Unilateral thalamic deep brain stimulation for refractory essential tremor and Parkinson's disease tremor

Model-based closed-loop control of thalamic deep brain stimulation

Introduction: Closed-loop control of deep brain stimulation (DBS) is beneficial for effective and automatic treatment of various neurological disorders like Parkinson's disease (PD) and essential tremor (ET). Manual (open-loop) DBS programming solely based on clinical observations relies on neurologists' expertise and patients' experience. Continuous stimulation in open-loop DBS may decrease battery life and cause side effects. On the contrary, a closed-loop DBS system uses a feedback biomarker/signal to track worsening (or improving) of patients' symptoms and offers several advantages compared to the open-loop DBS system. Existing closed-loop DBS control systems do not incorporate physiological mechanisms underlying DBS or symptoms, e.g., how DBS modulates dynamics of synaptic plasticity. Methods: In this work, we propose a computational framework for development of a model-based DBS controller where a neural model can describe the relationship between DBS and neural activity and a polynomial-based approximation can estimate the relationship between neural and behavioral activities. A controller is used in our model in a quasi-real-time manner to find DBS patterns that significantly reduce the worsening of symptoms. By using the proposed computational framework, these DBS patterns can be tested clinically by predicting the effect of DBS before delivering it to the patient. We applied this framework to the problem of finding optimal DBS frequencies for essential tremor given electromyography (EMG) recordings solely. Building on our recent network model of ventral intermediate nuclei (Vim), the main surgical target of the tremor, in response to DBS, we developed neural model simulation in which physiological mechanisms underlying Vim-DBS are linked to symptomatic changes in EMG signals. By using a proportional-integral-derivative (PID) controller, we showed that a closed-loop system can track EMG signals and adjust the stimulation frequency of Vim-DBS so that the power of EMG reaches a desired control target. Results and discussion: We demonstrated that the model-based DBS frequency aligns well with that used in clinical studies. Our model-based closed-loop system is adaptable to different control targets and can potentially be used for different diseases and personalized systems.

Proceedings of the 11th Annual Deep Brain Stimulation Think Tank: pushing the forefront of neuromodulation with functional network mapping, biomarkers for adaptive DBS, bioethical dilemmas, AI-guided neuromodulation, and translational advancements

The Deep Brain Stimulation (DBS) Think Tank XI was held on August 9-11, 2023 in Gainesville, Florida with the theme of "Pushing the Forefront of Neuromodulation". The keynote speaker was Dr. Nico Dosenbach from Washington University in St. Louis, Missouri. He presented his research recently published in Nature inn a collaboration with Dr. Evan Gordon to identify and characterize the somato-cognitive action network (SCAN), which has redefined the motor homunculus and has led to new hypotheses about the integrative networks underpinning therapeutic DBS. The DBS Think Tank was founded in 2012 and provides an open platform where clinicians, engineers, and researchers (from industry and academia) can freely discuss current and emerging DBS technologies, as well as logistical and ethical issues facing the field. The group estimated that globally more than 263,000 DBS devices have been implanted for neurological and neuropsychiatric disorders. This year's meeting was focused on advances in the following areas: cutting-edge translational neuromodulation, cutting-edge physiology, advances in neuromodulation from Europe and Asia, neuroethical dilemmas, artificial intelligence and computational modeling, time scales in DBS for mood disorders, and advances in future neuromodulation devices.

Surgical Advances in Parkinson's Disease

While symptomatic pharmacological therapy remains the main therapeutic strategy for Parkinson's disease (PD), over the last two decades, surgical approaches have become more commonly used to control levodopa-induced motor complications and dopamine-resistant and non-motor symptoms of PD. In this paper, we discuss old and new surgical treatments for PD and the many technological innovations in this field. We have initially reviewed the relevant surgical anatomy as well as the pathological signaling considered to be the underlying cause of specific symptoms of PD. Subsequently, early attempts at surgical symptom control will be briefly reviewed. As the most well-known surgical intervention for PD is deep brain stimulation, this subject is discussed at length. As deciding on whether a patient stands to benefit from DBS can be quite difficult, the different proposed paradigms for precisely this are covered. Following this, the evidence regarding different targets, especially the subthalamic nucleus and internal globus pallidus, is reviewed as well as the evidence for newer proposed targets for specific symptoms. Due to the rapidly expanding nature of knowledge and technological capabilities, some of these new and potential future capabilities are given consideration in terms of their current and future use. Following this, we have reviewed newer treatment modalities, especially magnetic resonance-guided focused ultrasound and other potential surgical therapies, such as spinal cord stimulation for gait symptoms and others. As mentioned, the field of surgical alleviation of symptoms of PD is undergoing a rapid expansion, and this review provides a general overview of the current status and future directions in the field.

Deep Brain Stimulation for Pediatric Dystonia: Clinicians' Perspectives on the Most Pressing Ethical Challenges

INTRODUCTION

Pediatric deep brain stimulation (pDBS) is commonly used to manage treatment-resistant primary dystonias with favorable results and more frequently used for secondary dystonia to improve quality of life. There has been little systematic empirical neuroethics research to identify ethical challenges and potential solutions to ensure responsible use of DBS in pediatric populations.

METHODS

Clinicians (n = 29) who care for minors with treatment-resistant dystonia were interviewed for their perspectives on the most pressing ethical issues in pDBS.

RESULTS

Using thematic content analysis to explore salient themes, clinicians identified four pressing concerns: (1) uncertainty about risks and benefits of pDBS (22/29; 72%) that poses a challenge to informed decision-making; (2) ethically navigating decision-making roles (15/29; 52%), including how best to integrate perspectives from diverse stakeholders (patient, caregiver, clinician) and how to manage surrogate decisions on behalf of pediatric patients with limited capacity to make autonomous decisions; (3) information scarcity effects on informed consent and decision quality (15/29; 52%) in the context of patient and caregivers' expectations for treatment; and (4) narrow regulatory status and access (7/29; 24%) such as the lack of FDA-approved indications that contribute to decision-making uncertainty and liability and potentially limit access to DBS among patients who may benefit from it.

CONCLUSION

These results suggest that clinicians are primarily concerned about ethical limitations of making difficult decisions in the absence of informational, regulatory, and financial supports. We discuss two solutions already underway, including supported decision-making to address uncertainty and further data sharing to enhance clinical knowledge and discovery.

Chronic basal forebrain activation improves spatial memory, boosts neurotrophin receptor expression, and lowers BACE1 and Aβ42 levels in the cerebral cortex in mice

The etiology of Alzheimer's dementia has been hypothesized in terms of basal forebrain cholinergic decline, and in terms of reflecting beta-amyloid neuropathology. To study these different biological elements, we activated the basal forebrain in 5xFAD Alzheimer's model mice and littermates. Mice received 5 months of 1 h per day intermittent stimulation of the basal forebrain, which includes cholinergic projections to the cortical mantle. Then, mice were behaviorally tested followed by tissue analysis. The 5xFAD mice performed worse in water-maze testing than littermates. Stimulated groups learned the water maze better than unstimulated groups. Stimulated groups had 2-3-fold increases in frontal cortex immunoblot measures of the neurotrophin receptors for nerve growth factor and brain-derived neurotrophic factor, and a more than 50% decrease in the expression of amyloid cleavage enzyme BACE1. Stimulation also led to lower Aβ42 in 5xFAD mice. These data support a causal relationship between basal forebrain activation and both neurotrophin activation and reduced Aβ42 generation and accumulation. The observation that basal forebrain activation suppresses Aβ42 accumulation, combined with the known high-affinity antagonism of nicotinic receptors by Aβ42, documents bidirectional antagonism between acetylcholine and Aβ42.

Water-soluble conjugated polymers for bioelectronic systems

Bioelectronics is an interdisciplinary field of research that aims to establish a synergy between electronics and biology. Contributing to a deeper understanding of bioelectronic processes and the built bioelectronic systems, a variety of new phenomena, mechanisms and concepts have been derived in the field of biology, medicine, energy, artificial intelligence science, etc. Organic semiconductors can promote the applications of bioelectronics in improving original performance and creating new features for organisms due to their excellent photoelectric and electrical properties. Recently, water-soluble conjugated polymers (WSCPs) have been employed as a class of ideal interface materials to regulate bioelectronic processes between biological systems and electronic systems, relying on their satisfying ionic conductivity, water-solubility, good biocompatibility and the additional mechanical and electrical properties. In this review, we summarize the prominent contributions of WSCPs in the aspect of the regulation of bioelectronic processes and highlight the latest advances in WSCPs for bioelectronic applications, involving biosynthetic systems, photosynthetic systems, biophotovoltaic systems, and bioelectronic devices. The challenges and outlooks of WSCPs in designing high-performance bioelectronic systems are also discussed.

