Neuromodulation - Science and Practice in Epilepsy: Vagus Nerve Stimulation, Thalamic Deep Brain Stimulation, and Responsive NeuroStimulation

Various pharmacological agents in the pipeline against intractable epilepsy

Epilepsy is a noncommunicable chronic neurological disorder affecting people of all ages, with the highest prevalence in low and middle-income countries. Despite the pharmacological armamentarium, the plethora of drugs in the market, and other treatment options, 30%-35% of individuals still show resistance to the current medication, termed intractable epilepsy/drug resistance epilepsy, which contributes to 50% of the mortalities due to epilepsy. Therefore, the development of new drugs and agents is needed to manage this devastating epilepsy. We reviewed the pipeline of drugs in "ClinicalTrials. gov," which is the federal registry of clinical trials to identify drugs and other treatment options in various phases against intractable epilepsy. A total of 31 clinical trials were found regarding intractable epilepsy. Among them, 48.4% (15) are about pharmacological agents, of which 26.6% are in Phase 1, 60% are in Phase 2, and 13.3% are in Phase 3. The mechanism of action or targets of the majority of these agents are different and are more diversified than those of the approved drugs. In this article, we summarized various pharmacological agents in clinical trials, their backgrounds, targets, and mechanisms of action for the treatment of intractable epilepsy. Treatment options other than pharmacological ones, such as devices for brain stimulation, ketogenic diets, gene therapy, and others, are also summarized.

Neurostimulation treatments for epilepsy: Deep brain stimulation, responsive neurostimulation and vagus nerve stimulation

Epilepsy is a common and debilitating neurological disorder, and approximately one-third of affected individuals have ongoing seizures despite appropriate trials of two anti-seizure medications. This population with drug-resistant epilepsy (DRE) may benefit from neurostimulation approaches, such as vagus nerve stimulation (VNS), deep brain stimulation (DBS) and responsive neurostimulation (RNS). In some patient populations, these techniques are FDA-approved for treating DRE. VNS is used as adjuvant therapy for children and adults. Acting via the vagus afferent network, VNS modulates thalamocortical circuits, reducing seizures in approximately 50 ​% of patients. RNS uses an adaptive (closed-loop) system that records intracranial EEG patterns to activate the stimulation at the appropriate time, being particularly well-suited to treat seizures arising within eloquent cortex. For DBS, the most promising therapeutic targets are the anterior and centromedian nuclei of the thalamus, with anterior nucleus DBS being used for treating focal and secondarily generalized forms of DRE and centromedian nucleus DBS being applied for treating generalized epilepsies such as Lennox-Gastaut syndrome. Here, we discuss the indications, advantages and limitations of VNS, DBS and RNS in treating DRE and summarize the spatial distribution of neuroimaging observations related to epilepsy and stimulation using NeuroQuery and NeuroSynth.

Utility of Chronic Intracranial Electroencephalography in Responsive Neurostimulation Therapy

Responsive neurostimulation (RNS) therapy is an effective treatment for reducing seizures in some patients with focal epilepsy. Utilizing a chronically implanted device, RNS involves monitoring brain activity signals for user-defined patterns of seizure activity and delivering electrical stimulation in response. Devices store chronic data including counts of detected activity patterns and brief recordings of intracranial electroencephalography signals. Data platforms for reviewing stored chronic data retrospectively may be used to evaluate therapy performance and to fine-tune detection and stimulation settings. New frontiers in RNS research can leverage raw chronic data to reverse engineer neurostimulation mechanisms and improve therapy effectiveness.

Patterns of utilization and cost of healthcare services and pharmacotherapy among patients with drug-resistant epilepsy during the two-year period before neurostimulation: A descriptive analysis of the journey to implantation based on analyses of a large United States healthcare claims database

OBJECTIVE

To conduct a descriptive assessment of patterns of utilization and cost of healthcare services and pharmacotherapies among patients with drug-resistant epilepsy (DRE) before neurostimulator implantation.

