Overview of essential tremor

A machine-learning method isolating changes in wrist kinematics that identify age-related changes in arm movement

Normal aging often results in an increase in physiological tremors and slowing of the movement of the hands, which can impair daily activities and quality of life. This study, using lightweight wearable non-invasive sensors, aimed to detect and identify age-related changes in wrist kinematics and response latency. Eighteen young (ages 18-20) and nine older (ages 49-57) adults performed two standard tasks with wearable inertial measurement units on their wrists. Frequency analysis revealed 5 kinematic variables distinguishing older from younger adults in a postural task, with best discrimination occurring in the 9-13 Hz range, agreeing with previously identified frequency range of age-related tremors, and achieving excellent classifier performance (0.86 AUROC score and 89% accuracy). In a second pronation-supination task, analysis of angular velocity in the roll axis identified a 71 ms delay in initiating arm movement in the older adults. This study demonstrates that an analysis of simple kinematic variables sampled at 100 Hz frequency with commercially available sensors is reliable, sensitive, and accurate at detecting age-related increases in physiological tremor and motor slowing. It remains to be seen if such sensitive methods may be accurate in distinguishing physiological tremors from tremors that occur in neurological diseases, such as Parkinson's Disease.

Demographics of focused ultrasound thalamotomy for essential tremor and trends in deep brain stimulation surgery after its introduction in the USA

Background

Essential tremor (ET) is a movement disorder that affects 4%-5% of adults >65 years. For patients with medically refractory ET, neurosurgical interventions such as deep brain stimulation (DBS) and unilateral MR-guided focused ultrasound thalamotomy (MRgFUS) are available. In this retrospective cohort study, we examined the demographics of patients with ET who have received MRgFUS and evaluated trends in DBS usage in the USA after the introduction of MRgFUS in 2016.

Methods

We used multiple databases to examine the demographics of patients who received DBS and MRgFUS, and trends in DBS. To assess the demographics, we queried the TriNetX database from 2003 to 2022 to identify patients diagnosed with ET and stratify them by DBS or MRgFUS treatment by using Current Procedural Terminology codes. Patient demographics were reported as frequencies and percentages. To examine the trends in DBS for ET, the yearly frequency of DBS procedures done for ET between 2012 and 2019 was extracted from the National Inpatient Sample (NIS) database, and breakpoint analysis was performed. Additionally, the yearly frequency of MRgFUS procedures for ET was obtained from Insightec Exlabate.

Results

Most of the patients (88.69%) in the cohort extracted from TriNetX database self-identified as white, followed by black or African American (2.40%) and Asian (0.52%). A higher percentage of black patients received MRgFUS treatment than DBS (4.10% vs 1.88%). According to the NIS database, from 2012 to 2020, 13 525 patients received DBS for ET.

Conclusion

This study provides an overview of the characteristics of patients who undergo DBS or MRgFUS. We found notable differences in sex and race among patients who underwent each treatment type. Additionally, until at least the beginning of 2020, the number of DBS procedures for ET was not negatively affected after the introduction of MRgFUS.

Treatment patterns in essential tremor: Real-world evidence from a United Kingdom and France primary care database

BACKGROUND AND PURPOSE

Essential tremor (ET) is one of the most common neurological disorders, but information on treatment pattern is still scant. The aim of this study was to describe the demographic and clinical characteristics, treatment patterns, and determinants of drug use in patients with newly diagnosed ET in France and the United Kingdom.

METHODS

Incident cases of ET diagnosed between January 1, 2015 and December 31, 2018 with 2 years of follow-up were identified by using The Health Improvement Network (THIN®) general practice database. During the follow-up, we assessed the daily prevalence of use and potential switches from first-line to second-line treatment or other lines of treatment. Logistic regression models were conducted to assess the effect of demographic and clinical characteristics on the likelihood of receiving ET treatment.

RESULTS

A total of 2957 and 3249 patients were selected in the United Kingdom and France, respectively. Among ET patients, drug use increased from 12 months to 1 month prior the date of index diagnosis (ID). After ID, nearly 40% of patients received at least one ET treatment, but during follow-up drug use decreased and at the end of the follow-up approximately 20% of patients were still on treatment. Among treated patients, ≤10% maintained the same treatment throughout the entire follow-up, nearly 20% switched, and 40%-75% interrupted any treatment. Results from the multivariate analysis revealed that, both in France and the United Kingdom, patients receiving multiple concomitant therapies and affected by psychiatric conditions were more likely to receive an ET medication.

CONCLUSION

This study shows that ET is an undertreated disease with a lower-than-expected number of patients receiving and maintaining pharmacological treatment. Misclassification of ET diagnosis should be acknowledged; thus, results require cautious interpretation.

