Antiepileptic effect of high-frequency stimulation of the subthalamic nucleus (corpus luysi) in a case of medically intractable epilepsy caused by focal dysplasia: a 30-month follow-up: technical case report

Neutrophil extracellular traps in cancer

Neutrophil extracellular traps (NETs), which consist of chromatin DNA studded with granule proteins, are released by neutrophils in response to both infectious and sterile inflammation. Beyond the canonical role in defense against pathogens, the extrusion of NETs also contributes to the initiation, metastasis, and therapeutic response of malignant diseases. Recently, NETs have been implicated in the development and therapeutic responses of various types of tumors. Although extensive work regarding inflammation in tumors has been reported, a comprehensive summary of how these web-like extracellular structures initiate and propagate tumor progression under the specific microenvironment is lacking. In this review, we demonstrate the initiators and related signaling pathways that trigger NETs formation in cancers. Additionally, this review will outline the current molecular mechanisms and regulatory networks of NETs during dormant cancer cells awakening, circulating tumor cells (CTCs) extravasation, and metastatic recurrence of cancer. This is followed by a perspective on the current and potential clinical potential of NETs as therapeutic targets in the treatment of both local and metastatic disease, including the improvement of the efficacy of existing therapies.

Long-term efficacy of deep brain stimulation of the subthalamic nucleus in patients with pharmacologically intractable epilepsy: A case series of six patients

OBJECTIVE

Epilepsy is one of the widespread neurological illnesses, and about 20%-40% of epilepsy patients are pharmacoresistant. We aimed to assess the long-term efficacy of subthalamic nucleus (STN) deep brain stimulation (DBS) for drug-resistant epilepsy.

METHODS

We included pharmacologically intractable epilepsy patients who had STN-DBS at the Chinese People's Liberation Army General Hospital between June 2016 and December 2018. We retrospectively evaluated pre- and postoperative clinical outcomes, including seizure frequency, seizure type, anti-seizure medication, cognitive function, anatomical target coordinates, stimulation parameters, and adverse events following the surgical procedure. Six patients with a mean follow-up of 49.3 ± 10.2 months, were included.

RESULTS

Seizure frequency decreased by an average of 64.0% after STN-DBS at last year follow-up (p = .046), and one patient (1/6) achieved seizure-free status. For seizure type, anti-seizure medication, and cognitive function, there were no significant differences between pre-and post-operation (p > .05). In terms of stimulation parameters, the pulse width, amplitude, and frequency were 58.3 ± 9.4 μs, 2.5 ± .7 V, and 122.5 ± 15.7 Hz, respectively. None of the patients showed normal electroencephalography during the electroencephalography reexamination. There were no surgery-related complications, and chronic STN stimulation was generally well tolerated in five patients. However, one patient (1/6) had a difficulty of dyskinesia in the right arm.

SIGNIFICANCE

In conclusion, neuromodulation of the STN by DBS is a promising option for patients with pharmacologically intractable epilepsy, especially for whose epileptic zone originates mainly from the frontoparietal region and who are unsuitable for resective surgery. Further prospective multicenter studies with a larger sample size are necessary for further exploration.

Subthalamic nucleus stimulation attenuates motor seizures via modulating the nigral orexin pathway

Background

Focal motor seizures that originate in the motor region are a considerable challenge because of the high risk of permanent motor deficits after resection. Deep brain stimulation of the subthalamic nucleus (STN-DBS) is a potential treatment for motor epilepsy that may enhance the antiepileptic actions of the substantia nigra pars reticulata (SNr). Orexin and its receptors have a relationship with both STN-DBS and epilepsy. We aimed to investigate whether and how STN inputs to the SNr regulate seizures and the role of the orexin pathway in this process.

Methods

A penicillin-induced motor epileptic model in adult male C57BL/6 J mice was established to evaluate the efficacy of STN-DBS in modulating seizure activities. Optogenetic and chemogenetic approaches were employed to regulate STN-SNr circuits. Selective orexin receptor type 1 and 2 antagonists were used to inhibit the orexin pathway.

Results

First, we found that high-frequency ipsilateral or bilateral STN-DBS was effective in reducing seizure activity in the penicillin-induced motor epilepsy model. Second, inhibition of STN excitatory neurons and STN-SNr projections alleviates seizure activities, whereas their activation amplifies seizure activities. In addition, activation of the STN-SNr circuits also reversed the protective effect of STN-DBS on motor epilepsy. Finally, we observed that STN-DBS reduced the elevated expression of orexin and its receptors in the SNr during seizures and that using a combination of selective orexin receptor antagonists also reduced seizure activity.

