Deep brain stimulation of the subthalamic nucleus as adjunct treatment for refractory epilepsy

Effects of electrical stimulation of the lateral cerebellar nucleus on PTZ-kindled seizures

BACKGROUND

In recent years, the cerebellum and its nuclei have become an essential target for understanding and suppressing the mechanisms of seizures. This study aimed to investigate the effects of electrical stimulation (ES) applied to the Lateral Cerebellar Nucleus (LCN) in rats at the early and fully developed pentylenetetrazol (PTZ) kindled seizures.

METHODS

The experimental groups were represented by the male Wistar rats kindled with PTZ (35.0 mg/kg, i.p.) to myoclonus (9-11 PTZ injections) and generalized tonic-clonic seizures (21 PTZ injections). Unilateral ES (100 Hz) was delivered daily for five days after the last kindled PTZ administration, with PTZ seizure testing after ES. Seizures were videotaped, and the severity score was determined in a blinded manner.

RESULTS

ES of LCN performed at the early stage of kindling facilitated the appearance of myoclonus, and increased seizure severity by 30.2 % points compared to the control group (H = 6.94; df = 2; p = 0.037) with the spikes frequency generation increased during the poststimulation period (H = 27.34; df = 5; p < 0.001). In fully developed kindling, ES prevented generalized seizure and reduced seizure severity by 27.5 % (H = 9.385; df = 2; p = 0.009), while myoclonuses were present with spikes generation in brain structures.

CONCLUSION

The data obtained showed that repeated ES of LCN at the early stage promoted myoclonic seizures, while in fully PTZ-kindled rats, it suppressed generalized seizure fits, which were substituted with myoclonus.

Invasive Neurostimulation for the Treatment of Epilepsy

Although electricity has been used in medicine for thousands of years, bioelectronic medicine for treating epilepsy has become increasingly common in recent years. Invasive neurostimulation centers primarily around three approaches: vagus nerve stimulation (VNS), responsive neurostimulation (RNS), and deep brain stimulation (DBS). These approaches differ by target (e.g., cranial nerve, cortex, or thalamus) and stimulation parameters (e.g., triggered stimulation or continuous stimulation). Although typically noncurative, these approaches can dramatically reduce the seizure burden and offer patients new treatment options. There remains much to be understood about optimal targets and individualized stimulation protocols. Objective markers of seizure burden and biomarkers that quickly quantify neural excitability are still needed. In the future, bioelectronic medicine could become a curative approach that remodels neural networks to reduce pathological activity.

Deep brain stimulation targets in drug-resistant epilepsy: Systematic review and meta-analysis of effectiveness and predictors of response

PURPOSE

Anterior nucleus of the thalamus (ANT) is the only deep brain stimulation (DBS) target that is approved by the FDA for treatment of drug-resistant epilepsy (DRE). Hippocampus (HC) and centromedian nucleus (CMN) have been reported as potential DBS targets for DRE. This study aimed to assess the effectiveness and predictors of response among DRE patients treated with DBS in general and among ANT, HC and CMN DBS-targets.

METHODS

A systematic search was executed on PubMed, SCOPUS and the Cochrane Central Register of Controlled Trials (CENTRAL) electronic databases between Jan 1, 2000 and June 29, 2020. Patients with DRE who underwent DBS treatment with at least three months of follow-up were included. Individual patient data (IPD) meta-analysis was conducted on DBS studies with available IPD. Response was defined as ≥50 % reduction in seizures frequency. Responders group was compared with non-responders group in terms of demographics, epilepsy/seizure characteristics, MRI findings, and DBS targets and duration of use. Subsequently, predictors of response to different DBS targets were investigated.

RESULTS

Thirty-nine studies with a total of 296 patients (ANT: 69 %, HC: 11 %, CMN: 21 %) were included. The responders group constituted of 209 patients (70.6 %). The response was significantly higher in patients with generalized seizures compared to those with focal seizures (93.2% vs 63.9 %; p < 0.001). Response was significantly higher with CMN (83.9 %) and HC (77.4 %) compared with ANT (65.5 %) as DBS targets (p = 0.014). Response was also significantly associated with longer duration of DBS use (p = 0.008). The responder rate was higher among the patients with lesional MRIs (76.7 %) than those with non-lesional MRIs (66.7 %), but with no statistically significant difference (p = 0.134). Age, gender, epilepsy etiology, onset zone of focal seizures, and previous use of VNS had no significant differences between the responders and non-responders. A binary logistic regression including the seizure type, MRI findings, DBS targets, and DBS duration showed, after controlling for confounders, that the duration of DBS use was the only significant predictor of response (adjusted OR 1.061; 95 % CI 1.019-1.106; p = 0.005). Regarding DBS targets, the response rate in patients with symptomatic etiology was significantly higher with HC or CMN targets than the ANT (p = 0.003). In patients with non-lesional MRI, response rate was significantly higher with the CMN target compared to the other two targets (p = 0.008).

CONCLUSION

DBS proves to be effective in DRE, with progressive success upon longer treatment and possibility of improving quality of life. In addition to focal seizures, DBS has potential for treating generalized seizures as well. While the ANT stands as the most utilized and only approved DBS target for DRE, CMN and HC are alternative targets with high seizure control potential. Patients with symptomatic etiology showed significant seizure reduction when HC or CMN were targeted. Studies revealed noticeable effectiveness of CMN-DBS in treating patients with non-lesional MRI. Despite ANT prominence in research, our findings suggest promising outcomes with CMN and HC, emphasizing the need for future larger-scale comparative clinical trials to better understand the efficacy of different DBS targets.

