Vagal nerve stimulation for the treatment of medically refractory epilepsy: a review of the current literature

Retrospective Clinical Analysis of Epilepsy Treatment for Children with Drug-Resistant Epilepsy (A Single-Center Experience)

Objectives: This retrospective cohort study investigated the clinical characteristics and seizure outcomes of patients aged 1−14 years with drug-resistant epilepsy (DRE) who were treated by different typologies of therapy. Methods: Four hundred and eighteen children with DRE were recruited from Sanbo Brain Hospital of Capital Medical University from April 2008 to February 2015. The patients were divided into three groups: medication (n = 134, 32.06%), resection surgery (n = 185, 44.26%), and palliative surgery (n = 99, 23.68%) groups. Demographic characteristics were attained from medical records. All patients were followed up for at least 5 years, with seizure outcomes classified according to International League Against Epilepsy criteria. The psychological outcome was evaluated with the development quotient and Wechsler Intelligence Quotient Scale for children (Chinese version). Results: The most frequent seizure type was generalized tonic seizure in 53.83% of patients. Age at seizure onset in 54.55% of patients was <3 years. The most frequent etiologies were focal cortical dysplasia (FCD). West syndrome was the most common epilepsy syndrome. Favorable seizure outcomes at the 5-year follow-up in the medication, resection surgery, and palliative surgery groups were 5.22%, 77.30%, and 14.14%, respectively. The patients showed varying degrees of improvement in terms of developmental and intellectual outcomes post-treatment. Conclusions: Pediatric patients with DRE were characterized by frequent seizures, a variety of seizure types, and complex etiology. Recurrent seizures severely affected the cognitive function and development of children. Early surgical intervention would be beneficial for seizure control and prevention of mental retardation. Palliative surgery was also a reasonable option for patients who were not suitable candidates for resection surgery.

The role of vagus nerve stimulation in the treatment of refractory epilepsy: Clinical outcomes and impact on quality of life

BACKGROUND

Vagus nerve stimulation (VNS) is used as a complementary therapy to pharmacological treatment in patients with refractory epilepsy. This study aims to evaluate the efficacy of VNS in reducing seizure frequency, severity, and duration; reducing the number of antiepileptic drugs administered; and improving patients' quality of life.

MATERIAL AND METHODS

We analysed the clinical progression of 70 patients with refractory epilepsy treated with VNS at Hospital Universitario de Alicante and Hospital Clínico de Valencia. Data were collected before and after the procedure. The difference in seizure frequency pre- and post-VNS was classified using the McHugh scale. Data were also collected on seizure duration and severity, the number of drugs administered, and quality of life.

RESULTS

According to the McHugh classification, 12.86% of the patients were Class I, 44.29% were Class II, 40% were Class III, and the remaining 2.86% of patients were Class IV-V. A≥50% reduction in seizure frequency was observed in 57.15% of patients. Improvements were observed in seizure duration in 88% of patients and in seizure severity in 68%; the number of drugs administered was reduced in 66% of patients, and 93% reported better quality of life.

CONCLUSIONS

VNS is effective for reducing seizure frequency, duration, and severity and the number of antiepileptic drugs administered. It also enables an improvement in patients' quality of life.

Shoulder transcutaneous electric nerve stimulation decreases heart rate via potentiating vagal tone

By enhancing vagal activity, auricle transcutaneous electric nerve stimulation (TENS) is developed as a non-invasive therapy for heart failure. Nevertheless, though shoulder TENS used for treating adhesive capsulitis could affect vagal tone, its potential impact on heart functions remains unclear. In this study, electrocardiogram (ECG) and heart rate (HR) of subjects in response to sham, right-sided, or left-sided shoulder TENS (TENS-S, TENS-R, and TENS-L, respectively; 5 min) were recorded and analyzed. During the stimulation period, TENS-R constantly and TENS-L transiently decreased the HR of subjects; both TENS-R and TENS-L increased powers of the low- and high-frequency spectra. While TENS-R exhibiting no effect, TENS-L increased the ratio of low/high-frequency power spectrum indicating TENS-R decreased the HR through potentiating cardiac vagal tone. Collectively, these results suggest TENS could be an early and non-invasive therapy for heart failure patients before considering implant devices or devices are not feasible; moreover, therapists/physicians need to carefully monitor the potential adverse events during treatment for patient safety.

Trial registration: The study protocol was registered in ClinicalTrials.gov (NCT03982472; 11/06/2019).

Outcomes following surgical management of vagus nerve stimulator-related infection: a retrospective multi-institutional study

OBJECTIVE

Surgical site infection (SSI) is a rare but significant complication after vagus nerve stimulator (VNS) placement. Treatment options range from antibiotic therapy alone to hardware removal. The optimal therapeutic strategy remains open to debate. Therefore, the authors conducted this retrospective multicenter analysis to provide insight into the optimal management of VNS-related SSI (VNS-SSI).

METHODS

Under institutional review board approval and utilizing an institutional database with 641 patients who had undergone 808 VNS-related placement surgeries and 31 patients who had undergone VNS-related hardware removal surgeries, the authors retrospectively analyzed VNS-SSI.

RESULTS

Sixteen cases of VNS-SSI were identified; 12 of them had undergone the original VNS placement procedure at the authors' institutions. Thus, the incidence of VNS-SSI was calculated as 1.5%. The mean (± standard deviation) time from the most recent VNS-related surgeries to infection was 42 (± 27) days. Methicillin-sensitive staphylococcus was the usual causative bacteria (58%). Initial treatments included antibiotics with or without nonsurgical procedures (n = 6), nonremoval open surgeries for irrigation (n = 3), generator removal (n = 3), and total or near-total removal of hardware (n = 4). Although 2 patients were successfully treated with antibiotics alone or combined with generator removal, removal of both the generator and leads was eventually required in 14 patients. Mild swallowing difficulties and hoarseness occurred in 2 patients with eventual resolution.

CONCLUSIONS

Removal of the VNS including electrode leads combined with antibiotic administration is the definitive treatment but has a risk of causing dysphagia. If the surgeon finds dense scarring around the vagus nerve, the prudent approach is to snip the electrode close to the nerve as opposed to attempting to unwind the lead completely.