Propranolol Modulates Cerebellar Circuit Activity and Reduces Tremor

Tremor is the most common movement disorder. Several drugs reduce tremor severity, but no cures are available. Propranolol, a β-adrenergic receptor blocker, is the leading treatment for tremor. However, the in vivo circuit mechanisms by which propranolol decreases tremor remain unclear. Here, we test whether propranolol modulates activity in the cerebellum, a key node in the tremor network. We investigated the effects of propranolol in healthy control mice and Car8^wdl/wdl mice, which exhibit pathophysiological tremor and ataxia due to cerebellar dysfunction. Propranolol reduced physiological tremor in control mice and reduced pathophysiological tremor in Car8^wdl/wdl mice to control levels. Open field and footprinting assays showed that propranolol did not correct ataxia in Car8^wdl/wdl mice. In vivo recordings in awake mice revealed that propranolol modulates the spiking activity of control and Car8^wdl/wdl Purkinje cells. Recordings in cerebellar nuclei neurons, the targets of Purkinje cells, also revealed altered activity in propranolol-treated control and Car8^wdl/wdl mice. Next, we tested whether propranolol reduces tremor through β₁ and β₂ adrenergic receptors. Propranolol did not change tremor amplitude or cerebellar nuclei activity in β₁ and β₂ null mice or Car8^wdl/wdl mice lacking β₁ and β₂ receptor function. These data show that propranolol can modulate cerebellar circuit activity through β-adrenergic receptors and may contribute to tremor therapeutics.

A PVT-Robust AFE-Embedded Error-Feedback Noise-Shaping SAR ADC With Chopper-Based Passive High-Pass IIR Filtering for Direct Neural Recording

This paper presents a PVT-robust error-feedback (EF) noise-shaping SAR (NS-SAR) ADC for direct neural-signal recording. For closed-loop bidirectional neural interfaces enabling the next generation neurological devices, a wide-dynamic-range neural recording circuit is required to accommodate stimulation artifacts. A recording structure using an NS-SAR ADC can be a good candidate because the high resolution and wide dynamic range can be obtained with a low oversampling ratio and power consumption. However, NS-SAR ADCs require an additional gain stage to obtain a well-shaped noise transfer function (NTF), and a dynamic amplifier is often used as the gain stage to minimize power overhead at the cost of vulnerability to PVT variations. To overcome this limitation, the proposed work reutilizes the capacitive-feedback amplifier, which is the analog front-end of the neural recording circuit, as a PVT-robust gain stage to achieve a reliable NS performance. In addition, a new chopper-based implementation of a passive high-pass IIR filter is proposed, achieving an improved NTF compared to prior EF NS-SAR ADCs. Fabricated in a 180-nm CMOS process, the proposed NS-SAR ADC consumes 4.3-μW power and achieves a signal-to-noise-and-distortion ratio (SNDR) of 71.7 dB and 82.7 dB for a bandwidth of 5 kHz and 300 Hz, resulting in a Schreier figure of merit (FOM) of 162.4 dB and 162.1 dB, respectively. Direct neural recording using the proposed NS-SAR ADC is demonstrated successfully in vivo, and also its tolerance against stimulation artifacts is validated in vitro.

A review on pathology, mechanism, and therapy for cerebellum and tremor in Parkinson's disease

Tremor is one of the core symptoms of Parkinson’s disease (PD), but its mechanism is poorly understood. The cerebellum is a growing focus in PD-related researches and is reported to play an important role in tremor in PD. The cerebellum may participate in the modulation of tremor amplitude via cerebello-thalamo-cortical circuits. The cerebellar excitatory projections to the ventral intermediate nucleus of the thalamus may be enhanced due to PD-related changes, including dopaminergic/non-dopaminergic system abnormality, white matter damage, and deep nuclei impairment, which may contribute to dysregulation and resistance to levodopa of tremor. This review summarized the pathological, structural, and functional changes of the cerebellum in PD and discussed the role of the cerebellum in PD-related tremor, aiming to provide an overview of the cerebellum-related mechanism of tremor in PD.

Benefits and Risks of a Staged‐Bilateral VIM versus Unilateral VIM DBS for Essential Tremor

Background

Despite over 30 years of clinical experience, high‐quality studies on the efficacy of bilateral versus unilateral deep brain stimulation (DBS) of the ventral intermediate (VIM) nucleus of the thalamus for medically refractory essential tremor (ET) remain limited.

Objectives

To compare benefits and risks of bilateral versus unilateral VIM DBS using the largest ET DBS clinical trial dataset available to date.

Methods

Participants from the US St. Jude/Abbott pivotal ET DBS trial who underwent staged‐bilateral VIM implantation constituted the primary cohort in this sub‐analysis. Their assessments “on” DBS at six months after second‐side VIM DBS implantation were compared to the assessments six months after unilateral implantation. Two control cohorts of participants with unilateral implantation only were also used for between‐group comparisons.

Results

The primary cohort consisted of n = 38 ET patients (22M/16F; age of 65.3 ± 9.5 years). The second side VIM‐DBS resulted in a 29.6% additional improvement in the total motor CRST score (P < 0.001), with a 64.1% CRST improvement in the contralateral side (P < 0.001). An added improvement was observed in the axial tremor score (21.4%, P = 0.005), and CRST part B (24.8%, P < 0.001) score. Rate of adverse events was slightly higher after bilateral stimulation.

Conclusions

In the largest ET DBS study to date, staged‐bilateral VIM DBS was a highly effective treatment for ET with bilateral implantation resulting in greater reduction in total motor tremor scores when compared to unilateral stimulation alone.

Symptom-specific differential motor network modulation by deep brain stimulation in Parkinson's disease

OBJECTIVE

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an established neurosurgical treatment for the motor symptoms of Parkinson's disease (PD). While often highly effective, DBS does not always yield optimal therapeutic outcomes, and stimulation-induced adverse effects, including paresthesia, muscle contractions, and nausea/lightheadedness, commonly occur and can limit the efficacy of stimulation. Currently, objective metrics do not exist for monitoring neural changes associated with stimulation-induced therapeutic and adverse effects.

METHODS

In the present study, the authors combined intraoperative functional MRI (fMRI) with STN DBS in 20 patients with PD to test the hypothesis that stimulation-induced blood oxygen level-dependent signals contained predictive information concerning the therapeutic and adverse effects of stimulation.

RESULTS

As expected, DBS resulted in blood oxygen level-dependent activation in myriad motor regions, including the primary motor cortex, caudate, putamen, thalamus, midbrain, and cerebellum. Across the patients, DBS-induced improvements in contralateral Unified Parkinson's Disease Rating Scale tremor subscores correlated with activation of thalamic, brainstem, and cerebellar regions. In addition, improvements in rigidity and bradykinesia subscores correlated with activation of the primary motor cortex. Finally, activation of specific sensorimotor-related subregions correlated with the presence of DBS-induced adverse effects, including paresthesia and nausea (cerebellar cortex, sensorimotor cortex) and unwanted muscle contractions (caudate and putamen).

CONCLUSIONS

These results suggest that DBS-induced activation patterns revealed by fMRI contain predictive information with respect to the therapeutic and adverse effects of DBS. The use of fMRI in combination with DBS therefore may hold translational potential to guide and improve clinical stimulator optimization in patients.

