Long-term seizure outcome during continuous bipolar hippocampal deep brain stimulation in patients with temporal lobe epilepsy with or without mesial temporal sclerosis: An observational, open-label study

Deep Brain Stimulation Therapy for Drug-Resistant Epilepsy: Present and Future Perspectives

Drug-resistant epilepsy (DRE) remains a formidable clinical challenge, affecting nearly 30-40% of patients despite optimized pharmacotherapy. In patients for whom resective surgery is contraindicated or poses unacceptable risks, neuromodulatory therapies-most notably deep brain stimulation (DBS)-have emerged as viable and reversible treatment options. This narrative review critically examines the current applications of DBS for DRE, with a focus on major targets including the anterior thalamic nucleus, centromedian nucleus, hippocampus, and emerging targets such as the pulvinar. We provide an in-depth discussion of the therapeutic mechanisms underlying DBS-from local cellular inhibition and desynchronization to widespread network modulation and neuroplasticity induction-and review the latest advances in sensing technologies, patient-specific connectivity mapping, and closed loop stimulation paradigms. In addition to integrating data from randomized controlled trials, long-term observational studies, and advanced imaging investigations, we discuss limitations, persistent challenges, and future research directions that will guide clinical decision-making and optimize therapeutic outcomes.

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.

Comparison of Deep Brain Stimulation of the Hippocampus to Thalamic Targets and Responsive Neurostimulation for Adult Intractable Epilepsy: A Systematic Review and Meta-Analysis

OBJECTIVE

Stereotactic neuromodulation, such as deep brain stimulation (DBS) and responsive neurostimulation (RNS), have emerged as some of the more promising means for managing drug-resistant epilepsy. This study serves as a comprehensive analysis of DBS of the anterior nucleus of the thalamus (ANT), centromedian nucleus of the thalamus, and hippocampus and RNS for seizure reduction in adult intractable epilepsy.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a systematic review was conducted of PubMed, Cochrane Library, and Embase databases from January 2000 to January 2024 to objectively assess the effectiveness of the various neuromodulation modalities on seizure reduction. Different software such as EndNote and Rayyan was used to organize the 1996 total reviewed studies and to run a blinded multiphase review process.

RESULTS

A total of 25 studies were included for review with 21 studies and 166 patients suitable for the meta-analysis. DBS ANT, DBS hippocampus, and RNS were all found to have significant individual seizure reductions of 54.0%, 70.0%, and 63.5%, respectively. DBS centromedian nucleus of the thalamus was excluded since only 1 study met inclusion criteria and was, therefore, not suitable for meta-analysis. Furthermore, the 3 analyzed procedures were found to be not significant when compared to one another. Focal versus general epilepsy in DBS ANT also had no significant difference. DBS hippocampus had a significantly higher reduction rate in patients with mesial temporal sclerosis compared to patients with normal imaging findings.

CONCLUSIONS

These results provide a vast amount of supporting data for these neurostimulation procedures while also indicating no significant difference between operations. Therefore, in this target population, operative decisions can be made based on surgeon preference and patient circumstance without affecting seizure reduction outcomes.

Non-invasive Temporal Interference Stimulation of the Hippocampus Suppresses Epileptic Biomarkers in Patients with Epilepsy: Biophysical Differences between Kilohertz and Amplitude Modulated Stimulation