Conclusion

STN-DBS helps reduce motor seizure activity by inhibiting the STN-SNr circuit. Additionally, orexin receptor antagonists show potential in suppressing motor seizure activity and may be a promising therapeutic option in the future.

Deep brain stimulation of the subthalamic nucleus for epilepsy

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is a promising palliative option for patients with refractory epilepsy. However, crucial questions remain unanswered: Which patients are the optimal candidates? How, where, and when to stimulate the STN? And what is the mechanism of STN-DBS action on epilepsy? Thus, we reviewed the clinical evidence on the antiepileptic effects of STN-DBS and its possible mechanisms on drug-resistant epilepsy, its safety, and the factors influencing stimulation outcomes. This information may guide clinical decision-making. In addition, based on the current knowledge on the effect of STN-DBS on epilepsy, we suggest research that needs to be carried out in the future.

Neuromodulation in Drug Resistant Epilepsy

Epilepsy affects approximately 70 million people worldwide, and it is a significant contributor to the global burden of neurological disorders. Despite the advent of new AEDs, drug resistant-epilepsy continues to affect 30-40% of PWE. Once identified as having drug-resistant epilepsy, these patients should be referred to a comprehensive epilepsy center for evaluation to establish if they are candidates for potential curative surgeries. Unfortunately, a large proportion of patients with drug-resistant epilepsy are poor surgical candidates due to a seizure focus located in eloquent cortex, multifocal epilepsy or inability to identify the zone of ictal onset. An alternative treatment modality for these patients is neuromodulation. Here we present the evidence, indications and safety considerations for the neuromodulation therapies in vagal nerve stimulation (VNS), responsive neurostimulation (RNS), or deep brain stimulation (DBS).

Not Part of the Temporal Lobe, but Still of Importance? Substantia Nigra and Subthalamic Nucleus in Epilepsy

The most researched brain region in epilepsy research is the temporal lobe, and more specifically, the hippocampus. However, numerous other brain regions play a pivotal role in seizure circuitry and secondary generalization of epileptic activity: The substantia nigra pars reticulata (SNr) and its direct input structure, the subthalamic nucleus (STN), are considered seizure gating nuclei. There is ample evidence that direct inhibition of the SNr is capable of suppressing various seizure types in experimental models. Similarly, inhibition via its monosynaptic glutamatergic input, the STN, can decrease seizure susceptibility as well. This review will focus on therapeutic interventions such as electrical stimulation and targeted drug delivery to SNr and STN in human patients and experimental animal models of epilepsy, highlighting the opportunities for overcoming pharmacoresistance in epilepsy by investigating these promising target structures.

Different modalities of invasive neurostimulation for epilepsy

Epilepsy affects 1% of the general population, about one-third of which is pharmacologically resistant. Uncontrolled seizures are associated with an increased risk of traumatic injury and sudden unexpected death of epilepsy. There is a considerable psychological and financial burden on caregivers of patients with epilepsy, particularly among pediatric patients. Epilepsy surgery, when indicated, is the most promising cure for epilepsy. However, when surgery is contraindicated or refused by the patient, neurostimulation is an alternative palliative approach, albeit with a lower chance of entirely curing patients of seizures. There are many options for neurostimulation. The three most commonly used invasive neurostimulation procedures that consistently show evidence of being safe and efficacious are vagal nerve stimulation, responsive neuro stimulation, or anterior thalamic nucleus deep brain stimulation. The goal of this review is to summarize the current evidence supporting the use of these three techniques, which are approved by most regulatory bodies, and discuss different factors that may enable epilepsy surgeons to choose the most appropriate modality for each patient.

A Review of Neurostimulation for Epilepsy in Pediatrics

Neurostimulation for epilepsy refers to the application of electricity to affect the central nervous system, with the goal of reducing seizure frequency and severity. We review the available evidence for the use of neurostimulation to treat pediatric epilepsy, including vagus nerve stimulation (VNS), responsive neurostimulation (RNS), deep brain stimulation (DBS), chronic subthreshold cortical stimulation (CSCS), transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). We consider possible mechanisms of action and safety concerns, and we propose a methodology for selecting between available options. In general, we find neurostimulation is safe and effective, although any high quality evidence applying neurostimulation to pediatrics is lacking. Further research is needed to understand neuromodulatory systems, and to identify biomarkers of response in order to establish optimal stimulation paradigms.

