Effects of vagus nerve stimulation on amino acids and other metabolites in the CSF of patients with partial seizures

Expanding therapeutic options: Devices and the treatment of refractory epilepsy

Alternative treatments to anticonvulsants and resective surgery are needed for patients with refractory epilepsy. The renewed interest in brain stimulation and device therapy is exciting and is based on expanding human and animal research. Many important questions remain, such as where and how the stimuli should be applied. If we assume that neural networks are responsible for seizure generation and propagation, it seems reasonable to assume that seizures can be affected by electrical stimulation of more than one brain region. As research continues, we may discover that stimulation of a particular brain region is more effective for a specific type of epilepsy. In addition to finding the ideal site for treatment, the optimum stimulation parameters must be defined. We may find that different brain regions require different stimulation parameters. Presently, the Vagus Nerve Stimulator is the only alternative treatment to anticonvulsive drugs or surgery that is currently available. However, as technology advances and our understanding of epilepsy grows, we are likely to see increasingly sophisticated devices. Some of these devices may have the capacity to accurately detect seizures and to respond with the most appropriate type of stimulation.

Down syndrome and epilepsy: a nutritional connection?

Non-Asian individuals with Down syndrome are much more likely to develop epileptic seizure disorders than individuals without Down syndrome. Examination of nutrient and metabolite levels in patients with these two seemingly disparate disorders reveals numerous similarities. Compared to individuals without these disorders, individuals with Down syndrome and individuals with seizures may have lower levels of vitamin A, vitamin B1, folate, vitamin B12, vitamin C, magnesium, manganese, selenium, zinc, carnitine, carnosine, choline, and possibly serine. Excesses of copper, cysteine, phenylalanine, and superoxide dismutase are also sometimes encountered in both disorders. In addition to common nutritional lower levels and excesses, disorders of metabolism involving vitamin B6, vitamin D, calcium, and tryptophan may play a common role. This paper hypothesizes that nutritional factors may account for the high joint occurrence of these conditions. Further examination of these data may provide insights into nutritional, metabolic and pharmacological treatments for both conditions.

Mechanisms of the anti-ischemic effect of vagus nerve stimulation in the gerbil hippocampus

The neuroprotective mechanisms of cervical vagus nerve stimulation (VNS) in transient ischemia were investigated. Left VNS (0.4 mA, 40 Hz) was performed during 5 min ischemia in gerbils. About 50% of the hippocampal neurons were rescued from ischemic insult by VNS, and this effect was prevented by transection of the vagus nerve centrally to the site of cervical stimulation. VNS significantly attenuated both ischemia-induced glutamate release and transient increase of hippocampal blood flow during reperfusion. Hyperemia as well as excessive glutamate release after ischemia is regarded as an important factor in ischemic brain damage as it leads to generate considerable reactive oxygen species. Thus, VNS might protect neurons from ischemia-induced glutamate excitotoxicity and reperfusion injury via the afferent path-way of the vagus.

Episodic phrenic-inhibitory vagus nerve stimulation paradoxically induces phrenic long-term facilitation in rats

All respiratory long-term facilitation (LTF) is induced by inspiratory-excitatory stimulation, suggesting that LTF needs inspiratory augmentation and is the result of a Hebbian mechanism (coincident pre- and post-synaptic activity strengthens synapses). The present study examined the long-term effects of episodic inspiratory-inhibitory vagus nerve stimulation (VNS) on phrenic nerve activity. We hypothesized that episodic VNS would induce phrenic long-term depression. The results are compared with those obtained following serotonin receptor antagonism or episodic carotid sinus nerve stimulation (CSNS). Integrated phrenic neurograms were measured before, during and after three episodes of 5 min VNS (50 Hz, 0.1 ms), each separated by a 5 min interval, at a low (approximately 50 microA), medium (approximately 200 microA) or high (approximately 500 microA) stimulus intensity in anaesthetized, vagotomized, neuromuscularly blocked and artificially ventilated rats. Medium- and high-intensity VNS eliminated rhythmic phrenic activity during VNS, while low-intensity VNS only reduced phrenic burst frequency. At 60 min post-VNS, phrenic amplitude was higher than baseline (35 +/- 5% above baseline, mean +/- S.E.M., P < 0.05) in the high-intensity group but not in the low- (-4 +/- 4%) or medium-intensity groups (-10 +/- 15%), or in the high-intensity with methysergide group (4 mg kg(-1), i.p.) (-11 +/- 5%). These data, which are inconsistent with our hypothesis, indicate that phrenic-inhibitory VNS induces a serotonin-dependent phrenic LTF similar to that induced by phrenic-excitatory CSNS (33 +/- 7%) and may require activation of high-threshold afferent fibres. These data also suggest that the synapses on phrenic motoneurons do not use the Hebbian mechanism in this LTF, as these motoneurons were suppressed during VNS.