Prediction of Clinical Deep Brain Stimulation Target for Essential Tremor From 1.5 Tesla MRI Anatomical Landmarks

Background: Deep brain stimulation is an efficacious treatment for refractory essential tremor, though targeting the intra-thalamic nuclei remains challenging. Objectives: We sought to develop an inverse approach to retrieve the position of the leads in a cohort of patients operated on with optimal clinical outcomes from anatomical landmarks identifiable by 1.5 Tesla magnetic resonance imaging. Methods: The learning database included clinical outcomes and post-operative imaging from which the coordinates of the active contacts and those of anatomical landmarks were extracted. We used machine learning regression methods to build three different prediction models. External validation was performed according to a leave-one-out cross-validation. Results: Fifteen patients (29 leads) were included, with a median tremor improvement of 72% on the Fahn-Tolosa-Marin scale. Kernel ridge regression, deep neural networks, and support vector regression (SVR) were used. SVR gave the best results with a mean error of 1.33 ± 1.64 mm between the predicted target and the active contact position. Conclusion: We report an original method for the targeting in deep brain stimulation for essential tremor based on patients' radio-anatomical features. This approach will be tested in a prospective clinical trial.

Comparison of efficacy of deep brain stimulation and focused ultrasound in parkinsonian tremor: a systematic review and network meta-analysis

To compare the efficacy of deep brain stimulation (DBS) and MRI-guided focused ultrasound (MRIgFUS) in parkinsonian tremor. We performed a network meta-analysis based on a Bayesian framework. We searched the literature for articles published between January 1990 and October 2020 using three databases: PubMed, Embase and Cochrane Library (The Cochrane Database of Systematic Reviews). A total of 24 studies were included in our analysis, comprising data from 784 participants. Our findings revealed similar efficacy of DBS and MRIgFUS in parkinsonian tremor suppression. Compared with internal globus pallidus (GPi)-MRIgFUS, GPi-DBS -1.84 (-6.44, 2.86), pedunculopontine nucleus (PPN)_DBS -3.28 (-9.28, 2.78), PPN and caudal zona incerta (cZI)-DBS 0.40 (-6.16, 6.87), subthalamic nucleus (STN)_DBS 0.89 (-3.48, 5.30), STN and cZI-DBS 1.99 (-4.74, 8.65), ventral intermediate nucleus(VIM)_DBS 1.75 (-2.87, 6.48), VIM_FUS 0.72 (-5.27, 6.43), cZI-DBS 0.27 (-4.75, 5.36) were no significantly difference. Compared with VIM-MRIgFUS, GPi-DBS -2.55(-6.94, 2.21), GPi-FUS -0.72 (-6.43, 5.27), PPN_DBS -4.01(-9.97, 2.11), PPN and cZI-DBS -0.32 (-6.73, 6.36), STN_DBS 0.16 (-3.98, 4.6), STN and cZI-DBS 1.31(-5.18,7.87), VIM-DBS 1.00(-3.41, 5.84)and cZI-DBS -0.43 (-5.07, 4.68) were no significantly difference. With respect to the results for the treatment of motor symptoms, GPi-DBS, GPi-MRIgFUS, STN-DBS and cZI-DBS were significantly more efficacious than baseline (GPi-DBS 15.24 (5.79, 24.82), GPi-MRIgFUS 13.46 (2.46, 25.10), STN-DBS 19.62 (12.19, 27.16), cZI-DBS 14.18 (1.73, 26.89). The results from the surface under the cumulative ranking results showed that STN-DBS ranked first, followed by combined PPN and cZI-DBS, and PPN-DBS ranked last. MRIgFUS, an efficacious intervention for improving parkinsonian tremor, has not demonstrated to be inferior to DBS in parkinsonian tremor suppression. Hence, clinicians should distinguish individual patients' symptoms to ensure that the appropriate intervention and therapeutic approach are applied.

Deep brain stimulation and other surgical modalities for the management of essential tremor

INTRODUCTION

Surgical treatments are considered for essential tremor (ET) when patients do not respond to oral pharmacological therapies. These treatments mainly comprise radiofrequency (RF) thalamotomy, gamma knife radiosurgery (GKRS), deep brain stimulation (DBS), and focused ultrasound (FUS) procedures.

AREAS COVERED

We reviewed the strengths and weaknesses of each procedure and clinical outcomes for 7 RF studies (n = 85), 11 GKRS (n = 477), 33 DBS (n = 1061), and 13 FUS studies (n = 368). A formal comparison was not possible given the heterogeneity in studies. Improvements were about 42%-90% RF, 10%-79% GKRS, 45%-83% DBS, 42%-83% FUS at short-term follow-up (<12 months) and were about 54%-82% RF, 11%-84% GKRS, 18%-92% DBS, and 42%-80% FUS at long-term follow-up (>12 months).

EXPERT OPINION

We found DBS with inherent advantages of being an adjustable and reversible procedure as the most frequently employed surgical procedure for control of ET symptoms. FUS is a promising procedure but has limited applicability for unilateral control of symptoms. RF is invasive, and GKRS has unpredictable delayed effects. Each of these surgical modalities has advantages and limitations that need consideration when selecting a treatment for the ET patients.

Comprehensive Evaluation of Voice-Specific Outcomes in Patients With Essential Tremor Before and After Deep Brain Stimulation

OBJECTIVE

Deep brain stimulation (DBS) is a treatment for medically refractory essential tremor (ET), but there is a paucity of literature examining the effects of DBS on voice in patients with ET pre-DBS and post-DBS. This study aimed to report a comprehensive evaluation of voice in patients with ET pre-DBS and 6-months post-DBS.

STUDY DESIGN

Case series.

METHODS

Five patients receiving DBS for ET underwent voice evaluations pre-DBS and 6-months post-DBS. One patient had concurrent ET of the vocal tract (ETVT). The evaluation included patient-reported, perceptual, acoustic, and phonatory aerodynamic analyses of voice. Voice Handicap Index-10, Grade, Roughness, Breathiness, Asthenia, Strain Scale, perturbation measures, cepstral spectral index of dysphonia, cepstral peak prominence, and mean phonatory airflow measures were also among the data collected.

RESULTS

Patients with ET presented with minimal changes in perceptual, acoustic, and phonatory aerodynamic parameters. Perceived vocal roughness significantly increased 6-months post-DBS (P = 0.047). The patient with ETVT presented with clinically significant improvement in almost all collected voice parameters 6-months post-DBS.

CONCLUSION

This is the first study to provide data encompassing auditory perceptual voice analysis, voice-specific patient-reported quality of life measures, acoustic, and phonatory aerodynamic outcomes in patients pre-DBS and 6-months post-DBS for ET. The results of our preliminary study have implications for the use of a comprehensive voice assessment to identify and measure change in voice outcomes in patients with ET and ETVT pre- and postsurgery.

Rebound effect in deep brain stimulation for essential tremor and symptom severity estimation from neural data

Deep brain stimulation (DBS) is a safe and established treatment for essential tremor (ET). However, there remains considerable room for improvement due to concerns associated with the initial implant surgery, semi-regular revision surgeries for battery replacements, and side effects including paresthesia, gait ataxia, and emotional disinhibition that have been associated with continuous, or conventional, DBS (cDBS) treatment. Adaptive DBS (aDBS) seeks to ameliorate some of these concerns by using feedback from either an external wearable or implanted sensor to modulate stimulation parameters as needed. aDBS has been demonstrated to be as or more effective than cDBS, but the purely binary control system most commonly deployed by aDBS systems likely still provides sub-optimal treatment and may introduce new issues. One example of these issues is rebound effect, in which the tremor symptoms of an ET patient receiving DBS therapy temporarily worsen after cessation of stimulation before leveling out to a steady state. Here is presented a quantitative analysis of rebound effect in 3 patients receiving DBS for ET. Rebound was evident in all 3 patients by both clinical assessment and inertial measurement unit data, peaking by the latter at T_p = 6.65 minutes after cessation of stimulation. Using features extracted from neural data, linear regression was applied to predict tremor severity, with $R_{avg{\text{ }}}^2 = 0.82$. These results strongly suggest that rebound effect and the additional information made available by rebound effect should be considered and exploited when designing novel aDBS systems.

Deep brain stimulation effects on lower urinary tract function: Systematic review and meta-analysis

INTRODUCTION

While efficacy of deep brain stimulation for motor symptoms of neurological disorders is well accepted, its effects on the autonomic system remain controversial. We aimed to systematically assess all available evidence of deep brain stimulation effects on lower urinary tract function.

METHODS

This systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Studies were identified by electronic search of Cochrane Central Register of Controlled Trials, Embase, Medline, Scopus, and Web of Science (last search July 12, 2019) and by screening of reference lists and reviews.