Medication refractory focal epilepsy creates a significant challenge, with approximately 30% of patients ineligible for surgery due to the involvement of eloquent cortex in the epileptogenic network. For such patients with limited surgical options, electrical neuromodulation represents a promising alternative therapy. In this study, we investigate the potential of non-invasive temporal interference (TI) electrical stimulation to reduce epileptic biomarkers in patients with epilepsy by comparing intracerebral recordings obtained before, during, and after TI stimulation, to recordings during low and high kHz frequency (HF) sham stimulation. Thirteen patients with symptoms of mesiotemporal epilepsy (MTLE) and implanted with stereoelectroencephalography (sEEG) depth electrodes received TI stimulation with an amplitude modulation (AM) frequency of 130Hz (df), where the AM was delivered with lower frequency kHz carriers (1kHz + 1.13kHz), or higher frequency carriers (9kHz + 9.13kHz), targeting the hippocampus, a common epileptic focus and consequently stimulation target in MTLE. Our results show that TI stimulation yields a statistically significant decrease in interictal epileptiform discharges (IEDs) and pathological high-frequency oscillations (HFOs) specifically fast ripples (FR), where the suppression is apparent in the hippocampal focus and propagation from the focus is reduced brain-wide. HF sham stimulation at 1kHz frequency also impacted the IED rate in the cortex, but without reaching the hippocampal focus. The HF sham effect diminished with increasing frequencies (2, 5, and 9kHz, respectively), specifically as a function of depth into the cortex. This depth dependence was not observed with the TI, independent of the employed carrier frequency (low or high kHz). Furthermore, a strong carry-over effect, i.e., suppression of epileptic biomarkers for a period of time after the end of stimulation, was observed for TI but not for kHz. Our findings underscore the possible application of TI in epilepsy, as an additional non-invasive brain stimulation tool, potentially offering opportunities to assess brain region response to electrical neuromodulation before committing to a deep brain stimulation (DBS) or responsive neurostimulation (RNS) implants. Our results further demonstrate distinct biophysical differences between kHz and focal AM stimulation.

Hippocampal deep brain stimulation for drug-resistant epilepsy: Insights from bilateral temporal lobe and posterior epilepsy cases

PURPOSE

This study evaluates the long-term efficacy of hippocampal deep brain stimulation (Hip-DBS) in patients with drug-resistant epilepsy (DRE), specifically focusing on bilateral temporal lobe epilepsy (BTLE) and posterior epilepsy (PE).

METHODS

A retrospective analysis was conducted on 15 DRE patients (11 BTLE, 4 PE) who underwent bilateral Hip-DBS at Samsung Medical Center over an eight-year period. Medical records, seizure diaries, and neuropsychological assessments were reviewed. The surgical and follow-up protocols were adapted from our previous clinical research.

RESULTS

The median seizure reduction rate was 77.8 % for disabling seizures (DS) and 47.9 % for non-disabling seizures (NDS). Subgroup analysis revealed a 77.8 % reduction in DS for BTLE patients and 68.8 % for PE patients. The overall responder rate was 86.7 % for DS and 50 % for NDS. Neuropsychological evaluations showed stable cognitive functions post-treatment, with a non-significant trend towards improvement in non-verbal and visuo-spatial cognitive domains.

CONCLUSION

This study provides preliminary evidence supporting the efficacy of Hip-DBS in reducing seizure frequency in both BTLE and PE patients, with a more pronounced effect on disabling seizures. The potential cognitive preservation and possible enhancement in specific domains warrant further investigation. Despite limitations such as the retrospective design and reliance on self-reported seizure frequencies, these findings encourage further exploration of Hip-DBS as a treatment modality for DRE, particularly in cases where resective surgery is contraindicated.

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.

The role of neuromodulation in the management of drug-resistant epilepsy

Drug-resistant epilepsy (DRE) poses significant challenges in terms of effective management and seizure control. Neuromodulation techniques have emerged as promising solutions for individuals who are unresponsive to pharmacological treatments, especially for those who are not good surgical candidates for surgical resection or laser interstitial therapy (LiTT). Currently, there are three neuromodulation techniques that are FDA-approved for the management of DRE. These include vagus nerve stimulation (VNS), deep brain stimulation (DBS), and responsive neurostimulation (RNS). Device selection, optimal time, and DBS and RNS target selection can also be challenging. In general, the number and localizability of the epileptic foci, alongside the comorbidities manifested by the patients, substantially influence the selection process. In the past, the general axiom was that DBS and VNS can be used for generalized and localized focal seizures, while RNS is typically reserved for patients with one or two highly localized epileptic foci, especially if they are in eloquent areas of the brain. Nowadays, with the advance in our understanding of thalamic involvement in DRE, RNS is also very effective for general non-focal epilepsy. In this review, we will discuss the underlying mechanisms of action, patient selection criteria, and the evidence supporting the use of each technique. Additionally, we explore emerging technologies and novel approaches in neuromodulation, such as closed-loop systems. Moreover, we examine the challenges and limitations associated with neuromodulation therapies, including adverse effects, complications, and the need for further long-term studies. This comprehensive review aims to provide valuable insights on present and future use of neuromodulation.