Targeting neural oscillations with transcranial alternating current stimulation

Neural oscillations at the network level synchronize activity between regions and temporal scales. Transcranial alternating current stimulation (tACS), the delivery of low-amplitude electric current to the scalp, provides a tool for investigating the causal role of neural oscillations in cognition. The parameter space for tACS is vast and optimization is required in terms of temporal and spatial targeting. We review emerging techniques and suggest novel approaches that capitalize on the non-sinusoidal and transient nature of neural oscillations and leverage the flexibility provided by a customizable electrode montage and electrical waveform. The customizability and safety profile of tACS make it a promising tool for precision intervention in psychiatric illnesses.

Monitoring the frequency and duration of epileptic seizures: "A journey through time"

Seizure monitoring plays an undeniably important role in diagnosing and managing epileptic seizures. Establishing the frequency and duration of seizures is crucial for assessing the burden of this chronic neurological disease, selecting treatment methods, determining how frequently these methods are applied, and informing short and long-term therapeutic decisions. Over the years, seizure monitoring tools and methods have evolved and become increasingly sophisticated; from home seizure diaries to EEG monitoring to cutting-edge responsive neurostimulation systems. In this article, the various methods of seizure monitoring are reviewed.

The role of vagus nerve stimulation in the treatment of refractory epilepsy: clinical outcomes and impact on quality of life

BACKGROUND

Vagus nerve stimulation (VNS) is used as a complementary therapy to pharmacological treatment in patients with refractory epilepsy. This study aims to evaluate the efficacy of VNS in reducing seizure frequency, severity, and duration; reducing the number of antiepileptic drugs administered; and improving patients' quality of life.

MATERIAL AND METHODS

We analysed the clinical progression of 70 patients with refractory epilepsy treated with VNS at Hospital Universitario de Alicante and Hospital Clínico de Valencia. Data were collected before and after the procedure. The difference in seizure frequency pre- and post-VNS was classified using the McHugh scale. Data were also collected on seizure duration and severity, the number of drugs administered, and quality of life.

RESULTS

According to the McHugh classification, 12.86% of the patients were Class I, 44.29% were Class II, 40% were Class III, and the remaining 2.86% of patients were Class IV-V. A ≥ 50% reduction in seizure frequency was observed in 57.15% of patients. Improvements were observed in seizure duration in 88% of patients and in seizure severity in 68%; the number of drugs administered was reduced in 66% of patients, and 93% reported better quality of life.

CONCLUSIONS

VNS is effective for reducing seizure frequency, duration, and severity and the number of antiepileptic drugs administered. It also enables an improvement in patients' quality of life.

Non-Pharmacological Approaches to Headaches: Non-Invasive Neuromodulation, Nutraceuticals, and Behavioral Approaches

Significant side effects or drug interactions can make pharmacological management of headache disorders very difficult. Non-conventional and non-pharmacological treatments are becoming increasingly used to overcome these issues. In particular, non-invasive neuromodulation, nutraceuticals, and behavioral approaches are well tolerated and indicated for specific patient categories such as adolescents and pregnant women. This paper aims to present the main approaches reported in the literature in the management of headache disorders. We therefore reviewed the available literature published between 2010 and 2020 and performed a narrative presentation for each of the three categories (non-invasive neuromodulation, nutraceuticals, and behavioral therapies). Regarding non-invasive neuromodulation, we selected transcranial magnetic stimulation, supraorbital nerve stimulation, transcranial direct current stimulation, non-invasive vagal nerve stimulation, and caloric vestibular stimulation. For nutraceuticals, we selected Feverfew, Butterbur, Riboflavin, Magnesium, and Coenzyme Q10. Finally, for behavioral approaches, we selected biofeedback, cognitive behavioral therapy, relaxation techniques, mindfulness-based therapy, and acceptance and commitment therapy. These approaches are increasingly seen as a valid treatment option in headache management, especially for patients with medication overuse or contraindications to drug treatment. However, further investigations are needed to consider the effectiveness of these approaches also with respect to the long-term effects.

Saudi Arabian Consensus Statement on Vagus Nerve Stimulation for Refractory Epilepsy

Vagus nerve stimulation (VNS) is an approved adjunctive therapy for refractory epilepsy and used in patients who are not candidates for resective epilepsy surgery. In Saudi Arabia, VNS device implantation is being performed since 2008 by several comprehensive epilepsy programs, but with variable protocols. Therefore, to standardize the use of VNS, a task force was established to create a national consensus. This group consisted of epileptologists, epilepsy surgeons and a VNS nurse coordinator working in comprehensive epilepsy centers and dealing with refractory epilepsy cases. The group intensively reviewed the literature using Medline, EMBASE, Web of Science and Cochrane Library, in addition to physician's manual. Evidence is reported as three stages: preimplantation and patient selection, a perioperative phase involving all stakeholders and post-operative care with specific programming pathways.

Efficacy of VNS for Drug-Resistant Epilepsy in Structural Brain Lesions

Background:

Vagus nerve stimulation (VNS) has been used for the treatment of drug-resistant epilepsy, especially in patients who are not candidates for surgical intervention. In fact, it was approved by the US FDA in 1997 as an adjunctive treatment for medically intractable epilepsy.

Objective:

In this study, we investigated the efficacy of VNS in drug-resistant epilepsy associated with structural brain lesions (SBLs).

Methods:

We retrospectively analyzed the effect of VNS on 25 patients diagnosed with intractable epilepsy-associated SBL, and compared the results to 19 patients with intractable epilepsy and normal neuroimaging. All patients underwent VNS insertion at the National Neurosciences Institute, King Fahad Medical City (Riyadh, Saudi Arabia) between 2008 and 2018.

Results:

The response rate (RR) for patients with drug-resistant epilepsy-associated SBL was 24% after 3 months, 36% after 6 months, and 48% after 1 year, reaching 76% over time. The mean follow-up period was 63.3 months. For non-SBL patients, the RR was 10.5% after 3 months, 36.8% after 6 months, and 47.4% after 1 year, reaching 73.7% over time. The mean follow-up period was 59.2 months. There was no statistically significant difference between the two groups regarding RR, VNS settings, and other parameters, including anti-epileptic drug use and demographics data.