RESULTS

After screening 577 articles, we included 29 studies enrolling a total of 1293 patients. Deep brain stimulation of the globus pallidus internus (GPi), pedunculopontine nucleus (PPN), and subthalamic nucleus (STN) had an inhibitory effect on detrusor function, while deep brain stimulation of the ventral intermediate nucleus of the thalamus (VIM) showed an excitatory effect. In the meta-analysis, deep brain stimulation of the STN led to a significant increase in maximum bladder capacity (mean difference 124 mL, 95% confidence interval 60-187 mL, p = 0.0001) but had no clinically relevant effects on other urodynamic parameters. Adverse events (reported in thirteen studies) were most commonly respiratory issues, postural instability, and dysphagia. Risk of bias and confounding was relatively low.

CONCLUSIONS

Deep brain stimulation does not impair lower urinary tract function and might even have beneficial effects. This needs to be considered in the deep brain stimulation decision-making process helping to encourage and to reassure prospective patients.

Progress in Brain-Compatible Interfaces with Soft Nanomaterials

Neural interfaces facilitating communication between the brain and machines must be compatible with the soft, curvilinear, and elastic tissues of the brain and yet yield enough power to read and write information across a wide range of brain areas through high-throughput recordings or optogenetics. Biocompatible-material engineering has facilitated the development of brain-compatible neural interfaces to support built-in modulation of neural circuits and neurological disorders. Recent developments in brain-compatible neural interfaces that use soft nanomaterials more suitable for complex neural circuit analysis and modulation are reviewed. Preclinical tests of the compatibility and specificity of these interfaces in animal models are also discussed.

Deep Brain Stimulation Target Selection in Co-Morbid Essential Tremor and Parkinson's Disease

Clinical Vignette

A 64-year-old man with essential tremor (ET) and Parkinson's disease (PD) presented with medically refractory, large amplitude, debilitating rest and action tremor in his extremities.

Clinical Dilemma

Ventral intermediate nucleus of the thalamus (VIM) deep brain stimulation (DBS) improves tremor in ET and PD but does not ameliorate bradykinesia and rigidity in PD. The comparative efficacy of subthalamic nucleus (STN) DBS in managing action ET tremor remains unclear.

Clinical Solution

Bilateral STN was selected as the DBS target. Moderate improvement in rest tremor and mild improvement in action tremor were noted following initial programming.

Gap In Knowledge

There are no head-to-head trials to guide DBS target selection in patients with both ET and PD. Current evidence is limited to a few small head-to-head trials that have demonstrated equivalent efficacy in tremor reduction in PD patients using VIM as DBS target and in ET patients using STN.

Expert Commentary

Due to limited evidence, DBS treatment of complex cases, such as combined Parkinson's disease and essential tremor, remains based on expert consensus at each institution. Further multi-approach efforts, using imaging, electrophysiologic, and animal data, will be needed to answer the identified gap in knowledge.

Highlights

There is limited evidence to guide deep brain target selection in patients with essential tremor and Parkinson's disease. We review existing literature and propose strategies to manage tremor in these patients.

Individualized Anatomy-Based Targeting for VIM-cZI DBS in Essential Tremor

BACKGROUND

Deep brain stimulation of the ventral intermediate nucleus (VIM) or caudal zona incerta (cZI) is effective for refractory essential tremor (ET). To refine stereotactic planning for lead placement, we developed a unique individualized anatomy-based planning protocol that targets both the VIM and the cZI in patients with ET.

METHODS

33 patients with ET underwent VIM-cZI lead implantation with targeting based on our protocol. Indirect targeting was adjusted based on anatomic landmarks as reference lines bisecting the red nuclei and ipsilateral subthalamus. Outcomes were evaluated through the follow-up of 31.1 ± 18.4 months. Active contact coordinates were obtained from reconstructed electrodes in the Montreal Neurological Institute space using the MATLAB Lead-DBS toolbox.

RESULTS

Mean tremor improvement was 79.7% ± 22.4% and remained stable throughout the follow-up period. Active contacts at last postoperative visit had mean Montreal Neurological Institute coordinates of 15.5 ± 1.6 mm lateral to the intercommissural line, 15.3 ± 1.8 mm posterior to the anterior commissure, and 1.4 ± 2.9 mm below the intercommissural plane. No hemorrhagic complications were observed in the analyzed group.

CONCLUSIONS

Individualized anatomy-based VIM-cZI targeting is feasible and safe and is associated with favorable tremor outcomes.

Natural history of neuromodulation devices and therapies: a patient-centered survival analysis

OBJECTIVE

Despite rapid development and expansion of neuromodulation technologies, knowledge about device and/or therapy durability remains limited. The aim of this study was to evaluate the long-term rate of hardware and therapeutic failure of implanted devices for several neuromodulation therapies.

METHODS

The authors performed a retrospective analysis of patients' device and therapy survival data (Kaplan-Meier survival analysis) for deep brain stimulation (DBS), vagus nerve stimulation (VNS), and spinal cord stimulation (SCS) at a single institution (years 1994-2015).

RESULTS

During the study period, 450 patients underwent DBS, 383 VNS, and 128 SCS. For DBS, the 5- and 10-year initial device survival was 87% and 73%, respectively, and therapy survival was 96% and 91%, respectively. For VNS, the 5- and 10-year initial device survival was 90% and 70%, respectively, and therapy survival was 99% and 97%, respectively. For SCS, the 5- and 10-year initial device survival was 50% and 34%, respectively, and therapy survival was 74% and 56%, respectively. The average initial device survival for DBS, VNS, and SCS was 14 years, 14 years, and 8 years while mean therapy survival was 18 years, 18 years, and 12.5 years, respectively.

CONCLUSIONS

The authors report, for the first time, comparative device and therapy survival rates out to 15 years for large cohorts of DBS, VNS, and SCS patients. Their results demonstrate higher device and therapy survival rates for DBS and VNS than for SCS. Hardware failures were more common among SCS patients, which may have played a role in the discontinuation of therapy. Higher therapy survival than device survival across all modalities indicates continued therapeutic benefit beyond initial device failures, which is important to emphasize when counseling patients.

Integrative and Network-Specific Connectivity of the Basal Ganglia and Thalamus Defined in Individuals

The basal ganglia, thalamus, and cerebral cortex form an interconnected network implicated in many neurological and psychiatric illnesses. A better understanding of cortico-subcortical circuits in individuals will aid in development of personalized treatments. Using precision functional mapping-individual-specific analysis of highly sampled human participants-we investigated individual-specific functional connectivity between subcortical structures and cortical functional networks. This approach revealed distinct subcortical zones of network specificity and multi-network integration. Integration zones were systematic, with convergence of cingulo-opercular control and somatomotor networks in the ventral intermediate thalamus (motor integration zones), dorsal attention and visual networks in the pulvinar, and default mode and multiple control networks in the caudate nucleus. The motor integration zones were present in every individual and correspond to consistently successful sites of deep brain stimulation (DBS; essential tremor). Individually variable subcortical zones correspond to DBS sites with less consistent treatment effects, highlighting the importance of PFM for neurosurgery, neurology, and psychiatry.

A retrospective evaluation of automated optimization of deep brain stimulation parameters

OBJECTIVE

We performed a retrospective analysis of an optimization algorithm for the computation of patient-specific multipolar stimulation configurations employing multiple independent current/voltage sources. We evaluated whether the obtained stimulation configurations align with clinical data and whether the optimized stimulation configurations have the potential to lead to an equal or better stimulation of the target region as manual programming, while reducing the time required for programming sessions.

APPROACH

For three patients (five electrodes) diagnosed with essential tremor, we derived optimized multipolar stimulation configurations using an approach that is suitable for the application in clinical practice. To evaluate the automatically derived stimulation settings, we compared them to the results of the monopolar review.

MAIN RESULTS

We observe a good agreement between the findings of the monopolar review and the optimized stimulation configurations, with the algorithm assigning the maximal voltage in the optimized multipolar pattern to the contact that was found to lead to the best therapeutic effect in the clinical monopolar review in all cases. Additionally, our simulation results predict that the optimized stimulation settings lead to the activation of an equal or larger volume fraction of the target compared to the manually determined settings in all cases.