Correlation between GABA(A) receptor density and vagus nerve stimulation in individuals with drug-resistant partial epilepsy

Vagus nerve stimulation (VNS) is an important option for the treatment of drug-resistant epilepsy. Through delivery of a battery-supplied intermittent current, VNS protects against seizure development in a manner that correlates experimentally with electrophysiological modifications. However, the mechanism by which VNS inhibits seizures in humans remains unclear. The impairment of gamma-aminobutyric acid (GABA)-mediated neuronal inhibition associated with epilepsy has suggested that GABA(A) receptors might contribute to the therapeutic efficacy of VNS. We have now applied single photon emission computed tomography (SPECT) with the benzodiazepine receptor inverse agonist [123I]iomazenil to examine cortical GABA(A) receptor density (GRD) before and 1 year after implantation of a VNS device in 10 subjects with drug-resistant partial epilepsy. VNS therapeutic responses resulted significantly correlated with the normalization of GRD. Moreover, a comparable control group, scheduled for a possible VNS implant, failed to show significant GRD variations after 1 year of a stable anti-epileptic treatment. These results suggest that VNS may modulate the cortical excitability of brain areas associated with epileptogenesis and that GABA(A) receptor plasticity contributes to this effect.

Cervical vagus nerve stimulation for treatment-resistant depression

Therapeutic brain stimulation through left cervical VNS now has established safety and efficacy as a long-term adjunct treatment for medication-resistant epilepsy. There is considerable evidence from both animal and human studies that the vagus nerve carries afferent signals to limbic and higher cortical brain regions, providing a rationale for its possible role in the treatment of psychiatric disorders. Open-label studies in patients with treatment-resistant depression have produced promising results, especially when response rates at longer term (1 year and 2 years) follow-up time points are considered. Short-term (10 weeks) treatment with VNS failed to demonstrate statistical superiority over sham treatment in a recently completed double-blind study, so antidepressant efficacy has not yet been established. Longer term data on VNS in depressed patients as well as further information regarding the possible dose-response relation will help to determine the place of VNS in the armament of therapeutic modalities available for major depression.

Stimulation of the nervous system for the management of seizures: current and future developments

Vagal nerve stimulation (VNS) for the treatment of refractory epilepsy appears to have started from the theory that since VNS can alter the EEG, it may influence epilepsy. It proved effective in several models of epilepsy and was then tried in short-term, open-label and double-blind trials, leading to approval in Canada, Europe and the US. Follow-up observations in these patients demonstrated continued improvement in seizure control for up to 2 years. Close to 50% of treated patients have achieved at least a 50% reduction in seizure frequency. This therapy was also useful as rescue therapy for ongoing seizures in some patients; many patients are more alert. The initial trials were completed in patients >/=12 years of age with refractory partial seizures. Subsequently, similar benefits were shown in patients with tuberous sclerosis complex, Lennox-Gastaut syndrome, hypothalamic hamartomas and primary generalised seizures. Implanting the generator and leads is technically easy, and complications are few. The method of action is largely unknown, although VNS appears to alter metabolic activity in specific brain nuclei. Considering that improvement in mood is frequently found in patients using VNS, it has undergone trials in patients with depression. Other illnesses deserving exploration with this unusual therapy are Alzheimer's disease and autism. Some aspects of VNS have proven disappointing. Although patients have fewer seizures, the number of antiepileptic drugs they take is not significantly reduced. In addition, there is no way to accurately predict the end of life of the generator. Optimal stimulation parameters, if they exist, are unknown. Deep brain stimulation is a new method for controlling medically refractory seizures. It is based on the observation that thalamic stimulation can influence the EEG over a wide area. Several thalamic nuclei have been the object of stimulation in different groups of patients. Intraoperative brain imaging is essential for electrode placement. The procedure is done under local anaesthesia. Experience with this therapy is currently limited, but growing.

Neurostimulation therapy for epilepsy: current modalities and future directions

Neurostimulation is a recent development in the treatment of epilepsy. Vagus nerve stimulation (VNS), the only approved neurostimulation therapy for epilepsy to date, has proved to be a viable adjunctive treatment option. The exact mechanism of action of VNS is not fully understood. In 2 randomized double-blind trials, seizure frequency declined approximately 30% after 3 months of treatment. Long-term follow-up studies suggest that response improves over time, with approximately 35% of patients experiencing a 50% reduction and 20% experiencing a 75% reduction in seizure frequency after 18 months of treatment. Unfortunately, the number of patients rendered medication-free and seizure-free with VNS is low. Vagus nerve stimulation is best viewed as an option for patients who are not surgical candidates or who hesitate to take the risk of surgery yet continue to have seizures despite maximal medical therapy. Stimulation of other regions of the central nervous system for treating epilepsy, including the anterior and centromedian nuclei of the thalamus, the hippocampus, the subthalamic nucleus, and the cerebral neocortex, is currently under investigation. We review the history, proposed mechanisms of action, clinical trials, adverse effects, and future direction of VNS and other modalities of neurostimulation therapy for epilepsy.

