Director, Regional Epilepsy Program Kaiser Permanente Sacramento Medical Center Sacramento, California
Rationale: The NeuroPace RNS is FDA-approved closed-loop system providing responsive stimulation treatment to the epileptic focus/foci when a seizure is being detected. Apart from treatment, long-term ambulatory electrocorticography (EcoG) provided by RNS systems also has diagnostic implication. Seizure onset lateralization/localization is a pre-request for RNS implantation. A few clinical researches reported better seizure treatment outcome when the RNS device is implanted close to the seizure onset zone. Other papers reported good seizure treatment outcome if the RNS is stimulating the epileptic network. Therefore, it remains debatable how close the device should be, within the vicinity of the seizure onset zone verses within the seizure propagation network. We reported a unique case with dual RNS implantation, guided by careful investigation of recorded long-term ambulatory EcoG along with other clinical data. Methods: Case report analyzing scalp EEG, invasive sEEG (stereo-EEG), long-term ambulatory EcoG data provided by RNS, along with clinical data of seizure frequency and severity. Results: Forty-four-year-old right-handed man had medically refractory seizure due to left temporal ganglioglioma status post resection at age 24. He was seizure free for three years before recurrence. Seizure occurred one to two times every month with semiology of deja vu aura; lip smacking, and funny looking when having seizure. He was amnestic to the seizure and had three to five days of post-ictal confusion and declined cognitive function. Phase I study was able to record typical events, the semiology indicated left temporal seizures spreading to the right temporal regions. However, scalp EEG failed to provide lateralization information. He then had phase II invasive monitoring with bi-temporal sEEG coverage, which confirmed R mesial temporal onset seizures. Left side onset seizure was not clearly seen, but there was some independent repetitive sharp wave activity from the left insula at times. RNS with right hippocampal depth and subtemporal strip was implanted. Since the implantation, the patient continued to have monthly events. After two-year follow up with the initial RNS implantation, the RNS stimulation did not exert effects on reducing either the seizure frequency or the severity. It was also concerning if he had left temporal onset seizures as he reported clinical events without RNS EcoG correlates. He was instructed to use magnet swiping to time-stamp the seizure events. EcoG data showed 10-20 seconds delay between magnet swiping and the onset of right temporal ictal pattern (Figure 1). A repeat Phase I study confirmed the clinical onset of seizures were 10-20 seconds proceeding to the RNS EcoG recording. Based on all the available data, a second RNS device was implanted targeting the left hippocampal tail and left insula. Ambulatory EcoG data from these dual RNS devices showed that the left insular ictal pattern preceded the right temporal lobe seizures (Figure 2), and such seizures were all correlated with reported clinical events. At one-year follow up post the second RNS implantation, the patient had, by average, one seizure every two months, with a five-month seizure-free interval. A 50% reduction of seizure frequency was noted. The treatment outcome achieved expected efficacy. Conclusions: Data from our case presents the possibility that seizures recorded with the first RNS device may represent a spread pattern from seizure onset zone that are not sampled by electrodes, which may explain why our patient's non-responding to the RNS stimulation. The investigation of ambulatory EcoG data provided valuable information to guide the second RNS device implantation with in the more close vicinity of the seizure onset zone, which leads to a better seizure control outcome. Funding: Please list any funding that was received in support of this abstract.: None
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