SIGNIFICANCE

Our results demonstrate the feasibility of an automatic determination of optimal DBS configurations and motivate a further evaluation of the applied optimization algorithm.

Deep brain stimulation for intractable neuropathic facial pain

OBJECTIVE Deep brain stimulation (DBS) is a well-established, evidence-based therapy with FDA approval for Parkinson's disease and essential tremor. Despite the early successful use of DBS to target the sensory thalamus for intractable facial pain, subsequent studies pursuing various chronic pain syndromes reported variable efficacy, keeping DBS for pain as an investigational and "off-label" use. The authors report promising results for a contemporary series of patients with intractable facial pain who were treated with DBS. METHODS Pain outcomes for 7 consecutive patients with unilateral, intractable facial pain undergoing DBS of the ventral posteromedial nucleus of the thalamus (VPM) and the periaqueductal gray (PAG) were retrospectively reviewed. Pain was assessed preoperatively and at multiple postoperative time points using the visual analog scale (VAS), the Short-Form McGill Pain Questionnaire-2 (SF-MPQ-2), and the Pain Disability Index (PDI). RESULTS VAS scores significantly decreased from a mean ± SD of 9.0 ± 1.3 preoperatively to 2.6 ± 1.5 at 1 year postoperatively (p = 0.001). PDI scores decreased from a mean total of 48.5 to 28.5 (p = 0.01). SF-MPQ-2 scores decreased from a mean of 4.6 to 2.4 (p = 0.03). Notably, several patients did not experience maximum improvement until 6-9 months postoperatively, correlating with repeated programming adjustments. CONCLUSIONS DBS of the VPM and PAG is a potential therapeutic option for patients suffering from severe, intractable facial pain refractory to other interventions. Improved efficacy may be observed over time with close follow-up and active DBS programming adjustments.

A meta-analysis of outcomes and complications of magnetic resonance-guided focused ultrasound in the treatment of essential tremor

OBJECTIVE Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel technique that uses high-intensity focused ultrasound to achieve target ablation. Like a lens focusing the sun's rays, the ultrasound waves are focused to generate heat. This therapy combines the noninvasiveness of Gamma Knife thalamotomy and the real-time ablation of deep brain stimulation with acceptable complication rates. The aim of this study was to analyze the overall outcomes and complications of MRgFUS in the treatment of essential tremor (ET). METHODS A meta-analysis in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was made by searching PubMed, Cochrane library database, Web of Science, and Cumulative Index to Nursing and Allied Health Literature (CINAHL). Patients with the diagnosis of ET who were treated with MRgFUS were included in the study. The change in the Clinical Rating Scale for Tremor (CRST) score after treatment was analyzed. The improvement in disability was assessed with the Quality of Life in Essential Tremor Questionnaire (QUEST) score. The pooled data were analyzed by the DerSimonian-Laird random-effects model. Tests for bias and heterogeneity were performed. RESULTS Nine studies with 160 patients who had ET were included in the meta-analysis. The ventral intermediate nucleus was the target in 8 of the studies. The cerebellothalamic tract was targeted in 1 study. There was 1 randomized controlled trial, 6 studies were retrospective, and 2 were prospective. The mean number of sonications given in various studies ranged from 11 ± 3.2 to 22.5 ± 7.5 (mean ± SD). The maximum delivered energy ranged from 10,320 ± 4537 to 14,497 ± 6695 Joules. The mean of peak temperature reached ranged from 53°C ± 2.3°C to 62.0°C ± 2.5°C. On meta-analysis with the random-effects model, the pooled percentage improvements in the CRST Total, CRST Part A, CRST Part C, and QUEST scores were 62.2%, 62.4%, 69.1%, and 46.5%, respectively. Dizziness was the most common in-procedure complication, occurring in 45.5%, followed by nausea and vomiting in 26.85% (pooled percentage). At 3 months, ataxia was the most common complication, occurring in 32.8%, followed by paresthesias in 25.1% of the patients. At 12 months posttreatment, the ataxia had significantly recovered and paresthesias became the most common persisting complication, at 15.3%. CONCLUSIONS The MRgFUS therapy for ET significantly improves the CRST scores and improves the quality of life in patients with ET, with an acceptable complication rate. Therapy with MRgFUS is a promising frontier in functional neurosurgery.

Treatment of essential tremor: current status

Essential tremor is the most common cause of tremor involving upper limbs, head and voice. The first line of treatment for limb tremor is pharmacotherapy with propranolol or primidone. However, these two drugs reduce the tremor severity by only half. In medication refractory and functionally disabling tremor, alternative forms of therapy need to be considered. Botulinum toxin injections are likely efficacious for limb, voice and head tremor but are associated with side effects. Surgical interventions include deep brain stimulation; magnetic resonance-guided focused ultrasound and thalamotomy for unilateral and deep brain stimulation for bilateral procedures. Recent consensus classification for essential tremor has included a new subgroup, ‘Essential tremor plus’, who have associated subtle neurological ‘soft signs’, such as dystonic posturing of limbs and may require a different treatment approach. In this review, we have addressed the current management of essential tremor with regard to different anatomical locations of tremor as well as different modalities of treatment.

Comparison of elderly and young patient populations treated with deep brain stimulation for Parkinson's disease: long-term outcomes with up to 7 years of follow-up

OBJECTIVE

Deep brain stimulation (DBS) is the procedure of choice for Parkinson's disease (PD). It has been used in PD patients younger than 70 years because of better perceived intra- and postoperative outcomes than in patients 70 years or older. However, previous studies with limited follow-up have demonstrated benefits associated with the treatment of elderly patients. This study aims to evaluate the long-term outcomes in elderly PD patients treated with DBS in comparison with a younger population.

METHODS

PD patients treated with DBS at the authors' institution from 2008 to 2014 were divided into 2 groups: 1) elderly patients, defined as having an age at surgery ≥ 70 years, and 2) young patients, defined as those < 70 years at surgery. Functional and medical treatment outcomes were evaluated using the Unified Parkinson's Disease Rating Scale part III (UPDRS III), levodopa-equivalent daily dose (LEDD), number of daily doses, and number of anti-PD medications. Study outcomes were compared using univariate analyses, 1-sample paired t-tests, and 2-sample t-tests.

RESULTS

A total of 151 patients were studied, of whom 24.5% were ≥ 70 years. The most common preoperative Hoehn and Yahr stages for both groups were 2 and 3. On average, elderly patients had more comorbidities at the time of surgery than their younger counterparts (1 vs 0, p = 0.0001) as well as a higher average LEDD (891 mg vs 665 mg, p = 0.008). Both groups experienced significant decreases in LEDD following surgery (elderly 331.38 mg, p = 0.0001; and young 108.6 mg, p = 0.0439), with a more significant decrease seen in elderly patients (young 108.6 mg vs elderly 331.38 mg, p = 0.0153). Elderly patients also experienced more significant reductions in daily doses (young 0.65 vs elderly 3.567, p = 0.0344). Both groups experienced significant improvements in motor function determined by reductions in UPDRS III scores (elderly 16.29 vs young 12.85, p < 0.0001); however, reductions in motor score between groups were not significant. Improvement in motor function was present for a mean follow-up of 3.383 years postsurgery for the young group and 3.51 years for the elderly group. The average follow-up was 40.6 months in the young group and 42.2 months in the elderly group.

CONCLUSIONS

This study found long-term improvements in motor function and medication requirements in both elderly and young PD patients treated with DBS. These outcomes suggest that DBS can be successfully used in PD patients ≥ 70 years. Further studies will expand on these findings.