Neuromodulation: What the neurointerventionalist needs to know

Neuromodulation is the alteration of neural activity in the central, peripheral, or autonomic nervous systems. Consequently, this term lends itself to a variety of organ systems including but not limited to the cardiac, nervous, and even gastrointestinal systems. In this review, we provide a primer on neuromodulation, examining the various technological systems employed and neurological disorders targeted with this technology. Ultimately, we undergo a historical analysis of the field's development, pivotal discoveries and inventions gearing this review to neuro-adjacent subspecialties with a specific focus on neurointerventionalists.

Abolition of seizures following Forel-H-tomy for drug-resistant epilepsy: A case report

A 62-year-old female experienced an extensive cerebral contusion in the left frontotemporal lobe due to an acute subdural hematoma at the age of 44 years. Six months after the injury, the patient developed epileptic seizures. The seizures were generalized with right cervical rotation and fencing posture. Despite prescriptions for four antiepileptic drugs, partial seizures occurred several times a month and focal to bilateral tonic-clonic seizures once every 2 months. Video-electroencephalography showed epileptic discharges in the left frontal lobe. The patient was subsequently referred to our department for palliative surgery. The patient underwent a left Forel-H-tomy. The prescription of antiepileptic drugs was not changed, and the patient was seizure free for 1 year. Forel-H-tomy, a surgical procedure for intractable epilepsy, was pioneered by Dennosuke Jinnai. Despite its previously reported remarkable efficacy, Forel-H-tomy has not been performed for several decades. Nevertheless, it remains a potential alternative treatment option for drug-resistant epilepsy.

Deep brain stimulation in a patient with progressive myoclonic epilepsy and ataxia due to potassium channel mutation (MEAK). A case report and review of the literature

Progressive myoclonic epilepsy (PME) is characterized by prominent myoclonus, generalized tonic-clonic seizures, and less often focal, tonic, or absence seizures. The KCNC1 mutation is responsible for specific clinical phenotype of PME which has been defined as myoclonic epilepsy and ataxia due to potassium channel mutation (MEAK). We present a case of a 44 years-old male patient with genetically proven MEAK who underwent subthalamic nucleus/substantia nigra (STN/SNr) deep brain stimulation (DBS) for his pharmacological-refractory myoclonus and drug-resistant epilepsy (DRE). Since the age of 4-5 years, the patient had been suffering from intention tremor, and later the myoclonic jerks, ataxia involving the upper limbs and walking difficulties worsened. The first bilateral tonic-clonic seizure (BTCS) occurred at the age of 22. The patient agreed to staged bilateral implantation of DBS electrodes placed in the STN/SNr region. The follow-up lasts more than 24 months. The myoclonic jerks assessed by Unified Myoclonus Rating Scale (UMRS) were reduced by nearly 70 % and BTCS was completely abolished. The patient's ataxia and dysarthria did not improve. Early diagnosis with genetic testing may significantly help in counseling patients with PME and enables to undertake the surgical approach targeting the STN/SNr.

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 in the Subthalamic Nucleus Can Improve Skilled Forelimb Movements and Retune Dynamics of Striatal Networks in a Rat Stroke Model

Recovery of upper limb (UL) impairment after stroke is limited in stroke survivors. Since stroke can be considered as a network disorder, neuromodulation may be an approach to improve UL motor dysfunction. Here, we evaluated the effect of high-frequency stimulation (HFS) of the subthalamic nucleus (STN) in rats on forelimb grasping using the single-pellet reaching (SPR) test after stroke and determined costimulated brain regions during STN-HFS using 2-[18F]Fluoro-2-deoxyglucose-([18F]FDG)-positron emission tomography (PET). After a 4-week training of SPR, photothrombotic stroke was induced in the sensorimotor cortex of the dominant hemisphere. Thereafter, an electrode was implanted in the STN ipsilateral to the infarction, followed by a continuous STN-HFS or sham stimulation for 7 days. On postinterventional day 2 and 7, an SPR test was performed during STN-HFS. Success rate of grasping was compared between these two time points. [18F]FDG-PET was conducted on day 2 and 3 after stroke, without and with STN-HFS, respectively. STN-HFS resulted in a significant improvement of SPR compared to sham stimulation. During STN-HFS, a significantly higher [18F]FDG-uptake was observed in the corticosubthalamic/pallidosubthalamic circuit, particularly ipsilateral to the stimulated side. Additionally, STN-HFS led to an increased glucose metabolism within the brainstem. These data demonstrate that STN-HFS supports rehabilitation of skilled forelimb movements, probably by retuning dysfunctional motor centers within the cerebral network.

Neuromodulation for temporal lobe epilepsy: a scoping review

Temporal lobe epilepsy (TLE) is difficult to treat as it is often refractory to treatment. Apart from traditional medical treatment, surgical resection is also a choice of treatment, but it may be associated with significant cognitive deficits. ‌As a result, treatment strategies using targeted and adjustable stimulation of malfunctioning brain circuits have been developed. These neuromodulatory therapies using approaches of electric and magnetic neuromodulation are already in clinical use for refractory epilepsy while others such as optogenetics, chemo-genetics and ultrasound modulation are being tested in pre-clinical TLE animal models. In this review, we conducted an in-depth literature search on the clinically available neuromodulatory approaches for TLE, focusing on the possible mechanism of action and the clinical outcomes including adverse effects. Techniques that are currently explored in preclinical animal models but may have therapeutic applications in future are also discussed. The efficacy and subsequent adverse effects vary among the different neuromodulatory approaches and some still have unclear mechanisms of action in TLE treatment. Further studies evaluating the benefits and potential limitations are needed. Continued research on the therapeutic mechanisms and the epileptic brain network is critical for improving therapies for TLE.