METHODS

Using a large United States healthcare claims database, we identified all patients with DRE who were implanted with neurostimulators between January 1, 2012, and December 31, 2019. Patients without an epilepsy diagnosis on their implantation date were excluded, as were those without (1) anti-seizure medication (ASM) dispenses within 12 months of implantation date, and (2) continuous enrollment for the 24-month period before this date. Demographic and clinical characteristics were assessed over the two-year period before implantation, as were patterns of utilization and cost of healthcare services and pharmacotherapy. Care was assessed as all-cause or epilepsy-related, with the latter defined as all medical (inpatient and outpatient) care resulting in diagnoses of epilepsy and all ASM dispenses.

RESULTS

Eight hundred sixty patients met all selection criteria. Among these patients, comorbidities were common, including depression (27%), anxiety (30%), and learning disabilities (25%). Fifty-nine percent of patients had ≥1 all-cause hospitalizations; 57% had ≥1 epilepsy-related admissions. Patients averaged 8.6 epilepsy-related visits to physicians' offices, including 5.1 neurologist visits. Mean all-cause and epilepsy-related healthcare costs during the pre-implantation period were $123,500 and $91,995, respectively; corresponding median values were $74,567 and $53,029. Median monthly all-cause healthcare costs increased by 138% during the 24-month period (from $1,042 to $2,481 in the month prior to implantation); median epilepsy-related costs, by 290% (from $383 to $1,492).

CONCLUSIONS

The two-year period before neurostimulator implantation is a long and costly journey. Estimates likely minimize the burden experienced during this period, given that seizure frequency and severity-and corresponding impacts on quality of life-were unavailable in these data. Further research is needed to understand the clinical, economic, and psychological impact of the time between DRE onset and implantation among qualifying patients.

Deep brain stimulation of thalamus for epilepsy

Neuromodulation (neurostimulation) is a relatively new and rapidly growing treatment for refractory epilepsy. Three varieties are approved in the US: vagus nerve stimulation (VNS), deep brain stimulation (DBS) and responsive neurostimulation (RNS). This article reviews thalamic DBS for epilepsy. Among many thalamic sub-nuclei, DBS for epilepsy has been targeted to the anterior nucleus (ANT), centromedian nucleus (CM), dorsomedial nucleus (DM) and pulvinar (PULV). Only ANT is FDA-approved, based upon a controlled clinical trial. Bilateral stimulation of ANT reduced seizures by 40.5% at three months in the controlled phase (p = .038) and 75% by 5 years in the uncontrolled phase. Side effects related to paresthesias, acute hemorrhage, infection, occasional increased seizures, and usually transient effects on mood and memory. Efficacy was best documented for focal onset seizures in temporal or frontal lobe. CM stimulation may be useful for generalized or multifocal seizures and PULV for posterior limbic seizures. Mechanisms of DBS for epilepsy are largely unknown, but animal work points to changes in receptors, channels, neurotransmitters, synapses, network connectivity and neurogenesis. Personalization of therapies, in terms of connectivity of the seizure onset zone to the thalamic sub- nucleus and individual characteristics of the seizures, might lead to improved efficacy. Many questions remain about DBS, including the best candidates for different types of neuromodulation, the best targets, the best stimulation parameters, how to minimize side effects and how to deliver current noninvasively. Despite the questions, neuromodulation provides useful new opportunities to treat people with refractory seizures not responding to medicines and not amenable to resective surgery.

Impact of Vagus Nerve Stimulation for the Treatment of Drug-Resistant Epilepsy on Patterns of Use and Cost of Health Care Services and Pharmacotherapy: Comparisons of the 24-Month Periods Before and After Implantation

PURPOSE

This study examines the impact of vagus nerve stimulation (VNS) as treatment for drug-resistant epilepsy (DRE) on the use and cost of health care services and pharmacotherapy.

METHODS

Using a large US health care claims database, we identified all patients with DRE who underwent VNS between January 1, 2012 and December 31, 2019. VNS implantation date was designated as the index date, and patients had to be continuously enrolled for the 24-month period before this date (preindex period). Outcomes included all-cause and epilepsy-related hospitalization, emergency department (ED) visits, and health care costs; health care claims resulting in an epilepsy diagnosis and all claims for antiseizure medications were deemed epilepsy related. Preindex data, except care related to preoperative medical clearance for VNS, were used to estimate multivariate regression models predicting outcomes during the 24-month postindex period (follow-up period). Predicted outcomes during follow-up were then compared with observed values. As a sensitivity analysis, we also replicated all analyses among subgroups defined by comorbid depression.