Vagus nerve stimulation in awake rats reduces formalin-induced nociceptive behaviour and fos-immunoreactivity in trigeminal nucleus caudalis

Besides its well-established efficacy in epilepsy, vagus nerve stimulation (VNS) may be of potential interest in pain treatment. It has, however, not yet been assessed in animal pain models with the devices and stimulation protocols used in humans. We have therefore studied in awake rats the effects of left cervical VNS on trigeminal nociception using an implantable electrode and stimulator (NCP-Cyberonics). VNS was applied for 24h at 2 mA intensity, 20 Hz frequency, 0.5 ms pulse width and a duty cycle of 20s ON/18s OFF. As a nociceptive stimulus, we injected formalin into the left mystacial vibrissae, assessed behaviour for 45 min and sacrificed the animals 45 min later. Fos-immunoreactive (Fos-Ir) neurons were counted in laminae I-II of trigeminal nucleus caudalis (TNC) on both sides. We used three groups of control animals: VNS without formalin, formalin without VNS and sham VNS (implanted without stimulation or formalin). Whereas sham VNS had no significant effect, VNS alone increased Fos expression in ipsilateral TNC in addition to the expected increase in nucleus tractus solitarius. It also significantly attenuated the increase of Fos-Ir neurons observed in ipsilateral TNC laminae I-II after formalin injection. If the proper VNS effect on Fos-expression was subtracted, the reduction of formalin-induced nociceptor activation was 55%. VNS also reduced nociceptive behaviour on average by 96.1% during the early phase (0-6 min) and by 60.7% during the late phase (6-45 min) after the formalin injection. These results suggest that VNS applied with a device used in human therapy may have in awake rats a significant antinociceptive effect in a model of trigeminal pain.

Vagus-nerve stimulation for the treatment of epilepsy

Vagus-nerve stimulation (VNS) is now an accepted treatment for patients with refractory epilepsy. There have been many studies suggesting that VNS affects the brain in such areas as the thalamus and other limbic structures. In addition, there is some evidence that norepinephrine is important in the prophylactic antiseizure effects of VNS. The efficacy of VNS has been established for partial seizure types, even in refractory patients who did not respond to surgical treatment for epilepsy. There are also data, from open-label studies, that suggest efficacy in other seizure types. Therefore, VNS seems to be a broad-spectrum treatment for epilepsy. Improvement is not immediate but increases over 18-24 months of treatment. Most studies report subjective improvements in various quality-of-life measurements during treatment with VNS--objective trials have confirmed this observation. Side-effects are mainly stimulation related and reversible and they tend to decrease over time. They are generally mild to moderate and seldom necessitate the removal of the device. No idiosyncratic side-effects have been reported in 12 years of experience, and VNS does not interact with antiepileptic drugs. Most adverse events are predictable and related to the specific stimulation regimen. VNS does not have cognitive and systemic side-effects and can, therefore, be a valuable treatment approach even for patients who have poor tolerance of antiepileptic drugs.

Cerebral activation during vagus nerve stimulation: a functional MR study

PURPOSE

To study the short-term effects of vagus nerve stimulation (VNS) on brain activation and cerebral blood flow by using functional magnetic resonance imaging (fMRI).

METHODS

Five patients (three women, two men; mean age, 35.4 years) who were treated for medically refractory epilepsy with VNS, underwent fMRI. All patients had a nonfocal brain MRI. The VNS was set at 30 Hz, 0.5-2.0 mA for intervals of activation of 30 s on and 30 s off, during which the fMRI was performed. Statistical parametric mapping (SPM) was used to determine significant areas of activation or inhibition during vagal nerve stimulation (p < 0.05).

RESULTS

VNS-induced activation was detected in the thalami bilaterally (left more than right), insular cortices bilaterally, ipsilateral basal ganglia and postcentral gyri, right posterior superior temporal gyrus, and inferomedial occipital gyri (left more than right). The most robust activation was seen in the thalami (left more than right) and insular cortices.

CONCLUSIONS

VNS-induced thalamic and insular cortical activation during fMRI suggests that these areas may play a role in modulating cerebral cortical activity, and the observed decrease in seizure frequency in patients who are given VNS may be a consequence of this increased activation.

Effect of electrical stimulation of the nucleus of the solitary tract on the development of electrical amygdaloid kindling in the cat

PURPOSE

This work analyzed the effect of electrical stimulation of the nucleus of the solitary tract (NTS) on the development of electrical amygdaloid kindling (AK) in freely moving cats.

METHODS

Nine male adult cats with implanted electrodes in both amygdalae (basolateral nucleus), both lateral geniculate bodies, left NTS, and both prefrontal cortices were used. Electromyogram and electrooculogram also were recorded. The AK was performed every 24 h (1-s train, 1-ms pulses, 60 Hz, 300-600 microA). The NTS was stimulated previously for 1 min (0.5-ms pulses, 30 Hz, 150-300 microA), just before the AK at 10:00 a.m., and then every 60 min, 4 times, from 11:00 a.m. to 2:00 p.m. On different days, all NTS stimulation was suspended, and AK was continued until stage VI kindling was reached.

RESULTS

Behavioral changes produced by the stimulation of the NTS were blinking, immobility periods with upward sight, licking, and swallowing. Animals with simultaneous stimulation of NTS and AK did not reach stage VI, remaining in behavioral stages I-III. Stage VI was reached after NTS stimulation was intentionally suspended. The amplitude, duration, and the propagation of the amygdaloid afterdischarge did not exhibit progressive evolution during NTS stimulation. A regression analysis was performed between the number of days with only AK stimulation and days with simultaneous NTS stimulation, which showed a positive correlation (values of r = 0.84).