Towards network-guided neuromodulation for epilepsy

Epilepsy is well-recognized as a disorder of brain networks. There is a growing body of research to identify critical nodes within dynamic epileptic networks with the aim to target therapies that halt the onset and propagation of seizures. In parallel, intracranial neuromodulation, including deep brain stimulation and responsive neurostimulation, are well-established and expanding as therapies to reduce seizures in adults with focal-onset epilepsy; and there is emerging evidence for their efficacy in children and generalized-onset seizure disorders. The convergence of these advancing fields is driving an era of 'network-guided neuromodulation' for epilepsy. In this review, we distil the current literature on network mechanisms underlying neurostimulation for epilepsy. We discuss the modulation of key 'propagation points' in the epileptogenic network, focusing primarily on thalamic nuclei targeted in current clinical practice. These include (i) the anterior nucleus of thalamus, now a clinically approved and targeted site for open loop stimulation, and increasingly targeted for responsive neurostimulation; and (ii) the centromedian nucleus of the thalamus, a target for both deep brain stimulation and responsive neurostimulation in generalized-onset epilepsies. We discuss briefly the networks associated with other emerging neuromodulation targets, such as the pulvinar of the thalamus, piriform cortex, septal area, subthalamic nucleus, cerebellum and others. We report synergistic findings garnered from multiple modalities of investigation that have revealed structural and functional networks associated with these propagation points - including scalp and invasive EEG, and diffusion and functional MRI. We also report on intracranial recordings from implanted devices which provide us data on the dynamic networks we are aiming to modulate. Finally, we review the continuing evolution of network-guided neuromodulation for epilepsy to accelerate progress towards two translational goals: (i) to use pre-surgical network analyses to determine patient candidacy for neurostimulation for epilepsy by providing network biomarkers that predict efficacy; and (ii) to deliver precise, personalized and effective antiepileptic stimulation to prevent and arrest seizure propagation through mapping and modulation of each patients' individual epileptogenic networks.

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: A review of current knowledge

Nearly 1% of the global population suffers from epilepsy. Drug-resistant epilepsy (DRE) affects one-third of epileptic patients who are unable to treat their condition with existing drugs. For the treatment of DRE, neuromodulation offers a lot of potential. The background, mechanism, indication, application, efficacy, and safety of each technique are briefly described in this narrative review, with an emphasis on three approved neuromodulation therapies: vagus nerve stimulation (VNS), deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS), and closed-loop responsive neurostimulation (RNS). Neuromodulatory approaches involving direct or induced electrical currents have been developed to lessen seizure frequency and duration in patients with DRE since the notion of electrical stimulation as a therapy for neurologic diseases originated in the early nineteenth century. Although few people have attained total seizure independence for more than 12 months using these treatments, more than half have benefitted from a 50% drop in seizure frequency over time. Although promising outcomes in adults and children with DRE have been achieved, challenges such as heterogeneity among epilepsy types and etiologies, optimization of stimulation parameters, a lack of biomarkers to predict response to neuromodulation therapies, high-level evidence to aid decision-making, and direct comparisons between neuromodulatory approaches remain. To solve these existing gaps, authorize new kinds of neuromodulation, and develop personalized closed-loop treatments, further research is needed. Finally, both invasive and non-invasive neuromodulation seems to be safe. Implantation-related adverse events for invasive stimulation primarily include infection and pain at the implant site. Intracranial hemorrhage is a frequent adverse event for DBS and RNS. Other stimulation-specific side-effects are mild with non-invasive stimulation.

The Possible Role of Nitric Oxide signaling and NMDA Receptors in Allopurinol effect on Maximal Electroshock- and Pentylenetetrazol-Induced Seizures in Mice

Allopurinol, a uric-acid-lowering medication, has shown its efficacy in several studies suggesting that allopurinol can be prescribed as adjunctive cure meant for intractable epilepsy. The exact mechanism of allopurinol is still unknown. This study evaluates allopurinol's effect on seizure threshold, seizure incidence, and mortality rate in mice models. Moreover, the possible involvement of nitric oxide (NO) pathway and N-methyl-D-aspartate (NMDA) receptors are investigated. To evaluate the effect of allopurinol on seizure, we used the pentylenetetrazole (PTZ)-induced seizure along with maximal electroshock (MES)-induced seizure. To assess the underlying mechanism behind the allopurinol activity, we used nitric oxide synthase (NOS) substrate (L-arginine), NOS inhibitors (L-NAME, aminoguanidine, 7-nitroindazole), and NMDA receptor antagonist (MK-801). Intraperitoneal allopurinol administration at a dose of 50 mg/kg in mice showed a significant (p<0.001) anti-convulsant activity in the PTZ-induced seizure. Even though pre-treatment with L-Arginine (60 mg/kg) potentiates allopurinol's anti-convulsant effect in the PTZ-induced seizure, pre-treatment with L-NAME (10 mg/kg), aminoguanidine (100 mg/kg), and 7-nitroindazole (30 mg/kg) reversed the anti-convulsant effect of allopurinol in the PTZ-induced seizure. In addition, pre-treatment with MK-801 also decreased the anti-convulsant effect of allopurinol in the PTZ-induced seizure. While allopurinol at a dose of 50 mg/kg and 100 mg/kg did not induce protection against seizure incidence in the MES-induced seizure, it revealed a remarkable effect in reducing the mortality rate in the MES-induced seizure. Allopurinol increases the seizure threshold in PTZ-induced seizure and enhances the survival rate in MES-induced seizure. Allopurinol exerts its anti-convulsant effect, possibly through targeting NO pathway and NMDA receptors.