Conclusion:

VNS is strongly considered for intractable epilepsy in SBL patients, especially if they are not candidates for surgical intervention. Over time, those patients will receive increased benefits from VNS therapy.

Vagus nerve stimulation and Neurotrophins: a biological psychiatric perspective

Since 2004, vagus nerve stimulation (VNS) has been used in treatment-resistant or treatment-intolerant depressive episodes. Today, VNS is suggested as possible therapy for a larger spectrum of psychiatric disorders, including schizophrenia, obsessive compulsive disorders, and panic disorders. Despite a large body of literature supports the application of VNS in patients' treatment, the exact mechanism of action of VNS remains not fully understood. In the present study, the major knowledges on the brain areas and neuronal pathways regulating neuroimmune and autonomic response subserving VNS effects are reviewed. Furthermore, the involvement of the neurotrophins (NTs) Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF) in vagus nerve (VN) physiology and stimulation is revised. The data on brain NGF/BDNF synthesis and in turn on the activity-dependent plasticity, connectivity rearrangement and neurogenesis, are presented and discussed as potential biomarkers for optimizing stimulatory parameters for VNS. A vagus nerve-neurotrophin interaction model in the brain is finally proposed as a working hypothesis for future studies addressed to understand pathophysiology of psychiatric disturbance.

Modulation of neural oscillations by vagus nerve stimulation in posttraumatic multifocal epilepsy: case report

The putative mechanism of vagus nerve stimulation (VNS) for medically refractory epilepsy is desynchronization of hippocampal and thalamocortical circuitry; however, the nature of the dose-response relationship and temporal dynamics is poorly understood. For greater elucidation, a study in a nonepileptic rat model was previously conducted and showed that rapid-cycle (RC) VNS achieved superior desynchrony compared to standard-cycle (SC) VNS. Here, the authors report on the first in-human analysis of the neuromodulatory dose-response effects of VNS in a patient with posttraumatic, independent, bilateral mesial temporal lobe epilepsy refractory to medications and SC-VNS who was referred as a potential candidate for a responsive neurostimulation device. During stereotactic electroencephalography (SEEG) recordings, the VNS device was initially turned off, then changed to SC-VNS and then RC-VNS settings. Spectral analysis revealed a global reduction of power in the theta (4-8 Hz) and alpha (8-15 Hz) bands with both SC- and RC-VNS compared to the stimulation off setting (p < 0.001). Furthermore, in the alpha band, both SC- and RC-VNS were associated with greater global desynchrony compared to the off setting (p < 0.001); and, specifically, in the bilateral epileptogenic hippocampi, RC-VNS further reduced spectral power compared to SC-VNS (p < 0.001). The dose-response and temporal effects suggest that VNS modulates regional and global dynamics differently.

Vagus nerve stimulation for pediatric patients with intractable epilepsy between 3 and 6 years of age: study protocol for a double-blind, randomized control trial

BACKGROUND

Recent clinical observations have reported the potential benefit of vagus nerve stimulation (VNS) as an adjunctive therapy for pediatric epilepsy. Preliminary evidence suggests that VNS treatment is effective for seizure reduction and mental development in young participants between 3 and 6 years of age who suffer from intractable epilepsy. However, robust clinical evidence for quantifying the difference of the efficacy and safety of VNS treatment in this specific patient population has yet to be reported.

METHODS/DESIGN

A two-armed, multicenter, randomized, double-blind, prospective trial will be carried out to evaluate whether VNS is beneficial and safe for pediatric epilepsy. Pediatric participants aged between 3 to 6 years old with intractable epilepsy will be recruited and randomly assigned to experimental and control groups with a 1:1 allocation using a computer-generating randomization schedule. Before enrollment, informed consent will be signed by the parents of the participants and the study researchers. Participants in the experimental group will receive electrical stimulation over 24 weeks under standard stimulation parameters. Participants in the control group will not receive any stimulation during the 12 weeks of the double-blind period. The guardians of the participants are required to keep a detailed diary to record seizure activity. Outcome assessments including seizure frequency, Gesell Mental Developmental Scale scores, use of antiepileptic drugs and dosages, and adverse events will be collected at baseline, 6, 12, 18 and/or 24 weeks after electrical stimulation is initiated. The effects of treatment will be analyzed with time and treatment group comparisons.

DISCUSSION

This trial will evaluate quantitative differences in efficacy and safety with/without VNS treatment for pediatric participants aged between 3 to 6 years with intractable epilepsy and will explore whether the current age range of VNS therapy can be expanded.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT03062514 , Registered on 23 February 2017.

Changes in self-perception in patients treated with neurostimulating devices

BACKGROUND

In recent years, qualitative changes in self-perception have been reported in individual patients undergoing brain stimulation to treat their neurological disease. We here report a first systematic study addressing these unwanted treatment effects in a semiquantitative way.

HYPOTHESES

Hypothesis 1 (H1): Changes in self-perception can be detected and documented in patients following interventions with various neurostimulating devices using standardized assessment tools. Hypothesis 2 (H2): Central nervous-implanted neurostimulating devices (deep brain stimulation [DBS]) will have a greater impact on the patient's self-perception than "peripheral" implanted devices (implanted vagus nerve stimulation [iVNS]) and external devices (transcutaneous vagus nerve stimulation [tVNS] or transcutaneous electrical trigeminal nerve stimulation [eTNS]).

METHODS

Application of a newly developed semiquantitative questionnaire (FST-questionnaire [Fragebogen zur Veränderung der Selbstwahrnehmung unter tiefer Hirnstimulation]: Questionnaire regarding changes in self-perception while treated with DBS) to systematically assess changes in self-perception in a single-center, cross-sectional pilot-study at the University Hospital Freiburg, Germany on 50 patients (44% male; age 50 years [range: 27-73 years]), undergoing neurostimulation (DBS, iVNS, tVNS, or eTNS) to treat Parkinson's disease or epilepsy.