Deep Brain Stimulation and Drug-Resistant Epilepsy: A Review of the Literature

Introduction: Deep brain stimulation is a safe and effective neurointerventional technique for the treatment of movement disorders. Electrical stimulation of subcortical structures may exert a control on seizure generators initiating epileptic activities. The aim of this review is to present the targets of the deep brain stimulation for the treatment of drug-resistant epilepsy. Methods: We performed a structured review of the literature from 1980 to 2018 using Medline and PubMed. Articles assessing the impact of deep brain stimulation on seizure frequency in patients with DRE were selected. Meta-analyses, randomized controlled trials, and observational studies were included. Results: To date, deep brain stimulation of various neural targets has been investigated in animal experiments and humans. This article presents the use of stimulation of the anterior and centromedian nucleus of the thalamus, hippocampus, basal ganglia, cerebellum and hypothalamus. Anterior thalamic stimulation has demonstrated efficacy and there is evidence to recommend it as the target of choice. Conclusion: Deep brain stimulation for seizures may be an option in patients with drug-resistant epilepsy. Anterior thalamic nucleus stimulation could be recommended over other targets.

Stimulation and Neuromodulation in the Treatment of Epilepsy

Invasive brain stimulation technologies are allowing the improvement of multiple neurological diseases that were non-manageable in the past. Nowadays, this technology is widely used for movement disorders and is undergoing multiple clinical and basic science research for development of new applications. Epilepsy is one of the conditions that can benefit from these emerging technologies. The objective of this manuscript is to review literature about historical background, current principles and outcomes of available modalities of neuromodulation and deep brain stimulation in epilepsy patients.

Deep brain stimulation for the treatment of epilepsy: circuits, targets, and trials

Deep brain stimulation (DBS) has proven remarkably safe and effective in the treatment of movement disorders. As a result, it is being increasingly applied to a range of neurologic and psychiatric disorders, including medically refractory epilepsy. This review will examine the use of DBS in epilepsy, including known targets, mechanisms of neuromodulation and seizure control, published clinical evidence, and novel technologies. Cortical and deep neuromodulation for epilepsy has a long experimental history, but only recently have better understanding of epileptogenic networks, precise stereotactic techniques, and rigorous trial design combined to improve the quality of available evidence and make DBS a viable treatment option. Nonetheless, underlying mechanisms, anatomical targets, and stimulation parameters remain areas of active investigation.

Deep brain stimulation for refractory epilepsy

Deep brain stimulation (DBS) is a method of treatment utilized to control medically refractory epilepsy (RE). Patients with medically refractory epilepsy who do not achieve satisfactory control of seizures with pharmacological treatment or surgical resection of the epileptic focus and those who do not qualify for surgery could benefit from DBS. The most frequently used stereotactic targets for DBS are the anterior thalamic nucleus, subthalamic nucleus, central-medial thalamic nucleus, hippocampus, amygdala and cerebellum. The DBS is believed to be an effective method of treatment for various types of epilepsy among adults and adolescents. Side effects may be associated with implantation of electrodes and with the stimulation itself. An increasing number of publications and growing interest in DBS application for RE may result in standardization of the qualification and treatment protocol for RE with DBS.

Modeling noninvasive neurostimulation in epilepsy as stochastic interference in brain networks

Noninvasive brain stimulation is one of very few potential therapies for medically refractory epilepsy. However, its efficacy remains suboptimal and its therapeutic value has not been consistently assessed. This is in part due to the nonoptimized spatio-temporal application of stimulation protocols for seizure prevention or arrest, and incomplete knowledge of the neurodynamics of seizure evolution. Through simulations, this study investigated electroencephalography (EEG)-guided, stochastic interference with aberrantly coordinated neuronal networks, to prevent seizure onset or interrupt a propagating partial seizure, and prevent it from spreading to large areas of the brain. Brain stimulation was modeled as additive white or band-limited noise, and simulations using real EEGs and data generated from a network of integrate-and-fire neuronal ensembles were used to quantify spatio-temporal noise effects. It was shown that additive stochastic signals (noise) may destructively interfere with network dynamics and decrease or abolish synchronization associated with progressively coupled networks. Furthermore, stimulation parameters, particularly amplitude and spatio-temporal application, may be optimized based on patient-specific neurodynamics estimated directly from noninvasive EEGs.