Pre-operative smoking history increases risk of infection in deep brain stimulation surgery

Although general risk of deep brain stimulation (DBS) therapy has been previously described, application of risk prediction at the individual patient level is still largely at the discretion of a treating physician or a multidisciplinary team. To explore associations between potentially modifiable patient characteristics and common adverse events following DBS surgery, we retrospectively reviewed consecutive adult patients who had undergone new DBS electrode placement surgeries at two high-volume tertiary referral centers between October 1997 and May 2018. Among 501 patients included in the analysis (mean age (SD), 64.6 (10.4) years), 165 (32.9%) were female, 67 (13.4%) had diabetes, 231 (46.1%) had hypertension, 25 (5.0%) were smokers, 27 (5.4%) developed an infection, 15 (3.0%) had intracranial or intraventricular hemorrhage, and 53 (10.6%) had an unplanned return to the operating room. Patients who developed a surgical site infection were more likely to report history of smoking before DBS surgery (16% vs 5%, p = 0.04). There was a trend for patients with hypertension to be at risk for intracranial hemorrhage (p = 0.11). In conclusion, this multicenter study demonstrated an association between preoperative smoking and increased risk of infection following new DBS implantation surgery. Counseling about this risk should be considered in preoperative evaluation of patients who are considering undergoing a DBS procedure.

Physiological mechanisms of thalamic ventral intermediate nucleus stimulation for tremor suppression

Ventral intermediate thalamic deep brain stimulation is a standard therapy for the treatment of medically refractory essential tremor and tremor-dominant Parkinson's disease. Despite the therapeutic benefits, the mechanisms of action are varied and complex, and the pathophysiology and genesis of tremor remain unsubstantiated. This intraoperative study investigated the effects of high frequency microstimulation on both neuronal firing and tremor suppression simultaneously. In each of nine essential tremor and two Parkinson's disease patients who underwent stereotactic neurosurgery, two closely spaced (600 µm) microelectrodes were advanced into the ventral intermediate nucleus. One microelectrode recorded action potential firing while the adjacent electrode delivered stimulation trains at 100 Hz and 200 Hz (2-5 s, 100 µA, 150 µs). A triaxial accelerometer was used to measure postural tremor of the contralateral hand. At 200 Hz, stimulation led to 68 ± 8% (P < 0.001) inhibition of neuronal firing and a 53 ± 5% (P < 0.001) reduction in tremor, while 100 Hz reduced firing by 26 ± 12% (not significant) with a 17 ± 6% (P < 0.05) tremor reduction. The degree of cell inhibition and tremor suppression were significantly correlated (P < 0.001). We also found that the most ventroposterior stimulation sites, closest to the border of the ventral caudal nucleus, had the best effect on tremor. Finally, prior to the inhibition of neuronal firing, microstimulation caused a transient driving of neuronal activity at stimulus onset (61% of sites), which gave rise to a tremor phase reset (73% of these sites). This was likely due to activation of the excitatory glutamatergic cortical and cerebellar afferents to the ventral intermediate nucleus. Temporal characteristics of the driving responses (duration, number of spikes, and onset latency) significantly differed between 100 Hz and 200 Hz stimulation trains. The subsequent inhibition of neuronal activity was likely due to synaptic fatigue. Thalamic neuronal inhibition seems necessary for tremor reduction and may function in effect as a thalamic filter to uncouple thalamo-cortical from cortico-spinal reflex loops. Additionally, our findings shed light on the gating properties of the ventral intermediate nucleus within the cerebello-thalamo-cortical tremor network, provide insight for the optimization of deep brain stimulation technologies, and may inform controlled clinical studies for assessing optimal target locations for the treatment of tremor.

MDS evidence-based review of treatments for essential tremor

BACKGROUND

Essential tremor is one of the most prevalent movement disorders. Many treatments for essential tremor have been reported in clinical practice, but it is uncertain which options have the most robust evidence. The International Parkinson and Movement Disorder Society commissioned a task force on tremor to review clinical studies of treatments for essential tremor.

OBJECTIVES

To conduct an evidence-based review of current pharmacological and surgical treatments for essential tremor, using standardized criteria defined a priori by the International Parkinson and Movement Disorder Society.

METHODS

We followed the recommendations of the International Parkinson and Movement Disorder Society Evidence Based Medicine Committee.

RESULTS

Sixty-four studies of pharmacological and surgical interventions were included in the review. Propranolol and primidone were classified as clinically useful, similar to Topiramate, but only for doses higher than 200 mg/day. Alprazolam and botulinum toxin type A were classified as possibly useful. Unilateral Ventralis intermedius thalamic DBS, radiofrequency thalamotomy, and MRI-guided focused ultrasound thalamotomy were considered possibly useful. All the above recommendations were made for limb tremor in essential tremor. There was insufficient evidence for voice and head tremor as well as for the remaining interventions.

CONCLUSION

Propranolol, primidone, and topiramate (>200 mg/day) are the pharmacological interventions in which the data reviewed robustly supported efficacy. Their safety profile and patient preference may guide the prioritization of these interventions in clinical practice. MRI-guided focused ultrasound thalamotomy was, for the first time, assessed and was considered to be possibly useful. There is a need to improve study design in essential tremor and overcome the limitation of small sample sizes, cross-over studies, short-term follow-up studies, and use of nonvalidated clinical scales. © 2019 International Parkinson and Movement Disorder Society.

The Ventral Intermediate Nucleus Differently Modulates Subtype-Related Networks in Parkinson's Disease

Background: Posture instability gait difficulty-dominant (PIGD) and tremor-dominant (TD) are two subtypes of Parkinson's disease (PD). The thalamus is involved in the neural circuits of both subtypes. However, which subregion of the thalamus has an influence on the PD subtypes remains unclear. Objective: To explore the core subregion of the thalamus showing a significant influence on the PD subtypes and its directional interaction between the PD subtypes. Methods: A total of 79 PD patients (43 TD and 36 PIGD) and 31 normal controls (NC) were enrolled, and the gray matter volume and perfusion characteristics in the thalamus were compared between the three groups. The subregion of the thalamus with significantly different perfusion and volume among three groups was used as the seed of a Granger causality analysis (GCA) to compare the causal connectivity between different subtypes. Results: Perfusion with an increased gradient among the three groups (TD > PIGD > NC) in the bilateral ventral intermediate nucleus (Vim) was observed, which was positively correlated with the clinical tremor scores. The GCA revealed that TD patients had enhanced causal connectivity from the bilateral Vim to the bilateral paracentral gyrus, M1 and the cerebellum compared with the NC group, while the PIGD subtype revealed an increased causal connectivity from the bilateral Vim to the bilateral premotor cortex (preM) and putamen. Additionally, there were positive correlations between the tremor scores and a causal connectivity from the Vim to the cerebellum. The connectivity from the right Vim to the right preM and the right putamen was positively correlated with the PIGD scores. Conclusion: This multilevel analysis showed that the Vim had a significant influence on the PD subtypes and that it differentially mediated the TD and PIGD-related causal connectivity pattern in PD.

Validation of a precision tremor measurement system for multiple sclerosis

BACKGROUND

Tremor is a debilitating symptom of Multiple Sclerosis (MS). Little is known about its pathophysiology and treatments are limited. Clinical trials investigating new interventions often rely on subjective clinical rating scales to provide supporting evidence of efficacy.

NEW METHOD

We present a novel instrument (TREMBAL) which uses electromagnetic motion capture technology to quantify MS tremor. We aim to validate TREMBAL by comparison to clinical ratings using regression modelling with 310 samples of tremor captured from 13 MS participants who performed five different hand exercises during several follow-up visits. Minimum detectable change (MDC) and test-retest reliability were calculated and comparisons were made between MS tremor and data from 12 healthy volunteers.

RESULTS

Velocity of the index finger was most congruent with clinical observation. Regression modelling combining different features, sensor configurations, and labelling exercises did not improve results. TREMBAL MDC was 84% of its initial measurement compared to 91% for the clinical rating. Intra-class correlations for test-retest reliability were 0.781 for TREMBAL and 0.703 for clinical ratings. Tremor was lower (p =  0.002) in healthy subjects.

COMPARISON WITH EXISTING METHODS

Subjective scales have low sensitivity, suffer from ceiling effects, and mitigation against inter-rater variability is challenging. Inertial sensors are ubiquitous, however, their output is nonlinearly related to tremor frequency, compensation is required for gravitational artefacts, and their raw data cannot be intuitively comprehended.

CONCLUSIONS

TREMBAL, compared with clinical ratings, gave measures in agreement with clinical observation, had marginally lower MDC, and similar test-retest reliability.

Hydrogel bioelectronics

Hydrogels have emerged as a promising bioelectronic interfacing material. This review discusses the fundamentals and recent advances in hydrogel bioelectronics.