Ethical considerations in the surgical and neuromodulatory treatment of epilepsy

Surgical resection and neuromodulation are well-established treatments for those with medically refractory epilepsy. These treatments entail important ethical considerations beyond those which extend to the treatment of epilepsy generally. In this paper, the authors explore these unique considerations through a framework that relates foundational principles of bioethics to features of resective epilepsy surgery and neuromodulation. The authors conducted a literature review to identify ethical considerations for a variety of epilepsy surgery procedures and to examine how foundational principles in bioethics may inform treatment decisions. Healthcare providers should be cognizant of how an increased prevalence of somatic and psychiatric comorbidities, the dynamic nature of symptom burden over time, the individual and systemic barriers to treatment, and variable sociocultural contexts constitute important ethical considerations regarding the use of surgery or neuromodulation for the treatment of epilepsy. Moreover, careful attention should be paid to how resective epilepsy surgery and neuromodulation relate to notions of patient autonomy, safety and privacy, and the shared responsibility for device management and maintenance. A three-tiered approach-(1) gathering information and assessing the risks and benefits of different treatment options, (2) clear communication with patient or proxy with awareness of patient values and barriers to treatment, and (3) long-term decision maintenance through continued identification of gaps in understanding and provision of information-allows for optimal treatment of the individual person with epilepsy while minimizing disparities in epilepsy care.

The inhibition mechanism of epilepsy disease in a computational model

BACKGROUND

The mechanism of prevention and treatment of epilepsy is a hot issue in theoretical research.

OBJECTIVE

In this paper, we studied the control mechanism of the generalized spike-and-wave discharges (GSWD) by different types of external electrical stimulation acting on the subthalamic nucleus (STN) in a computational model.

METHODS

Firstly, we analyzed the pathological mechanism of seizures, which were induced by different parameters in the thalamocortical (TC) circuit. Then, a voltage V was exerted in the STN. At last, we used the sine wave and square wave current stimulation in the STN.

RESULTS

We found that seizures can be inhibited by tuning stimulus intensity into suitable range, and the direction of adjustment depended on the size of the parameter. We observed that the seizure can also be inhibited by tuning different parameters in current.

CONCLUSIONS

Different inhibition mechanisms can be explained in this model, which may provide theoretical evidences for selecting the optimal treatment scheme in the clinical.

Surgery procedures in temporal lobe epilepsies

Temporal lobe epilepsy (TLE) is the most common cause of refractory epilepsy amenable for surgical treatment and seizure control. Surgery for TLE is a safe and effective strategy. The seizure-free rate after surgical resection in patients with mesial or neocortical TLE is about 70%. Resective surgery has an advantage over stereotactic radiosurgery in terms of seizure outcomes for mesial TLE patients. Both techniques have similar results for safety, cognitive outcomes, and associated costs. Stereotactic radiosurgery should therefore be seen as an alternative to open surgery for patients with contraindications for or with reluctance to undergo open surgery. Laser interstitial thermal therapy (LITT) has also shown promising results as a curative technique in mesial TLE but needs to be more deeply evaluated. Brain-responsive stimulation represents a palliative treatment option for patients with unilateral or bilateral MTLE who are not candidates for temporal lobectomy or who have failed a prior mesial temporal lobe resection. Overall, despite the expansion of innovative techniques in recent years, resective surgery remains the reference treatment for TLE and should be proposed as the first-line surgical modality. In the future, ultrasound therapies could become a credible therapeutic option for refractory TLE patients.

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).

Deep Brain Stimulation for Treatment of Refractory Epilepsy

Deep brain stimulation (DBS) has been used in the treatment of motor diseases with remarkable safety and efficacy, which abet the interest of its application in the management of other neurologic and psychiatric disorders such as epilepsy. Experimental data demonstrated that electric current could modulate distinct brain circuits and decrease the neuronal hypersynchronization seen in epileptic activity. The ability to carefully choose the most suitable anatomical target as well as to define the most reasonable stimulation parameters is highly dependable on the comprehension of the underlying mechanisms of action, which remain unclear. This review aimed to explore the relevant clinical data regarding the use of DBS in the treatment of refractory epilepsy.

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.

Subthalamic Nucleus Stimulation Modulates Motor Epileptic Activity in Humans

OBJECTIVE

Pharmaco-refractory focal motor epileptic seizures pose a significant challenge. Deep brain stimulation (DBS) is a recently recognized therapeutic option for the treatment of refractory epilepsy. To identify the specific target for focal motor seizures, we evaluate the modulatory effects of the subthalamic nucleus (STN) stimulation because of the critical role of STN in cortico-subcortical motor processing.

METHODS

Seven patients with epilepsy with refractory seizures who underwent chronic stereoelectroencephalography (SEEG) monitoring were studied in presurgical evaluation. Seizure onset zone was hypothesized to be partially involved in the motor areas in 6 patients. For each patient, one electrode was temporally implanted into the STN that was ipsilateral to the seizure onset zone. The cortical-subcortical seizure propagation was systemically evaluated. The simultaneously electrophysiological responses over distributed cortical areas to STN stimulation at varied frequencies were quantitatively assessed.

RESULTS

We observed the consistent downstream propagation of seizures from the motor cortex toward the ipsilateral STN and remarkable cortical responses on motor cortex to single-pulse STN stimulation. Furthermore, we showed frequency-dependent upstream modulatory effect of STN stimulation on motor cortex specifically. In contrast to the enhanced effects of low frequency stimulation, high-frequency stimulation of the STN can significantly reduce interictal spikes, high-frequency oscillations over motor cortex disclosing effective connections to the STN.

INTERPRETATION

This result showed that the STN is not only engaged in as a propagation network of focal motor seizures but STN stimulation can profoundly modulate the epileptic activity of motor cortex in humans, suggesting a mechanism-based alternative for patients suffering from refractory focal motor seizures. ANN NEUROL 2020;88:283-296.

Threshold for Tonic Motor Effects from Random Waveform in a Rat Experimental Model of Frontal Cortex Stimulation

BACKGROUND

Brain stimulation is utilized to treat a variety of neurological disorders. Clinical brain stimulation technologies currently utilize charge-balanced pulse stimulation. The brain may better respond to other stimulation waveforms. This study was designed to evaluate the motor threshold of the brain to stimulation with various waveforms.