Electrical stimulation for epilepsy: experimental approaches

Direct electrical stimulation of the brain is an increasingly popular means of treating refractory epilepsy. Although there has been moderate success in human trials, the rate of seizure freedom does not yet compare favorably to resective surgery. It therefore remains critical to advance experimental investigations aimed toward understanding brain stimulation and its utility. This article introduces the concepts necessary for understanding these experimental studies, describing recording and stimulation technology, animal models of epilepsy, and various subcortical targets of stimulation. Bidirectional and closed-loop device technologies are also highlighted, along with the challenges presented by their experimental use.

Development of a large animal model for investigation of deep brain stimulation for epilepsy

BACKGROUND/OBJECTIVES

To better understand the mechanism of action of deep brain stimulation (DBS) for epilepsy and to investigate implantable device features, it is desirable to have a large animal model to evaluate clinical-grade systems. This study assessed the suitability of an ovine model of epilepsy for this purpose.

METHODS

Animals were anesthetized for surgery and 1.5 T MRIs collected. Unilateral anterior thalamic DBS leads, hippocampal depth electrodes and catheters were implanted using a frameless stereotactic system. Evoked responses and local field potentials were collected and stored for off-line analysis.

RESULTS

Despite limited neuroanatomic information for this species, it was possible to reliably implant leads into the target structures using MR-guided techniques. Stimulation of these regions produced robust evoked potentials within this circuit that were dependent on stimulus location and parameters. High-frequency thalamic DBS produced a clear inhibition of both spontaneous and penicillin-induced ictal activity in the hippocampus which far outlasted the duration of the stimulation.

CONCLUSIONS

These preliminary results suggest that the sheep model may be useful for further investigation of DBS for epilepsy. The demonstration of marked suppression of network excitability with high-frequency stimulation supports a potential therapeutic mechanism for this DBS therapy.

Current and future indications for deep brain stimulation in pediatric populations

Deep brain stimulation (DBS) has proven to be an effective and safe treatment option in patients with various advanced and treatment-refractory conditions. Thus far, most of the experience with DBS has been in the movement disorder literature, and more specifically in the adult population, where its use in conditions such as Parkinson disease has revolutionized management strategies. The pediatric population, however, can also be afflicted by functionally incapacitating neurological conditions that remain refractory despite the clinicians' best efforts. In such cases, DBS offers an additional treatment alternative. In this paper, the authors review their institution's experience with DBS in the pediatric population, and provide an overview of the literature on DBS in children. The authors conclude that DBS in children can and should be considered a valid and effective treatment option, albeit in highly specific and carefully selected cases.

Deep brain stimulation: current and future perspectives

Deep brain stimulation (DBS) has been used to treat various neurological and psychiatric disorders. Over the years, the most suitable surgical candidates and targets for some of these conditions have been characterized and the benefits of DBS well demonstrated in double-blinded randomized trials. This review will discuss some of the areas of current investigation and potential new applications of DBS.

Intraventricular and intracerebral delivery of anti-epileptic drugs in the kindling model

A means to avoid the pharmacokinetic problems affecting the anti-epileptic drugs may be their direct intracerebroventricular (ICV) or intracerebral delivery. This approach may achieve a greater drug concentration at the epileptogenic area while minimizing it in other brain or systemic areas, and thus it could be an interesting therapeutic alternative in drug-resistant epilepsies. The objective of this article is to review a series of experiments, ranging from actute ICV injection to continuous intracerebral infusion of anti-epileptic drugs or grafting of neurotransmitter producing cells, in experimental models, especially in the kindling model of epilepsy in the rat. Acute ICV injection of phenytoin, phenobarbital or carbamacepine is able to diminish the intensity of kindling seizures, but it is also associated with a high neurologic toxicity, especially phenobarbital. Continuous ICV infusion of anti-epileptic drugs can effectively control seizures, but neurologic toxicity is not improved compared with systemic delivery. However, systemic toxicity may be improved, as in the case of valproic acid, whose continuous ICV infusion results in very low plasmatic or hepatic drug concentrations. Continuous intracerebral infusion at the epileptogenic area was studied as an alternative to minimize neurologic toxicity. Thus, intra-amygdalar infusion of gamma-aminobutyric acid (GABA) controls seizures with minimal neurotoxicity in amygdala-kindled rats. Similarly, continuous infusion of GABA into the dorsomedian nucleus of the thalamus improves seizure spread, while not affecting the local epileptogenic activity at the amygdala. Grafting of GABA releasing cells may reduce kindling parameter severity without behavioral side effects. We may conclude that ICV or intracerebral delivery of anti-epileptic drugs or neurotransmitters may be a useful technique to modulate epilepsy.

