Long-term seizure reduction in generalized epilepsy after anterior nucleus of the thalamus stimulation

INTRODUCTION

In 2018 the FDA approved the use of anterior nucleus of the thalamus (ANT) deep brain stimulation (DBS) for focal epilepsy in response to the results of the Stimulation of the Anterior Nucleus of Thalamus for Epilepsy (SANTÉ) double-blind randomized controlled trial. While generalized epilepsy (GE) was never assessed in this trial, subsequent follow up clarified that focal to bilateral tonic-clonic seizures were reduced in these subjects. In rare cases ANT DBS has nonetheless been pursued for patients with GE.

METHODS

We report a 27-year-old male with idiopathic GE who was successfully treated with ANT DBS. Prior to DBS, the patient typically had three or four generalized tonic-clonic seizures (GTCS) per week, amongst other seizures, and was refractory to both medication and vagal nerve stimulation (VNS). We also systematically reviewed the literature to understand the extent to which ANT DBS has been used in GE, under what circumstances, and with what results.

RESULTS

Five years since the introduction of ANT DBS, the patient has remained free of GTCS. Over this time, other seizures were also markedly reduced. For the systematic review, a comprehensive literature search using PubMed, Cochrane, and Google Scholar identified 23 GE patients treated with ANT DBS across 13 publications. 13 patients had patient-specific seizure outcomes reported. Clinical findings, seizure characteristics, and outcomes were summarized, demonstrating that ANT DBS surgery typically occurred after failed VNS and was usually effective, including 3 patients who became free of GTCS.

CONCLUSION

This anecdotal evidence of effectiveness suggests that some GE networks can be modulated by high-frequency stimulation at the ANT node. When established therapies have failed, ANT DBS is a therapeutic option, but the treatment requires further structured research in treating GE.

Effect of deep brain stimulation on the severity of seizures and the quality of life in patients with multifocal drug-resistant epilepsy in Iran: A pilot review of local experience

This study investigates the impact of the anterior nucleus of the thalamus deep brain stimulation (ANT-DBS) on patients with drug-resistant epilepsy (DRE) in Iran, specifically focusing on its effects on seizure metrics, severity and its influence on quality of life over time. A cohort of eight patients with DRE in Iran who underwent ANT-DBS was evaluated. Pre-operative assessments included comprehensive documentation of seizure frequency, duration, severity scores, and the Quality of Life in Epilepsy Inventory (QOLIE-13). Each patient also underwent high-resolution imaging using a 1.5 Tesla MRI, with targeted electrode placement in the anterior thalamic area. Post-operative evaluations measured changes in seizure frequency, severity scores, duration, and quality of life indicators. All subjects presented with DRE, and the mean age of participants was 24.62 years. Post-operative data revealed significantly reduced seizure frequency, duration, and severity scores. Notably, this reduction was more pronounced at the 6-month follow-up than the 3-month assessment, indicating a progressive therapeutic effect. All patients demonstrated a response to ANT-DBS, with two individuals achieving seizure freedom. Additionally, there was a marked improvement in quality of life, particularly in the domains of energy/fatigue and social functioning. ANT-DBS has been established as a promising and safe therapeutic intervention for patients with DRE. In a cohort of DRE patients in Iran, the treatment demonstrated comparable efficacy in decreasing seizure frequency and severity and enhancing self-reported quality of life, consistent with findings reported in the existing literature. The therapeutic benefits of ANT-DBS appear to augment over time.

Efficacy and safety of deep brain stimulation in drug resistance epilepsy: A systematic review and meta-analysis

In the context of drug-resistant epilepsy, deep brain stimulation (DBS) has received FDA approval. However, there have been reports of potential adverse effects, such as depression and memory impairment associated with DBS.This systematic review and meta-analysis aimed to investigate the impact of DBS on the quality of life (QoL), and seizure frequency of patients who had DRE, and assess its potential adverse events. The study followed PRISMA guidelines and thoroughly assessed databases, including Pubmed, Scopus, Embase, Web of Science, and the Cochrane Library, up to 31 July. Statistical analysis, fixed effect model analysis, performed by the Comprehensive Meta-analysis software (CMA) version 3.0. Additionally, Cochran's Q test was conducted to determine the statistical heterogeneity. The systematic review encompassed 54 studies, with 38 studies included in the subsequent meta-analysis. The total number of patients included in the studies was 999. The findings indicated a significant decrease in the mean seizure frequency of subjects following DBS (SMD: 0.609, 95% CI: 0.519 to 0.700, p-value < 0.001). Moreover, patients' QoL significantly improved after DBS (SMD: -0.442, 95% CI: -0.576 to -0.308, p-value < 0.001). The hippocampus displayed the most notable effect size among the different DBS targets. Subgroup analysis based on follow-up duration revealed increased DBS efficacy after two years. There are few reports of adverse events, such as insertional-related complications, infection, and neuropsychiatric complications, but the majority of these were temporary and non-fatal. DBS emerged as an effective and safe procedure for reducing seizure frequency and enhancing the quality of life in DRE patients, with minimal adverse events. Furthermore, the efficacy of DBS was observed to improve over time.

Subcortical Alterations in Newly Diagnosed Epilepsy and Associated Changes in Brain Connectivity and Cognition

Patients with chronic focal epilepsy commonly exhibit subcortical atrophy, particularly of the thalamus. The timing of these alterations remains uncertain, though preliminary evidence suggests that observable changes may already be present at diagnosis. It is also not yet known how these morphological changes are linked to the coherence of white matter pathways throughout the brain, or to neuropsychological function often compromised before antiseizure medication treatment. This study investigates localized atrophy in subcortical regions using surface shape analysis in individuals with newly diagnosed focal epilepsy (NDfE) and assesses their implications on brain connectivity and cognitive function. We collected structural (T1w) and diffusion-weighted MRI and neuropsychological data from 104 patients with NDfE and 45 healthy controls (HCs) matched for age, sex, and education. A vertex-based shape analysis was performed on subcortical structures to compare patients with NDfE and HC, adjusting for age, sex, and intracranial volume. The mean deformation of significance areas (pcor < 0.05) was used to identify white matter pathways associated with overall shape alterations in patients relative to controls using correlational tractography. Additionally, the relationship between significant subcortical shape values and neuropsychological outcomes was evaluated using a generalized canonical correlation approach. Shape analysis revealed bilateral focal inward deformation (a proxy for localized atrophy) in anterior areas of the right and left thalamus and right pallidum in patients with NDfE compared to HC (FWE corrected). No structures showed areas of outward deformation in patients. The connectometry analysis revealed that fractional anisotropy (FA) was positively correlated with thalamic and pallidal shape deformation, that is, reduced FA was associated with inward deformation in tracts proximal to and or connecting with the thalamus including the fornix, frontal, parahippocampal, and corticothalamic pathways. Thalamic and pallidal shape changes were also related to increased depression and anxiety and reduced memory and cognitive function. These findings suggest that atrophy of the thalamus, which has previously been associated with the generation and maintenance of focal seizures, may present at epilepsy diagnosis and relate to alterations in both white matter connectivity and cognitive performance. We suggest that at least some alterations in brain structure and consequent impact on cognitive and affective processes are the result of early epileptogenic processes rather than exclusively due to the chronicity of longstanding epilepsy, recurrent seizures, and treatment with antiseizure medication.

Advancing thalamic neuromodulation in epilepsy: Bridging adult data to pediatric care

Thalamic neuromodulation has emerged as a treatment option for drug-resistant epilepsy (DRE) with widespread and/or undefined epileptogenic networks. While deep brain stimulation (DBS) and responsive neurostimulation (RNS) depth electrodes offer means for electrical stimulation of the thalamus in adult patients with DRE, the application of thalamic neuromodulation in pediatric epilepsy remains limited. To address this gap, the Neuromodulation Expert Collaborative was established within the Pediatric Epilepsy Research Consortium (PERC) Epilepsy Surgery Special Interest Group. In this expert review, existing evidence and recommendations for thalamic neuromodulation modalities using DBS and RNS are summarized, with a focus on the anterior (ANT), centromedian(CMN), and pulvinar nuclei of the thalamus. To-date, only DBS of the ANT is FDA approved for treatment of DRE in adult patients based on the results of the pivotal SANTE (Stimulation of the Anterior Nucleus of Thalamus for Epilepsy) study. Evidence for other thalamic neurmodulation indications and targets is less abundant. Despite the lack of evidence, positive responses to thalamic stimulation in adults with DRE have led to its off-label use in pediatric patients. Although caution is warranted due to differences between pediatric and adult epilepsy, the efficacy and safety of pediatric neuromodulation appear comparable to that in adults. Indeed, CMN stimulation is increasingly accepted for generalized and diffuse onset epilepsies, with recent completion of one randomized trial. There is also growing interest in using pulvinar stimulation for temporal plus and posterior quadrant epilepsies with one ongoing clinical trial in Europe. The future of thalamic neuromodulation holds promise for revolutionizing the treatment landscape of childhood epilepsy. Ongoing research, technological advancements, and collaborative efforts are poised to refine and improve thalamic neuromodulation strategies, ultimately enhancing the quality of life for children with DRE.

