the occurrence rates of ADs and N1, and N2 in response to stimulation of all electrode pairs among the implanted electrodes.
Results:
A total of 757 electrodes (mean ± SD: 94.6 ± 8.4 electrodes) and 316 electrode pairs (mean ± SD: 39.5 ± 5.8 pairs) were analyzed. The overall occurrence rates were 12.4% for ADs, 37.5% for N1, and 47.8% for N2. The presence of ADs was significantly associated with the occurrence of N1, N2, or either (N1: 71.8%, N2: 81.5%, either: 87.5%; all p < 0.001). In the SOZ, the occurrence rate of ADs without N1, N2, or either was significantly higher than that in non-SOZ (p = 0.01, 0.002, and < 0.001, respectively). In contrast, the occurrence rates of ADs accompanied by N1, N2, or either were not significantly different between SOZ and non-SOZ (p = 0.66, 0.57, and 0.56, respectively).