Probing hippocampal stimulation in experimental temporal lobe epilepsy with functional MRI

Electrical neurostimulation is currently used to manage epilepsy, but the most effective approach for minimizing seizure occurrence is uncertain. While functional MRI (fMRI) can reveal which brain areas are affected by stimulation, simultaneous deep brain stimulation (DBS)-fMRI examinations in patients are rare and the possibility to investigate multiple stimulation protocols is limited. In this study, we utilized the intrahippocampal kainate mouse model of mesial temporal lobe epilepsy (mTLE) to systematically examine the brain-wide responses to electrical stimulation using fMRI. We compared fMRI responses of saline-injected controls and epileptic mice during stimulation in the septal hippocampus (HC) at 10 Hz and demonstrated the effects of different stimulation amplitudes (80-230 μA) and frequencies (1-100 Hz) in epileptic mice. Motivated by recent studies exploring 1 Hz stimulation to prevent epileptic seizures, we furthermore investigated the effect of prolonged 1 Hz stimulation with fMRI. Compared to sham controls, epileptic mice showed less propagation to the contralateral HC, but significantly stronger responses in the ipsilateral HC and a wider spread to the entorhinal cortex and septal region. Varying the stimulation amplitude had little effect on the resulting activation patterns, whereas the stimulation frequency represented the key parameter and determined whether the induced activation remained local or spread from the hippocampal formation into cortical areas. Prolonged stimulation of epileptic mice at 1 Hz caused a slight reduction in local excitability. In this way, our study contributes to a better understanding of these stimulation paradigms.

Effects of acute hippocampal stimulation in the nonhuman primate penicillin model of temporal lobe seizures

Asynchronous distributed multielectrode stimulation (ADMES) is a novel approach to deep brain stimulation for medication resistant temporal lobe epilepsy that has shown promise in rodent and in vitro seizure models. To further evaluate its effects on a pre-clinical model, we characterized the effect of unilateral ADMES in an NHP model of temporal lobe seizures induced by intra-hippocampal injection of penicillin (PCN). Four non-human primates were used for this study in two contemporaneous cohorts. One cohort (n = 3 hemispheres) was implanted with the Medtronic RC + S stimulation (GIN cohort) and recording system connected to two 4-contact ring electrodes to evaluate three unilateral stimulation patterns: 7 Hz Ring ADMES, 20 Hz Dual Ring, and 125 Hz Dual Ring (analog of clinical stimulation). In an additional cohort (EPC cohort, n = 2), two 12-contact segmented electrodes were implanted in the right hippocampus and connected to an externalized recording and stimulation system to allow more flexibility in the stimulation pattern. In this second cohort, 4 variations of stimulation were evaluated (7 Hz Full ADMES, 7 Hz Ring ADMES, 31 Hz Wide Ring, and 31 Hz Dual Ring). In the GIN cohort, we found an increase in seizure frequency and time spent in seizure during the 7 Hz Ring ADMES stimulation compared to the respective post-stimulation. A similar post-stimulation effect was found in the EPC cohort. We also found an increase in seizure frequency during the 7Hz full ADMES compared to the respective post-stimulation. However, we did not find a difference between pre-stimulation and stimulation conditions suggesting a possible post stimulation effect of the 7Hz hippocampal stimulation. In conclusion, in the NHP PCN model of temporal lobe seizures, acute asynchronous hippocampal stimulation was not therapeutic, however, our findings related to the post-stimulation effect can support future studies using hippocampal stimulation for the treatment of temporal lobe epilepsy.

The comparison of DBS and RNS for adult drug-resistant epilepsy: a systematic review and meta-analysis

Objective

Neuromodulation has been proven to be a promising alternative treatment for adult patients with drug-resistant epilepsy (DRE). Deep brain stimulation (DBS) and responsive neurostimulation (RNS) were approved by many countries for the treatment of DRE. However, there is a lack of systematic studies illustrating the differences between them. This meta-analysis is performed to assess the efficacy and clinical characteristics of DBS and RNS in adult patients with DRE.