Implantation of a responsive neurostimulator device in patients with refractory epilepsy

Object

The authors summarize one center's experience with a novel device, the Responsive Neurostimulation (RNS) system, which is used to treat seizures, and they provide technical details regarding the implantation procedure.

Methods

The authors reviewed seizure detection, cortical stimulation, and clinical data obtained in 7 patients in whom the RNS system was implanted. Data pertaining to seizure alteration are provided for the first 4 implant-treated patients. The implantation procedure in the case of one patient with occipital lobe heterotopia is included.

Results

Based on patients' seizure diaries, the implanted devices functioned at a high sensitivity for clinical seizure detection. Reductions in seizure frequency, based on their diaries and on clinic follow-up notes, ranged from 50 to 75%. No adverse stimulation-induced side effects were noted, and no hardware malfunctions requiring explantation occurred. Generator replacements for battery depletion were required at 11, 17, and 20 months in 3 patients. The implantation procedure was well tolerated, and postoperative hospital stays were short. A revision cranioplasty for a skull defect was performed in the index patient, whose case will be discussed in the most detail.

Conclusions

The results obtained in this small preliminary series demonstrate a safe implantation method for the responsive neurostimulation device.

Technology insight: neuroengineering and epilepsy-designing devices for seizure control

Despite substantial innovations in antiepileptic drug therapy over the past 15 years, the proportion of patients with uncontrolled epilepsy has not changed, highlighting the need for new treatment strategies. New implantable antiepileptic devices, which are currently under development and in pivotal clinical trials, hold great promise for improving the quality of life of millions of people with epileptic seizures worldwide. A broad range of strategies to stop seizures is currently being investigated, with various modes of control and intervention. The success of novel antiepileptic devices rests upon collaboration between neuroengineers, physicians and industry to adapt new technologies for clinical use. The initial results with these technologies are exciting, but considerable development and controlled clinical trials will be required before these treatments earn a place in our standard of clinical care.

Electrical stimulation devices in the treatment of epilepsy

Over the last ten years there has been a progressively increasing interest in the research and clinical application of implantable electrical brain stimulation devices in the treatment of drug-resistant epilepsy. The concept is not new, but the efforts were strengthened and accelerated after the efficacy of vagus nerve stimulation in controlling epilepsy was first demonstrated in the early 1990s and gained subsequently the approval of the USA Food and Drug Administration in 1997. This chapter reviews the progress made in this field. Special emphasis is given to the most important available evidence from animal and human studies, the neuroanatomical pathways and the role of the relevant neurotransmitters, the stimulation devices and the significance of correct programming of the stimulation parameters. The chapter also examines the antiepileptic efficacy of stimulation in all the known targets including vagus nerve, cerebellum, thalamus, subthalamic nucleus, locus ceruleus, and epileptogenic cortex. On the basis of the current evidence, the future directions of this exciting field are described.

Electrical stimulation of the anterior nucleus of the thalamus for intractable epilepsy: a long-term follow-up study

PURPOSE

The anterior nucleus of the thalamus (ANT) modulates temporal lobe and hypothalamic activities, and relays information to the cingulate gyrus and entorhinal cortex. Deep brain stimulation (DBS) of the ANT has been reported to decrease seizure activity in a limited number of human subjects. However, long-term effect of chronic ANT stimulation on such patients remains unknown. We report long-term follow-up results in four patients receiving ANT stimulation for intractable epilepsy.

METHODS

Four patients underwent stereotactic implantation of quadripolar stimulating electrodes in the bilateral ANT, guided by single-unit microelectrode recording. Electrode location was confirmed by postoperative magnetic resonance imaging (MRI). The stimulator was activated 2-4 weeks following electrode insertion; initial stimulation parameters were 4-5 V, 90-110 Hz, and 60-90 micros. Seizure frequency was monitored and compared with preimplantation baseline frequency. Intelligence quotient (IQ) test and auditory P300 response were performed before and after implantation of electrodes.

RESULTS

Four patients (one man with generalized seizures, and three women with partial seizures and secondary generalization) aged 18-45 years old were studied with mean follow-up period of 43.8 months. The four patients demonstrated a sustained effect of 49% (range, 35-76%) seizure reduction to ANT stimulation. Simple insertion of DBS electrodes (Sham period, no stimulation) produced a mean reduction in seizures of 67% (range, 44-94%). One patient was seizure-free for 15 months with anticonvulsant medications. One patient had a small frontal hemorrhage and a second patient had extension erosion over scalp; no resultant major or permanent neurological deficit was observed. Preoperative IQ index and auditory P300 were not significantly different with those after electrodes implantation.