Bilateral centromedian nucleus of thalamus responsive neurostimulation for pediatric-onset drug-resistant epilepsy

Neuromodulation therapies offer an efficacious treatment alternative for patients with drug-resistant epilepsy (DRE), particularly those unlikely to benefit from surgical resection. Here we present our retrospective single-center case series of patients with pediatric-onset DRE who underwent responsive neurostimulation (RNS) depth electrode implantation targeting the bilateral centromedian nucleus (CM) of the thalamus between October 2020 and October 2022. Sixteen patients were identified; seizure outcomes, programming parameters, and complications at follow-up were reviewed. The median age at implantation was 13 years (range 3.6-22). Six patients (38%) were younger than 12 years of age at the time of implantation. Ictal electroencephalography (EEG) patterns during patients' most disabling seizures were reliably detected. Ten patients (62%) achieved 50% or greater reduction in seizure frequency at a median 1.3 years (range 0.6-2.6) of follow-up. Eight patients (50%) experienced sensorimotor side effects, and three patients (19%) had superficial pocket infection, prompting the removal of the RNS device. Side effects of stimulation were experienced mostly in monopolar-cathodal configuration and alleviated with programming change to bipolar configuration or low-frequency stimulation. Closed-loop neurostimulation using RNS targeting bilateral CM is a feasible and useful therapy for patients with pediatric-onset DRE.

Neurophysiologic Characteristics of the Anterior Nucleus of the Thalamus during Deep Brain Stimulation Surgery for Epilepsy

INTRODUCTION

Anterior nucleus of the thalamus (ANT) deep brain stimulation (DBS) is an increasingly promising treatment option for refractory epilepsy. Optimal therapeutic benefit has been associated with stimulation at the junction of ANT and the mammillothalamic tract (mtt), but electrophysiologic markers of this target are lacking. The present study examined microelectrode recordings (MER) during DBS to identify unique electrophysiologic characteristics of ANT and the ANT-mtt junction.

METHODS

Ten patients with medically refractory epilepsy underwent MER during ANT-DBS implantation under general anesthesia. MER locations were determined based on coregistration of preoperative MRI, postoperative CT, and a stereotactic atlas of the thalamus (Morel atlas). Several neurophysiological parameters including single unit spiking rate, bursting properties, theta and alpha power and cerebrospinal fluid (CSF)-normalized root mean square (NRMS) of multiunit activity were characterized at recording depths and compared to anatomic boundaries.

RESULTS

From sixteen hemispheres, 485 recordings locations were collected from a mean of 30.3 (15.64 ± 5.0 mm) recording spans. Three-hundred and ninety-four of these recording locations were utilized further for analysis of spiking and bursting rates, after excluding recordings that were more than 8 mm above the putative ventral ANT border. The ANT region exhibited discernible features including: (1) mean spiking rate (7.52 Hz ± 6.9 Hz; one-way analysis of variance test, p = 0.014 when compared to mediodorsal nucleus of the thalamus [MD], mtt, and CSF), (2) the presence of bursting activity with 40% of ANT locations (N = 59) exhibited bursting versus 24% the mtt (χ2; p < 0.001), and 32% in the MD (p = 0.38), (3) CSF-NRMS, a proxy for neuronal density, exhibited well demarcated changes near the entry and exit of ANT (linear regression, R = -0.33, p < 0.001). Finally, in the ANT, both theta (4-8 Hz) and alpha band power (9-12 Hz) were negatively correlated with distance to the ventral ANT border (linear regression, p < 0.001 for both). The proportion of recordings with spiking and bursting activity was consistently highest 0-2 mm above the ventral ANT border with the mtt.

CONCLUSION

We observed several electrophysiological markers demarcating the ANT superior and inferior borders including multiple single cell and local field potential features. A local maximum in neural activity just above the ANT-mtt junction was consistent with the previously described optimal target for seizure reduction. These features may be useful for successful targeting of ANT-DBS for epilepsy.

Assessing short-term and long-term security and efficacy of anterior nucleus of the thalamus deep brain stimulation for treating drug-resistant epilepsy: A systematic review and single-arm meta-analysis

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is a widespread invasive procedure for treating drug-resistant epilepsy. Nonetheless, there is a persistent debate regarding the short-term and long-term efficacy and safety of ANT-DBS. Thus we conducted a systematic review and meta-analysis. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), we searched PubMed, Cochrane, Embase, and Web of Science for studies treating refractory epilepsy with ANT-DBS. Short-term analysis was considered for studies with a mean follow-up of 3 years or less. The following outcomes were assessed for data extraction: procedure responders and nonresponders, increased seizure frequency, complications, and procedure-related mortality. Of 650 studies, 25 fit our inclusion criteria, involving 427 patients. Previous surgical treatments have been reported in 214 patients (50.1%) and a median average baseline seizure frequency of 64.9 monthly seizures. In the short-term analysis, we observed a proportion of 67% (95% confidence interval [CI] 54%-79%) of responders and 33% (95% CI 21%-46%) of nonresponders. In addition, 4% (95% CI 0%-9%) of the patients presented increased seizure frequency. In the long-term analysis, we observed 72% (95% CI 66%-78%) responders and 27% (95% CI 21%-34%) nonresponders. Moreover, there was a 2% (95% CI 0%-5%) increase in seizure frequency. No procedure-related mortality was reported at any follow-up. ANT-DBS effectively treats refractory epilepsy, with lasting short-term and long-term benefits. It remains safe and efficient despite complications, showing no procedure-linked fatalities, high patient responsiveness, and minimal increased seizures. Consistent results over time and low morbidity/mortality rates emphasize its worth. Further research is necessary to diminish the discrepancy among results.

Epileptiform discharges in the anterior thalamus of epilepsy patients

Anterior thalamus (ANT) deep-brain stimulation (DBS) is an approved therapy for drug resistant epilepsy. We aimed to identify interictal epileptiform discharges (IED) in the ANT and to investigate their relationship with surface IEDs. Fifteen patients were monitored for two consecutive nights with externalized thalamic leads to analyze the intrathalamic epileptiform activities (TIED). Forty-six % of all contacts were located within the ANT. We found that all the responders had TIEDs within the ANT, while this held true only for 44% of the non-responders. The overall response rate (RR) at 1-year follow-up was 40%, while it was 44% in bilateral ANT hit patients and 45% in epileptic focus side hit. However, in case of TIEDs present in the focus side the RR reached as high as 71%. TIED activity may prove the pathophysiological connection to the seizure focus, and stimulation of this area might have a better suppressing effect on seizures.

Insertional effect following electrode implantation: an underreported but important phenomenon

Deep brain stimulation has revolutionized the treatment of movement disorders and is gaining momentum in the treatment of several other neuropsychiatric disorders. In almost all applications of this therapy, the insertion of electrodes into the target has been shown to induce some degree of clinical improvement prior to stimulation onset. Disregarding this phenomenon, commonly referred to as 'insertional effect', can lead to biased results in clinical trials, as patients receiving sham stimulation may still experience some degree of symptom amelioration. Similar to the clinical scenario, an improvement in behavioural performance following electrode implantation has also been reported in preclinical models. From a neurohistopathologic perspective, the insertion of electrodes into the brain causes an initial trauma and inflammatory response, the activation of astrocytes, a focal release of gliotransmitters, the hyperexcitability of neurons in the vicinity of the implants, as well as neuroplastic and circuitry changes at a distance from the target. Taken together, it would appear that electrode insertion is not an inert process, but rather triggers a cascade of biological processes, and, as such, should be considered alongside the active delivery of stimulation as an active part of the deep brain stimulation therapy.