FINDINGS

A total of 659 patients underwent VNS for DRE and met the selection criteria. For the composite outcome of all-cause hospitalizations and ED visits, observed values were 42% lower than expected during the 24-month follow-up period; for the composite outcome of epilepsy-related hospitalizations and ED visits, observed values were 49% lower (P < 0.001 for both). Observed mean total all-cause costs, inclusive of costs of the procedure, were not significantly different than expected costs by month 19 of follow-up; mean total epilepsy-related costs were comparable by month 18. Findings were similar in subgroups with and without depression, although nominally greater differences (observed - expected) were seen in those with comorbid depression.

IMPLICATIONS

Our findings suggest that VNS is associated with decreased risk of hospitalization or ED visits (all cause and epilepsy related) during the 2-year period subsequent to implantation and may become cost-neutral within 2 years of implantation (vs continued medical management of DRE without VNS). Although expected outcomes were estimated based on the 24-month period before implantation, the degree to which they approximated what would have happened in the absence of VNS is unknowable. Further research is needed to better understand the extend and duration of the impact of VNS on seizure frequency and severity and health-related quality of life, including its performance among those with and without comorbid depression.

The intralaminar thalamus: a review of its role as a target in functional neurosurgery

The intralaminar thalamus, in particular the centromedian-parafascicular complex, forms a strategic node between ascending information from the spinal cord and brainstem and forebrain circuitry that involves the cerebral cortex and basal ganglia. A large body of evidence shows that this functionally heterogeneous region regulates information transmission in different cortical circuits, and is involved in a variety of functions, including cognition, arousal, consciousness and processing of pain signals. Not surprisingly, the intralaminar thalamus has been a target area for (radio)surgical ablation and deep brain stimulation (DBS) in different neurological and psychiatric disorders. Historically, ablation and stimulation of the intralaminar thalamus have been explored in patients with pain, epilepsy and Tourette syndrome. Moreover, DBS has been used as an experimental treatment for disorders of consciousness and a variety of movement disorders. In this review, we provide a comprehensive analysis of the underlying mechanisms of stimulation and ablation of the intralaminar nuclei, historical clinical evidence, and more recent (experimental) studies in animals and humans to define the present and future role of the intralaminar thalamus as a target in the treatment of neurological and psychiatric disorders.

Pulsed-Focused Ultrasound Provides Long-Term Suppression of Epileptiform Bursts in the Kainic Acid-Induced Epilepsy Rat Model

Focused ultrasound (FUS) has potential utility for modulating regional brain excitability and possibly aiding seizure control; however, the duration of any beneficial effect is unknown. This study explores the efficacy and time course of a short series of pulsed FUS in suppressing EEG epileptiform spikes/bursts in a kainic acid (KA) animal model of temporal lobe epilepsy. Forty-four male Sprague-Dawley rats were recorded for 14 weeks with EEG while software calculated EEG numbers of epileptiform spikes and bursts (≥ 3 spikes/s). Four regimens of FUS given in a single session at week 7 were evaluated, with mechanical index (MI) ranging from 0.25 to 0.75, intensity spatial peak temporal average (ISPTA) from 0.1 to 2.8 W per cm2, duty cycle from 1 to 30%, and three consecutive pulse trains for 5 or 10 min each. Controls included sham injections in four and KA without FUS in eleven animals. Histological analysis investigated tissue effects. All animals receiving KA evidenced EEG spikes, averaging 10,378 ± 1651 spikes per 8 h and 1255 ± 199 bursts per 8 h by weeks 6-7. The KA-only group showed a 30% of increase in spikes and bursts by week 14. Compared to the KA-only group, spike counts were reduced by about 25%, burst counts by about 33%, and burst durations by about 50% with FUS. Behavioral seizures were not analyzed, but electrographic seizures longer than 10 s declined up to 70% after some FUS regimens. Repeated-measure ANOVA showed a significant effect of higher intensity and longer sonication duration FUS treatment using 0.75-MI, ISPTA 2.8 W/cm2, 30% duty cycle for 10-min sonications (group effect, F (4, 15) = 6.321, p < 0.01; interaction effect, F (44, 165) = 1.726, p < 0.01), with the hippocampal protective effect lasting to week 14, accompanied by decreased inflammation and gliosis effect. In contrast, spike and burst suppression were achieved using an FUS regimen with 0.25-MI ISPTA 0.5 W/cm2, 30% duty cycle for 10-min sonications. This regimen reduced inflammation and gliosis at weeks 8-14 and protected hippocampal tissue. This study demonstrates that low-intensity pulsed ultrasound can modulate epileptiform activity for up to 7 weeks and, if replicated in the clinical setting, might be a practical treatment for epilepsy.

