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(Abst. 2.048), 2018

Chronic Ambulatory ECoG Seizure Onset Patterns in Mesial Temporal Lobe Epilepsy
Authors: George Nune, University of Southern California; Babak Razavi, Stanford University Medical Center; Erik J. Kobylarz, Dartmouth-Hitchcock Medical Center; Sharanya Arcot Desai, NeuroPace, Inc.; Tara L. Skarpaas, NeuroPace, Inc.; and Martha J. Morrell, Stanford University / NeuroPace, Inc.
Content: Rationale: The RNS® System provides brain-responsive neurostimulation for the treatment of adults with medically intractable partial onset seizures and records snapshots of ambulatory electrocorticographic (ECoG) activity as patients go about their daily lives. The present study assessed the morphology at the onset of electrographic seizures from the mesial temporal lobe (the seizure onset pattern) and assessed relationships between the seizure onset pattern (SOP) and time after implant, patient clinical characteristics, and change in seizure frequency with responsive stimulation. Methods: The SOPs were analyzed for 59 patients with MTLE who had at least one depth lead placed in the hippocampus. Electrographic seizures were identified by visual review of all stored ECoG records during months 1 and 5 post-implant. SOPs were categorized into 5 general categories (Table 1) by independent review of two epileptologists (GN and BR) with a third epileptologist (EK) serving as a tiebreaker. The most frequent type of SOP was identified for each patient. The presence or absence of mesial temporal sclerosis (MTS) and changes in patient-reported clinical seizure frequency were collected as part of the clinical trial. Changes in clinical seizure frequency were calculated for the most recent 3 months compared to the pretreatment baseline as of 11/01/2016. Results: For the majority of patients, the predominant SOP was similar between months 1 and 5 after implantation. Across all patients, low voltage fast (LVF; n=18) and hypersynchronous (Hyp; n=16) were the most common across all 5 SOPs. No differences in clinical response were observed with the 5 different SOPs; the median percent change in seizure frequency for each of the SOPs ranged from -65 to -76.5%.Differences in the most common SOP were observed between patients with (n=32) and without (n=27) MTS. For patients with MTS, Hyp was the most common SOP (13/32 = 40.6% of patients); for patients without MTS, LVF was the most common SOP (12/27 = 44.4% of patients). For LVF SOPs, the median % change in clinical seizure frequency was -51.6% (IQR: -33.6 to -77.5%) for patients with MTS and -83% (IQR: -53.4 to -100%) for patients without MTS (n=12). For Hyp SOPs, the median % change in clinical seizure frequency was -70% (IQR: -62.5 to -100%) for patients with MTS (n=13). Hyp was the predominant SOP for only 3 subjects without MTS; their change in seizure frequency was 153%, 47% and -40%. Conclusions: The predominant SOPs within a patient did not differ between months 1 and 5, suggesting that a patient’s SOP is not altered by the implant effect [Sun et al., 2018]. Consistent with the literature, the predominant SOP recorded by the RNS System may be influenced by the underlying pathology [Perucca et al., 2014; Frauscher et al., 2017]. Finally, clinical outcomes may vary within SOPs when comparing patients with and without sclerosis; however, the sample size is too small to make a definite conclusion. Funding: None
Figure 1