Prior-guided individualized thalamic parcellation based on local diffusion characteristics

Comprising numerous subnuclei, the thalamus intricately interconnects the cortex and subcortex, orchestrating various facets of brain functions. Extracting personalized parcellation patterns for these subnuclei is crucial, as different thalamic nuclei play varying roles in cognition and serve as therapeutic targets for neuromodulation. However, accurately delineating the thalamic nuclei boundary at the individual level is challenging due to intersubject variability. In this study, we proposed a prior-guided parcellation (PG-par) method to achieve robust individualized thalamic parcellation based on a central-boundary prior. We first constructed probabilistic atlas of thalamic nuclei using high-quality diffusion MRI datasets based on the local diffusion characteristics. Subsequently, high-probability voxels in the probabilistic atlas were utilized as prior guidance to train unique multiple classification models for each subject based on a multilayer perceptron. Finally, we employed the trained model to predict the parcellation labels for thalamic voxels and construct individualized thalamic parcellation. Through a test-retest assessment, the proposed prior-guided individualized thalamic parcellation exhibited excellent reproducibility and the capacity to detect individual variability. Compared with group atlas registration and individual clustering parcellation, the proposed PG-par demonstrated superior parcellation performance under different scanning protocols and clinic settings. Furthermore, the prior-guided individualized parcellation exhibited better correspondence with the histological staining atlas. The proposed prior-guided individualized thalamic parcellation method contributes to the personalized modeling of brain parcellation.

Impedance Characteristics of Stimulation Contacts in Deep Brain Stimulation of the Anterior Nucleus of the Thalamus and Its Relationship to Seizure Outcome in Patients With Refractory Epilepsy

BACKGROUND

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is an emerging form of adjunctive therapy in focal refractory epilepsy. Unlike conventional DBS targets, the ANT is both encapsulated by white matter layers and located immediately adjacent to the cerebrospinal fluid (CSF) space. Owing to the location of the ANT, implantation has most commonly been performed using a transventricular trajectory. Previous studies suggest different electrical conductivity between gray matter, white matter, and CSF.

OBJECTIVES

In this study, we asked whether therapeutic impedance values from a fully implanted DBS device could be used to deduce the actual location of the active contact to optimize the stimulation site. Secondly, we tested whether impedance values correlate with patient outcomes.

MATERIALS AND METHODS

A total of 16 patients with ANT-DBS for refractory epilepsy were evaluated in this prospective study. Therapeutic impedance values were recorded on regular outpatient clinic visits. Contact locations were analyzed using delayed contrast-enhanced postoperative computed tomography-3T magnetic resonance imaging short tau inversion recovery fusion images previously shown to demonstrate anatomical details around the ANT.

RESULTS

Transventricularly implanted contacts immediately below the CSF surface showed overall lower and slightly decreasing impedances over time compared with higher and more stable impedances in contacts with deeper parenchymal location. Impedance values in transventricularly implanted contacts in the ANT were significantly lower than those in transventricularly implanted contacts outside the ANT or extraventricularly implanted contacts that were typically at the posterior/inferior/lateral border of the ANT. Increasing contact distance from the CSF surface was associated with a linear increase in therapeutic impedance. We also found that therapeutic impedance values were significantly lower in contacts with favorable therapy response than in nonresponding contacts. Finally, we observed a significant correlation between the left- and right-side averaged impedance and the reduction of the total number of seizures.

CONCLUSIONS

Valuable information can be obtained from the noninvasive measurement of therapeutic impedances. The selection of active contacts to target stimulation to the anterior nucleus may be guided by therapeutic impedance measurements to optimize outcome.

MR-Guided Focused Ultrasound for Refractory Epilepsy: Where Are We Now?

Epilepsy is one of the most common neurological diseases in both adults and children. Despite improvements in medical care, 20 to 30% of patients are still resistant to the best medical treatment. The quality of life, neurologic morbidity, and even mortality of patients are significantly impacted by medically intractable epilepsy. Nowadays, conservative therapeutic approaches consist of increasing medication dosage, changing to a different anti-seizure drug as monotherapy, and combining different antiseizure drugs using an add-on strategy. However, such measures may not be sufficient to efficiently control seizure recurrence. Resective surgery, ablative procedures and non-resective neuromodulatory (deep-brain stimulation, vagus nerve stimulation) treatments are the available treatments for these kinds of patients. However, invasive procedures may involve lengthy inpatient stays for the patients, risks of long-term neurological impairment, general anesthesia, and other possible surgery-related complications (i.e., hemorrhage or infection). In the last few years, MR-guided focused ultrasound (MRgFUS) has been proposed as an emerging treatment for neurological diseases because of technological advancements and the goal of minimally invasive neurosurgery. By outlining the current knowledge obtained from both preclinical and clinical studies and discussing the technical opportunities of this therapy for particular epileptic phenotypes, in this perspective review, we explore the various mechanisms and potential applications (thermoablation, blood-brain barrier opening for drug delivery, neuromodulation) of high- and low-intensity ultrasound, highlighting possible novel strategies to treat drug-resistant epileptic patients who are not eligible or do not accept currently established surgical approaches. Taken together, the available studies support a possible role for lesional treatment over the anterior thalamus with high-intensity ultrasound and neuromodulation of the hippocampus via low-intensity ultrasound in refractory epilepsy. However, more studies, likely conceiving epilepsy as a network disorder and bridging together different scales and modalities, are required to make ultrasound delivery strategies meaningful, effective, and safe.

Functional network dynamics between the anterior thalamus and the cortex in deep brain stimulation for epilepsy

Owing to its unique connectivity profile with cortical brain regions, and its suggested role in the subcortical propagation of seizures, the anterior nucleus of the thalamus (ANT) has been proposed as a key deep brain stimulation (DBS) target in drug-resistant epilepsy. However, the spatio-temporal interaction dynamics of this brain structure, and the functional mechanisms underlying ANT DBS in epilepsy remain unknown. Here, we study how the ANT interacts with the neocortex in vivo in humans and provide a detailed neurofunctional characterization of mechanisms underlying the effectiveness of ANT DBS, aiming at defining intraoperative neural biomarkers of responsiveness to therapy, assessed at 6 months post-implantation as the reduction in seizure frequency. A cohort of 15 patients with drug-resistant epilepsy (n = 6 males, age = 41.6 ± 13.79 years) underwent bilateral ANT DBS implantation. Using intraoperative cortical and ANT simultaneous electrophysiological recordings, we found that the ANT is characterized by high amplitude θ (4-8 Hz) oscillations, mostly in its superior part. The strongest functional connectivity between the ANT and the scalp EEG was also found in the θ band in ipsilateral centro-frontal regions. Upon intraoperative stimulation in the ANT, we found a decrease in higher EEG frequencies (20-70 Hz) and a generalized increase in scalp-to-scalp connectivity. Crucially, we observed that responders to ANT DBS treatment were characterized by higher EEG θ oscillations, higher θ power in the ANT, and stronger ANT-to-scalp θ connectivity, highlighting the crucial role of θ oscillations in the dynamical network characterization of these structures. Our study provides a comprehensive characterization of the interaction dynamic between the ANT and the cortex, delivering crucial information to optimize and predict clinical DBS response in patients with drug-resistant epilepsy.

Clinical efficacy and safety of anterior thalamic deep brain stimulation for intractable drug resistant epilepsy

BACKGROUND

Deep brain stimulation of the anterior nucleus of the thalamus (ANT DBS) is a neuromodulation therapy for patients with refractory focal seizures evolving into bilateral tonic-clonic seizures when pharmacotherapy as well other neuromodulation techniques including vagus nerve stimulation or responsive neurostimulation have failed.

OBJECTIVE

We performed a prospective single-center study investigating the clinical efficacy and exact ANT DBS lead location in patients with DRE.

METHODS

The primary outcome measure was the proportion of patients with more than 50 % reduction in diary-recorded seizures when compared to three preoperative months (baseline seizure frequency). The close postoperative follow-up was performed every 3 months. The seizure frequency, stimulation settings and adverse events were closely monitored during follow-up visits. We also analyzed the seizure outcome with location of ANT DBS active contacts.

RESULTS

Between May 2020 and October 2022, 10 adult patients with a mean age of 38.5 years (range, 30-48 years) underwent bilateral ANT DBS surgery (mean duration of DRE 28.6 years, range 16-41 years). The median seizure count in three months period preceding surgery (baseline seizure count) was 43.2 (range, 4-150). Nine patients achieved more than 50 % seizure reduction at the last follow-up (mean range 3-33 13.6 months, months). ANT DBS caused seizure reduction 3 months after procedure as well as at last follow-up by 60.4 % and 73.3 %, respectively. Due to relatively small number of studying individuals we cannot precisely locate the area within ANT associated with good clinical outcome. Patients with temporal lobe epilepsy had a remarkable reduction of seizure frequency. No patient suffered transient or permanent neurological deficits.

CONCLUSIONS

Clinical efficacy of ANT DBS may support more widespread utilization of this neuromodulation technique especially for seizures originating from temporal lobes.