RESULTS

Standardized assessment detected alterations in self-perception in all treatment groups (H1 approved). This included rare self-alienating changes in self-perception. Unexpectedly, peripheral neurostimulation had similar effects as central stimulation techniques.

CONCLUSIONS

Properly designed questionnaires - like the FST-questionnaire as standardized assessment tool - can detect changes in self-perception in patients during neurostimulatory treatment in a wide spectrum of brain stimulation techniques. This may provide a strategy to systematically identify the subgroup of patients liable to experience such problems during treatment already prior to treatment decisions.

Vagus nerve stimulation (VNS) therapy update

Epilepsy affects millions of people worldwide. Approximately one-third have pharmacoresistant epilepsy, and of these, the majority are not candidates for epilepsy surgery. Vagus nerve stimulation (VNS) therapy has been an option to treat pharmacoresistant seizures for 30 years. In this update, we will review the clinical data that support the device's efficacy in children, adolescents, and adults. We will also review its side-effect profile, quality of life and cost benefits, and the impact the device has on sudden unexpected death in epilepsy (SUDEP). We will then discuss candidate selection and provide guidance on dosing and future models. Vagus nerve stimulation therapy is an effective treatment for many seizure types and epilepsy syndromes with a predictable and benign side-effect profile that supports its role as the most commonly prescribed device to treat pharmacoresistant epilepsy. "This article is part of the Supplement issue Neurostimulation for Epilepsy."

Specificity, Versatility, and Continual Development: The Power of Optogenetics for Epilepsy Research

Optogenetics is a powerful and rapidly expanding set of techniques that use genetically encoded light sensitive proteins such as opsins. Through the selective expression of these exogenous light-sensitive proteins, researchers gain the ability to modulate neuronal activity, intracellular signaling pathways, or gene expression with spatial, directional, temporal, and cell-type specificity. Optogenetics provides a versatile toolbox and has significantly advanced a variety of neuroscience fields. In this review, using recent epilepsy research as a focal point, we highlight how the specificity, versatility, and continual development of new optogenetic related tools advances our understanding of neuronal circuits and neurological disorders. We additionally provide a brief overview of some currently available optogenetic tools including for the selective expression of opsins.

Cervical vagus nerve morphometry and vascularity in the context of nerve stimulation - A cadaveric study

Vagus nerve stimulation (VNS) has become a well-established therapy for epilepsy and depression, and is emerging to treat inflammatory disease, with the cervical vagus nerve (CVN) as major stimulation site. CVN morphometries are missing for VNS, considering its variability. Morphometric data were obtained from CVNs in 27 cadavers, including branching patterns and histology. Cross-sectional area, greater and lesser diameters averaged 7.2 ± 3.1 mm², 5.1 ± 1.5 and 4.1 ± 1.3 mm, and were ≤11.0 mm², ≤7.0 and ≤5.8 mm in 90% of the specimens, respectively. Midline distance (position lateral to the laryngeal eminence) and skin distance (anterior-posterior from skin) averaged 34.5 ± 6.2 and 36.2 ± 9.4 mm, ≤49.0 and ≤41.0 mm in 90%, respectively. Nerve dimensions and surface topography correlated closely, but without gender-, side- or branching-dependent differences. The nerve fascicle number averaged 5.2 ± 3.5. Vagal arteries were observed in 49% of the cases. Negative correlations were found for age and cross-sectional area, as well as subperineural vessel count. Detailed anatomical data on the CVN and its vascularity are given, forming the morphometric basis for VNS refinement, filling an evident gap in light of the CVN being a structure with variable positions and branching. A 35 × 35-mm rule may apply for the CVN position, irrespective of branching or positional variation.

Marginal decision-making in the treatment of refractory epilepsy

OBJECTIVE

Epilepsy surgery is one of the most effective treatments in modern medicine. Yet, it remains largely under-utilized, in spite of its proven efficacy. The referrals for epilepsy surgery are often delayed until it is too late to prevent the detrimental psychosocial effects of refractory seizures. The reluctance towards epilepsy surgery is influenced by the perceived risks of the procedure by practitioners and patients. This review discusses how, in general decision-making processes, one faces a natural tendency towards emphasizing the risks of the most immediate and operational decision (surgery), at times without contrasting these risks with the alternative (uncontrolled epilepsy).

METHODS

In the field of economics, this bias is well recognized and can be overcome through marginal analysis, formally defined as focusing on incremental changes as opposed to absolute levels.

RESULTS

Regarding epilepsy surgery, the risks and benefits of surgery are considered separately from the risks of uncontrolled epilepsy. For instance, even though surgery carries an ∼0.1-0.5% risk of perioperative mortality, the chance of sudden unexpected death with refractory epilepsy can be as high as 0.6-0.9% per year. It is suggested that the inadequate way of phrasing clinical questions can be a crucial contributing factor for the under-utilization of epilepsy surgery.

SIGNIFICANCE

It is proposed that examining decision-making for epilepsy surgery in the context of marginal analysis may enable providers and patients to make more accurate informed decisions.

Non-invasive vagus nerve stimulation (nVNS) as symptomatic treatment of migraine in young patients: a preliminary safety study

Recent clinical experiences and clinical trials have demonstrated the safety, tolerability, and efficacy of non-invasive vagus nerve stimulation (nVNS; gammaCore^®) for the acute and prophylactic treatment of migraine. nVNS has a favorable adverse event profile, making it an attractive option for sensitive patient populations. We explored the safety, tolerability, and efficacy of nVNS as acute migraine treatment in adolescents. A group of adolescent patients suffering from migraine without aura were trained to use gammaCore to manage their migraine attacks. 46.8% of the treated migraine attacks (22/47) were considered successfully treated and did not require any rescue medication. No device-related adverse events were recorded. This preliminary study suggests that nVNS may represent a safe, well-tolerated, and effective for acute migraine treatment in adolescents.