Stem cell-derived brain organoids for controlled studies of transcranial neuromodulation

Transcranial neuromodulation methods have the potential to diagnose and treat brain disorders at their neural source in a personalized manner. However, it has been difficult to investigate the direct effects of transcranial neuromodulation on neurons in human brain tissue. Here, we show that human brain organoids provide a detailed and artifact-free window into neuromodulation-evoked electrophysiological effects. We derived human cortical organoids from induced pluripotent stem cells and implanted 32-channel electrode arrays. Each organoid was positioned in the center of the human skull and subjected to low-intensity transcranial focused ultrasound. We found that ultrasonic stimuli modulated network activity in the gamma and delta ranges of the frequency spectrum. The effects on the neural networks were a function of the ultrasound stimulation frequency. High gamma activity remained elevated for at least 20 minutes following stimulation offset. This approach is expected to provide controlled studies of the effects of ultrasound and other transcranial neuromodulation modalities on human brain tissue.

Essential Tremor - Deep Brain Stimulation vs. Focused Ultrasound

INTRODUCTION

Essential Tremor (ET) is one of the most common tremor syndromes typically presented as action tremor, affecting mainly the upper limbs. In at least 30-50% of patients, tremor interferes with quality of life, does not respond to first-line therapies and/or intolerable adverse effects may occur. Therefore, surgery may be considered.

AREAS COVERED

In this review, the authors discuss and compare unilateral ventral intermedius nucleus deep brain stimulation (VIM DBS) and bilateral DBS with Magnetic Resonance-guided Focused Ultrasound (MRgFUS) thalamotomy, which comprises focused acoustic energy generating ablation under real-time MRI guidance. Discussion includes their impact on tremor reduction and their potential complications. Finally, the authors provide their expert opinion.

EXPERT OPINION

DBS is adjustable, potentially reversible and allows bilateral treatments; however, it is invasive requires hardware implantation, and has higher surgical risks. Instead, MRgFUS is less invasive, less expensive, and requires no hardware maintenance. Beyond these technical differences, the decision should also involve the patient, family, and caregivers.

Sustained modulation of primate deep brain circuits with focused ultrasonic waves

BACKGROUND

Transcranial focused ultrasound has the potential to noninvasively modulate deep brain circuits and impart sustained, neuroplastic effects.

OBJECTIVE

Bring the approach closer to translations by demonstrating sustained modulation of deep brain circuits and choice behavior in task-performing non-human primates.

METHODS

Low-intensity transcranial ultrasound of 30 s in duration was delivered in a controlled manner into deep brain targets (left or right lateral geniculate nucleus; LGN) of non-human primates while the subjects decided whether a left or a right visual target appeared first. While the animals performed the task, we recorded intracranial EEG from occipital screws. The ultrasound was delivered into the deep brain targets daily for a period of more than 6 months.

RESULTS

The brief stimulation induced effects on choice behavior that persisted up to 15 minutes and were specific to the sonicated target. Stimulation of the left/right LGN increased the proportion of rightward/leftward choices. These effects were accompanied by an increase in gamma activity over visual cortex. The contralateral effect on choice behavior and the increase in gamma, compared to sham stimulation, suggest that the stimulation excited the target neural circuits. There were no detrimental effects on the animals' discrimination performance over the months-long course of the stimulation.

CONCLUSION

This study demonstrates that brief, 30-s ultrasonic stimulation induces neuroplastic effects specifically in the target deep brain circuits, and that the stimulation can be applied daily without detrimental effects. These findings encourage repeated applications of transcranial ultrasound to malfunctioning deep brain circuits in humans with the goal of providing a durable therapeutic reset.

Transcranial low-intensity ultrasound stimulation for treating central nervous system disorders: A promising therapeutic application

Transcranial ultrasound stimulation is a neurostimulation technique that has gradually attracted the attention of researchers, especially as a potential therapy for neurological disorders, because of its high spatial resolution, its good penetration depth, and its non-invasiveness. Ultrasound can be categorized as high-intensity and low-intensity based on the intensity of its acoustic wave. High-intensity ultrasound can be used for thermal ablation by taking advantage of its high-energy characteristics. Low-intensity ultrasound, which produces low energy, can be used as a means to regulate the nervous system. The present review describes the current status of research on low-intensity transcranial ultrasound stimulation (LITUS) in the treatment of neurological disorders, such as epilepsy, essential tremor, depression, Parkinson's disease (PD), and Alzheimer's disease (AD). This review summarizes preclinical and clinical studies using LITUS to treat the aforementioned neurological disorders and discusses their underlying mechanisms.

Remus: System for remote deep brain interventions

Transcranial-focused ultrasound brings personalized medicine to the human brain. Ultrasound can modulate neural activity or release drugs in specific neural circuits but this personalized approach requires a system that delivers ultrasound into specified targets flexibly and on command. We developed a remote ultrasound system (Remus) that programmatically targets deep brain regions with high spatiotemporal precision and in a multi-focal manner. We validated these functions by modulating two deep brain nuclei—the left and right lateral geniculate nucleus—in a task-performing nonhuman primate. This flexible system will enable researchers and clinicians to diagnose and treat specific deep brain circuits in a noninvasive yet targeted manner, thus embodying the promise of personalized treatments of brain disorders.