Functional connectomic profile correlates with effective anterior thalamic stimulation for refractory epilepsy

BACKGROUND

Deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) is an effective treatment for refractory epilepsy; however, seizure outcome varies among individuals. Identifying a reliable noninvasive biomarker to predict good responders would be helpful.

OBJECTIVES

To test whether the functional connectivity between the ANT-DBS sites and the seizure foci correlates with effective seizure control in refractory epilepsy.

METHODS

We performed a proof-of-concept pilot study of patients with focal refractory epilepsy receiving ANT-DBS. Using normative human connectome data derived from 1000 healthy participants, we investigated whether intrinsic functional connectivity between the seizure foci and the DBS site was associated with seizure outcome. We repeated this analysis controlling for the extent of seizure foci, distance between the seizure foci and DBS site, and using functional connectivity of the ANT instead of the DBS site to test the contribution of variance in DBS sites.

RESULTS

Eighteen patients with two or more seizure foci were included. Greater functional connectivity between the seizure foci and the DBS site correlated with more favorable outcome. The degree of functional connectivity accounted for significant variance in clinical outcomes (DBS site: |r| = 0.773, p < 0.001 vs ANT-atlas: |r| = 0.715, p = 0.001), which remained significant when controlling for the extent of the seizure foci (|r| = 0.773, p < 0.001) and the distance between the seizure foci and DBS site (|r| = 0.777, p < 0.001). Significant correlations were independent of variance in the DBS sites (|r| = 0.148, p = 0.57).

CONCLUSION

These findings suggest that functional connectomic profile is a potential reliable non-invasive biomarker to predict ANT-DBS outcomes. Accordingly, the identification of ANT responders could decrease the surgical risk for patients who may not benefit and optimize the cost-effective allocation of health care resources.

Deep brain stimulation of the anterior nucleus of the thalamus increases slow wave activity in non-rapid eye movement sleep

OBJECTIVE

Previous studies suggest that intermittent deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) affects physiological sleep architecture. Here, we investigated the impact of continuous ANT DBS on sleep in epilepsy patients in a multicenter crossover study in 10 patients.

METHODS

We assessed sleep stage distribution, delta power, delta energy, and total sleep time in standardized 10/20 polysomnographic investigations before and 12 months after DBS lead implantation.

RESULTS

In contrast to previous studies, we found no disruption of sleep architecture or alterations of sleep stage distribution under active ANT DBS (p = .76). On the contrary, we observed more consolidated and deeper slow wave sleep (SWS) under continuous high-frequency DBS as compared to baseline sleep prior to DBS lead implantation. In particular, biomarkers of deep sleep (delta power and delta energy) showed a significant increase post-DBS as compared to baseline (36.67 ± 13.68 μV2 /Hz and 799.86 ± 407.56 μV2 *s, p < .001). Furthermore, the observed increase in delta power was related to the location of the active stimulation contact within the ANT; we found higher delta power and higher delta energy in patients with active stimulation in more superior contacts as compared to inferior ANT stimulation. We also observed significantly fewer nocturnal electroencephalographic discharges in DBS ON condition. In conclusion, our findings suggest that continuous ANT DBS in the most cranial part of the target region leads to more consolidated SWS.

SIGNIFICANCE

From a clinical perspective, these findings suggest that patients with sleep disruption under cyclic ANT DBS could benefit from an adaptation of stimulation parameters to more superior contacts and continuous mode stimulation.

A phase 1 open-label trial evaluating focused ultrasound unilateral anterior thalamotomy for focal onset epilepsy

OBJECTIVE

Focused ultrasound ablation (FUSA) is an emerging treatment for neurological and psychiatric diseases. We describe the initial experience from a pilot, open-label, single-center clinical trial of unilateral anterior nucleus of the thalamus (ANT) FUSA in patients with treatment-refractory epilepsy.

METHODS

Two adult subjects with treatment-refractory, focal onset epilepsy were recruited. The subjects received ANT FUSA using the Exablate Neuro (Insightec) system. We determined the safety and feasibility (primary outcomes), and changes in seizure frequency (secondary outcome) at 3, 6, and 12 months. Safety was assessed by the absence of side effects, that is, new onset neurological deficits or performance deterioration on neuropsychological testing. Feasibility was defined as the ability to create a lesion within the anterior nucleus. The monthly seizure frequency was compared between baseline and postthalamotomy.

RESULTS

The patients tolerated the procedure well, without neurological deficits or serious adverse events. One patient experienced a decline in verbal fluency, attention/working memory, and immediate verbal memory. Seizure frequency reduced significantly in both patients; one patient was seizure-free at 12 months, and in the second patient, the frequency reduced from 90-100 seizures per month to 3-6 seizures per month.

SIGNIFICANCE

This is the first known clinical trial to assess the safety, feasibility, and preliminary efficacy of ANT FUSA in adult patients with treatment-refractory focal onset epilepsy.

Deep brain stimulation of thalamus for epilepsy

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

Neuro-stimulation in focal epilepsy: A systematic review and meta-analysis

OBJECTIVES

Different neurostimulation modalities are available to treat drug-resistant focal epilepsy when surgery is not an option including vagus nerve stimulation (VNS), responsive neurostimulation (RNS), and deep brain stimulation (DBS). Head-to-head comparisons of efficacy do not exist between them nor are likely to be available in the future. We performed a meta-analysis on VNS, RNS, and DBS outcomes to compare seizure reduction efficacy for focal epilepsy.

METHODS

We systematically reviewed the literature for reported seizure outcomes following implantation with VNS, RNS, and DBS in focal-onset seizures and performed a meta-analysis. Prospective or retrospective clinical studies were included.

RESULTS

Sufficient data were available at years one (n = 642, two (n = 480), and three (n = 385) for comparing the three modalities with each other. Seizure reduction for the devices at years one, two, and three respectively were: RNS: 66.3%, 56.0%, 68.4%; DBS- 58.4%, 57.5%, 63.8%; VNS 32.9%, 44.4%, 53.5%. Seizure reduction at year one was greater for RNS (p < 0.01) and DBS (p < 0.01) compared to VNS.

CONCLUSIONS

Our findings indicate the seizure reduction efficacy of RNS is similar to DBS, and both had greater seizure reductions compared to VNS in the first-year post-implantation, with the differences diminishing with longer-term follow-up.

SIGNIFICANCE

The results help guide neuromodulation treatment in eligible patients with drug-resistant focal epilepsy.

DBS of the ANT for refractory epilepsy: A single center experience of seizure reduction, side effects and neuropsychological outcomes

Objective

Evaluation of the antiseizure efficacy, side effects and neuropsychological effects of Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT). ANT-DBS is a treatment option for patients with difficult-to-treat epilepsy. Though several works outline the cognitive and/or mood effects of ANT-DBS for the treatment of epilepsy, data on the intersection between antiseizure efficacy, cognitive and undesired effects are scarce.

Methods

We retrospectively analyzed the data of our cohort of 13 patients. Post-implantation seizure frequencies were measured at 6 months, 12 months and last follow-up, as well as averaged throughout follow-up. These values were then compared with mean seizure frequencies in the 6 months before implantation. To address acute cognitive effects of DBS a baseline assessment was performed after implantation and before stimulation, and a follow-up assessment was conducted under DBS. The long-term effects of DBS on cognition were assessed by comparing the preoperative neuropsychological profile with a long-term follow-up under DBS.

Results

In the entire cohort, 54.5% of patients were responders, with an average seizure reduction of 73.6%. One of these patients achieved temporary seizure freedom and near-total seizure reduction during the entire follow-up. Seizure reduction of &lt;50% was achieved in 3 patients. Non-responders suffered an average seizure increase of 27.3%. Eight of twenty-two active electrodes (36,4%) were off-target. Two of our patients had both electrodes implanted off-target. When removing these two patients from the analysis and averaging seizure frequency during the entire follow-up period, four patients (44.4%) were responders and three experienced a seizure reduction of &lt;50%. Intolerable side effects arose in 5 patients, mostly psychiatric. Regarding acute cognitive effects of DBS, only one patient showed a significant decline in executive functions. Long-term neuropsychological effects included significant intraindividual changes in verbal learning and memory. Figural memory, attention and executive functions, confrontative naming and mental rotation were mostly unchanged, and improved in few cases.

Significance

In our cohort, more than half of patients were responders. Psychiatric side effects seem to have been more prevalent compared to other published cohorts. This may be partially explained by a relatively high occurrence of off-target electrodes.

Thalamic neuromodulation in epilepsy: A primer for emerging circuit-based therapies

INTRODUCTION

Epilepsy is a common, often debilitating disease of hyperexcitable neural networks. While medically intractable cases may benefit from surgery, there may be no single, well-localized focus for resection or ablation. In such cases, approaching the disease from a network-based perspective may be beneficial.

