Abstracts

Rationale:
Responsive neurostimulation (RNS) is a therapeutic option for medically refractory focal epilepsy not amenable to epilepsy surgery.  However, its pediatric application, particularly in patients younger than 12 years has been limited despite its safety and efficacy in adults. 
Method:
Here, we present 2 pediatric patients who underwent RNS implantation, providing evidence for safety and efficacy of RNS in pediatric populations.
Results:
The first patient is a 9-year-old female with refractory focal epilepsy from left parietal region, supplemental motor area/motor cortex, allowing incomplete resection (2015). Repeat SEEG (2017) confirmed seizure onset in motor cortex/supplementary motor area.     The patient was implanted with NeuroPace closed loop RNS in April 2019 at age 8, with 4-5 seizure clusters/day. Two cortical strips with 10mm intercontact spacing were placed > 1cm apart in left frontoparietal cortex, with initial device settings in detection mode to collect electrocorticographic information on magnet swipes for aura, ictal events, signal saturation and long episodes of ≥ 20 seconds.   Between implantation and March 2020, detection changes were made to increase detector specificity for patient’s seizure types. Incrementally stimulation changes increased charge by 0.5uC/cm2 after beginning at 0.5uC/cm2. Changes were made to the time parameter for storing long episodes (from 20 seconds to 25 seconds), to eliminate shorter electrographic events that weren’t proven to be clinically significant. Figures 1 to 3 show seizure examples. Some, but not all, are categorized with attenuation in signal prior to events (Fig 1C). Other events begin with slow, rhythmic patterns (Figs 1A,B).   The patient, seen every 2-4 months after implant, will continue to be observed with potential future changes as indicated. Currently, she has 1 or 2 seizures monthly.   The second patient is an 18-year-old male who had invasive subdural monitoring with grids/depth electrodes over left posterior frontal/parietal areas resulting in posterior F2 resection in front of motor cortex, without seizure remission. Repeat stereo EEG in 2019, confirmed onset in motor and sensory cortex.    The patient was implanted with NeuroPace closed loop RNS in Dec. 2019, with a baseline seizure history of 1 larger event each month and monthly hand tingling. Two cortical strip leads with 10mm inter-contact spacing were placed adjacently, flanking the motor strip superiorly and inferiorly, with initial device setting in detection mode to collect electrocorticographic information on magnet swipes (marking aura or ictal events), signal saturation and long episodes ≥ 20 seconds.   Between implantation and June 2020, no ictal events were observed. The patient swiped magnet for tingling in his hand without ictal neurophysiology.   First event was seen mid-June lasting 20 seconds, with sharp, slow spikes on the inferior lead (Inf1 – Inf2, figures 2A, B), followed 2 weeks later by a 2nd, electroclinical event starting with low voltage fast activity on channels 2 and 4, (Sup3 – Sup4 and Inf3 – Inf4, respectively, figures 2 C,D). Bandpass filters were added to pre-existing line length detectors to identify ictal activity mimicking onset patterns. Stimulation was turned on in a monopolar montage at a 1.0mA current on each burst of therapy, for a charge density of 0.5uC/cm2.  The threshold for long episodes was shortened to 15 seconds to detect shorter events.    The patient will return in 2 months to review response to current therapy thresholds and to be considered for further changes.
Conclusion:
These results provide preliminary evidence that RNS can be a safe and efficacious therapeutic option for medically refractory seizures originating from eloquent cortical regions in pediatric patients.
Funding:
:None