A Short Review of the Non-invasive Transcutaneous Pericranial Electrical Stimulation Techniques and their Application in Headache

PURPOSE OF REVIEW

In this short review, the most common non-invasive neuromodulatory techniques will be described, along with their advantages and disadvantages and their application in headache. Available preventive treatments can be unhelpful or may have unpleasant side effects; moreover, the rate of response to preventive drugs does not exceed 50%, lower in chronic migraine; alternative options would be welcome. Though the concept of neuromodulation was originally developed with invasive methods, newer non-invasive techniques are appearing.

RECENT FINDINGS

The novel neuromodulatory techniques have been developed with encouraging results: compared with traditional pharmacotherapy, advantages of non-invasive neuromodulation include reduced incidence of adverse effects, improved adherence, and safety and ease of use. The results are encouraging for acute or preventive treatment of different kinds of headache. A variety of neuromodulatory approaches is expanding fastly and has opened new possibilities for treatment of patients suffering from many forms of headache, especially those who have failed traditional pharmacotherapy. The non-invasive treatments can be seen as supplementing traditional management in refractory patients. Current study results are encouraging but preliminary and larger and more rigorous trials are needed to clarify benefit and mode of action.

First demonstration of velocity selective recording from the pig vagus using a nerve cuff shows respiration afferents

Neural interfaces have great potential to treat disease and disability by modulating the electrical signals within the nervous system. However, whilst neural stimulation is a well-established technique, current neural interfaces are limited by poor recording ability. Low signal amplitudes necessitate the use of highly invasive techniques that divide or penetrate the nerve, and as such are unsuitable for chronic implantation. In this paper, we present the first application of the velocity selective recording technique to the detection of respiration activity in the vagus nerve, which is involved with treatments for epilepsy, depression, and rheumatoid arthritis. Further, we show this using a chronically implantable interface that does not divide the nerve. We also validate our recording setup using electrical stimulation and we present an analysis of the recorded signal amplitudes. The recording interface was formed from a cuff containing ten electrodes implanted around the intact right vagus nerve of a Danish Landrace pig. Nine differential amplifiers were connected to adjacent electrodes, and the resulting signals were processed to discriminate neural activity based on conduction velocity. Despite the average single channel signal-to-noise ratio of - 5.8 dB, it was possible to observe distinct action potentials travelling in both directions along the nerve. Further, contrary to expectation given the low signal-to-noise ratio, we have shown that it was possible to identify afferent neural activity that encoded respiration. The significance of this is the demonstration of a chronically implantable method for neural recording, a result that will transform the capabilities of future neuroprostheses.

Electrical stimulation for the treatment of obstructive sleep apnoea: a review of the evidence

INTRODUCTION

Obstructive sleep apnoea is an increasingly prevalent clinical condition with significant impact on individuals and public health. Continuous positive airway pressure therapy is the standard treatment, but adherence is limited and alternative treatments are needed. In this context, non-invasive and invasive methods for the electrical stimulation of upper airway dilator muscles have been demonstrated to be effective in selected patients. Areas covered: This review will cover investigations on the clinical effects, safety, and tolerability of non-invasive and invasive electrical stimulation of the upper airway for the management of obstructive sleep apnoea. Following a search of the relevant literature published on PubMed this review is focused mainly on data obtained from randomized clinical trials and clinical studies. Expert commentary: The available evidence provides a rationale to consider upper airway electrical stimulation as treatment for selected patients with obstructive sleep apnoea, who have poor adherence or experience difficulties with continuous positive airway pressure therapy. Non-invasive stimulation using transcutaneous electrodes and implantable hypoglossal nerve stimulator technologies may provide an alternative to continuous positive airway pressure for the treatment of obstructive sleep apnoea via restoration of neuromuscular tone and improved upper airway patency.

Values of vanillylmandelic acid and homovanillic acid in the urine as potential prognostic biomarkers in ischaemic stroke patients

BACKGROUND

Suitable biomarkers that have prognostic values are one of the key points of interest in ischaemic stroke. Increased sympathetic nervous system activity in ischaemic stroke causes multiple local and systemic effects that can be detrimental to the outcome. The mechanism of action is increased secretion and activity of catecholamines, whose end metabolic products are vanillylmandelic acid and homovanilic acid. Aim of our study was to determine whether these compounds can be used as potential prognostic biomarkers in ischaemic stroke, as a unique insight into the activity of the sympathetic nervous system.

METHODS

Urine samples of 96 patients with ischaemic stroke and transitory ischaemic attacks were analysed. Values of vanillylmandelic and homovanillic acids in urine were tested using liquid chromatography on the first and third day post-stroke. Severity of stroke was determined using the NIHSS scale, while functional outcome was determined using the Modified Rankin Scale.

RESULTS

Values of vanillylmandelic and homovanillic acids positively correlated with functional outcome of ischaemic stroke. Favorable outcomes correlated with decreased values, on contrary to increased values, which were associated with unfavourable outcomes.

CONCLUSION

Determining the values of these compounds in the urine is an easily available prognostic tool for the ischaemic stroke outcome, while also influencing potential therapeutic changes.

Vagus Nerve Stimulation in children: A focus on intellectual disability

INTRODUCTION

Vagus Nerve Stimulation (VNS) can be an efficacious add-on treatment in patients with drug-resistant epilepsy, who are not eligible for surgery. Evidence of VNS efficacy in children with intellectual disability (ID) is scarce.

OBJECTIVES

The purpose of this study was to review all available VNS data in the pediatric population (≤18 years old) and focus on the subpopulation with ID since appropriate treatment of these children is often challenging and complex.

METHODS

Cochrane, EMBASE, PubMed and MEDLINE were used to collect all research associated to VNS and ID (or synonyms) leading to a total of 37 studies. Seven studies showed the results of patients with ID and those without separately; thereby only these studies were included in the VNS meta-analysis.

RESULTS

Our meta-analysis showed that VNS was less effective in pediatric epilepsy patients with ID compared to those without ID (Mantel-Haenszel meta-analysis; p = 0.028, OR 0.18 (CI 95% 0.039-0.84)). However, there were no prospective controlled studies. Numerous studies reported quality of life (QoL) improvements in this subpopulation. The most common adverse events were transient and well tolerated. Side effects on cognition and behavior were not reported.