METHODS

Three stimulation waveforms were utilized on rats with surgically implanted brain electrodes: pulses, square waves, and random waveform. The peak-to-peak stimulation voltage was increased in a step-wise manner until motor signs were elicited.

RESULTS

The random waveform had the highest motor threshold with brain stimulation compared to the other waveforms. Random waveform stimulation reached maximum voltage without motor side effects while stimulating through both 1 and 8 electrodes. In contrast, the stimulation thresholds for motor side effects of the other two waveforms were on average less than half of the maximum voltage and lower for stimulation through 8 electrodes than stimulation through 1 electrode (p < 0.0005).

CONCLUSION

The random waveform was better tolerated than the other waveforms and may allow for the use of higher stimulation voltage without side effects.

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.

Comparison and Selection of Current Implantable Anti-Epileptic Devices

Implantable neural stimulators represent an advanced treatment adjunct to medication for pharmacoresistant epilepsy and alternative for patients that are not good candidates for resective surgery. Three treatment modalities are currently FDA-approved: vagus nerve stimulation, responsive neurostimulation, and deep brain stimulation. These devices were originally trialed in very similar patient populations with focal epilepsy, but head-to-head comparison trials have not been performed. As such, device selection may be challenging due to large overlaps in clinical indications and efficacy. Here we will review the data reported in the original pivotal clinical trials as well as long-term experience with these technologies. We will highlight differences in their features and mechanisms of action which may help optimize device selection on a case-by-case basis.

Deep brain stimulation for seizure control in drug-resistant epilepsy

Antiepileptic drugs prevent morbidity and death in a large number of patients suffering from epilepsy. However, it is estimated that approximately 30% of epileptic patients will not have adequate seizure control with medication alone. Resection of epileptogenic cortex may be indicated in medically refractory cases with a discrete seizure focus in noneloquent cortex. For patients in whom resection is not an option, deep brain stimulation (DBS) may be an effective means of seizure control. Deep brain stimulation targets for treating seizures primarily include the thalamic nuclei, hippocampus, subthalamic nucleus, and cerebellum. A variety of stimulation parameters have been studied, and more recent advances in electrical stimulation to treat epilepsy include responsive neurostimulation. Data suggest that DBS is effective for treating drug-resistant epilepsy.

An Open-Label Clinical Trial of Hypothalamic Deep Brain Stimulation for Human Morbid Obesity: BLESS Study Protocol

BACKGROUND

Human morbid obesity is increasing worldwide in an alarming way. The hypothalamus is known to mediate its mechanisms. Deep brain stimulation (DBS) of the ventromedial hypothalamus (VMH) may be an alternative to treat patients refractory to standard medical and surgical therapies.

OBJECTIVE

To assess the safety, identify possible side effects, and to optimize stimulation parameters of continuous VMH-DBS. Additionally, this study aims to determine if continuous VMH-DBS will lead to weight loss by causing changes in body composition, basal metabolism, or food intake control.

METHODS

The BLESS study is a feasibility study, single-center open-label trial. Six patients (body mass index &gt; 40) will undergo low-frequency VMH-DBS. Data concerning timing, duration, frequency, severity, causal relationships, and associated electrical stimulation patterns regarding side effects or weight changes will be recorded.

EXPECTED OUTCOMES

We expect to demonstrate the safety, identify possible side effects, and to optimize electrophysiological parameters related to VMH-DBS. No clinical or behavioral adverse changes are expected. Weight loss ≥ 3% of the basal weight after 3 mo of electrical stimulation will be considered adequate. Changes in body composition and increase in basal metabolism are expected. The amount of food intake is likely to remain unchanged.

DISCUSSION

The design of this study protocol is to define the safety of the procedure, the surgical parameters important for target localization, and additionally the safety of long-term stimulation of the VMH in morbidly obese patients. Novel neurosurgical approaches to treat metabolic and autonomic diseases can be developed based on the data made available by this investigation.

Activation of the subthalamic nucleus suppressed by high frequency stimulation: A c-Fos immunohistochemical study

Deep brain stimulation applied at high frequency (HFS) to the subthalamic nucleus (STN) is used to ameliorate the symptoms of Parkinson's disease. The mechanism by which this is achieved remains controversial. In particular, it is uncertain whether HFS has a suppressive or excitatory action locally within the STN. Brief exposure of rats to ether anesthesia evokes pathological burst firing and associated expression of the immediate early gene c-Fos in STN neurons. We used this ether model of STN activation to test the effect of a range of HFS parameters on c-Fos expression evoked by the anesthetic. The elevated baseline of c-Fos expression afforded the possibility of detecting further excitatory, or suppressive effects of STN HFS. Four HFS protocols were examined; 130, 200 and 260 Hz with 60 µs, and 130 Hz with 90 µs pulse width (HFS intensity:150-300 µA). All HFS protocols were applied for 20 min while the animals were exposed to ether. Ether-evoked expression of c-Fos immunoreactivity was suppressed by HFS at 200 and 260 Hz with a pulse width of 60 µs, and by 130 Hz when the pulse width was increased to 90 µs. HFS at 130 Hz with the 60 µs pulse width had no significant effect and HFS alone caused negligible c-Fos expression in the STN. These findings suggest that HFS of the STN causes significant suppression of evoked neuronal activity. It remains to be determined whether this locally suppressive property of HFS is associated with the efficacy of STN deep brain stimulation to relieve the symptoms of Parkinson's disease.

Deep brain stimulation for drug-resistant epilepsy

OBJECTIVES

To review clinical evidence on the antiepileptic effects of deep brain stimulation (DBS) for drug-resistant epilepsy, its safety, and the factors influencing individual outcomes.