Comparison of utilization and cost of healthcare services and pharmacotherapy following implantation of vagus nerve stimulation vs. responsive neurostimulation or deep brain stimulation for the treatment of drug-resistant epilepsy: analyses of a large United States healthcare claims database

AIM

Vagus nerve stimulation (VNS), responsive neurostimulation (RNS), and deep brain stimulation (DBS) all are options for drug-resistant epilepsy (DRE). However, little is known about how the choice of neurostimulation impacts subsequent healthcare costs.

MATERIALS AND METHODS

We used a large US healthcare claims database to identify all patients with epilepsy who underwent neurostimulation between 2012 and 2019. Eligible patients were identified and stratified based on procedure received (VNS vs. RNS/DBS). VNS patients were matched by propensity scoring to RNS/DBS patients. Use and cost of healthcare resources and pharmacotherapy were ascertained over the 24-month period following neurostimulation, incorporating all-cause and epilepsy-related measures. Disease-related care was defined based on diagnoses of claims for medical care and relevant pharmacotherapies.

RESULTS

Seven hundred and ninety-two patients met all selection criteria. VNS patients were younger, were prescribed a higher pre-index mean number of anti-seizure medications (ASMs), and had higher pre-index levels of use and cost of epilepsy-related healthcare services. We propensity matched 148 VNS patients to an equal number of RNS/DBS patients. One year following index date (inclusive), mean total all-cause healthcare costs were 50% lower among VNS patients than RNS/DBS patients, and mean epilepsy-related costs were 55% lower; corresponding decreases at the two-year mark were 41% and 48%, respectively.

LIMITATIONS

Some clinical variables, such as seizure frequency and severity, quality of life, and functional status were unavailable in the database, precluding our ability to comprehensively assess differences between devices. Administrative claims data are subject to billing code errors, inaccuracies, and missing data, resulting in possible misclassification and/or unmeasured confounding.

CONCLUSIONS

After matching, VNS was associated with significantly lower all-cause and epilepsy-related costs for the two-year period following implantation. All-cause and epilepsy-related costs remained statistically significantly lower for VNS even after costs of implantation were excluded.

Neuromodulation in epilepsy: state-of-the-art approved therapies

Three neuromodulation therapies have been appropriately tested and approved in refractory focal epilepsies: vagus nerve stimulation (VNS), deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS), and closed-loop responsive neurostimulation of the epileptogenic zone or zones. These therapies are primarily palliative. Only a few individuals have achieved complete freedom from seizures for more than 12 months with these therapies, whereas more than half have benefited from long-term reduction in seizure frequency of more than 50%. Implantation-related adverse events primarily include infection and pain at the implant site. Intracranial haemorrhage is a frequent adverse event for ANT-DBS and responsive neurostimulation. Other stimulation-specific side-effects are observed with VNS and ANT-DBS. Biomarkers to predict response to neuromodulation therapies are not available, and high-level evidence to aid decision making about when and for whom these therapies should be preferred over other antiepileptic treatments is scant. Future studies are thus needed to address these shortfalls in knowledge, approve other forms of neuromodulation, and develop personalised closed-loop therapies with embedded machine learning. Until then, neuromodulation could be considered for individuals with intractable seizures, ideally after the possibility of curative surgical treatment has been carefully assessed and ruled out or judged less appropriate.

