Authors :
Presenting Author: Marco Malaga Julca, MD – Baylor College of Medicine
Gina Kayal, MD – Baylor College of Medicine
Christopher Bi, BS – Baylor College of Medicine
Anthony Allam, BS – Baylor Colloge of Medicne
Alisa Lu, BS – Baylor College of Medicine
Sophie Li, BS – Baylor College of Medicine
Zulfi Haneef, MBBS MD – Baylor College of Medicine
Rationale:
Although RNS is suspected to improve seizure outcomes through ictal suppression by direct stimulation, recent studies suggest that network modulation may be another important mechanism. Thus, precise electrode placement in the epileptogenic zone may not be necessary, as long as the stimulation area leads to network-wide effects. We aimed to evaluate whether accurate RNS depth electrode placement in the hippocampus impacted seizure outcomes in patients with presumed hippocampal epilepsy.
Methods:
Patients with RNS depth electrodes placed in either one or both hippocampi were included. RNS electrode location was reconstructed from co-registered pre-op MRI and post-op CT scans through LeadDBS. To delimit the hippocampus, the Melbourne subcortex atlas was used. Distance from each contact to the hippocampus was calculated and averaged. Seizure outcomes were retrospectively obtained through chart review. Patients were classified as responders if there was a decrease of 50% in seizure frequency from baselineA generalized linear model was fitted with both relative clinical and electrographic event reduction as the dependent variable, using average distance to the hippocampus as the independent variable.
Results:
There were 18 patients with hippocampal depth electrodes (16 bilateral, 2 left-sided): 10 were responders (56%) and 8 non-responders (44%) (Fig 1). Clinical seizure average baseline rate was 6.3±7.8, and LE average was 255±326. Following treatment, average seizure reduction was 33.1%, (Responders: 86.5%; Non-responders-34.0%) and average LE reduction was 38.4% (Responders: 29.9%, Non-responders: 49.1%). Our mixed effect model (Fig 2) showed a statistically significant effect of average contact distance to the hippocampus on seizure reduction (β=-3.7, 95% CI -7.1; -0.3, p=0.034), with no significant improvement in the coefficientof determination 0.251, 0.253 and 0.261, respectively). Average distance was not a significant predictor of responder status.
Conclusions:
RNS location accuracy may be a predictor of clinical seizure reduction in patients with temporal depth electrodes for the management of temporal lobe epilepsy . However, further studies can aim in determining whether this improvement is mediated through direct stimulation or network-wide modulation.
Funding: ZH was supported by DoD grant Award # HT94252410355.