CONCLUSIONS

Our results suggest that NTS stimulation interferes with the development of convulsive evolution and secondary generalization. This delay effect may be due to the activation of the locus ceruleus and some areas of the midbrain reticular formation, among other structures, which has been demonstrated to inhibit experimental convulsive seizures.

VNS therapy in clinical practice in children with refractory epilepsy

OBJECTIVES

To study the efficacy, tolerability and safety of the vagus nerve stimulation (VNS) therapy in clinical practice, in 16 children and adolescents with refractory epilepsy.

METHODOLOGY

We assessed the efficacy of VNS therapy, retrospectively by comparing seizure frequency, duration and severity at the time of most recent follow up (av: 24.9 months) to that in the 4 weeks prior to VNS surgery. Changes in quality of life, sleep and behaviour at last review was compared with that prior to VNS. Adverse effects elicited by specific questioning, spontaneous reporting and clinical examination are described.

RESULTS

Vagus nerve stimulation resulted in a >50% reduction in seizure frequency in 62.5% of children with 25% achieving a >90% reduction. Vagus nerve stimulation was well tolerated in all but one of our cohort, with no serious side-effects.

CONCLUSION

Our results support its role as one of the options in intractable childhood epilepsy.

Vagus nerve stimulation in pediatric epilepsy: a review

Therapeutic options for intractable epilepsy include new and investigational antiepileptic drugs, ketogenic diet, epilepsy surgery, and, now, vagus nerve stimulation, which is approved by the U.S. Food and Drug Administration for the treatment of refractory partial seizures in adolescents and adults. The exact mechanisms of action are unknown. Although the use of vagus nerve stimulation in children has increased, including those younger than 12 years of age or those with generalized epilepsy, there has been no large controlled pediatric study to date. The identification of favorable prognostic indicators, especially in children, would be useful. Preliminary results suggest that children with Lennox-Gastaut syndrome may have a favorable response, with improvement in both seizure control and global evaluation scores. Improved global evaluation scores have occurred even without an associated improvement in seizure control.

Major Psychiatric Disorders Subsequent to Treating Epilepsy by Vagus Nerve Stimulation

Purpose. The goal of this work was documentation of incidence, phenomenology, pathogenesis, and treatment of psychiatric disorders occurring subsequent to treating epilepsy by vagus nerve stimulation (VNS).Methods. In a series of 81 patients treated by VNS, all patients who developed major psychiatric complications underwent systematic psychiatric evaluation and treatment with psychotropic medication; VNS was modified if necessary.Results. After the seizure frequency was reduced by at least 75%, 7 of 81 patients (9%) developed major psychiatric disorders: Six became severely dysphoric (5 with catastrophic rage and 4 with psychotic symptoms), and one became psychotic. All 7 patients had experienced dysphoric disorders and 2 had experienced psychotic episodes prior to the VNS treatment. Five patients had frequent daily seizures prior to treatment. Remission or satisfactory improvement was achieved with psychotropic medication in 6 patients, aided by decreasing or interrupting VNS in two patients. One patient was noncompliant and suffered a fatal outcome.Conclusion. Severe interictal dysphoric disorders associated with catastrophic rage and psychotic episodes may develop on suppressing seizures by VNS in patients with previous epilepsy-related psychiatric disorders. Patients with multiple daily seizures may be more vulnerable to this occurrence. The phenomenon corresponds to the common finding of interictal dysphoric and psychotic symptoms emerging when inhibitory mechanisms predominate (alternative psychiatric disorders in the absence of seizures, or forced normalization of the EEG). The dysphoric symptom of catastrophic rage appears to occur more often on seizure suppression by VNS than by antiepileptic drugs. Psychiatric intervention, primarily with antidepressant medication, must be available to secure a good outcome; decrease of VNS may occasionally be required.

Vagus nerve stimulation: clinical experience in a large patient series

During the last decade, intermittent electrical stimulation of the left cervical vagus nerve was established as a new add-on treatment of drug-resistant seizures. Particularly in Europe, the acceptance of vagus nerve stimulation (VNS) was tentative in the beginning because of unknown mechanisms of action. We report the outcome in a sample of 95 adult patients with drug-resistant seizures who have received implants since 1998. The last available follow-up data are included. Unavoidable medication changes (e.g., intoxication) were accepted to examine VNS under usual clinical conditions. Median percentage of reduction in seizure frequency as compared to baseline was 30%. The seizure responder rate (> or =50% reduction) was 45%. Four patients experienced total release from seizures. Adverse effects were mild in general. Seizure outcome was positively correlated with VNS duration. No potential clinical factor (e.g., syndrome, cause, or lesion) could be identified as an indicator of favorable outcome. Patients with on stimulation-on periods of 30 seconds (standard cycle) had a better outcome than patients with stimulation-on periods of 7 seconds (rapid cycle). During an embedded, randomized, controlled trial, no evidence was found for a differential outcome of initial standard cycle versus initial rapid cycle stimulation conditions. Taking into account the good cost-benefit ratio as well as positive effects on well-being, VNS has to be considered an appropriate strategy for the add-on treatment of drug-resistant seizures, particularly in cases not suitable for epilepsy surgery.