Chronic electroencephalography in epilepsy with a responsive neurostimulation device: current status and future prospects

INTRODUCTION

Implanted neurostimulation devices are gaining traction as therapeutic options for people with certain forms of drug-resistant focal epilepsy. Some of these devices enable chronic electroencephalography (cEEG), which offers views of the dynamics of brain activity in epilepsy over unprecedented time horizons.

AREAS COVERED

This review focuses on clinical insights and basic neuroscience discoveries enabled by analyses of cEEG from an exemplar device, the NeuroPace RNS® System. Applications of RNS cEEG covered here include counting and lateralizing seizures, quantifying medication response, characterizing spells, forecasting seizures, and exploring mechanisms of cognition. Limitations of the RNS System are discussed in the context of next-generation devices in development.

EXPERT OPINION

The wide temporal lens of cEEG helps capture the dynamism of epilepsy, revealing phenomena that cannot be appreciated with short duration recordings. The RNS System is a vanguard device whose diagnostic utility rivals its therapeutic benefits, but emerging minimally invasive devices, including those with subscalp recording electrodes, promise to be more applicable within a broad population of people with epilepsy. Epileptology is on the precipice of a paradigm shift in which cEEG is a standard part of diagnostic evaluations and clinical management is predicated on quantitative observations integrated over long timescales.

Experience and consensus on stimulation of the anterior nucleus of thalamus for epilepsy

Deep brain stimulation of the anterior nuclei of thalamus (ANT-DBS) is effective for reduction of seizures, but little evidence is available to guide practitioners in the practical use of this therapy. In an attempt to fill this gap, a questionnaire with 37 questions was circulated to 578 clinicians who were either engaged in clinical trials of or known users of DBS for epilepsy, with responses from 141, of whom 58.2% were epileptologists and 28.4% neurosurgeons. Multiple regions of the world were represented. The survey found that the best candidates for DBS were considered those with temporal or frontal seizures, refractory to at least two medicines. Motivations for renewing therapy upon battery depletion were reduced convulsive, impaired awareness, and severe seizures and improved quality of life. Targeting of leads mainly was by magnetic resonance imaging, sometimes with intraoperative imaging or microelectrode recording. The majority used transventricular approaches. Stimulation parameters mostly imitated the SANTE study parameters, except for initial stimulation amplitudes in the 2-3-V or -mA range, versus 5 V in the SANTE study. Stimulation intensity was most often increased or reduced, respectively, for lack of efficacy or side effects, but changes in active contacts, cycle time, and pulse duration were also employed. Mood or memory problems or paresthesias were the side effects most responsible for adjustments. Off-label sites stimulated included centromedian thalamus, hippocampus, neocortex, and a few others. Several physicians used DBS in conjunction with vagus nerve stimulation or responsive neurostimulation, although our study did not track efficacy for combined use. Experienced users varied more from published parameters than did inexperienced users. In conclusion, surveys of experts can provide Class IV evidence for the most prevalent practical use of ANT-DBS. We present a flowchart for one protocol combining common practices. Controlled comparisons will be needed to choose the best approach.

Compositional and morphological properties of platinum-iridium electrodeposited on carbon fiber microelectrodes

Objective. Neural interfaces based on carbon fiber (CF) electrodes have demonstrated key positive attributes such as minimal foreign body response and mechanical strength to self-insert in brain tissue. However, carbon does not form a low impedance electrode interface with neural tissue. Electrodeposited platinum iridium (PtIr) has been used to improve electrode interface properties for metallic bioelectrodes.Approach. In this study, a PtIr electrodeposition process has been performed on CF microelectrode arrays to improve the interfacial properties of these arrays. We study the film morphology and composition as well as electrode durability and impedance.Results. A PtIr coating with a composition of 70% Pt, 30% Ir and a thickness of ∼400 nm was observed. Pt and Ir were evenly distributed within the film. Impedance was decreased by 89% @ 1 kHz. Accelerated soak testing in a heated (T= 50∘C) saline solution showed impedance increase (@ 1 kHz) of ∼12% after 36 days (89 equivalent) of soaking.