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Remus delivers ultrasound into deep brain targets of task-performing subjects

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Targets are specified programmatically and at high spatial and temporal precision

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Brief pulses delivered to deep brain regions modulate visual choice behavior

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The system enables reproducible daily applications and continuous safety monitoring

Multiple Comorbidities, Psychiatric Disorders, Healthcare Resource Utilization and Costs Among Adults with Essential Tremor: A Retrospective Observational Study in a Large US Commercially Insured and Medicare Advantage Population

Background: Essential tremor (ET), the most common movement disorder, often impairs patients' ability to perform activities of daily living, mental health, and quality of life. Objectives: To assess comorbidities, psychiatric disorders, healthcare resource utilization (HCRU), and costs among patients with ET compared with patients without ET. Methods: This retrospective observational study was conducted using a large US administrative claims database. Patients with ET were identified during the study period (1/1/2017-12/31/2019). The earliest claim date with ET diagnosis was identified as the index date. An index date was assigned randomly for each non-ET patient. Patients had to be at least 22 years old and be enrolled in the health plan for at least 6 months before and at least 12 months after the index date. Patients with and those without ET were matched 1:1 on age, gender, payer type, and first 3 digits of their ZIP code. Comorbidities were assessed using data within 6 months prior to the index date. Psychiatric disorders, HCRU, and costs were examined using data within 12 months after the index date. Results: The mean (SD) age of ET patients (n = 5286) was 70.8 (11.8) years, 49.1% were female, and 82.9% were Medicare Advantage members. In the 12 months following the index date, 26.0% of patients had no insurance claims for ET-related pharmacotherapy or invasive therapies. Patients with ET had a higher number of comorbidities than non-ET patients (5.3 [3.2] vs 4.0 [3.3]); a higher prevalence of psychiatric disorders (depression: 25.6% vs 15.3%; adjusted odds ratio (AOR) [95% CI], 1.56 [1.41-1.73]; anxiety: 27.7% vs 15.5%, AOR: 1.78 [1.61-1.96]); and higher total healthcare costs: $17 560 [$39 972] vs $13 237 [$27 098], adjusted cost ratio [95% CI]: 1.11 [1.06-1.16]; all P<.0001. Discussion: Highly prevalent multiple comorbidities and psychiatric disorders should be considered in the context of clinical decision-making to optimize ET management. Conclusions: This study represents the largest observational study to report ET disease and economic burdens in a real-world setting. The data demonstrate increased comorbidity, mental health, and healthcare cost burdens among ET patients compared with matched non-ET patients. These findings underscore the need for innovative care for this complex population.

Is inferior olive central to the pathophysiology of essential tremor? No

Essential tremor (ET) represents one of the commonest movement disorder worldwide and is the most common tremor disorder. ET manifests with various combinations of motor and nonmotor symptoms. The clinical hallmark is a kinetic tremor of upper limbs. Historically, the pathogenesis of ET has been based on the hypothesis of an overactivity of the inferior olive (inferior olive hypothesis: IOH) where the inferior olive would act as the central pace-maker of ET, resulting in impaired electrophysiological discharges of the olivo-cerebellar tract. The absence of structural alterations in post-mortem studies of the inferior olive is a striking argument against the IOH. Furthermore, neuroimaging studies point towards the implication of the cerebello-thalamo-cerebral pathway rather than the IO, and the harmaline model which has been considered as an animal model of ET presents important weaknesses. By contrast, a series of experiments by Louis et al. have provided convincing evidence of impaired wiring of the Purkinje cell microcircuitry and progressive neurodegeneration of the cerebellar cortex. The Purkinje neuron appears as the primary culprit (Purkinjopathy). The cerebellar cortex hypothesis (CCH) has solid neuropathological signatures, unlike the purely physiological IOH. Rather than a dysregulatory electrophysiological disorder suggested by IOH, ET is a clinical-pathological entity similar to late onset neurodegenerative disorders such as Parkinson's disease or Alzheimer's disease. The CCH emphasizes the need to develop novel therapeutic strategies in order to maintain or promote the cerebellar reserve. The modern reconceptualization of ET in a genuine cerebellar disorder is cleaning the IOH to the light of histopathological studies. ET falls in the large basket of the neurodegenerative diseases and we have entered into a novel formulation of the disease pathogenesis with direct impacts on future therapies.