METHODS

A comprehensive search of the medical literature (PubMed, Medline) was conducted to identify relevant articles investigating DBS therapy for drug-resistant epilepsy. Reference lists of these articles were used to source further articles.

RESULTS

Stimulation of the anterior nucleus of the thalamus (ANT) and hippocampus (HC) has been shown to decrease the frequency of refractory seizures. Half of all patients from clinical studies experienced a 46%-90% seizure reduction with ANT-DBS, and a 48%-95% seizure reduction with HC-DBS. The efficacy of stimulating other targets remains inconclusive due to lack of evidence. Approximately three-fourths of patients receiving ANT, HC, or centromedian nucleus of the thalamus (CMT) stimulation are responders-experiencing a seizure reduction of at least 50%. The time course of clinical benefit varies dramatically, with both an initial lesional effect and ongoing stimulation effect at play. Improved quality of life and changes to cognition or mood may also occur. Side effects are similar in nature to those reported from DBS therapy for movement disorders. Several factors are potentially associated with stimulation efficacy, including an absence of structural abnormality on imaging for ANT and HC stimulation, and electrode position relative to the target. Certain seizure types or syndromes may respond more favorably to specific targets, including ANT stimulation for deep temporal or limbic seizures, and CMT stimulation for generalized seizures and Lennox-Gastaut syndrome.

SIGNIFICANCE

We have identified several patient, disease, and stimulation factors that potentially predict seizure outcome following DBS. More large-scale clinical trials are needed to explore different stimulation parameters, reevaluate the indications for DBS, and identify robust predictors of patient response.

Controlling mechanism of absence seizures by deep brain stimulus applied on subthalamic nucleus

Based on a classical model of the basal ganglia thalamocortical network, in this paper, we employed a type of the deep brain stimulus voltage on the subthalamic nucleus to study the control mechanism of absence epilepsy seizures. We found that the seizure can be well controlled by turning the period and the duration of current stimulation into suitable ranges. It is the very interesting bidirectional periodic adjustment phenomenon. These parameters are easily regulated in clinical practice, therefore, the results obtained in this paper may further help us to understand the treatment mechanism of the epilepsy seizure.

Neurostimulation as a promising epilepsy therapy

The revolution in theory, swift technological developments, and invention of new devices have driven tremendous progress in neurostimulation as a third‐line treatment for epilepsy. Over the past decades, neurostimulation took its place in the field of epilepsy as an advanced treatment technique and opened up a new world. Numerous animal studies have proven the physical efficacy of stimulation of the brain and peripheral nerves. Based on this optimistic fundamental research, new advanced techniques are being explored in clinical practice. Over the past century, drawing on the benefits brought about by vagus nerve stimulation for the treatment of epilepsy, various new neurostimulation modalities have been developed to control seizures. Clinical studies including case reports, case series, and clinical trials have been booming in the past several years. This article gives a comprehensive review of most of these clinical studies. In addition to highlighting the advantages of neurostimulation for the treatment of epilepsy, concerns with this modality and future development directions are also discussed. The biggest advantage of neurostimulation over pharmacological treatments for epilepsy is the modulation of the epilepsy network by delivering stimuli at a specific target or the “hub.” Conversely, however, a lack of knowledge of epilepsy networks and the mechanisms of neurostimulation may hinder further development. Therefore, theoretical research on the mechanism of epileptogenesis and epilepsy networks is needed in the future. Within the multiple modalities of neuromodulation, the final choice should be made after full discussion with a multidisciplinary team at a presurgical conference. Furthermore, the establishment of a neurostimulation system with standardized parameters and rigorous guidelines is another important issue. To achieve this goal, a worldwide collaboration of epilepsy centers is also suggested in the future.

Deep brain and cortical stimulation for epilepsy

BACKGROUND

Despite optimal medical treatment, including epilepsy surgery, many epilepsy patients have uncontrolled seizures. Since the 1970s interest has grown in invasive intracranial neurostimulation as a treatment for these patients. Intracranial stimulation includes both deep brain stimulation (DBS) (stimulation through depth electrodes) and cortical stimulation (subdural electrodes). This is an updated version of a previous Cochrane review published in 2014.

OBJECTIVES

To assess the efficacy, safety and tolerability of DBS and cortical stimulation for refractory epilepsy based on randomized controlled trials (RCTs).

SEARCH METHODS

We searched the Cochrane Epilepsy Group Specialized Register on 29 September 2015, but it was not necessary to update this search, because records in the Specialized Register are included in CENTRAL. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library 2016, Issue 11, 5 November 2016), PubMed (5 November 2016), ClinicalTrials.gov (5 November 2016), the WHO International Clinical Trials Registry Platform ICTRP (5 November 2016) and reference lists of retrieved articles. We also contacted device manufacturers and other researchers in the field. No language restrictions were imposed.

SELECTION CRITERIA

RCTs comparing deep brain or cortical stimulation versus sham stimulation, resective surgery, further treatment with antiepileptic drugs or other neurostimulation treatments (including vagus nerve stimulation).

DATA COLLECTION AND ANALYSIS

Four review authors independently selected trials for inclusion. Two review authors independently extracted the relevant data and assessed trial quality and overall quality of evidence. The outcomes investigated were seizure freedom, responder rate, percentage seizure frequency reduction, adverse events, neuropsychological outcome and quality of life. If additional data were needed, the study investigators were contacted. Results were analysed and reported separately for different intracranial targets for reasons of clinical heterogeneity.