CONCLUSIONS

Implantation of electrodes in the ANT and subsequent stimulation is associated with a significant reduction in seizure frequency. However, our study could not differentiate whether the implantation itself, the subsequent stimulation or postimplantation drug manipulation had the greatest impact. These experimental results prompt further controlled study in a large patient population.

Chronic deep brain stimulation of subthalamic and anterior thalamic nuclei for controlling refractory partial epilepsy

OBJECTIVES

Experimental data and case reports of intractable epilepsy patients treated with deep brain stimulation (DBS) of the internal nuclei suggest a considerable anticonvulsant effect. We intended to describe the results of DBS on subthalamic nuclei and anterior thalamic nuclei (STN and ATN) from our patients and to evaluate the long-term efficiency and safety of DBS for controlling intractable epilepsy.

METHODS

Six patients with refractory epilepsy and inadequate for surgery were implanted with DBS electrodes (3 in STN and 3 in ATN, respectively), switched on after a week of insertion followed by chronological observation. Seizure counts were monitored and compared with pre-implantation baseline.

RESULTS

There was significant clinical improvement in respect of reduction of seizure frequency as well as the alleviation of ictal severity in almost patients. The mean reduction in seizure frequency was 62.3% (49.1% from STN vs. 75.4% from ATN). Except one patient (patient 3) with accidental infection on the right anterior chest, no complication or withdrawal of DBS was seen during our study.

CONCLUSION

DBS on STN and ATN demonstrated their clear efficiency and relative safety comparable or superior to previous studies during long term follow-up. Subsequent, well designed studies warrant the further increase of the knowledge about antiepileptic effect of DBS.

Rationale, mechanisms of efficacy, anatomical targets and future prospects of electrical deep brain stimulation for epilepsy

Electrical stimulation of deep brain structures is a promising new technology for the treatment of medically intractable seizures. Performed in vitro and on animal models of epilepsy, electrical stimulation has shown to reduce seizure frequency. Preliminary results on humans are encouraging. However, such improvements emerge despite a lack of understanding of the precise mechanisms underlying electrical stimulation either delivered directly on the epileptogenic zone (direct control) or through an anatomical relay of cortico-subcortical networks (remote control). Anatomical targets such as the thalamus (centromedian nucleus, anterior thalamus, mamillary body and mamillothalamic tracts), the subthalamic nucleus, the caudate nucleus and direct stimulation of the hippocampal formation have been successfully investigated. Although randomized controlled studies are still missing, deep brain stimulation is a promising treatment option for a subgroup of carefully selected patients with intractable epilepsy who are not candidates for resective surgery. The effectiveness, the optimal anatomic targets, the ideal stimulation parameters and devices, as well as patient selection criteria are still to be defined.

Electrical stimulation and gene-based neuromodulation for control of medically-refractory epilepsy

The failure of available antiepileptic medications to adequately control seizures in a substantial number of patients underscores the need to develop novel epilepsy therapies. Recent advancements in technology and the success of neuromodulation in treating a variety of neurological disorders have spurred interest in exploring promising therapeutic alternatives, such as electrical stimulation and gene-based synaptic control. A variety of different stimulation approaches to seizure control targeting structures in the central or peripheral nervous system have been investigated. Most studies have been based on uncontrolled observations and empirical stimulation protocols. Today the vagus nerve stimulator is the only FDA approved adjunctive treatment for epilepsy that utilizes electrical stimulation. Other potential strategies including direct stimulation of the epileptogenic cortex and deep brain stimulation of various targets are currently under investigation. Chronically implanted devices for electrical stimulation have a variety of limitations. First, they are susceptible to malfunction and infection. Second, most systems require battery replacement. Finally, electrical stimulation is incapable of manipulating neuronal function in a transmitter specific fashion. Gene delivery to epileptogenic targets or targets implicated in regulating seizure threshold has been investigated as an alternative means of neuromodulation in animal models. In summary, positive preliminary results and the lack of alternative treatment options provide the impetus for further exploration of electrical stimulation and gene-based therapies in pharmacoresistant epilepsy. Various specific targets and approaches to modulating their activity have been investigated in human studies.