Vagus nerve stimulation for refractory epilepsy

Vagus nerve stimulation (VNS) is a neurophysiological treatment for patients with medically or surgically refractory epilepsy. Since the first human implant in 1989, more than 10 000 patients have been treated with VNS. Two randomized controlled studies have shown a statistically significant decrease in seizure frequency during a 12-week treatment period versus a baseline period when 'high stimulation' mode was compared with 'low stimulation' mode. The efficacy appears to increase over time. In general, one third of the patients show a >50% reduction of seizure frequency; one third show a 30-50% seizure reduction, and one third of patients show no response. Few patients become seizure-free. Side effects during stimulation are mainly voice alteration, coughing, throat paraesthesia and discomfort. When studied on a long-term basis, VNS is an efficacious, safe and cost-effective treatment not only in adults but also in children and the elderly. The precise mechanism of action remains to be elucidated. In recent years much progress has been made through neurophysiological, neuroanatomical, neurochemical and cerebral blood flow studies in animals and patients treated with VNS. Further elucidation of the mechanism of action of VNS may increase its clinical efficacy and our general understanding of some physiopathological aspects of epilepsy. Finally, VNS may become an alternative treatment for other conditions such as depression and pain.

The mechanism of action of vagus nerve stimulation for refractory epilepsy: the current status

Vagus nerve stimulation (VNS) is a neurophysiologic treatment for patients with medically or surgically refractory epilepsy. Since the first human implant in 1989, more than 10,000 patients have been treated with VNS. The precise mechanism of action remains to be elucidated. Animal experiments with VNS were initially performed to demonstrate efficacy and safety preceding the clinical trials in human patients. Mechanism of action research involving animal experiments can provide essential clues. Animal experiments are often labor-intensive even in the hands of experienced researchers, however, and the results remain only a reflection of the complicated pathophysiologic systems of the human brain. Mechanism of action research in human patients treated with VNS is particularly challenging because of safety concerns, the large number of patients required, and the heterogeneous nature of various small patient series. This study provides an overview of the progress that has been made in the past 10 years through neurophysiologic, neuroanatomic, neurochemical, and cerebral blood flow studies in animals and patients treated with VNS. Further elucidation of the mechanism of action of VNS may increase its clinical efficacy. It may also provide inspiration for the development of new therapeutic modalities for refractory epilepsy.

Vagus nerve stimulation in depression

Ever since the introduction of chemical and electrical convulsive treatment for psychiatric disorders in the 1930s and 1940s, biological techniques have been used extensively in the amelioration of a variety of psychiatric disorders. Techniques of recent vintage have included transcranial magnetic stimulation, deep brain stimulation and vagus nerve stimulation (VNS). Since VNS attenuates seizures in animal models, the treatment was initially developed and approved by the FDA for treatment of drug-resistant partial-onset epilepsy. Additional data, including the known neuroanatomy of the vagus nerve, effects of VNS on monoamines and mood improvement in patients with epilepsy who were treated with VNS, provided a rationale for further investigation in patients with primary mood disorders. VNS has been administered acutely for 10 weeks to 60 patients with treatment-resistant depression. Longer-term follow-up data has been analysed for the first 30 patients. Response rates have been at least 30% in the acute study. Similar to findings in epilepsy and in contrast to the usual results of long-term medication trials, longer term data regarding symptomatic and functional outcomes of depressed patients receiving VNS continue to look promising. As opposed to electroconvulsive therapy, VNS is not associated with cognitive impairment. These results have led to approval of VNS for the treatment of resistant depression (unipolar or bipolar) in both Europe and Canada. Currently, a pivotal double-blind acute study is underway in the US.

Vagus nerve stimulation and the ketogenic diet

Antiepileptic drugs are the primary form of treatment for patients with epilepsy. In the United States, hundreds of thousands of people do not achieve seizure control, or have significant side effects, or both. Only a minority of patients with intractable epilepsy are candidates for traditional epilepsy surgery. Vagus nerve stimulation is now the second most common treatment for epilepsy in the United States. Additionally, the ketogenic diet has established itself as a valid treatment. This article discusses the history, mechanism of action, patient selection, efficacy, initiation, complications, and advantages of vagus nerve stimulation and the ketogenic diet.

Vagus nerve stimulation. A potential therapy for resistant depression?

VNS builds on a long history of investigating the relationship of autonomic signals to limbic and cortical function and is one of the newest methods to physically alter brain function. VNS is a clinically useful anticonvulsant therapy in treatment resistant patients with epilepsy, and pilot data suggest that it has potential as an antidepressant therapy. The known anatomic projections of the vagus nerve suggest that VNS also might have other neuropsychiatric applications. Additional research is needed to clarify the mechanisms of action of VNS and the potential clinical utility of this intriguing new somatic portal into the CNS.