AREAS COVERED

Herein, the authors provide a narrative review of normal thalamic anatomy and physiology and propose general strategies for preventing and/or aborting seizures by modulating this structure. Additionally, they make specific recommendations for targeting the thalamus within different contexts, motivated by a more detailed discussion of its distinct nuclei and their respective connectivity. By describing important principles governing thalamic function and its involvement in seizure networks, the authors aim to provide a primer for those now entering this fast-growing field of thalamic neuromodulation for epilepsy.

EXPERT OPINION

The thalamus is critically involved with the function of many cortical and subcortical areas, suggesting it may serve as a compelling node for preventing or aborting seizures, and so it has increasingly been targeted for the surgical treatment of epilepsy. As various thalamic neuromodulation strategies for seizure control are developed, there is a need to ground such interventions in a mechanistic, circuit-based framework.

Therapeutic ultrasound: The future of epilepsy surgery?

Epilepsy is one of the leading neurological diseases in both adults and children and in spite of advancement in medical treatment, 20 to 30% of patients remain refractory to current medical treatment. Medically intractable epilepsy has a real impact on a patient's quality of life, neurologic morbidity and even mortality. Actual therapy options are an increase in drug dosage, radiosurgery, resective surgery and non-resective neuromodulatory treatments (deep brain stimulation, vagus nerve stimulation). Resective, thermoablative or neuromodulatory surgery in the treatment of epilepsy are invasive procedures, sometimes requiring long stay-in for the patients, risks of permanent neurological deficit, general anesthesia and other potential surgery-related complications such as a hemorrhage or an infection. Radiosurgical approaches can trigger radiation necrosis, brain oedema and transient worsening of epilepsy. With technology-driven developments and pursuit of minimally invasive neurosurgery, transcranial MR-guided focused ultrasound has become a valuable treatment for neurological diseases. In this critical review, we aim to give the reader a better understanding of current advancement for ultrasound in the treatment of epilepsy. By outlining the current understanding gained from both preclinical and clinical studies, this article explores the different mechanisms and potential applications (thermoablation, blood brain barrier disruption for drug delivery, neuromodulation and cortical stimulation) of high and low intensity ultrasound and compares the various possibilities available to patients with intractable epilepsy. Technical limitations of therapeutic ultrasound for epilepsy surgery are also detailed and discussed.

Deep brain stimulation of the anterior nuclei of the thalamus in focal epilepsy

OBJECTIVE

To review the therapeutic effects of deep brain stimulation of the anterior nuclei of the thalamus (ANT-DBS) and the predictors of its effectiveness, safety, and adverse effects.

METHODS

A comprehensive search of the medical literature (PubMed) was conducted to identify relevant articles investigating ANT-DBS therapy for epilepsy. Out of 332 references, 77 focused on focal epilepsies were reviewed.

RESULTS

The DBS effect is probably due to decreased synchronization of epileptic activity in the cortex. The potential mechanisms from cellular to brain network levels are presented. The ANT might participate actively in the network elaborating focal seizures. The effects of ANT-DBS differed in various studies; ANT-DBS was linked with a 41% seizure frequency reduction at 1 year, 69% at 5 years, and 75% at 7 years. The most frequently reported adverse effects, depression and memory impairment, were considered non-serious in the long-term follow-up view. ANT-DBS also has been used in a few cases to treat status epilepticus.

CONCLUSIONS

We reviewed the clinical literature and identified several factors that may predict seizure outcome following DBS therapy. More large-scale trials are required since there is a need to explore stimulation settings, apply patient-tailored therapy, and identify the presurgical predictors of patient response.

SIGNIFICANCE

A critical review of the published literature on ANT-DBS in focal epilepsy is presented. ANT-DBS mechanisms are not fully understood; possible explanations are provided. Biomarkers of ANT-DBS effectiveness may lead to patient-tailored therapy.

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.

Microendoscopic transventricular deep brain stimulation of the anterior nucleus of the thalamus as a safe treatment in intractable epilepsy: A feasibility study

INTRODUCTION

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is proposed in patients with severe intractable epilepsy. When used, the transventricular approach increases the risk of bleeding due the anatomy around the entry point in the thalamus. To avoid such a complication, we used a transventricular microendoscopic technique.

METHODS

We performed a retrospective study of nine adult patients who were surgically treated for refractory epilepsy between 2010 and 2019 by DBS of the anterior thalamic nucleus.

RESULTS

Endoscopy provides a direct visual control of the entry point of the lead in the thalamus through the ventricle by avoiding ependymal vessels. No hemorrhage was recorded and accuracy was systematically checked by intraoperative stereotactic MRI. We reported a responder rate improvement in 88.9% of patients at 1 year and in 87.5% at 2 years. We showed a significant decrease in global seizure count per month one year after DBS (68.1%; P=0.013) leading to an overall improvement in quality of life. No major adverse effect was recorded during the follow-up. ANT DBS showed a prominent significant effect with a decrease of the number of generalized seizures.

CONCLUSION

We aimed at a better ANT/lead collimation using a vertical transventricular approach under microendoscopic monitoring. This technique permitted to demonstrate the safety and the accuracy of the procedure.

Focal non-invasive deep-brain stimulation with temporal interference for the suppression of epileptic biomarkers

Introduction

Neurostimulation applied from deep brain stimulation (DBS) electrodes is an effective therapeutic intervention in patients suffering from intractable drug-resistant epilepsy when resective surgery is contraindicated or failed. Inhibitory DBS to suppress seizures and associated epileptogenic biomarkers could be performed with high-frequency stimulation (HFS), typically between 100 and 165 Hz, to various deep-seated targets, such as the Mesio-temporal lobe (MTL), which leads to changes in brain rhythms, specifically in the hippocampus. The most prominent alterations concern high-frequency oscillations (HFOs), namely an increase in ripples, a reduction in pathological Fast Ripples (FRs), and a decrease in pathological interictal epileptiform discharges (IEDs).

Materials and methods

In the current study, we use Temporal Interference (TI) stimulation to provide a non-invasive DBS (130 Hz) of the MTL, specifically the hippocampus, in both mouse models of epilepsy, and scale the method using human cadavers to demonstrate the potential efficacy in human patients. Simulations for both mice and human heads were performed to calculate the best coordinates to reach the hippocampus.

Results

This non-invasive DBS increases physiological ripples, and decreases the number of FRs and IEDs in a mouse model of epilepsy. Similarly, we show the inability of 130 Hz transcranial current stimulation (TCS) to achieve similar results. We therefore further demonstrate the translatability to human subjects via measurements of the TI stimulation vs. TCS in human cadavers. Results show a better penetration of TI fields into the human hippocampus as compared with TCS.

Significance

These results constitute the first proof of the feasibility and efficiency of TI to stimulate at depth an area without impacting the surrounding tissue. The data tend to show the sufficiently focal character of the induced effects and suggest promising therapeutic applications in epilepsy.

Responsive Thalamic Neurostimulation: A Systematic Review of a Promising Approach for Refractory Epilepsy

Introduction

Responsive neurostimulation is an evolving therapeutic option for patients with treatment-refractory epilepsy. Open-loop, continuous stimulation of the anterior thalamic nuclei is the only approved modality, yet chronic stimulation rarely induces complete seizure remission and is associated with neuropsychiatric adverse effects. Accounts of off-label responsive stimulation in thalamic nuclei describe significant improvements in patients who have failed multiple drug regimens, vagal nerve stimulation, and other invasive measures. This systematic review surveys the currently available data supporting the use of responsive thalamic neurostimulation in primary and secondary generalized, treatment-refractory epilepsy.

Materials and Methods

A systematic review was performed using the following combination of keywords and controlled vocabulary: (“Seizures”[Mesh] AND “Thalamus”[Mesh] AND “Deep Brain Stimulation”[Mesh]) OR (responsive neurostim* AND (thalamus[MeSH])) OR [responsive neurostimulation AND thalamus AND (epilepsy OR seizures)]. In addition, a search of the publications listed under the PubMed “cited by” tab was performed for all publications that passed title/abstract screening in addition to manually searching their reference lists.

Results

Ten publications were identified describing a total of 29 subjects with a broad range of epilepsy disorders treated with closed-loop thalamic neurostimulation. The median age of subjects was 31 years old (range 10–65 years). Of the 29 subjects, 15 were stimulated in the anterior, 11 in the centromedian, and 3 in the pulvinar nuclei. Excluding 5 subjects who were treated for 1 month or less, median time on stimulation was 19 months (range 2.4–54 months). Of these subjects, 17/24 experienced greater than or equal to 50%, 11/24 least 75%, and 9/24 at least 90% reduction in seizures. Although a minority of patients did not exhibit significant clinical improvement by follow-up, there was a general trend of increasing treatment efficacy with longer periods on closed-loop thalamic stimulation.