Prediction of depression and anxiety via patient-assessed tremor severity, not physician-reported motor symptom severity, in patients with Parkinson's disease or essential tremor who have undergone deep brain stimulation

OBJECTIVEDeep brain stimulation (DBS) is an effective therapy for movement disorders such as idiopathic Parkinson's disease (PD) and essential tremor (ET). However, some patients who demonstrate benefit on objective motor function tests do not experience postoperative improvement in depression or anxiety, 2 important components of quality of life (QOL). Thus, to examine other possible explanations for the lack of a post-DBS correlation between improved objective motor function and decreased depression or anxiety, the authors investigated whether patient perceptions of motor symptom severity might contribute to disease-associated depression and anxiety.METHODSThe authors performed a retrospective chart review of PD and ET patients who had undergone DBS at the Cleveland Clinic in the period from 2009 to 2013. Patient demographics, diagnosis (PD, ET), motor symptom severity, and QOL measures (Primary Care Evaluation of Mental Disorders 9-item Patient Health Questionnaire [PHQ-9] for depression, Generalized Anxiety Disorder 7-item Scale [GAD-7], and patient-assessed tremor scores) were collected at 4 time points: preoperatively, postoperatively, 1-year follow-up, and 2-year follow-up. Multivariable prediction models with solutions for fixed effects were constructed to assess the correlation of predictor variables with PHQ-9 and GAD-7 scores. Predictor variables included age, sex, visit time, diagnosis (PD vs ET), patient-assessed tremor, physician-reported tremor, Unified Parkinson's Disease Rating Scale part III (UPDRS-III) score, and patient-assessed tremor over time.RESULTSSeventy PD patients and 17 ET patients were included in this analysis. Mean postoperative and 1-year follow-up UPDRS-III and physician-reported tremor scores were significantly decreased compared with preoperative scores (p < 0.0001). Two-year follow-up physician-reported tremor was also significantly decreased from preoperative scores (p < 0.0001). Only a diagnosis of PD (p = 0.0047) and the patient-assessed tremor rating (p < 0.0001) were significantly predictive of depression. A greater time since surgery, in general, significantly decreased anxiety scores (p < 0.0001) except when a worsening of patient-assessed tremor was reported over the same time period (p < 0.0013).CONCLUSIONSPatient-assessed tremor severity alone was predictive of depression in PD and ET following DBS. This finding suggests that a patient's perception of illness plays a greater role in depression than objective physical disability regardless of the time since surgical intervention. In addition, while anxiety may be attenuated by DBS, patient-assessed return of tremor over time can increase anxiety, highlighting the importance of long-term follow-up for behavioral health features in chronic neurological disorders. Together, these data suggest that the patient experience of motor symptoms plays a role in depression and anxiety-a finding that warrants consideration when evaluating, treating, and following movement disorder patients who are candidates for DBS.

Benefits and risks of unilateral and bilateral ventral intermediate nucleus deep brain stimulation for axial essential tremor symptoms

INTRODUCTION

Many experts assume bilateral deep brain stimulation (DBS) is necessary to improve axial tremor in essential tremor (ET). In the largest clinical trial of DBS for ET to date evaluating a non-directional, constant current device, we studied the effects of unilateral and staged bilateral DBS on axial tremor.

METHODS

We included all participants from the original trial with unilateral ventral intermediate nucleus (VIM) DBS and 90-day follow up at minimum. Primary outcomes were changes in pooled axial subscores in the Clinical Rating Scale for Tremor (CRST) at 90 and 180 days after activation of unilateral VIM DBS compared to pre-operative baseline (n=119). Additionally, we performed within-subject analyses for unilateral versus bilateral DBS at 180 days in the cohort who underwent staged surgery to bilateral DBS (n=39).

RESULTS

Unilateral VIM DBS improved midline tremor by 58% at 90 days (median[IQR]) (3[3] to 1[2], p<0.001) and 65% at 180 days (3[3] to 1[2], p<0.001) versus pre-op baseline. In the staged to bilateral DBS cohort, midline tremor scores further improved after bilateral DBS at 180 days by 63% versus unilateral DBS (3[3] to 1[3], p=0.007). There were, however, 35 additional DBS and surgery-related adverse events, 14 related to incoordination, gait impairment, or speech impairment, versus 6 after unilateral DBS.

CONCLUSION

Unilateral VIM DBS for ET significantly improved associated axial tremor. Staged bilateral DBS was associated with additional axial tremor improvement but also additional adverse events. Unilateral VIM DBS may be sufficient to achieve a goal of contralateral limb and axial tremor attenuation.

Current Status of Neuromodulatory Therapies for Disorders of Consciousness

Treatment for disorders of consciousness (DOCs) is still a Gordian knot. Evidence-based guidelines on the treatment of DOC patients are not currently available, while neuromodulation techniques are seen as a potential treatment. Multiple neuromodulation therapies have been applied. This article reviews the most relevant studies in the literature in order to describe a clear picture of the current state of neuromodulation therapies that could be used to treat DOC patients. Both invasive and non-invasive brain stimulation is discussed. Significant behavioral improvements in prolonged DOCs under neuromodulation therapies are rare. The efficacy of various such therapies remains a matter of debate. Further clinical investigations of existing techniques in larger samples properly controlling for spontaneous recovery are needed, and new approaches are awaited.

Numerical optimization of coordinated reset stimulation for desynchronizing neuronal network dynamics

Excessive synchronization in neural activity is a hallmark of Parkinson's disease (PD). A promising technique for treating PD is coordinated reset (CR) neuromodulation in which a neural population is desynchronized by the delivery of spatially-distributed current stimuli using multiple electrodes. In this study, we perform numerical optimization to find the energy-optimal current waveform for desynchronizing neuronal network with CR stimulation, by proposing and applying a new optimization method based on the direct search algorithm. In the proposed optimization method, the stimulating current is described as a Fourier series, and each Fourier coefficient as well as the stimulation period are directly optimized by evaluating the order parameter, which quantifies the synchrony level, from network simulation. This direct optimization scheme has an advantage that arbitrary changes in the dynamical properties of the network can be taken into account in the search process. By harnessing this advantage, we demonstrate the significant influence of externally applied oscillatory inputs and non-random network topology on the efficacy of CR modulation. Our results suggest that the effectiveness of brain stimulation for desynchronization may depend on various factors modulating the dynamics of the target network. We also discuss the possible relevance of the results to the efficacy of the stimulation in PD treatment.

The oscillatory boundary conditions of different frequency bands in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease that is common in the elderly population. The most important pathological change in PD is the degeneration and death of dopaminergic neurons in the substantia nigra of the midbrain, which results in a decrease in the dopamine (DA) content of the striatum. The exact cause of this pathological change is still unknown. Numerous studies have shown that the evolution of PD is associated with abnormal oscillatory activities in the basal ganglia, with different oscillation frequency ranges, such as the typical beta band (13-30 Hz), the alpha band (8-12 Hz), the theta band (4-7 Hz) and the delta band (1-3 Hz). Although some studies have implied that abnormal interactions between the subthalamic nucleus (STN) and globus pallidus (GP) neurons may be a key factor required to induce these oscillations, the relative mechanism is still unclear. The effects of other nerve nuclei in the basal ganglia, such as the striatum, on these oscillations are still unknown. The thalamus and cortex both have close input and output relationships with the basal ganglia, and many previous studies have indicated that they may also exert effects on Parkinson's disease oscillation, but the mechanisms involved are unclear. In this paper, we built a corticothalamic-basal ganglia (CTBG) mean firing-rate model to explore the onset mechanisms of these different oscillation phenomena. We found that, in addition to the STN-GP network, Parkinson's disease oscillations may also be induced by changing the coupling strength and delays in other pathways. Different frequency bands appear in the oscillating region, and various boundary conditions are depicted in parameter diagrams. The onset mechanism is well explained both by the model and by the numerical simulation results. Therefore, this model provides a unifying framework for studying the mechanism of Parkinson's disease oscillations, and we hope that the results obtained in this work can inspire future experimental studies.