Electricity in the treatment of nervous system disease

Electricity has been used in medicine for almost two millenniums beginning with electrical chocks from the torpedo fish and ending with the implantation of neuromodulators and neuroprostheses. These implantable stimulators aim to improve functional independence and quality of life in various groups of disabled people. New indications for neuromodulation are still evolving and the field is rapidly advancing. Thanks to modern science and computer technology, electrotherapy has reached a degree of sophistication where it can be applied relatively safely and effectively in a variety of nervous system diseases, including pain, movement disorders, epilepsy, Tourette syndrome, psychiatric disease, addiction, coma, urinary incontinence, impotence, infertility, respiratory paralysis, tinnitus and blindness.

Cerebral cavernous malformations and epilepsy

✓Seizures and epilepsy are frequent clinical manifestations of cerebral cavernous malformations (CCMs) and represent the most common symptomatic presentation of supratentorial lesions. Clinicians often diagnose CCMs in patients after a first seizure, or in some cases after obtaining neuroimaging studies in patients suffering from chronic epilepsy previously thought to be idiopathic. In some cases, the lesion is clinically significant solely because of its epileptogenicity, but in others there may be concern about potential hemorrhage or focal neurological deficits from a similar lesion.

The authors present current pathophysiological concepts related to epilepsy associated with CCMs. They discuss the spectrum of seizure disorders associated with these lesions and review the natural history, prognosis, and options for therapeutic intervention.

Deep brain stimulation as a functional scalpel

Since 1995, at the Istituto Nazionale Neurologico "Carlo Besta" in Milan (INNCB,) 401 deep brain electrodes were implanted to treat several drug-resistant neurological syndromes (Fig. 1). More than 200 patients are still available for follow-up and therapeutical considerations. In this paper our experience is reviewed and pioneered fields are highlighted. The reported series of patients extends the use of deep brain stimulation beyond the field of Parkinson's disease to new fields such as cluster headache, disruptive behaviour, SUNCt, epilepsy and tardive dystonia. The low complication rate, the reversibility of the procedure and the available image guided surgery tools will further increase the therapeutic applications of DBS. New therapeutical applications are expected for this functional scalpel.

Effect of Chronic Deep Brain Stimulation of the Subthalamic Nucleus for Frontal Lobe Epilepsy: Subtraction SPECT Analysis

OBJECTIVES

Experimental data and case reports of patients with intractable epilepsy treated with deep brain stimulation (DBS) of the subthalamic nucleus (STN) suggest a considerable anticonvulsant effect. However, no satisfactory mechanisms of action have yet been elucidated. We investigated the putative therapeutic mechanisms of DBS from cerebral perfusion changes as measured by subtracting the SPECT image of the pre-DBS period from that of the chronic post-DBS state.

METHODS

Two patients who had previous resective surgery on their right frontal cortices with or without anterior callosotomy were selected for DBS of the STN. Both of them showed frequent bilateral asymmetric tonic seizures (left > right) with rare drop attacks, and 1 patient's seizure frequency was more than 15/month during the pre-DBS period. They had both taken more than four antiepileptic agents for more than 10 years. After video-EEG monitoring, the irritative zones of the brain were delineated. The regional cerebral blood flow (rCBF) changes between the two SPECT images (pre-DBS and post-DBS after at least 6 months) were analyzed by SPECT subtraction with the volumetric MRI coregistration method using Analyze 5.0 software.

RESULTS

After chronic STN DBS (18 months, case 1; 6 months, case 2), both patients experienced markedly reduced seizure frequencies (86.7% reduction in patient 1, 88.6% in patient 2). In patient 1, the increased rCBF was observed in the right frontal areas (dorsolateral and inferior frontal area), which corresponded to the irritative zones as confirmed by previous EEG recording. Unexpectedly, there was definite hyperperfusion in the right superior and inferior temporal areas as well as rCBF increase in the right superior frontal area (SMA) in patient 2.

CONCLUSIONS

We demonstrated that the cerebral perfusion increase in the irritative zones of epilepsy patients is associated with favorable seizure reduction after STN DBS in 2 cases of frontal lobe epilepsy. Although the exact mechanism remains unknown, our findings suggest that the perfusion changes after STN DBS in frontal lobe epilepsy patients are quite different from those in subjects with Parkinson's disease. Our preliminary data suggest the clinical relevance of subtraction SPECT imaging in assessing the postprocedural outcome as well as the characteristics of SPECT perfusion patterns in other epilepsy syndromes.