Methods

PubMed, Web of Science, and Embase were retrieved to obtain related studies including adult DRE patients who accepted DBS or RNS. The clinical characteristics of these patients were compiled for the following statistical analysis.

Results

A total of 55 studies (32 of DBS and 23 of RNS) involving 1,568 adult patients with DRE were included in this meta-analysis. There was no significant difference in seizure reduction and responder rate between DBS and RNS for DRE. The seizure reduction of DBS and RNS were 56% (95% CI 50-62%, p > 0.05) and 61% (95% CI 54-68%, p > 0.05). The responder rate of DBS and RNS were 67% (95% CI 58-76%, p > 0.05) and 71% (95% CI 64-78%, p > 0.05). Different targets of DBS did not show significant effect on seizure reduction (p > 0.05). Patients with DRE who accepted DBS were younger than those of RNS (32.9 years old vs. 37.8 years old, p < 0.01). The mean follow-up time was 47.3 months for DBS and 39.5 months for RNS (p > 0.05).

Conclusion

Both DBS and RNS are beneficial and alternative therapies for adult DRE patients who are not eligible to accept resection surgery. Further and larger studies are needed to clarify the characteristics of different targets and provide tailored treatment for patients with DRE.

Deep brain stimulation of the subiculum in the treatment for refractory temporal lobe epilepsy due to unilateral mesial temporal lobe sclerosis

Temporal lobe epilepsy (TLE) is the most common form of drug-resistant epilepsy. The main pathological changes primarily involve hippocampal sclerosis (HS). Early resective surgery of the sclerotic hippocampus is typically associated with favorable clinical outcomes. However, not all patients are suitable candidates for resective surgery of mesial temporal lobe structures. Therefore, alternative treatment modalities should be considered. We present the case of a 50-year-old right-handed woman with left HS who underwent unilateral subiculum stimulation for drug-resistant epilepsy (DRE). Since the age of 10, the patient had been experiencing focal to bilateral tonic-clonic seizures (FBTCS). Despite multiple antiseizure medications, she experienced 12 to 17 FBTCS per month in the last two years. Due to concerns about potential memory decline and personal preferences, she refused resective surgery. As an alternative, the patient underwent left unilateral subiculum stimulation. The stimulation resulted in a nearly 67 % reduction in seizure frequency at the last follow-up (20 months after surgery). This case highlights that drug-resistant epilepsy may be effectively treated with subicular stimulation in patients with HS.

Black Phosphorus Flake-Enabled Wireless Neuromodulation for Epilepsy Treatment

Epilepsy is a prevalent and severe neurological disorder and generally requires prolonged electrode implantation and tether brain stimulation in refractory cases. However, implants may cause potential chronic immune inflammation and permanent tissue damage due to material property mismatches with soft brain tissue. Here, we demonstrated a nanomaterial-enabled near-infrared (NIR) neuromodulation approach to provide nongenetic and nonimplantable therapeutic benefits in epilepsy mouse models. Our study showed that crystal-exfoliated photothermal black phosphorus (BP) flakes could enhance neural activity by altering the membrane capacitive currents in hippocampus neurons through NIR photothermal neuromodulation. Optical stimulation facilitated by BP flakes in hippocampal slices evoked action potentials with a high spatiotemporal resolution. Furthermore, BP flake-enabled NIR neuromodulation of hippocampus neural circuits can suppress epileptic signals in epilepsy model mice with minimal invasiveness and high biocompatibility. Consequently, nanomaterial-enabled NIR neuromodulation may open up opportunities for nonimplantable optical therapy of epilepsy in nontransgenic organisms.

Combined Neuromodulation (Vagus Nerve Stimulation and Deep Brain Stimulation) in Patients With Refractory Generalized Epilepsy: An Observational Study

INTRODUCTION

This article describes our findings while treating patients with refractory generalized epilepsy with combined vagus nerve stimulation (VNS) and centro-median deep brain stimulation (CMDBS).