Conclusion

The data supporting off-label closed-loop thalamic stimulation for refractory epilepsy is limited to 29 adult and pediatric patients, many of whom experienced significant improvement in seizure duration and frequency. This encouraging progress must be verified in larger studies.

Palliative Surgery for Drug-Resistant Epilepsy in Adult Patients. A Systematic Review of the Literature and a Pooled Analysis of Outcomes

BACKGROUND

Several types of palliative surgery to treat drug-resistant epilepsy (DRE) have been reported, but the evidence that is available is insufficient to help physicians redirect patients with DRE to the most appropriate kind of surgery.

METHODS

A systematic search in the PubMed and Scopus databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to compare different clinical features, outcomes, and complications of adult patients submitted to callosotomy, vagal nerve stimulation, multiple subpial transections, deep brain stimulation, or responsive neurostimulation.

RESULTS

After 3447 articles were screened, 36 studies were selected, including the data of 1628 patients: 76 were treated with callosotomy, 659 were treated with vagal nerve stimulation, 416 were treated with deep brain stimulation, and 477 were treated with responsive neurostimulation. No studies including patients treated with multiple subpial transections met the inclusion criteria. The global weighted average seizure frequency reduction was 50.23%, and the global responder rate was 52.12%. There were significant differences among the palliative surgical procedures in term of clinical features of patients and epilepsy, seizure frequency reduction, and percentage of responders. Complications were differently distributed as well.

CONCLUSIONS

Our analysis highlights the necessity of prospective studies, possibly randomized controlled trials, to compare different forms of palliative epilepsy surgery. Moreover, by identifying the outcome predictors associated with each technique, the best responder may be profiled for each procedure.

Neuromodulation of the anterior thalamic nucleus as a therapeutic option for difficult-to-control epilepsy

Deep brain stimulation (DBS) consists of the electrical stimulation of the subcortical structures by implanting electrodes connected to a pulse generator. The thalamus, being a structure that has multiple connections with various parts of the central nervous system, is a suitable target for DBS. The anterior thalamic nucleus (ANT) serves as an important relay site for the limbic system by receiving input from the hippocampus and mammillary bodies, and sending input to the cingulate gyrus; thus forming the Papez circuit. Due to these connections, the ANT constitutes an ideal route for the propagation of epileptogenic activity. ANT-DBS has excellent results in the control of complex partial seizures. The vast majority of patients with ANT-DBS have shown a significant reduction in the frequency of their seizures of more than 50%.

Closed-loop controller based on reference signal tracking for absence seizures

Absent epilepsy is a kind of refractory epilepsy, which is characterized by 2–4 Hz spike and wave discharges (SWDs) in electroencephalogram. Open-loop deep brain stimulation (DBS) targeting the thalamic reticular nucleus (TRN) is an effective method to treat absent epilepsy by eliminating SWDs in the brain. Compared with open-loop DBS, closed-loop DBS has been recognized by researchers for its advantages of significantly inhibiting seizures and having fewer side effects. Since traditional trial-and-error methods for adjusting closed-loop controller parameters are too dependent on the experience of doctors, in this paper we designed two proportional integral (PI) controllers based on the basal ganglia-cortical-thalamic model, whose PI parameters are calculated from the stability of the system. The two PI controllers can automatically adjust the frequency and amplitude of DBS respectively according to the change of the firing rate detected by substantia nigra pars reticulata (SNr). The parameters of the PI controller are calculated based on the Routh-Hurwitz stability criterion of a linear system which transformed by the original system using controlled auto-regressive (CAR) model and recursive least squares (RLS) method. Numerical simulation results show that both PI controllers significantly destroy the SWDs of the cerebral cortex and restore it to the other two normal discharge modes according to the different target firing rate, which supplies a promising brain stimulation strategy.

Optimal targeting of the anterior nucleus of the thalamus for epilepsy: a meta-analysis

OBJECTIVE

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) has been shown to be an effective therapeutic option for select patients with limbic epilepsy. However, the optimal target and electrode position for this indication remains undefined. Therefore, the objective of this systematic review and meta-analysis is to quantify the association between active contact location and outcomes across all published series of ANT DBS.

METHODS

A literature search using PRISMA criteria was performed to identify all studies that reported both active contact locations and outcomes of DBS in the ANT for epilepsy. Patient, disease, treatment, and outcome data were extracted for statistical analysis. Contact locations of responders (defined as ≥ 50% seizure reduction at last follow-up) versus nonresponders to DBS were analyzed on a common reference frame. Centers of mass, weighted by clinical response, were computed for the contacts in each cohort.

RESULTS

From 555 studies that were screened for review, a total of 7 studies comprising 162 patients met criteria for inclusion and were analyzed. Across the cohort, the mean duration of epilepsy was 23 years and the mean pre-DBS seizure frequency was 56 seizures per month. DBS electrodes were implanted using direct targeting in 5 studies (n = 62, 38% of patient cohort) via a transventricular electrode trajectory in 4 studies (n = 123, 76%). At the mean follow-up duration of 2.3 years, 56% of patients were considered responders. Active contacts of responders were 1.6 mm anterior (95% CI 1.5-1.6 mm, p < 0.001) compared to those of nonresponders and were adjacent to the mammillothalamic tract (MTT).

CONCLUSIONS

Accurate targeting of the ANT is crucial to successful DBS outcomes in epilepsy. These findings suggest that stimulation within the ANT subregions adjacent to the MTT improves outcomes.

Deep brain stimulation targets in epilepsy: Systematic review and meta-analysis of anterior and centromedian thalamic nuclei and hippocampus

Deep brain stimulation (DBS) is a neuromodulatory treatment used in patients with drug-resistant epilepsy (DRE). The primary goal of this systematic review and meta-analysis is to describe recent advancements in the field of DBS for epilepsy, to compare the results of published trials, and to clarify the clinical utility of DBS in DRE. A systematic literature search was performed by two independent authors. Forty-four articles were included in the meta-analysis (23 for anterior thalamic nucleus [ANT], 8 for centromedian thalamic nucleus [CMT], and 13 for hippocampus) with a total of 527 patients. The mean seizure reduction after stimulation of the ANT, CMT, and hippocampus in our meta-analysis was 60.8%, 73.4%, and 67.8%, respectively. DBS is an effective and safe therapy in patients with DRE. Based on the results of randomized controlled trials and larger clinical series, the best evidence exists for DBS of the anterior thalamic nucleus. Further randomized trials are required to clarify the role of CMT and hippocampal stimulation. Our analysis suggests more efficient deep brain stimulation of ANT for focal seizures, wider use of CMT for generalized seizures, and hippocampal DBS for temporal lobe seizures. Factors associated with clinical outcome after DBS for epilepsy are electrode location, stimulation parameters, type of epilepsy, and longer time of stimulation. Recent advancements in anatomical targeting, functional neuroimaging, responsive neurostimulation, and sensing of local field potentials could potentially lead to improved outcomes after DBS for epilepsy and reduced sudden, unexpected death of patients with epilepsy. Biomarkers are needed for successful patient selection, targeting of electrodes and optimization of stimulation parameters.

Neuromodulation for Refractory Epilepsy

Three neuromodulation therapies, all using implanted device and electrodes, have been approved to treat adults with drug-resistant focal epilepsy, namely, the vagus nerve stimulation in 1995, deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) in 2018 (2010 in Europe), and responsive neurostimulation (RNS) in 2014. Indications for VNS have more recently extended to children down to age of 4. Limited or anecdotal data are available in other epilepsy syndromes and refractory/super-refractory status epilepticus. Overall, neuromodulation therapies are palliative, with only a minority of patients achieving long-term seizure freedom, justifying favoring such treatments in patients who are not good candidates for curative epilepsy surgery. About half of patients implanted with VNS, ANT-DBS, and RNS have 50% or greater reduction in seizures, with long-term data suggesting increased efficacy over time. Besides their impact on seizure frequency, neuromodulation therapies are associated with various benefits and drawbacks in comparison to antiseizure drugs. Yet, we lack high-level evidence to best position each neuromodulation therapy in the treatment pathways of persons with difficult-to-treat epilepsy.