DISCUSSION

These results might be a reason to consider VNS early on in the treatment of this subgroup. The significantly greater amount of retrospective studies, differences in follow-up (FU), lack of control data, heterogeneous series and limited number of patients could have biased the outcome measurements. Hence, current data do not exclude VNS for children with drug-resistant epilepsy and ID but should be interpreted with caution.

Magnetic facial nerve stimulation in animal models of active seizure

PURPOSE

As part of our efforts to develop a non-invasive facial nerve stimulator as an emergency treatment for ischemic stroke, we considered possible safety consequences if the technology was misapplied to stroke mimics, e.g., seizure. We hypothesized that magnetic facial nerve stimulation would worsen epileptiform activity in two animal models of active seizures. The rat intraperitoneal kainate model and pig intracortical penicillin model were employed. Magnetic facial nerve stimulation was delivered unilaterally at a variety of stimulation parameters, and the effect on ictal epileptiform activity measured by electroencephalography was determined according to an established categorical scale.

PRINCIPAL RESULTS

In 6 rats and 3 pigs evaluated with 83 stimulation trials, only a single stimulation trial was associated with worsening epileptiform activity according to a standard categorization scheme. Surprisingly, a reduction in the severity of the epileptiform activity was observed in 20 of 50 stimulation trials using patterned stimulation (3 pulses at 30Hz repeated at 0.5-10Hz) versus 2 of 33 stimulation trials using simple monotonic patterns (P<0.005, chi-squared test). The reduction of epileptiform activity after stimulation lasted a few minutes and was reproducible. Major Conclusions Epileptiform activity measured by electroencephalography was not reliably worsened by repetitive facial nerve stimulation with pulsed magnetic energy, even when significant brain exposure to the magnetic field occurred as in the rat model. To the contrary, a temporary reduction in epileptiform activity was often, but not invariably, observed with certain stimulation parameters.

Invasive and Non-invasive Electrical Pericranial Nerve Stimulation for the Treatment of Chronic Primary Headaches

Chronic primary headaches are widespread disorders which cause significant quality of life and socioprofessional impairment. Available pharmacological treatments have often a limited efficacy and/or can generate unbearable side effects. Electrical nerve stimulation is a well-known non-destructive method of pain modulation which has been recently applied to headache management. In this review, we summarise recent advances in invasive and non-invasive neurostimulation techniques targeting pericranial structures for the treatment of chronic primary headaches, chiefly migraine and cluster headache: occipital nerve, supraorbital nerve, vagus nerve, and sphenopalatine ganglion stimulations. Invasive neurostimulation therapies have offered a new hope to drug-refractory headache sufferers but are not riskless and should be proposed only to chronic patients who failed to respond to most existing preventives. Non-invasive neurostimulation devices are user-friendly, safe and well tolerated and are thus taking an increasing place in the multidisciplinary therapeutical armamentarium of primary headaches.

Positional Relations of the Cervical Vagus Nerve Revisited

OBJECTIVES

The cervical part of the vagus nerve (CVN) has become an important target for stimulation therapy to treat epilepsy and psychiatric conditions. For this purpose, the CVN is visualized in the carotid sheath, assuming it to be localized dorsomedially between the carotid artery (CA) and the internal jugular vein (JV). The aim of our morphological study was therefore to revisit the CVN relationships to the CA and JV, hypothesizing it to have common variations to this classical textbook anatomy.

MATERIALS AND METHODS

Positional relations of the CVN, CA and JV were investigated in the carotid sheath of 35 cadavers at the C3 to C6 level. Positional relations of the CVN, CA and JV were documented on the basis of a 3 × 3 chart.

RESULTS

Eighteen different arrangements of the CVN, CA and JV were observed. The typical topographic relationship of the CVN dorsomedially between the CA and JV was only found in 42% of all cases. The CVN was located dorsally or (dorso-)laterally to the CA in 80% and dorsally or (dorso-)medially of the JV in 96% of all cases.

CONCLUSIONS

Classical textbook anatomy of the CVN is only present in a minority of cases. Positional variations in contrast to textbook anatomy are considerably more frequent than previously described, which might be a hypothetical morphological explanation for the lack of efficacy or side effects of CVN stimulation. Furthermore, the position of the CVN relative to the internal jugular vein is more consistent than to the CA.

Vagus nerve stimulation inhibits cortical spreading depression

Vagus nerve stimulation has recently been reported to improve symptoms of migraine. Cortical spreading depression is the electrophysiological event underlying migraine aura and is a trigger for headache. We tested whether vagus nerve stimulation inhibits cortical spreading depression to explain its antimigraine effect. Unilateral vagus nerve stimulation was delivered either noninvasively through the skin or directly by electrodes placed around the nerve. Systemic physiology was monitored throughout the study. Both noninvasive transcutaneous and invasive direct vagus nerve stimulations significantly suppressed spreading depression susceptibility in the occipital cortex in rats. The electrical stimulation threshold to evoke a spreading depression was elevated by more than 2-fold, the frequency of spreading depressions during continuous topical 1 M KCl was reduced by ∼40%, and propagation speed of spreading depression was reduced by ∼15%. This effect developed within 30 minutes after vagus nerve stimulation and persisted for more than 3 hours. Noninvasive transcutaneous vagus nerve stimulation was as efficacious as direct invasive vagus nerve stimulation, and the efficacy did not differ between the ipsilateral and contralateral hemispheres. Our findings provide a potential mechanism by which vagus nerve stimulation may be efficacious in migraine and suggest that susceptibility to spreading depression is a suitable platform to optimize its efficacy.

Vagal Nerve Stimulation for Drug-Resistant Epilepsy: Adverse Events and Outcome in a Series of Patients with Long-Term Follow-Up

BACKGROUND

Vagal nerve stimulation (VNS) is a palliative treatment option for drug-resistant epilepsy. The aim of this study was to describe the clinical and demographic features of selected patients scheduled for VNS and to evaluate the long-term efficacy of VNS in seizure control.