Vagus nerve stimulation: a new form of therapeutic brain stimulation

Although the vagus nerve has traditionally been considered to perform efferent functions, in reality it performs significant afferent functions as well, carrying information from the body, head, and neck to the brain. Preliminary studies examining this afferent activity led to the theory that vagus nerve stimulation (VNS) could successfully control seizure activity in persons who are refractory to antiepileptic medications. Unlike other forms of brain stimulation, VNS is unable to directly stimulate multiple discrete areas of the brain; however, through several pathways, it is able to relay sensory information to higher brain regions. An implantable VNS device known as the VNSTM NeuroCybernetic Prosthesis (NCP) System has been used in approximately 9,000 epilepsy patients in Europe and the United States since 1994. The implant has reduced seizure frequency by an average of 25% to 30%, with minimal side effects. Studies underway are also showing some degree of success in the management of treatment-refractory depression. The future efficacy of the implantable system in other disorders may depend on whether the implant can be more precisely focused to affect different brain regions. Research in this area is underway.

Acute single photon emission computed tomographic study of vagus nerve stimulation in refractory epilepsy

PURPOSE

Left-sided vagus nerve stimulation (VNS) is an efficacious treatment for patients with refractory epilepsy. The precise mechanism of action remains to be elucidated. Only limited data on VNS-induced changes in regional cerebral blood flow (rCBF) are available. The aim of this study was to investigate rCBF changes during initial VNS with single-photon emission computed tomography (SPECT).

METHODS

In 12 patients (8 women, 4 men) with mean age of 32 years and mean duration of epilepsy of 19 years, VNS-induced rCBF changes were studied by means of a 99mTc-ethyl cysteinate dimer activation study with a single-day split-dose protocol before and immediately after initial stimulation. Images were acquired on a triple-head camera with fan-beam collimators and were reconstructed with scatter and attenuation correction. After coregistration to a standardized template, both a semiquantitative analysis using predefined volumes-of-interest (VOIs) as well as voxel-by-voxel analysis of the intrasubject activation were performed. During follow-up, efficacy of VNS in terms of seizure-frequency reduction was studied.

RESULTS

The semiquantitative analysis, with reference to the total counts in all VOIs, revealed a significant decrease of activity in the left thalamus immediately after the initial stimulation train. These results agreed with voxel-by-voxel analysis. In our study ipsilateral thalamic hypoperfusion was the most significant finding. Mean frequency of complex partial seizures was reduced from 30 per month before implantation to six per month after implantation.

CONCLUSIONS

VNS induces rCBF changes immediately after initial stimulation that can be studied with SPECT. VNS-induced changes in the thalamus may play an important role in suppression of seizures. However, no significant relation between the level of hypoperfusion and subsequent clinical efficacy was found.

Vagus nerve stimulation for epilepsy: a review

Vagus nerve stimulation is an empirically based method for treatment of epilepsy by repeated stimulation of the left vagus nerve through implanted electrodes. Despite studies in animals and man, which show changes in brain electrophysiology, metabolism and neurochemistry, the mode of action remains unknown. Clinical testing has presented methodological challenges, as it is difficult to assess under double blind conditions a treatment which requires surgery and produces a sensation every time the stimulator comes on. This has nevertheless been successfully addressed in parallel design, controlled trials comparing high and low stimulation schedules. These have been performed in adults with medically intractable partial seizures, and demonstrated efficacy, safety and good tolerability. Efficacy, both in the controlled trials and in numerous reports arising from the considerable post-marketing experience is modest. Some 30% of patients achieve a 50% seizure reduction after 3 months of treatment, but this proportion progressively increases to about 50% after 18 months. Side-effects comprise: discomfort in the face or neck when the stimulator is activated, coughing, breathlessness on exertion and hoarseness of voice. All are related to intensity of stimulation and rapidly habituate in most subjects. In those patients who respond, a stimulus level can therefore generally be found which is acceptable to the subject. No indication other than refractory partial seizures in adults has been the subject of controlled trials, but post-marketing experience and uncontrolled reports indicate comparable efficacy and safety in a wide range of epilepsies, partial and generalized, idiopathic, cryptogenic, or symptomatic, in patients of all ages.

A Pilot Study of Mood in Epilepsy Patients Treated with Vagus Nerve Stimulation

Context. Antiepileptic drugs (AEDs) are frequently used for their beneficial mood effects.Objective. We sought to determine if there was a quantifiable effect on mood of the vagus nerve stimulator (VNS) when used as an antiseizure treatment.Design. Mood was assessed before and 3 months after VNS implantation in adult epilepsy patients. A group of adult epilepsy patients on stable AED regimens were used as a comparison group. AED regimens were unchanged during the study. The change in mood scale scores across time was assessed by t test (intragroup) and two-factor repeated-measures ANOVA (intergroup).Setting. An epilepsy center in a university hospital was the setting.Subjects. Twenty consecutive adult epilepsy patients undergoing VNS implantation to improve seizure control and twenty adult seizure patients with no intervention were enrolled.Main outcome measures. The mood scales used were the Cornell Dysthymia Rating Scale (CDRS) and the Hamilton Depression (Ham-D), Hamilton Rating Scale for Anxiety (Ham-A), and Beck Depression Inventory (BDI) scales.Results. The VNS group showed a significant decrease in mood scale scores across time (t test CDRS P = 0.001, Ham-D P = 0.017, BDI P = 0.045), indicating a decrease in depressive symptoms. The Ham-A scores in the VNS group and the comparison group scores did not significantly change across time. There were no significant differences between groups across time, although the BDI approached significance at P = 0.07. The VNS group had a significant decrease in seizure frequency compared with the comparison group (P = 0.01). There was no difference in mood scales over time between the VNS treatment responders (defined by >50% decrease in seizure frequency) and nonresponders, suggesting dissociation between seizure frequency reduction and mood change.Conclusion. VNS treatment is associated with mood improvement as measured by multiple scales, but differences in mood scale scores over time between the VNS and a comparison group were not found.

