Rationale:
Surgical resection or ablation of the seizure focus can be curative in patients with drug resistant epilepsy (DRE); multiple seizure foci may exclude surgical candidacy. Patients with DRE can experience seizures in clusters. It is not established if seizures originating in a cluster are typically unifocal or multifocal. Data from recordings in epilepsy monitoring units typically are done with antiseizure medication (ASM) reductions designed to facilitate more frequent seizures.
Recent investigations using data from the Neuropace RNS system (responsive neurostimulation) provide unique opportunities to study long-term recordings from intracranial electrodes in humans with multifocal DRE on chronic ASM therapy. The long-term recordings from the RNS in patients with bilateral independent temporal onset seizures can be used to assess such characteristics as seizure clustering or predominance of one seizure focus. We hypothesize that the laterality of a cluster of seizures is different compared to seizures occurring outside of clusters.
Methods:
We reviewed 36 patients from our center with implanted RNS device. Seizures from four patients with bitemporal lobe epilepsy were studied.
Each patient had bilateral mesial temporal RNS depth electrode arrays. Data from the RNS Patient Data Management System were collected from October 2021 to October 2022 and reviewed by board-certified epileptologist and senior neurology resident for seizure validation, onset, lateralization, and spread.
Results:
A total of 469 events captured by the RNS device were reviewed from the four patients. Seizures occurrence was confirmed in 343 of the long events recordings. Patients displayed a predominant laterality in seizure onset (right sided frequency: 69%, 38%, 37%, and 4.5%, respectively). Many seizures throughout all patients exhibit various degrees of spread contralaterally. Seizure onset and laterality were analyzed to assess clustering effects within timeframes of one, two, four, six, 12, 24, and 48 hours. Three of the four patients displayed a significant predominance in laterality when seizures clustered in time. The most predominant influence of inter-seizure interval appeared for clusters of less than six hours. Patient #1 showed a 61% ratio of right vs. left onset seizures compared to 32% ratio outside of a 4h cluster (Figure 1). The cluster effect was even more dramatic for Patient #2, where there was a 92% right vs. left ratio of seizure onset within the 6h cluster whereas the ratio is only 38% outsize the cluster. (Figure 2).
Conclusions:
Long-term RNS recordings in four patients with bitemporal epilepsy were analyzed for seizure occurrence within clustered timeframes. Patients exhibit a significant predominance in laterality when seizures occurred within shorter intervals. This information provides valuable insight into clustering effects in patients with multifocal DRE. As chronic RNS data in patients with multifocal epilepsy is being used more for diagnostic purposes (e.g., determination of a predominant seizure focus) to expand surgical treatment options in patients previously deemed poor surgical candidates, the effects of seizure clustering on focal predominance must be considered.
Funding: NA