Effects of anterior thalamic nuclei stimulation on hippocampal activity: Chronic recording in a patient with drug-resistant focal epilepsy

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Devices for RNS and thalamic DBS were implanted in a single person with epilepsy.

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RNS electrocorticography enabled characterization of acute and chronic DBS effects.

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DBS caused acute, phasic, frequency-dependent responses in hippocampus and cortex.

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DBS modulated functional connectivity and suppressed epileptiform activity over time.

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Chronic electrocorticography elucidates progressive effects of thalamic stimulation.

Implanted neurostimulation devices are gaining traction as palliative treatment options for certain forms of drug-resistant epilepsy, but clinical utility of these devices is hindered by incomplete mechanistic understanding of their therapeutic effects. Approved devices for anterior thalamic nuclei deep brain stimulation (ANT DBS) are thought to work at a network level, but limited sensing capability precludes characterization of neurophysiological effects outside the thalamus. Here, we describe a patient with drug-resistant temporal lobe epilepsy who was implanted with a responsive neurostimulation device (RNS System), involving hippocampal and ipsilateral temporal neocortical leads, and subsequently received ANT DBS. Over 1.5 years, RNS System electrocorticography enabled multiscale characterization of neurophysiological effects of thalamic stimulation. In brain regions sampled by the RNS System, ANT DBS produced acute, phasic, frequency-dependent responses, including suppression of hippocampal low frequency local field potentials. ANT DBS modulated functional connectivity between hippocampus and neocortex. Finally, ANT DBS progressively suppressed hippocampal epileptiform activity in relation to the extent of hippocampal theta suppression, which informs stimulation parameter selection for ANT DBS. Taken together, this unique clinical scenario, involving hippocampal recordings of unprecedented chronicity alongside ANT DBS, sheds light on the therapeutic mechanism of thalamic stimulation and highlights capabilities needed in next-generation devices.

Potential surgical therapies for drug-resistant focal epilepsy

Drug-resistant focal epilepsy (DRFE), defined by failure of two antiepileptic drugs, affects 30% of epileptic patients. Epilepsy surgeries are alternative options for this population. Preoperative evaluation is critical to include potential candidates, and to choose the most appropriate procedure to maximize efficacy and simultaneously minimize side effects. Traditional procedures involve open skull surgeries and epileptic focus resection. Alternatively, neuromodulation surgeries use peripheral nerve or deep brain stimulation to reduce the activities of epileptogenic focus. With the advanced improvement of laser-induced thermal therapy (LITT) technique and its utilization in neurosurgery, magnetic resonance-guided LITT (MRgLITT) emerges as a minimal invasive approach for drug-resistant focal epilepsy. In the present review, we first introduce drug-resistant focal epilepsy and summarize the indications, pros and cons of traditional surgical procedures and neuromodulation procedures. And then, focusing on MRgLITT, we thoroughly discuss its history, its technical details, its safety issues, and current evidence on its clinical applications. A case report on MRgLITT is also included to illustrate the preoperational evaluation. We believe that MRgLITT is a promising approach in selected patients with drug-resistant focal epilepsy, although large prospective studies are required to evaluate its efficacy and side effects, as well as to implement a standardized protocol for its application.

The surgical treatment of epilepsy

In 2009, the Commission for Epilepsy Surgery of the Italian League Against Epilepsy (LICE) conducted an overview about the techniques used for the pre-surgical evaluation and the surgical treatment of epilepsies. The recognition that, in selected cases, surgery can be considered the first-line approach, suggested that the experience gained by the main Italian referral centers should be pooled in order to provide a handy source of reference. In light of the progress made over these past years, some parts of that first report have accordingly been updated. The present revision aims to harmonize the general principles regulating the patient selection and the pre-surgical work-up, as well as to expand the use of epilepsy surgery, that still represents an underutilized resource, regrettably. The objective of this contribution is drawing up a methodological framework within which to integrate the experiences of each group in this complex and dynamic sector of the neurosciences.

Augmentation of neural activity in peripheral nerve of sheep using 6 kHz subthreshold currents

OBJECTIVE

To determine how increased excitability from subthreshold currents would alter neural activity as it propagates through the subthreshold currents.