Vagus nerve stimulation: a new tool for brain research and therapy

Biological psychiatry has a long history of using somatic therapies to treat neuropsychiatric illnesses and to understand brain function. These methods have included neurosurgery, electroconvulsive therapy, and, most recently, transcranial magnetic stimulation. Fourteen years ago researchers discovered that intermittent electrical stimulation of the vagus nerve produces inhibition of neural processes, which can alter brain electrical activity and terminate seizures in dogs. Since then, approximately 6000 people worldwide have received vagus nerve stimulation for treatment-resistant epilepsy. We review the neurobiology and anatomy of the vagus nerve and provide an overview of the vagus nerve stimulation technique. We also describe the safety and potential utility of vagus nerve stimulation as a neuroscience research tool and as a putative treatment for psychiatric conditions. Vagus nerve stimulation appears to be a promising new somatic intervention that may improve our understanding of brain function and has promise in the treatment of neuropsychiatric disorders.

Vagus nerve prolonged stimulation in cats: effects on epileptogenesis (amygdala electrical kindling): behavioral and electrographic changes

PURPOSE

To analyze the effect of prolonged (daily) electrical vagus nerve stimulation (VNS) on daily amygdaloid kindling (AK) in freely moving cats.

METHODS

Fifteen adult male cats were implanted in both temporal lobe amygdalae, both lateral geniculate bodies, and prefrontal cortices. A bipolar hook (5-mm separation) stainless steel electrode also was implanted in the unsectioned left vagus nerve. AK only was performed on five of the cats as a control. The remaining 10 cats were recorded under the following experimental conditions: VNS (1.2-2.0 mA, 0.5-ms pulses, 30 Hz) for 1 min along with AK (1-s train, 1-ms pulses, 60 Hz, 300-600 microA), followed by VNS alone for 1 min, four times between 11:00 a.m. and 2 p.m. At different times, VNS was arrested, and AK was continued until stage VI kindling was reached.

RESULTS

The behavioral changes evoked by VNS were as follows: left miosis, blinking, licking, abdominal contractions, swallowing, and eventually yawning, meowing, upward gaze, and short head movements. Compulsive eating also was present with a variable latency. Outstanding polygraphic changes consisted of augmentation of eye movements and visual evoked potentials while the animal was awake and quiet, with immobility and upward gaze. An increase of the pontogeniculooccipital (PGO) wave density in rapid eye movement (REM) sleep also was noticeable. AK was completed (to stage VI) in the control animals without a vagus nerve implantation in 23.4+/-3.7 trials. In animals with VNS, the AK was significantly delayed, remaining for a long time in the behavioral stages I-III and showing a reduction of afterdischarge duration and frequency. Stage VI was never reached despite 50 AK trials, except when the vagus nerve electrodes were accidentally broken or vagal stimulation was intentionally arrested. Under these circumstances, 24.4+/-8.16 AK trials alone were necessary to reach stage VI of kindling.

CONCLUSIONS

Our results indicate that left, electrical VNS interferes with AK epileptogenesis. This anticonvulsant effect could be related to the increase of REM sleep.

Vagal nerve stimulation in epileptic encephalopathies

OBJECTIVE

To study the effect of vagal nerve stimulation (VNS) in children with epileptic encephalopathies.

METHODS AND MATERIALS

All children receiving VNS during a 2-year period at our center were studied prospectively for changes in seizure frequency, electroencephalogram (EEG), adaptive behavior, quality of life, and where appropriate, verbal/nonverbal performance. Assessments were made before and for at least 1 year after implant.

RESULTS

Sixteen children were studied. One device was removed because of infection. Of the remaining 15 children, 4 had a >50% reduction and 2 had a >50% increase in seizure frequency at 1 year after implant. Median reduction in seizure frequency was 17%. There was no trend toward improvement of the EEG or adaptive behavior. Quality of life was unchanged in most areas, except in perceived treatment side effects and general behavior that were improved. In 6 children undergoing further assessment, there was a significant improvement in verbal performance; this did not correlate with reduction in seizure frequency.

CONCLUSION

VNS did not significantly improve seizure frequency, severity, adaptive behavior, or the EEG during the first year of treatment for the group as a whole, although 4 children (27%) had a worthwhile reduction in seizure frequency. There were significant improvements in perceived treatment side effects and general behavior.

An institutional experience with cervical vagus nerve trunk stimulation for medically refractory epilepsy: rationale, technique, and outcome

OBJECTIVE

Intermittent stimulation of the left cervical vagus nerve trunk is emerging as a novel adjunct in the treatment of medically refractory seizures. We sought to evaluate theoretical and practical issues attendant to this concept. We review the anatomic and physiological background arguing for clinical application of vagus nerve stimulation, discuss salient aspects of patient selection and the nuances of surgical technique, and present our observations of and results from application of the method.