MATERIALS AND METHODS

Between 2006 and 2013, 32 consecutive epileptic patients (14 male and 18 female) were enrolled at our Institute for VNS implantation. In all cases resective surgery had previously been excluded by the use of a noninvasive presurgical study protocol. Mean age was 32 years (range 18-50), and mean epilepsy duration 23 years (range 11-39). All subjects were followed-up for at least 2 years (mean 6 years, range 2-9) after VNS implantation. Patients were considered responders when a reduction of seizures of more than 50 % was reported.

RESULTS

All patients had complex partial seizures, in 81 % of the patients with secondary generalization and in 56 % with drop attacks. Neurological examination revealed focal deficits in 19 % of the patients. Brain magnetic resonance imaging (MRI) was positive in 47 % of the patients. No surgical complications were observed in this series. Three patients were lost to follow-up. Twelve patients were classified as responders. Among the others, 1 patient experienced side effects (snoring and groaning during sleep) and the device was removed.

CONCLUSIONS

Our data confirm that VNS is a safe procedure and a valid palliative treatment option for drug-resistant epileptic patients not suitable for resective surgery.

Effectiveness of vagal nerve stimulation in medication-resistant epilepsy. Comparison between patients with and without medication changes

BACKGROUND

Vagal nerve stimulation (VNS) response is not immediate. A progressive decline in seizure frequency is usually found during a period of 12-18 months after implantation. During this time, the patient's medication is usually modified, which can create doubts about whether their clinical improvement is due to medication changes or to VNS itself. Our goal is to compare two groups of patients treated with VNS, with and without changes in their medication.

METHODS

We prospectively analyze 85 patients who were treated with VNS in our hospital between 2005 and 2014. In 43 patients, changes in the antiepileptic drugs (EAD) were not allowed during the postoperative follow-up and they were compared with 42 patients who were left at the option of neurologist make changes in medication. We analyzed the clinical situation at 18 months and compared the two groups.

RESULTS

Overall, 54.1% of patients had a reduction in seizures of 50% or higher (responders). In the group with no changes in medication, responders reached 63%, while in the group in which changes in medication were allowed, 45.2% were responders. Between responders and non-responders, there were no statistical differences in type of epilepsy, frequency, previous surgery, or intensity of stimulation.

CONCLUSIONS

We did not find a statistical difference in seizure frequency reduction between patients with or without changes in medication during their follow-up, so changes in medication did not improve the outcome. Furthermore, the absence of changes in AED can help to optimize the parameters of the stimulator in order to improve its effectiveness.

2015 ACVIM Small Animal Consensus Statement on Seizure Management in Dogs

This report represents a scientific and working clinical consensus statement on seizure management in dogs based on current literature and clinical expertise. The goal was to establish guidelines for a predetermined, concise, and logical sequential approach to chronic seizure management starting with seizure identification and diagnosis (not included in this report), reviewing decision‐making, treatment strategies, focusing on issues related to chronic antiepileptic drug treatment response and monitoring, and guidelines to enhance patient response and quality of life. Ultimately, we hope to provide a foundation for ongoing and future clinical epilepsy research in veterinary medicine.

Decreased heart rate and enhanced sinus arrhythmia during interictal sleep demonstrate autonomic imbalance in generalized epilepsy

We hypothesized that epilepsy affects the activity of the autonomic nervous system even in the absence of seizures, which should manifest as differences in heart rate variability (HRV) and cardiac cycle. To test this hypothesis, we investigated ECG traces of 91 children and adolescents with generalized epilepsy and 25 neurologically normal controls during 30 min of stage 2 sleep with interictal or normal EEG. Mean heart rate (HR) and high-frequency HRV corresponding to respiratory sinus arrhythmia (RSA) were quantified and compared. Blood pressure (BP) measurements from physical exams of all subjects were also collected and analyzed. RSA was on average significantly stronger in patients with epilepsy, whereas their mean HR was significantly lower after adjusting for age, body mass index, and sex, consistent with increased parasympathetic tone in these patients. In contrast, diastolic (and systolic) BP at rest was not significantly different, indicating that the sympathetic tone is similar. Remarkably, five additional subjects, initially diagnosed as neurologically normal but with enhanced RSA and lower HR, eventually developed epilepsy, suggesting that increased parasympathetic tone precedes the onset of epilepsy in children. ECG waveforms in epilepsy also displayed significantly longer TP intervals (ventricular diastole) relative to the RR interval. The relative TP interval correlated positively with RSA and negatively with HR, suggesting that these parameters are linked through a common mechanism, which we discuss. Altogether, our results provide evidence for imbalanced autonomic function in generalized epilepsy, which may be a key contributing factor to sudden unexpected death in epilepsy.

Managing drug-resistant epilepsy: challenges and solutions

Despite the development of new antiepileptic drugs (AEDs), ~20%-30% of people with epilepsy remain refractory to treatment and are said to have drug-resistant epilepsy (DRE). This multifaceted condition comprises intractable seizures, neurobiochemical changes, cognitive decline, and psychosocial dysfunction. An ongoing challenge to both researchers and clinicians alike, DRE management is complicated by the heterogeneity among this patient group. The underlying mechanism of DRE is not completely understood. Many hypotheses exist, and relate to both the intrinsic characteristics of the particular epilepsy (associated syndrome/lesion, initial response to AED, and the number and type of seizures prior to diagnosis) and other pharmacological mechanisms of resistance. The four current hypotheses behind pharmacological resistance are the "transporter", "target", "network", and "intrinsic severity" hypotheses, and these are reviewed in this paper. Of equal challenge is managing patients with DRE, and this requires a multidisciplinary approach, involving physicians, surgeons, psychiatrists, neuropsychologists, pharmacists, dietitians, and specialist nurses. Attention to comorbid psychiatric and other diseases is paramount, given the higher prevalence in this cohort and associated poorer health outcomes. Treatment options need to consider the economic burden to the patient and the likelihood of AED compliance and tolerability. Most importantly, higher mortality rates, due to comorbidities, suicide, and sudden death, emphasize the importance of seizure control in reducing this risk. Overall, resective surgery offers the best rates of seizure control. It is not an option for all patients, and there is often a significant delay in referring to epilepsy surgery centers. Optimization of AEDs, identification and treatment of comorbidities, patient education to promote adherence to treatment, and avoidance of triggers should be periodically performed until further insights regarding causative pathology can guide better therapies.