APPROACH

Experiments were performed on two Romney cross-breed sheep in vivo, by applying subthreshold currents either at the stimulus site or between the stimulus and recording sites. Neural recordings were obtained from nerve cuff implanted on the peroneal or sciatic nerve branches, while stimulus was applied to either the peroneal nerve or pins placed through the lower hindshank.

MAIN RESULTS

Showed that subthreshold currents applied to the same site as stimulus increased excitation of underlying nerve fibres (p < 0.005). With stimulus and subthreshold currents applied to different sites on the peroneal nerve, the primary compound action potential (CAP) in the sciatic displayed a temporal shift of -2.5 to -3 µs which agreed with changes observed in the CAP waveform (p > 0.05).

SIGNIFICANCE

These findings contribute to the understanding of mechanisms in myelinated fibres of subthreshold current neuromodulation therapies.

The RNS System: brain-responsive neurostimulation for the treatment of epilepsy

Introduction: Epilepsy affects more than 1% of the US population, and over 30% of adults with epilepsy do not respond to antiseizure medications without life-impacting medication-related side effects. Resection of the seizure focus is not an option for many patients because it would cause unacceptable neurological or cognitive harm. For these patients, neuromodulation has emerged as a nondestructive, effective, and safe alternative. The NeuroPace® RNS® System, the only brain-responsive neurostimulation device, records neural activity from leads placed at one or two seizure foci. When the neurostimulator detects epileptiform activity, as defined for each patient by his or her physician, brief pulses of electrical stimulation are delivered to normalize the activity.Areas covered: This review describes the RNS System, the results of multi-year clinical trials, and the research discoveries enabled by the chronic ambulatory brain data collected by the RNS System.Expert commentary: Brain-responsive neurostimulation could potentially be used to treat any episodic neurological disorder that's accompanied by a neurophysiological biomarker of severity. Combining advanced machine learning approaches with the chronic ambulatory brain data collected by the RNS System could eventually enable automatic fine-tuning of detection and stimulation for each patient, creating a general-purpose neurotechnological platform for precision medicine.

Sleep disruption is not observed with brain-responsive neurostimulation for epilepsy

OBJECTIVE

Neurostimulation devices that deliver electrical impulses to the nervous system are widely used to treat seizures in patients with medically refractory epilepsy, but the effects of these therapies on sleep are incompletely understood. Vagus nerve stimulation can contribute to obstructive sleep apnea, and thalamic deep brain stimulation can cause sleep disruption. A device for brain-responsive neurostimulation (RNS^® System, NeuroPace, Inc) is well tolerated in clinical trials, but potential effects on sleep are unknown.

METHODS

Six adults with medically refractory focal epilepsy treated for at least six months with the RNS System underwent a single night of polysomnography (PSG). RNS System lead locations included mesial temporal and neocortical targets. Sleep stages and arousals were scored according to standard guidelines. Stimulations delivered by the RNS System in response to detections of epileptiform activity were identified by artifacts on scalp electroencephalography.

RESULTS

One subject was excluded for technical reasons related to unreliable identification of stimulation artifact on EEG during PSG. In the remaining five subjects, PSG showed fragmented sleep with frequent arousals. Arousal histograms aligned to stimulations revealed a significant peak in arousals just before stimulation. In one of these subjects, the arousal peak began before stimulation and extended ~1 seconds after stimulation. A peak in arousals occurring only after stimulation was not observed.

SIGNIFICANCE

In this small cohort of patients, brain-responsive neurostimulation does not appear to disrupt sleep. If confirmed in larger studies, this could represent a potential clinical advantage of brain-responsive neurostimulation over other neurostimulation modalities.

Late-onset unexplained epilepsy: What are we missing?

With the aging of the US population, the incidence of epilepsy will increase, with 25 to 50% of new cases with no identifiable etiology diagnosed as late-onset unexplained epilepsy (LOUE). In the current targeted review, we discuss the possible role of cerebral small vessel ischemic disease, accumulation of amyloidβ and hyperphosphorylated tau, and sleep apnea as potential pathophysiologic mechanisms explaining LOUE. We highlight the impact of these processes on cognition and avenues for diagnosis and treatment.