METHODS

Each of 18 patients with medically refractory epilepsy and at least six complex partial or secondarily generalized seizures per month underwent placement of a NeuroCybernetic Prosthesis pulse generator (Cyberonics, Webster, TX) in the chest, connected to helical platinum leads applied to the left cervical vagus nerve trunk. The patients were then randomized in a double-blinded fashion to receive either high (presumably therapeutic) or low (presumably less therapeutic) levels of vagus nerve stimulation. Reduction in seizure frequency, global assessments of quality of life, physiological measurements, and adverse events were recorded during a 3-month period. Patients in the low group were then crossed over to high-stimulation paradigms during a 15-month extension trial.

RESULTS

All operations were successful, uneventful, and without adverse postoperative sequelae. One patient was excluded from analysis because of inadequate seizure calendars. Of the seven patients initially assigned to high stimulation, the mean reduction in seizure frequency was 71% at 3 months and 81% at 18 months. Five (72%) of these patients had a greater than 75% reduction in seizure frequency, and one (14%) remained seizure-free after more than 1.5 years of follow-up. The mean reduction in seizure frequency among the low-stimulation group was only 6% at 3 months. No serious complications, device failures, or physiological perturbations occurred.

CONCLUSION

In our experience, vagus nerve stimulation has proven to be a safe, feasible, and potentially effective method of reducing seizures in select patient populations. However, the elements of strict definition for the application of the method require further study.

Vagus nerve stimulation in 16 children with refractory epilepsy

PURPOSE

Vagus nerve stimulation (VNS) has been reported to produce >90% reduction in the number of seizures in children with intractable epilepsy. These encouraging results need confirmation.

METHODS

Sixteen children, 10 boys and 6 girls aged 4-19 years, were treated with VNS (Cyberonics, Webster, TX, U.S.A.) for 12-24 months. Seizure frequency, seizure severity, changes in quality of life (QOL: visual analogue scale), and side effects were recorded. Eight children had partial and 8 had generalized seizures; 4 of the latter had Lennox-Gastaut syndrome (LGS).

RESULTS

During the tenth to twelfth month of VNS, 6 of 16 children experienced > or =50% reduction in seizure frequency. One girl became seizure-free. Seizure severity showed an average decrease in the score from 15 to 11. After 10 months of treatment, QOL was estimated to have improved > or =50% in 6 of 16 children. Reduction in seizure frequency, decreased seizure severity, and reported improvement in QOL did not entirely coincide. Six children experienced hoarseness, 1 had neck pain, 2 had hypersalivation, 2 experienced tiredness, 2 had aspiration episodes during liquid intake, and 6 had electrical transmission problems; in 4 the problem has been surgically corrected. Five stimulators were turned off due to lack of efficacy.

CONCLUSIONS

Six of 16 children with refractory epilepsy treated with VNS improved, with a reduction not only in seizure frequency but also in seizure severity and in QOL.

Vagus nerve stimulation

Left vagus nerve stimulation (VNS) is a promising new treatment for epilepsy. In 1997, VNS was approved in the United States as an adjunctive treatment for medically refractory partial-onset seizures in adults and adolescents. For some patients with partial-onset seizures, the adverse effects of antiepileptic drugs (AEDs) are intolerable; for others, no single AED or combination of anticonvulsant agents is effective. Cerebral resective surgery is an option to pharmacotherapy in some cases, but many patients with partial-onset seizures are not optimal candidates for intracranial surgery. VNS entails implantation of a programmable signal generator--the Neuro-cybernetic Prosthesis (NCP)--in the chest cavity. The stimulating electrodes of the NCP carry electrical signals from the generator to the left vagus nerve. Although the mechanism of action of VNS is not known, controlled studies have shown that it is safe and well-tolerated by patients with long-standing partial-onset epilepsy. Side effects, which are generally of mild to moderate severity, almost always disappear after the stimulation settings are adjusted. Encouraging results have also been reported in pediatric patients.

Vagus nerve stimulation for symptomatic generalized epilepsy: a pilot study

PURPOSE

Patients with symptomatic generalized epilepsy (SGE) may have antiepileptic drug (AED)-resistant mixed generalized seizures. Vagus nerve stimulation (VNS) reduces partial seizures and may help SGE.

METHODS

We added VNS to stable AED therapy in five SGE patients. Nine-month postoperative VNS treatment seizure rates were compared to a 1-month preoperative baseline.

RESULTS

All patients had mixed generalized seizures, EEG generalized slow spike-and-wave and behavioral abnormalities. Median number of previous AEDs taken was 6 (range 5-12). Median baseline seizure rate was 75/month (range 29-110). VNS produced a median seizure rate production of -41% (range -40% - -85%). Adverse events reported in one patient each were: incisional infection, choking sensation and voice change; and coughing (noted by two patients). One patient discontinued VNS due to coughing.

CONCLUSIONS

We conclude that VNS may be useful add-on therapy for SGE. A larger, controlled, and blinded trial may be warranted.