Surgical treatments for essential tremor

INTRODUCTION

Essential tremor is the most common form of pathologic tremor. Surgical therapies disrupt tremorogenic oscillation in the cerebellothalamocortical pathway and are capable of abolishing severe tremor that is refractory to available pharmacotherapies. Surgical methods are raspidly improving and are the subject of this review. Areas covered: A PubMed search on 18 January 2018 using the query essential tremor AND surgery produced 839 abstracts. 379 papers were selected for review of the methods, efficacy, safety and expense of stereotactic deep brain stimulation (DBS), stereotactic radiosurgery (SRS), focused ultrasound (FUS) ablation, and radiofrequency ablation of the cerebellothalamocortical pathway. Expert commentary: DBS and SRS, FUS and radiofrequency ablations are capable of reducing upper extremity tremor by more than 80% and are far more effective than any available drug. The main research questions at this time are: 1) the relative safety, efficacy, and expense of DBS, SRS, and FUS performed unilaterally and bilaterally; 2) the relative safety and efficacy of thalamic versus subthalamic targeting; 3) the relative safety and efficacy of atlas-based versus direct imaging tractography-based anatomical targeting; and 4) the need for intraoperative microelectrode recordings and macroelectrode stimulation in awake patients to identify the optimum anatomical target. Randomized controlled trials are needed.

Treatment of the ventral intermediate nucleus for medically refractory tremor: A cost-analysis of stereotactic radiosurgery versus deep brain stimulation

INTRODUCTION

Medically refractory tremor treatment has evolved over the past half-century from intraoperative thalamotomy to deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM). Within the past 15years, unilateral radiosurgical VIM thalamotomy has emerged as a comparably efficacious treatment modality.

METHODS

An extensive literature search of VIM DBS series was performed; the total cost of VIM DBS was calculated from hospitals geographically representative of the entire United States using current procedural terminology and work relative value unit (RVU) codes. The 2016 Medicare Ambulatory Payment Classification for stereotactic radiosurgery (SRS) was added to the work RVU to determine the total cost of VIM SRS for both Gamma Knife and linear accelerator SRS. Cost estimates assumed that VIM DBS was performed without intraoperative microelectrode recording.

RESULT

The mean unilateral VIM DBS cost was $17,932.41 per patient. For SRS VIM, the total costs for Gamma Knife ($10,811.77) and linear accelerator ($10,726.40) were 40% less expensive than for unilateral VIM DBS.

CONCLUSION

Radiosurgery of the VIM is 40% less expensive than unilateral VIM DBS in treatment of medically refractory tremor, regardless of radiosurgical modality. This finding argues for increased radiation oncology involvement in the management of medically refractory tremor patients.

Thalamic deep brain stimulation for tremor in Parkinson disease, essential tremor, and dystonia

OBJECTIVE

To report on the long-term outcomes of deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) in Parkinson disease (PD), essential tremor (ET), and dystonic tremor.

METHODS

One hundred fifty-nine patients with PD, ET, and dystonia underwent VIM DBS due to refractory tremor at the Grenoble University Hospital. The primary outcome was a change in the tremor scores at 1 year after surgery and at the latest follow-up (21 years). Secondary outcomes included the relationship between tremor score reduction over time and the active contact position. Tremor scores (Unified Parkinson's Disease Rating Scale-III, items 20 and 21; Fahn, Tolosa, Marin Tremor Rating Scale) and the coordinates of the active contacts were recorded.

RESULTS

Ninety-eight patients were included. Patients with PD and ET had sustained improvement in tremor with VIM stimulation (mean improvement, 70% and 66% at 1 year; 63% and 48% beyond 10 years, respectively; p < 0.05). There was no significant loss of stimulation benefit over time (p > 0.05). Patients with dystonia exhibited a moderate response at 1-year follow-up (41% tremor improvement, p = 0.027), which was not sustained after 5 years (30% improvement, p = 0.109). The more dorsal active contacts' coordinates in the right lead were related to a better outcome 1 year after surgery (p = 0.029). During the whole follow-up, forty-eight patients (49%) experienced minor side effects, whereas 2 (2.0%) had serious events (brain hemorrhage and infection).

CONCLUSIONS

VIM DBS is an effective long-term (beyond 10 years) treatment for tremor in PD and ET. Effects on dystonic tremor were modest and transient.

CLASSIFICATION OF EVIDENCE

This provides Class IV evidence. It is an observational study.

Next-generation probes, particles, and proteins for neural interfacing

Bidirectional interfacing with the nervous system enables neuroscience research, diagnosis, and therapy. This two-way communication allows us to monitor the state of the brain and its composite networks and cells as well as to influence them to treat disease or repair/restore sensory or motor function. To provide the most stable and effective interface, the tools of the trade must bridge the soft, ion-rich, and evolving nature of neural tissue with the largely rigid, static realm of microelectronics and medical instruments that allow for readout, analysis, and/or control. In this Review, we describe how the understanding of neural signaling and material-tissue interactions has fueled the expansion of the available tool set. New probe architectures and materials, nanoparticles, dyes, and designer genetically encoded proteins push the limits of recording and stimulation lifetime, localization, and specificity, blurring the boundary between living tissue and engineered tools. Understanding these approaches, their modality, and the role of cross-disciplinary development will support new neurotherapies and prostheses and provide neuroscientists and neurologists with unprecedented access to the brain.

Revisiting bilateral thalamotomy for tremor

MRI guided focused ultrasound surgery (MRgFUS) has been FDA approved for unilateral treatment of essential tremor (ET). Before this non-incisional lesioning method can be applied to the treatment of both hemispheres the previous experience with bilateral thalamic ablation must be addressed. In particular, the high incidence of worsening of speech and balance associated with bilateral surgical thalamotomy, a rationale for the development of deep brain stimulation. The highest incidence of these complication occurred in the early years of surgery for movement disorders, when neither MRI nor current stereotactic methods were available. The vast majority of these initial patients suffering these complications had Parkinson's disease where approximately 30% developed worsening dysarthria and ataxia after bilateral thalamotomy. Patients suffering these complications commonly had baseline abnormalities in speech and balance or worsening symptoms after a first unilateral procedure. The more contemporary experience with bilateral thalamotomy in the ET population is both much more limited in patient numbers (includes patients after Gamma Knife radiosurgery), and shows a much lower rate of these complications (approximately 5%). This more recent experience suggests that bilateral thalamotomy using closed incisionless methods such as MRgFUS has the potential to safely improve ET patients with axial or bilateral limb involvement, if done in a staged manner excluding patients with baseline dysarthria or ataxia or transient worsening of these symptoms following a unilateral procedure.

Cost-effectiveness of focused ultrasound, radiosurgery, and DBS for essential tremor

BACKGROUND

Essential tremor remains a very common yet medically refractory condition. A recent phase 3 study demonstrated that magnetic resonance-guided focused ultrasound thalamotomy significantly improved upper limb tremor. The objectives of this study were to assess this novel therapy's cost-effectiveness compared with existing procedural options.

METHODS

Literature searches of magnetic resonance-guided focused ultrasound thalamotomy, DBS, and stereotactic radiosurgery for essential tremor were performed. Pre- and postoperative tremor-related disability scores were collected from 32 studies involving 83 magnetic resonance-guided focused ultrasound thalamotomies, 615 DBSs, and 260 stereotactic radiosurgery cases. Utility, defined as quality of life and derived from percent change in functional disability, was calculated; Medicare reimbursement was employed as a proxy for societal cost. Medicare reimbursement rates are not established for magnetic resonance-guided focused ultrasound thalamotomy for essential tremor; therefore, reimbursements were estimated to be approximately equivalent to stereotactic radiosurgery to assess a cost threshold. A decision analysis model was constructed to examine the most cost-effective option for essential tremor, implementing meta-analytic techniques.

RESULTS

Magnetic resonance-guided focused ultrasound thalamotomy resulted in significantly higher utility scores compared with DBS (P < 0.001) or stereotactic radiosurgery (P < 0.001). Projected costs of magnetic resonance-guided focused ultrasound thalamotomy were significantly less than DBS (P < 0.001), but not significantly different from radiosurgery.

CONCLUSIONS

Magnetic resonance-guided focused ultrasound thalamotomy is cost-effective for tremor compared with DBS and stereotactic radiosurgery and more effective than both. Even if longer follow-up finds changes in effectiveness or costs, focused ultrasound thalamotomy will likely remain competitive with both alternatives. © 2017 International Parkinson and Movement Disorder Society.