Vagus nerve stimulation therapy for treatment-resistant epilepsy: a 15-year experience at a single institution

OBJECTIVE

Treatment-resistant epilepsy (TRE) occurs in 20-30% of patients. The goal of this study is to assess the efficacy and safety of vagus nerve stimulation (VNS) in this group of patients, including adult and pediatric populations and several off-label indications.

METHODS

This is a retrospective review of 59 consecutive patients in whom 60 VNS devices were implanted at a single institution during a 15-year period. Patients were evaluated in the Multidisciplinary Epilepsy Committee and complete presurgical workup was performed. The series included indications not approved by the FDA, such as children under 12 years of age, pregnancy and right-sided VNS. Performing the procedure on an out-patient basis was recently adopted, minimizing hospital length of stay.

RESULTS

There were 42 adults and 17 children (14 under 12 years of age) and the mean age at implantation was 26 years. Duration of VNS therapy ranged from 6 months to 9 years. For the entire cohort, the mean percentage seizure reduction was 31.37%. Twenty patients (34.48%) were considered responders (seizure reduction ≥50%); 7 patients (12.06%) had seizure reduction of ≥75% and 2 patients had seizure control of ≥90% (3.4%). The patient in whom right-sided VNS was implanted achieved the same reduction in seizure burden and the patient who became pregnant could reduce antiepileptic drugs dosage, without complications. Side-effects were mild and there were no permanent nerve injuries. One patient died in the follow-up due to psychiatric disorders previously known.

CONCLUSIONS

VNS is a safe and effective palliative treatment for TRE patients. There are an increasing number of indications and further randomized trials would potentially expand the number of patients who may benefit from it. A multidisciplinary team is crucial for a complete preoperative evaluation and selection of the optimal candidates for the treatment.

Non-invasive vagus nerve stimulation for acute treatment of high-frequency and chronic migraine: an open-label study

BACKGROUND

The treatment of migraine headache is challenging given the lack of a standardized approach to care, unsatisfactory response rates, and medication overuse. Neuromodulation therapy has gained interest as an alternative to pharmacologic therapy for primary headache disorders. This study investigated the effects of non-invasive vagus nerve stimulation (nVNS) in patients with high-frequency episodic migraine (HFEM) and chronic migraine (CM).

FINDINGS

In this open-label, single-arm, multicenter study, patients with HFEM or CM self-treated up to 3 consecutive mild or moderate migraine attacks that occurred during a 2-week period by delivering two 120-s doses of nVNS at 3-min intervals to the right cervical branch of the vagus nerve. Of the 50 migraineurs enrolled (CM/HFEM: 36/14), 48 treated 131 attacks. The proportion of patients reporting pain relief, defined as a ≥50% reduction in visual analog scale (VAS) score, was 56.3% at 1 h and 64.6% at 2 h. Of these patients, 35.4% and 39.6% achieved pain-free status (VAS = 0) at 1 and 2 h, respectively. When all attacks (N = 131) were considered, the pain-relief rate was 38.2% at 1 h and 51.1% at 2 h, whereas the pain-free rate was 17.6% at 1 h and 22.9% at 2 h. Treatment with nVNS was safe and well tolerated.

CONCLUSION

Non-invasive vagus nerve stimulation may be effective as acute treatment for HFEM or CM and may help to reduce medication overuse and medication-associated adverse events.

Upper Airway Stimulation for Obstructive Sleep Apnea: Past, Present, and Future

ABSTRACT

Obstructive sleep apnea (OSA) is an increasingly prevalent clinical problem with significant effects on both personal and public health. Continuous positive airway pressure (CPAP) has demonstrated excellent efficacy and low morbidity; long-term adherence rates approach 50%. Although traditional upper airway surgical procedures target the anatomic component of obstruction, upper airway stimulation tackles the twin goals of improving anatomic and neuromuscular pathology. After decades of trials demonstrating proof of concept of hypoglossal nerve stimulation in animal and human subjects, the results of a large multicenter, prospective trial were recently published. The trial demonstrated that hypoglossal nerve stimulation led to significant improvements in objective and subjective measurements of the severity of OSA. This novel approach is the first to combine sleep surgery techniques with a titratable medical device for the treatment of OSA. Further research is required to define optimal patient selection and device performance and to demonstrate long-term effectiveness.

Partial to complete suppression of unilateral noise-induced tinnitus in rats after cyclobenzaprine treatment

Some forms of tinnitus are believed to arise from abnormal central nervous system activity following a single or repeated noise exposure, for which there are no widely accepted pharmacological treatments. One central site that could be related to tinnitus awareness or modulation is the locus coeruleus, a brainstem structure associated with stress, arousal, and attention. In the present study, we evaluated the effects of cyclobenzaprine, a drug known to act on the rat locus coeruleus, on noise-induced tinnitus using Gap Prepulse Inhibition of the Acoustic Startle (GPIAS). In untreated rats, brief silent gaps presented prior to a 5-10-kHz bandpass startling stimulus produced robust GPIAS. Treatment with cyclobenzaprine alone had no effect on the ability of gaps to suppress the startle response. When animals were exposed to intense narrow-band (126 dB SPL, 16 kHz, 100 Hz BW) unilateral noise, GPIAS was significantly reduced, suggesting the presence of tinnitus. Following the noise exposure, a subset of rats that maintained a robust startle response continued to show GPIAS impairment at 6-20 kHz, 40 days post-noise, suggesting chronic tinnitus. When this subset of animals was treated with cyclobenzaprine, at a dose that had no significant effects on the startle response (0.5 mg/kg), GPIAS recovered partially or to near baseline levels at the affected frequencies. These results were consistent with the absence of tinnitus. By 48 h post-treatment, evidence of tinnitus re-emerged. Our results suggest that cyclobenzaprine was effective in transiently suppressing noise-induced tinnitus in rats.