MATERIALS AND METHODS

A total of 11 consecutive patients with refractory generalized epilepsy (ten with Lennox-Gastaut syndrome) previously submitted to VNS and who subsequently underwent CMDBS were retrospectively studied. The VNS final parameters were 2 to 2.5 mA, 30 Hz, and 500 μs, cycling mode, 30 seconds "on" and 5 minutes "off" for all patients. The CMDBS final parameters were 4 to 5 V, 130 Hz, and 300 μs, bipolar, continuous stimulation in all patients.

RESULTS

There were eight male participants, ranging in age from eight to 49 years (mean 19 years). Follow-up time after VNS ranged from 18 to 132 months (mean 52 months) and from an additional 18 to 164 months (mean 42 months) during combined VNS-CMDBS. All patients had daily seizures. Atypical absences were noted in eight patients, tonic seizures in seven, bilateral tonic-clonic seizures in four, atonic seizures in three, and myoclonic seizures in two patients. Four patients were initially considered responders to VNS. All these patients also had an additional >50% seizure frequency reduction during combined VNS-CMDBS. Seven patients were not responders to VNS, and of those, four had an additional >50% seizure frequency reduction during combined VNS-CMDBS. Eight patients had an additional >50% reduction in seizure frequency when moved from VNS alone to VNS-CMDBS therapy. There were two nonresponders during combined VNS-CMDBS therapy, and both were nonresponders to VNS alone. Nine patients were considered responders during VNS-CMDBS combined therapy compared with baseline.

DISCUSSION

This study showed that combined VNS-CMDBS therapy was able to double the number of responders compared with VNS alone in a cohort of patients with refractory generalized epilepsy. We believe these data represent the first evidence that combined neuromodulation may be useful in this quite homogeneous patient population.

Emerging approaches in neurostimulation for epilepsy

PURPOSE OF REVIEW

Neurostimulation is a quickly growing treatment approach for epilepsy patients. We summarize recent approaches to provide a perspective on the future of neurostimulation.

RECENT FINDINGS

Invasive stimulation for treatment of focal epilepsy includes vagus nerve stimulation, responsive neurostimulation of the cortex and deep brain stimulation of the anterior nucleus of the thalamus. A wide range of other targets have been considered, including centromedian, central lateral and pulvinar thalamic nuclei; medial septum, nucleus accumbens, subthalamic nucleus, cerebellum, fornicodorsocommissure and piriform cortex. Stimulation for generalized onset seizures and mixed epilepsies as well as increased efforts focusing on paediatric populations have emerged. Hardware with more permanently implanted lead options and sensing capabilities is emerging. A wider variety of programming approaches than typically used may improve patient outcomes. Finally, noninvasive brain stimulation with its favourable risk profile offers the potential to treat increasingly diverse epilepsy patients.

SUMMARY

Neurostimulation for the treatment of epilepsy is surprisingly varied. Flexibility and reversibility of neurostimulation allows for rapid innovation. There remains a continued need for excitability biomarkers to guide treatment and innovation. Neurostimulation, a part of bioelectronic medicine, offers distinctive benefits as well as unique challenges.

Repeated long sessions of transcranial direct current stimulation reduces seizure frequency in patients with refractory focal epilepsy: An open-label extension study

OBJECTIVE

Although clinical trials have demonstrated that cathodal transcranial direct current stimulation (tDCS) is effective for seizure reduction, its long-term efficacy is unknown. This study aimed to determine the long-term effects of repeated cathodal long tDCS sessions on seizure suppression in patients with refractory epilepsy.

METHODS

Patients were recruited to participate in an extended phase of a previous randomized, double-blind, sham-controlled, three-arm, parallel, multicenter study on tDCS. The patients were divided into an active tDCS group (20 min of tDCS per day) and an intensified tDCS group (2 × 20 min of tDCS per day). Each tDCS session lasted 2 weeks and the patients underwent repeated sessions at intervals of 2 to 6 months. The cathode was placed over the epileptogenic focus with the current intensity set as 2 mA. Seizure frequency reduction from baseline was analyzed using the Wilcoxon signed-rank test for two related samples. A generalized estimating equation model was used to estimate group, time, and interaction effects.