MAIN RESULTS

Twelve RCTs were identified, eleven of these compared one to three months of intracranial neurostimulation with sham stimulation. One trial was on anterior thalamic DBS (n = 109; 109 treatment periods); two trials on centromedian thalamic DBS (n = 20; 40 treatment periods), but only one of the trials (n = 7; 14 treatment periods) reported sufficient information for inclusion in the quantitative meta-analysis; three trials on cerebellar stimulation (n = 22; 39 treatment periods); three trials on hippocampal DBS (n = 15; 21 treatment periods); one trial on nucleus accumbens DBS (n = 4; 8 treatment periods); and one trial on responsive ictal onset zone stimulation (n = 191; 191 treatment periods). In addition, one small RCT (n = 6) compared six months of hippocampal DBS versus sham stimulation. Evidence of selective reporting was present in four trials and the possibility of a carryover effect complicating interpretation of the results could not be excluded in five cross-over trials without any or a sufficient washout period. Moderate-quality evidence could not demonstrate statistically or clinically significant changes in the proportion of patients who were seizure-free or experienced a 50% or greater reduction in seizure frequency (primary outcome measures) after one to three months of anterior thalamic DBS in (multi)focal epilepsy, responsive ictal onset zone stimulation in (multi)focal epilepsy patients and hippocampal DBS in (medial) temporal lobe epilepsy. However, a statistically significant reduction in seizure frequency was found for anterior thalamic DBS (mean difference (MD), -17.4% compared to sham stimulation; 95% confidence interval (CI) -31.2 to -1.0; high-quality evidence), responsive ictal onset zone stimulation (MD -24.9%; 95% CI -40.1 to -6.0; high-quality evidence) and hippocampal DBS (MD -28.1%; 95% CI -34.1 to -22.2; moderate-quality evidence). Both anterior thalamic DBS and responsive ictal onset zone stimulation do not have a clinically meaningful impact on quality life after three months of stimulation (high-quality evidence). Electrode implantation resulted in postoperative asymptomatic intracranial haemorrhage in 1.6% to 3.7% of the patients included in the two largest trials and 2.0% to 4.5% had postoperative soft tissue infections (9.4% to 12.7% after five years); no patient reported permanent symptomatic sequelae. Anterior thalamic DBS was associated with fewer epilepsy-associated injuries (7.4 versus 25.5%; P = 0.01) but higher rates of self-reported depression (14.8 versus 1.8%; P = 0.02) and subjective memory impairment (13.8 versus 1.8%; P = 0.03); there were no significant differences in formal neuropsychological testing results between the groups. Responsive ictal-onset zone stimulation seemed to be well-tolerated with few side effects.The limited number of patients preclude firm statements on safety and tolerability of hippocampal DBS. With regards to centromedian thalamic DBS, nucleus accumbens DBS and cerebellar stimulation, no statistically significant effects could be demonstrated but evidence is of only low to very low quality.

AUTHORS' CONCLUSIONS

Except for one very small RCT, only short-term RCTs on intracranial neurostimulation for epilepsy are available. Compared to sham stimulation, one to three months of anterior thalamic DBS ((multi)focal epilepsy), responsive ictal onset zone stimulation ((multi)focal epilepsy) and hippocampal DBS (temporal lobe epilepsy) moderately reduce seizure frequency in refractory epilepsy patients. Anterior thalamic DBS is associated with higher rates of self-reported depression and subjective memory impairment. There is insufficient evidence to make firm conclusive statements on the efficacy and safety of hippocampal DBS, centromedian thalamic DBS, nucleus accumbens DBS and cerebellar stimulation. There is a need for more, large and well-designed RCTs to validate and optimize the efficacy and safety of invasive intracranial neurostimulation treatments.

Optogenetic Approaches for Controlling Seizure Activity

Optogenetics, a technique that utilizes light-sensitive ion channels or pumps to activate or inhibit neurons, has allowed scientists unprecedented precision and control for manipulating neuronal activity. With the clinical need to develop more precise and effective therapies for patients with drug-resistant epilepsy, these tools have recently been explored as a novel treatment for halting seizure activity in various animal models. In this review, we provide a detailed and current summary of these optogenetic approaches and provide a perspective on their future clinical application as a potential neuromodulatory therapy.

White matter stimulation for the treatment of epilepsy

Electrical stimulation in the treatment of epilepsy has been tried in numerous forms and with a variety of targets. Some of these, such as anterior thalamic stimulation, responsive cortical stimulation, and vagal nerve stimulation, have shown promise. A relatively novel concept, that of white matter stimulation, offers a different mechanism in that a small population of stimulated axons can transmit current to a large population of epileptogenic neurons. In theory, this allows for the modulation of seizure circuits and neural networks using lower stimulation volumes. Although clinical data is currently sparse, we review the relevant studies pertaining to white matter stimulation in epilepsy thus far, and offer explanations as to its effects, potential advantages, and utility.

Electrical control of epilepsy

Epilepsy afflicts approximately 1-2% of the world's population. The mainstay therapy for treating the chronic recurrent seizures that are emblematic of epilepsy are drugs that manipulate levels of neuronal excitability in the brain. However, approximately one-third of all epilepsy patients get little to no clinical relief from this therapeutic regimen. The use of electrical stimulation in many forms to treat drug-refractory epilepsy has grown markedly over the past few decades, with some devices and protocols being increasingly used as standard clinical treatment. This article seeks to review the fundamental modes of applying electrical stimulation-from the noninvasive to the nominally invasive to deep brain stimulation-for the control of seizures in epileptic patients. Therapeutic practices from the commonly deployed clinically to the experimental are discussed to provide an overview of the innovative neural engineering approaches being explored to treat this difficult disease.