Probabilistic mapping of thalamic nuclei and thalamocortical functional connectivity in idiopathic generalised epilepsy

It is well established that abnormal thalamocortical systems play an important role in the generation and maintenance of primary generalised seizures. However, it is currently unknown which thalamic nuclei and how nuclear‐specific thalamocortical functional connectivity are differentially impacted in patients with medically refractory and non‐refractory idiopathic generalised epilepsy (IGE). In the present study, we performed structural and resting‐state functional magnetic resonance imaging (MRI) in patients with refractory and non‐refractory IGE, segmented the thalamus into constituent nuclear regions using a probabilistic MRI segmentation method and determined thalamocortical functional connectivity using seed‐to‐voxel connectivity analyses. We report significant volume reduction of the left and right anterior thalamic nuclei only in patients with refractory IGE. Compared to healthy controls, patients with refractory and non‐refractory IGE had significant alterations of functional connectivity between the centromedian nucleus and cortex, but only patients with refractory IGE had altered cortical connectivity with the ventral lateral nuclear group. Patients with refractory IGE had significantly increased functional connectivity between the left and right ventral lateral posterior nuclei and cortical regions compared to patients with non‐refractory IGE. Cortical effects were predominantly located in the frontal lobe. Atrophy of the anterior thalamic nuclei and resting‐state functional hyperconnectivity between ventral lateral nuclei and cerebral cortex may be imaging markers of pharmacoresistance in patients with IGE. These structural and functional abnormalities fit well with the known importance of thalamocortical systems in the generation and maintenance of primary generalised seizures, and the increasing recognition of the importance of limbic pathways in IGE.

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

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

Palliative Epilepsy Surgery Procedures in Children

Surgical treatment of epilepsy typically focuses on identification of a seizure focus with subsequent resection and/or disconnection to "cure" the patient's epilepsy and achieve seizure freedom. Palliative epilepsy surgery modalities are efficacious in improving seizure frequency, severity, and quality of life. In this paper, we review palliative epilepsy surgical options for children: vagus nerve stimulation, responsive neurostimulation, deep brain stimulation, hemispherotomy, corpus callosotomy, lobectomy and/or lesionectomy and multiple subpial transection. Reoperation after surgical resection should also be considered. If curative resection is not a viable option for seizure freedom, these methods should be considered with equal emphasis and urgency in the treatment of drug-resistant epilepsy.

A high-resolution interactive atlas of the human brainstem using magnetic resonance imaging

Conventional atlases of the human brainstem are limited by the inflexible, sparsely-sampled, two-dimensional nature of histology, or the low spatial resolution of conventional magnetic resonance imaging (MRI). Postmortem high-resolution MRI circumvents the challenges associated with both modalities. A single human brainstem specimen extending from the rostral diencephalon through the caudal medulla was prepared for imaging after the brain was removed from a 65-year-old male within 24 h of death. The specimen was formalin-fixed for two weeks, then rehydrated and placed in a custom-made MRI compatible tube and immersed in liquid fluorocarbon. MRI was performed in a 7-Tesla scanner with 120 unique diffusion directions. Acquisition time for anatomic and diffusion images were 14 h and 208 h, respectively. Segmentation was performed manually. Deterministic fiber tractography was done using strategically chosen regions of interest and avoidance, with manual editing using expert knowledge of human neuroanatomy. Anatomic and diffusion images were rendered with isotropic resolutions of 50 μm and 200 μm, respectively. Ninety different structures were segmented and labeled, and 11 different fiber bundles were rendered with tractography. The complete atlas is available online for interactive use at https://www.civmvoxport.vm.duke.edu/voxbase/login.php?return_url=%2Fvoxbase%2F. This atlas presents multiple contrasting datasets and selected tract reconstruction with unprecedented resolution for MR imaging of the human brainstem. There are immediate applications in neuroanatomical education, with the potential to serve future applications for neuroanatomical research and enhanced neurosurgical planning through "safe" zones of entry into the human brainstem.

Imaging of Neuromodulation and Surgical Interventions for Epilepsy

About one-third of epilepsy cases are refractory to medical therapy. During the past decades, the availability of surgical epilepsy interventions has substantially increased as therapeutic options for this group of patients. A wide range of surgical interventions and electrophysiologic neuromodulation techniques are available, including lesional resection, lobar resection, thermoablation, disconnection, multiple subpial transections, vagus nerve stimulation, responsive neurostimulation, and deep brain stimulation. The indications and imaging features of potential complications of the newer surgical interventions may not be widely appreciated, particularly if practitioners are not associated with comprehensive epilepsy centers. In this article, we review a wide range of invasive epilepsy treatment modalities with a particular focus on their postoperative imaging findings and complications. A state-of-the-art treatment algorithm provides context for imaging findings by helping the reader understand how a particular invasive treatment decision is made.

What have we learned from 8 years of deep brain stimulation of the anterior thalamic nucleus? Experiences and insights of a single center

OBJECTIVE

In the absence of a standard or guideline for the treatment of epilepsy patients with deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT), systematic single-center investigations are essential to establish effective approaches. Here, the authors report on the long-term results of one of the largest single-center ANT DBS cohorts.

METHODS

The outcome data of 23 consecutive patients with transventricularly implanted electrodes were retrospectively analyzed with regard to adverse events, lead placement, stimulation-related side effects, and changes in seizure frequency. Depression and quality-of-life scores were collected in a subgroup of 9 patients.

RESULTS

All but 2 patients initially underwent bilateral implantation, and 84.4% of all DBS leads were successfully located within the ANT. The mean follow-up time was 46.57 ± 23.20 months. A seizure reduction > 50% was documented in 73.9% of patients, and 34.6% achieved an Engel class I outcome. In 3 patients, clinical response was achieved by switching the electrode contact or changing from the monopolar to bipolar stimulation mode. Unilateral implantation seemed ineffective, whereas bilateral stimulation with successful ANT implantation only on one side led to a clinical response. Double stimulation with additional vagus nerve stimulation was safe. Changes in cycling mode or stimulation amplitude influenced therapy tolerability and, only to a lesser extent, seizure frequency. Side effects were rare and typically vanished by lowering the stimulation amplitude or changing the active electrode contact. Furthermore, depression and aspects of quality of life significantly improved with ANT DBS treatment.

CONCLUSIONS

The transventricular approach as well as double stimulation proved safe. The anteroventral ANT appeared to be the most efficacious stimulation site. This systematic investigation with reluctant medication changes allowed for the development of a better idea of the association between parameter changes and outcome in ANT DBS patients, but larger samples are still needed to assess the potential of bipolar stimulation and distinct cycling frequencies. Furthermore, more multifaceted and objective assessments of treatment outcome are needed to fully assess the effects of ANT DBS treatment.

Anterior Nucleus of the Thalamus Deep Brain Stimulation with Concomitant Vagus Nerve Stimulation for Drug-Resistant Epilepsy

BACKGROUND

The Food and Drug Administration approved the deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) as an adjunctive therapy for drug-resistant epilepsy (DRE) in the United States in 2018. The DBS Therapy for Epilepsy Post-Approval Study is further evaluating the safety and effectiveness of ANT-DBS among different patients' groups. For this study, devices for vagus nerve stimulation (VNS) must be removed prior to enrolment.

OBJECTIVE

To investigate the outcomes of concomitant ANT-DBS and VNS treatment for DRE.

METHODS

A retrospective analysis was performed for 33 patients who underwent ANT-DBS using previous VNS to define distinct subgroups: standard ANT-DBS (9 subjects), ANT-DBS with functional VNS (12 subjects), and ANT-DBS with the VNS implantable pulse generator explanted or turned off at the time of the DBS (12 subjects). Effectiveness and safety data were analyzed across the whole population and among subgroups.

RESULTS

A mean decrease in seizure frequency of 55% was observed after a mean follow-up of 25.5 mo. Approximately 67% of patients experienced ≥50% reduction in seizure frequency. Seizure reduction percentage was not significantly different among groups. Approximately 50% of subjects with no appreciable improvement and 75% of those who showed benefit after VNS (including improvement in seizure frequency, seizure severity, and seizure duration or quality of life) achieved a seizure reduction ≥50% after ANT-DBS surgery. There were no complications related to concomitant VNS and ANT-DBS.

CONCLUSION

ANT-DBS for DRE provides excellent results despite previous and ongoing VNS therapy. Removal of VNS does not appear to be necessary before ANT-DBS.

Direct Targeting of the Anterior Nucleus of the Thalamus via 3 T Quantitative Susceptibility Mapping

Objective: Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is a potentially effective, minimally invasive, and reversible method for treating epilepsy. The goal of this study was to explore whether 3 T quantitative susceptibility mapping (QSM) could delineate the ANT from surrounding structures, which is important for the direct targeting of DBS surgery.