Tonic activation of presynaptic GABA(B) receptors on rat pallidosubthalamic terminals

AIM

The subthalamic nucleus plays a critical role in the regulation of movement, and abnormal activity of its neurons is associated with some basal ganglia motor symptoms. We examined the presence of functional presynaptic GABA(B) receptors on pallidosubthalamic terminals and tested whether they were tonically active in the in vitro subthalamic slices.

METHODS

Whole-cell patch-clamp recordings were applied to acutely prepared rat subthalamic nucleus slices. The effects of specific GABA(B) agonist and antagonist on action potential-independent inhibitory postsynaptic currents (IPSCs), as well as holding current, were examined.

RESULTS

Superfusion of baclofen, a GABA(B) receptor agonist, significantly reduced the frequency of GABA(A) receptor-mediated miniature IPSCs (mIPSCs), in a Cd2+-sensitive manner, with no effect on the amplitude, indicating presynaptic inhibition on GABA release. In addition, baclofen induced a weak outward current only in a minority of subthalamic neurons. Both the pre- and post-synaptic effects of baclofen were prevented by the specific GABA(B) receptor antagonist, CGP55845. Furthermore, CGP55845 alone increased the frequency of mIPSCs, but had no effect on the holding current.

CONCLUSION

These findings suggest the functional dominance of presynaptic GABA(B) receptors on the pallidosubthalamic terminals over the postsynaptic GABA(B) receptors on subthalamic neurons. Furthermore, the presynaptic, but not the postsynaptic, GABA(B) receptors are tonically active, suggesting that the presynaptic GABA(B) receptors in the subthalamic nucleus are potential therapeutic target for the treatment of Parkinson disease.

Preemptive Low-frequency Stimulation Decreases the Incidence of Amygdala-kindled Seizures

PURPOSE

The use of electrical stimulation as a therapy for epilepsy is currently being studied in experimental animals and in patients with epilepsy. This study examined the effect of preemptive, low-frequency, 1-Hz sine wave stimulation (LFS) on the incidence of amygdala-kindled seizures in the rat.

METHODS

Electrodes were implanted into the basolateral amygdalae of adult male rats. All animals received a kindling stimulus of 60-Hz, 400-microA, sine wave for 1 s twice a day. Experimental animals received an additional LFS consisting of 1 Hz, 50 microA for 30 s immediately before the kindling stimulus. Afterdischarge (AD) duration, behavioral seizure score, the number of stimulations required to elicit the first stage five seizure and to become fully kindled were measured. After 20 stimulations, a crossover procedure was performed. Fully kindled rats from each group were switched, so that the original controls received LFS plus the kindling stimulus, and the original experimental rats received only the kindling stimulus.

RESULTS

During kindling acquisition, LFS induced a significant decrease in AD duration. A significant increase in the number of times the kindling stimulus failed to elicit an AD was noted. Control rats exhibited an AD 99% of the time compared with 70% in experimental rats (p < 0.0001; Fisher's Exact test). In fully kindled animals, the incidence of stage five seizures in the original controls significantly decreased from 98% to 42% (p < 0.0001) when the LFS was added to the kindling paradigm.

CONCLUSIONS

The dramatic decrease in the incidence of stage 5 seizures in fully kindled animals after preemptive LFS strongly suggests that LFS may be an effective therapy for the prevention of seizures in patients with epilepsy.

[Electric brain stimulation for epilepsy therapy]

Attempts to control epileptic seizures by electrical brain stimulation have been performed for 50 years. Many different stimulation targets and methods have been investigated. Vagal nerve stimulation (VNS) is now approved for the treatment of refractory epilepsies by several governmental authorities in Europe and North America. However, it is mainly used as a palliative method when patients do not respond to medical treatment and epilepsy surgery is not possible. Numerous studies of the effect of deep brain stimulation (DBS) on epileptic seizures have been performed and almost invariably report remarkable success. However, a limited number of controlled studies failed to show a significant effect. Repetitive transcranial magnetic stimulation (rTMS) also was effective in open studies, and controlled studies are now being carried out. In addition, several uncontrolled reports describe successful treatment of refractory status epilepticus with electroconvulsive therapy (ECT). In summary, with the targets and stimulation parameters investigated so far, the effects of electrical brain stimulation on seizure frequency have been moderate at best. In the animal laboratory, we are now testing high-intensity, low-frequency stimulation of white matter tracts directly connected to the epileptogenic zone (e.g., fornix, corpus callosum) as a new methodology to increase the efficacy of DBS ("overdrive method").