A novel combinational approach of microstimulation and bioluminescence imaging to study the mechanisms of action of cerebral electrical stimulation in mice

Deep brain stimulation (DBS) is used to treat a number of neurological conditions and is currently being tested to intervene in neuropsychiatric conditions. However, a better understanding of how it works would ensure that side effects could be minimized and benefits optimized. We have thus developed a unique device to perform brain stimulation (BS) in mice and to address fundamental issues related to this methodology in the pre-clinical setting. This new microstimulator prototype was specifically designed to allow simultaneous live bioluminescence imaging of the mouse brain, allowing real time assessment of the impact of stimulation on cerebral tissue. We validated the authenticity of this tool in vivo by analysing the expression of toll-like receptor 2 (TLR2), corresponding to the microglial response, in the stimulated brain regions of TLR2-fluc-GFP transgenic mice, which we further corroborated with post-mortem analyses in these animals as well as in human brains of patients who underwent DBS to treat their Parkinson's disease. In the present study, we report on the development of the first BS device that allows for simultaneous live in vivo imaging in mice. This tool opens up a whole new range of possibilities that allow a better understanding of BS and how to optimize its effects through its use in murine models of disease.

Future of epilepsy treatment: integration of devices

ABSTRACT 

The use of devices in the treatment of epilepsy is an emerging therapy for those patients whose seizures are not controlled by medications. This article will discuss current treatment options with devices for vagus nerve stimulation, deep brain stimulation and responsive neurostimulation. Emerging therapies in noninvasive neurostimulation such as with trigeminal nerve stimulation, transcranial magnetic stimulation and transcranial direct current stimulation may prove to be promising solutions. Finally, new and enhanced techniques of drug delivery are discussed as well as other devices with potential use in the study and treatment of epilepsy.

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.

Electrical brain stimulation for epilepsy

Neurostimulation enables adjustable and reversible modulation of disease symptoms, including those of epilepsy. Two types of brain neuromodulation, comprising anterior thalamic deep brain stimulation and responsive neurostimulation at seizure foci, are supported by Class I evidence of effectiveness, and many other sites in the brain have been targeted in small trials of neurostimulation therapy for seizures. Animal studies have mainly assisted in the identification of potential neurostimulation sites and parameters, but much of the clinical work is only loosely based on fundamental principles derived from the laboratory, and the mechanisms by which brain neurostimulation reduces seizures remain poorly understood. The benefits of stimulation tend to increase over time, with maximal effect seen typically 1-2 years after implantation. Typical reductions of seizure frequency are approximately 40% acutely, and 50-69% after several years. Seizure intensity might also be reduced. Complications from brain neurostimulation are mainly associated with the implantation procedure and hardware, including stimulation-related paraesthesias, stimulation-site infections, electrode mistargeting and, in some patients, triggered seizures or even status epilepticus. Further preclinical and clinical experience with brain stimulation surgery should lead to improved outcomes by increasing our understanding of the optimal surgical candidates, sites and parameters.

Clinical utility of implantable neurostimulation devices as adjunctive treatment of uncontrolled seizures

About one third of patients with epilepsy are refractory to medical treatment. For these patients, alternative treatment options include implantable neurostimulation devices such as vagus nerve stimulation (VNS), deep brain stimulation (DBS), and responsive neurostimulation systems (RNS). We conducted a systematic literature review to assess the available evidence on the clinical efficacy of these devices in patients with refractory epilepsy across their lifespan. VNS has the largest evidence base, and numerous randomized controlled trials and open-label studies support its use in the treatment of refractory epilepsy. It was approved by the US Food and Drug Administration in 1997 for treatment of partial seizures, but has also shown significant benefit in the treatment of generalized seizures. Results in adult populations have been more encouraging than in pediatric populations, where more studies are required. VNS is considered a safe and well-tolerated treatment, and serious side effects are rare. DBS is a well-established treatment for several movement disorders, and has a small evidence base for treatment of refractory epilepsy. Stimulation of the anterior nucleus of the thalamus has shown the most encouraging results, where significant decreases in seizure frequency were reported. Other potential targets include the centromedian thalamic nucleus, hippocampus, cerebellum, and basal ganglia structures. Preliminary results on RNS, new-generation implantable neurostimulation devices which stimulate brain structures only when epileptic activity is detected, are encouraging. Overall, implantable neurostimulation devices appear to be a safe and beneficial treatment option for patients in whom medical treatment has failed to adequately control their epilepsy. Further large-scale randomized controlled trials are required to provide a sufficient evidence base for the inclusion of DBS and RNS in clinical guidelines.

Placement of deep brain electrodes in the dog using the Brainsight frameless stereotactic system: a pilot feasibility study

Background

Deep brain stimulation (DBS) together with concurrent EEG recording has shown promise in the treatment of epilepsy. A novel device is capable of combining these 2 functions and may prove valuable in the treatment of epilepsy in dogs. However, stereotactic implantation of electrodes in dogs has not yet been evaluated.

Objective

To evaluate the feasibility and safety of implanting stimulating and recording electrodes in the brain of normal dogs using the Brainsight system and to evaluate the function of a novel DBS and recording device.

Animals

Four male intact Greyhounds, confirmed to be normal by clinical and neurologic examinations and hematology and biochemistry testing.

Methods

MRI imaging of the brain was performed after attachment of fiducial markers. MRI scans were used to calculate trajectories for electrode placement in the thalamus and hippocampus, which was performed via burr hole craniotomy. Postoperative CT scanning was performed to evaluate electrode location and accuracy of placement was calculated. Serial neurologic examinations were performed to evaluate neurologic deficits and EEG recordings obtained to evaluate the effects of stimulation.

Results

Electrodes were successfully placed in 3 of 4 dogs with a mean accuracy of 4.6 ± 1.5 mm. EEG recordings showed evoked potentials in response to stimulation with a circadian variation in time‐to‐maximal amplitude. No neurologic deficits were seen in any dog.

Conclusions and Clinical Importance

Stereotactic placement of electrodes is safe and feasible in the dog. The development of a novel device capable of providing simultaneous neurostimulation and EEG recording potentially represents a major advance in the treatment of epilepsy.