RESULTS

Among the 19 patients who participated in the extended phase, 11 were in the active tDCS group and underwent 2-16 active tDCS sessions, and eight were in the intensified tDCS group and underwent 3-11 intensified tDCS sessions. Seizure reduction was significant from the first to the seventh follow-up, with a median seizure frequency reduction of 41.7%-83.3% (p < 0.05). Compared to the regular tDCS protocol, each intensified tDCS session substantially decreased seizure frequency by 0.3680 (p < 0.05). One patient experienced an increase of 8.5%-232.8% in the total number of seizures during three treatment sessions and follow-ups.

CONCLUSION

Repeated long cathodal tDCS sessions yielded significant and progressive long-term seizure reductions in patients with refractory focal epilepsy.

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.

Low-frequency stimulation of a fiber tract in bilateral temporal lobe epilepsy

OBJECTIVE

Pharmacoresistant bilateral mesial temporal lobe epilepsy often implies poor resective surgical candidacy. Low-frequency stimulation of a fiber tract connected to bilateral hippocampi, the fornicodorsocommissural tract, has been shown to be safe and efficacious in reducing seizures in a previous short-term study. Here, we report a single-blinded, within-subject control, long-term deep-brain stimulation trial of low-frequency stimulation of the fornicodorsocommissural tract in bilateral mesial temporal lobe epilepsy. Outcomes of interest included safety with respect to verbal memory scores and reduction of seizure frequency.

METHODS

Our enrollment goal was 16 adult subjects to be randomized to 2-Hz or 5-Hz low-frequency stimulation of the fornicodorsocommissural tract starting at 2 mA. The study design consisted of four two-month blocks of stimulation with a 50%-duty cycle, alternating with two-month blocks of no stimulation.

RESULTS

We terminated the study after enrollment of five subjects due to slow accrual. Fornicodorsocommissural tract stimulation elicited bilateral hippocampal evoked responses in all subjects. Three subjects underwent implantation of pulse generators and long-term low-frequency stimulation with mean monthly seizures of 3.14 ± 2.67 (median 3.0 [IQR 1-4.0]) during stimulation-off blocks, compared with 0.96 ± 1.23 (median 1.0 [IQR 0-1.0]) during stimulation-on blocks (p = 0.0005) during the blinded phase. Generalized Estimating Equations showed that low-frequency stimulation reduced monthly seizure-frequency by 0.71 per mA (p < 0.001). Verbal memory scores were stable with no psychiatric complications or other adverse events.

SIGNIFICANCE

The results demonstrate feasibility of stimulating both hippocampi using a single deep-brain stimulation electrode in the fornicodorsocommissural tract, efficacy of low-frequency stimulation in reducing seizures, and safety as regards verbal memory.

Deep Brain Stimulation for Refractory Temporal Lobe Epilepsy. Current Status and Future Trends

A comparative analysis of the targets for deep brain stimulation (DBS) to treat refractory temporal lobe epilepsy and the rationale for its use is presented, with an emphasis on the latency to obtain the significant antiepileptic effect and the long-term seizure control. The analysis includes consideration of surgical techniques currently used to optimize antiseizure effects and decrease surgical risks. Seizure control is similar for programed DBS and DBS responsive to abnormal cortical or subcortical electroencephalogram (EEG) activity. There is no difference in the long-term seizure control between programmed and responsive and intermittent or continuous DBS. However, intermittent programed DBS may have a significant antiseizure effect starting in the first month when applied to a non-sclerotic tissue such as the parahippocampal cortex. DBS induces no neuropsychological deterioration.

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.

Brain Stimulation Treatments in Epilepsy: Basic Mechanisms and Clinical Advances

Drug-resistant epilepsy, characterized by ongoing seizures despite appropriate trials of anti-seizure medications, affects approximately one-third of people with epilepsy. Brain stimulation has recently become available as an alternative treatment option to reduce symptomatic seizures in short and long-term follow-up studies. Several questions remain on how to optimally develop patient-specific treatments and manage therapy over the long term. This review aims to discuss the clinical use and mechanisms of action of Responsive Neural Stimulation and Deep Brain Stimulation in the treatment of epilepsy and highlight recent advances that may both improve outcomes and present new challenges. Finally, a rational approach to device selection is presented based on current mechanistic understanding, clinical evidence, and device features.