Methods: We obtained 3 T QSM, T1-weighted (T1w), and T2-weighted (T2w) images from 11 patients with Parkinson’s disease or dystonia who received subthalamic nucleus (STN) or globus pallidus interna (GPi) DBS surgery in our center. The ANT and its surrounding white matter structures on QSM were compared with available atlases. The contrast-to-noise ratios (CNRs) of ANT relative to the external medullary lamina (eml) were compared across the three imaging modalities. Additionally, the morphology and location of the ANT were depicted in the anterior commissure (AC)-posterior commissure (PC)-based system.

Results: ANT can be clearly distinguished from the surrounding white matter laminas and appeared hyperintense on QSM. The CNRs of the ANT-eml on QSM, T1w, and T2w images were 10.20 ± 4.23, 1.71 ± 1.03, and 1.35 ± 0.70, respectively. One-way analysis of variance (ANOVA) indicated significant differences in CNRs among QSM, T1w, and T2w imaging modalities [F(2) = 85.28, p < 0.0001]. In addition, both the morphology and location of the ANT were highly variable between patients in the AC–PC-based system.

Conclusion: The potential utility of QSM for the visualization of ANTs in clinical imaging is promising and may be suitable for targeting the ANT for DBS to treat epilepsy.

Analysis of Deep Brain Stimulation Lead Targeting in the Stimulation of Anterior Nucleus of the Thalamus for Epilepsy Clinical Trial

BACKGROUND

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is an effective therapy for patients with drug-resistant focal epilepsy. Best practices for surgical targeting of the ANT can be refined as new information becomes available regarding effective stimulation sites.

OBJECTIVE

To conduct a retrospective analysis of the relationship between outcomes (seizure reduction during year 1) and DBS lead locations in subjects from the SANTÉ pivotal trial (Stimulation of ANT for Epilepsy) based upon recent clinical findings.

METHODS

Postoperative images from SANTÉ subjects (n = 101) were evaluated with respect to lead trajectory relative to defined anatomic landmarks. A qualitative scoring system was used to rate each lead placement for proximity to an identified target region above the junction of the mammillothalamic tract with the ANT. Each subject was assigned a bilateral lead placement score, and these scores were then compared to clinical outcomes.

RESULTS

Approximately 70% of subjects had “good” bilateral lead placements based upon location with respect to the defined target. These subjects had a much higher probability of being a clinical responder (>50% seizure reduction) than those with scores reflecting suboptimal lead placements (43.5% vs 21.9%, P < .05).

CONCLUSION

Consistent with experience from more established DBS indications, our findings and other recent reports suggest that there may be specific sites within the ANT that are associated with superior clinical outcomes. It will be important to continue to evaluate these relationships and the evolution of other clinical practices (eg, programming) to further optimize this therapy.

Role of Neuromodulation for Treatment of Drug-Resistant Epilepsy

The choice of neuromodulation techniques has greatly increased over the past two decades. While vagal nerve stimulation (VNS) has become established, newer variations of VNS have been introduced. Following the SANTE's trial, deep brain stimulation (DBS) is now approved for clinical use. In addition, responsive neurostimulation (RNS) has provided exciting new opportunities for treatment of drug-resistant epilepsy. While neuromodulation mostly offers only a 'palliative' measure, it still provides a significant reduction of frequency and intensity of epilepsy. We provide an overview of all the techniques of neuromodulation which are available, along with long-term outcomes. Further research is required to delineate the exact mechanism of action, the indications and the stimulation parameters to extract the maximum clinical benefit from these techniques.

Clinical Efficacy and Safety Profile of Anterior Thalamic Stimulation for Intractable Epilepsy

INTRODUCTION

 Deep brain stimulation of the anterior nucleus of the thalamus (ANT DBS) is a neuromodulation therapy for patients with refractory partial seizures. The ANT is the structure of a limbic system with abundant neuronal connections to temporal and frontal brain regions that participate in seizure propagation circuitry.

STATE OF THE ART

 We have performed a literature search regarding the clinical efficacy of ANT DBS. We discuss the surgical technique of the implantation of DBS electrodes with special attention paid to the targeting methods of the ANT. Moreover, we present in detail the clinical efficacy of ANT DBS, with a special emphasis on the stimulation parameters, a stimulation mode, and polarity. We also report all adverse events and present the current limitations of ANT DBS.

CLINICAL IMPLICATIONS

 In general, the safety profile of DBS in intractable epilepsy patients is good, with a low rate of surgery, hardware-related, and stimulation-induced adverse events. No significant cognitive declines or worsening of depressive symptoms was noted. At long-term follow-up, the quality-of-life scores have improved. The limitations of ANT DBS studies include a limited number of patients treated and mostly open-label designs with only one double-blind, randomized multicenter trial. Most studies do not report the etiology of intractable epilepsy or they include nonhomogeneous groups of patients affected by intractable epilepsy. There are no guidelines for setting initial stimulation parameters. All the variables mentioned may have a profound impact on the final outcome.

CONCLUSIONS

 ANT DBS appears to be a safe and efficacious treatment, particularly in patients with refractory partial seizures (three-quarters of patients gained at least 50% seizure reduction after 5 years). ANT DBS reduces most effectively the seizures originating in the temporal and frontal lobes. The published results of ANT DBS highlight promise and hope for patients with intractable epilepsy.

Electrophysiologic Mapping for Target Acquisition in Deep Brain Stimulation May Become Unnecessary in the Era of Intraoperative Imaging

OBJECTIVE

Electrophysiologic mapping (EM) has been instrumental in advancing neuroscience and ensuring accurate lead placement for deep brain stimulation. However, EM is associated with increased operative time, expense, and potential risk. Intraoperative imaging to verify lead placement provides an opportunity to reassess the clinical role of EM. We investigated whether EM 1) provides new information that corrects suboptimal preoperative target selection by the physician or 2) simply corrects intraoperative stereotactic error, which can instead be quickly corrected with intraoperative imaging.

METHODS

Deep brain stimulation lead location errors were evaluated by measuring whether repositioning leads based on EM directed the final lead placement 1) away from or 2) toward the original target. We retrospectively identified 50 patients with 61 leads that required repositioning directed by EM. The stereotactic coordinates of each lead were determined with intraoperative computed tomography.

RESULTS

In 45 of 61 leads (74%), the electrophysiologically directed repositioning moved the lead toward the initial target. The mean radial errors between the preoperative plan and targeted contact coordinates before and after repositioning were 2.2 and 1.5 mm, respectively (P < 0.001). Microelectrode recording was more likely than test stimulation to direct leads toward the initial target (88% vs. 63%; P = 0.03). The nucleus targeted was associated with the likelihood of moving toward the initial target.

CONCLUSIONS

Electrophysiologic mapping corrected primarily for errors in lead placement rather than providing new information regarding errors in target selection. Thus, intraoperative imaging and improvements in stereotactic techniques may reduce or even eliminate dependence on EM.

Defining the optimal target for anterior thalamic deep brain stimulation in patients with drug-refractory epilepsy

OBJECTIVE

The anterior thalamic nucleus (ATN) is a common target for deep brain stimulation (DBS) for the treatment of drug-refractory epilepsy. However, no atlas-based optimal DBS (active contacts) target within the ATN has been definitively identified. The object of this retrospective study was to analyze the relationship between the active contact location and seizure reduction to establish an atlas-based optimal target for ATN DBS.

METHODS

From among 25 patients who had undergone ATN DBS surgery for drug-resistant epilepsy between 2016 and 2018, those who had follow-up evaluations for more than 1 year were eligible for study inclusion. After an initial stimulation period of 6 months, patients were classified as responsive (≥ 50% median decrease in seizure frequency) or nonresponsive (< 50% median decrease in seizure frequency) to treatment. Stimulation parameters and/or active contact positions were adjusted in nonresponsive patients, and their responsiveness was monitored for at least 1 year. Postoperative CT scans were coregistered nonlinearly with preoperative MR images to determine the center coordinate and atlas-based anatomical localizations of all active contacts in the Montreal Neurological Institute (MNI) 152 space.

RESULTS

Nineteen patients with drug-resistant epilepsy were followed up for at least a year following bilateral DBS electrode implantation targeting the ATN. Active contacts located more adjacent to the center of gravity of the anterior half of the ATN volume, defined as the anterior center (AC), were associated with greater seizure reduction than those not in this location. Intriguingly, the initially nonresponsive patients could end up with much improved seizure reduction by adjusting the active contacts closer to the AC at the final postoperative follow-up.

CONCLUSIONS

Patients with stimulation targeting the AC may have a favorable seizure reduction. Moreover, the authors were able to obtain additional good outcomes after electrode repositioning in the initially nonresponsive patients. Purposeful and strategic trajectory planning to target this optimal region may predict favorable outcomes of ATN DBS.