Non-invasive electrical stimulation of peripheral nerves for the management of tremor

Pathological tremor in patients with essential tremor and Parkinsons disease is typically treated using medication or neurosurgical interventions. There is a widely recognized need for new treatments that avoid the side effects of current medications and do not carry the risks of surgical interventions. Building on decades of research and engineering development, non-invasive electrical stimulation of peripheral nerves has emerged as a safe and effective strategy for reducing pathologic tremor in essential tremor. This review surveys the peripheral electrical stimulation (PES) literature and summarizes effectiveness, safety, clinical translatability, and hypothesized tremor-reduction mechanisms of various PES approaches. The review also proposes guidelines for assessing tremor in the context of evaluating new therapies that combine the strengths of clinician assessments, patient evaluations, and novel motion sensing technology. The review concludes with a summary of future directions for PES, including expanding clinical access for patients with Parkinson's disease and leveraging large, at-home datasets to learn more about tremor physiology and treatment effect that will better characterize the state of tremor management and accelerate discovery of new therapies. Growing evidence suggests that non-invasive electrical stimulation of afferent neural pathways provides a viable new option for management of pathological tremor, with one specific PES therapy cleared for prescription and home use, suggesting that PES be considered along with medication and neurosurgical interventions for treatment of tremor. This article is part of the Special Issue "Tremor" edited by Daniel D. Truong, Mark Hallett, and Aasef Shaikh.

Balance and cognitive impairments are prevalent and correlated with age in presurgical patients with essential tremor

INTRODUCTION

Essential tremor (ET) was long considered a monosymptomatic disorder, but this view has given way to a more comprehensive clinical picture that involves consideration of non-tremor symptoms (e.g., balance impairment, cognitive impairment). Recently, the novel designation of "ET-plus" was proposed to reclassify ET patients who demonstrate these non-tremor clinical features, but the prevalence of ET-plus remains poorly defined. The primary aim of our study was to estimate the prevalence of ET-plus among presurgical patients with ET by applying this reclassification scheme.

METHODS

We performed a retrospective review of patients with ET being considered for deep brain stimulation or focused ultrasound thalamotomy. Patient demographics and data from their clinical workups were collected. As part of their clinical workup, patients were screened for preexisting balance and cognitive impairment. Patients with ET were designated as ET-plus if they had balance impairment, cognitive impairment, or tremor at rest. We performed a series of Pearson correlations to examine how individual clinical and demographic variables were related.

RESULTS

We identified 92 patients who met the study criteria. Our results indicate that 87% of the presurgical patients in our cohort met the criteria for reclassification as ET-plus. In addition, we observed robust correlations between patient age and balance impairment, cognitive impairment, history of falls, family history of tremor, and ET-plus reclassification.

CONCLUSION

We propose that balance and gait impairment should be assessed preoperatively alongside neuropsychological evaluation to improve the counseling and treatment of patients with ET-plus.

A Non-Invasive IR Sensor Technique to Differentiate Parkinson's Disease from Other Neurological Disorders Using Autonomic Dysfunction as Diagnostic Criterion

Early diagnosis of Parkinson's disease (PD) plays a critical role in effective disease management and delayed disease progression. This study reports a technique that could diagnose and differentiate PD from essential tremor (ET) in its earlier stage using a non-motor phenotype. Autonomic dysfunction, an early symptom in PD patients, is caused by α-synuclein pathogenesis in the central nervous system and can be diagnosed using skin vasomotor response to cold stimuli. In this study, the investigations were performed using data collected from 20 PD, 20 ET and 20 healthy subjects. Infrared thermography was used for the cold stress test to observe subjects' hand temperature before and after cold stimuli. The results show that the recovery rate of hand temperature was significantly different between the groups. The data obtained in the cold stress test were verified using Pearson's cross-correlation technique, which showed that few disease parameters like medication and motor rating score had an impact on the recovery rate of hand temperature in PD subjects. The characteristics of the three groups were compared and classified using the k-means clustering algorithm. The sensitivity and specificity of these techniques were analyzed using an Receiver Operating Characteristic (ROC) curve analyzer. These results show that this non-invasive technique can be used as an effective tool in the diagnosis and differentiation of PD in its early stage.

Towards Essential Hand Tremor Suppression via Pneumatic Artificial Muscles

Essential tremor (ET) is one of the most common movement disorders and can occur unexpectedly and develop indefinitely to any population unit. According to the recorded statistics of people suffering from ET, the disorder affects 5% of people worldwide, thus creating an ever-increasing need to investigate ways for its suppression and treatment. In this article, we investigate the capability of Pneumatic Artificial Muscles (PAMs) to reduce or even suppress ET leading to the relief of the sufferers. In our work, we designed and constructed two iterations of a glovelike setup and attempted to explore the possibility of suppressing ET on different parts of the hand by exerting force on the index finger and metacarpal region. For both glove iterations, we established an experimental protocol based on the adjustment of a force controller. Finally, we evaluated exhaustively the performance of our setup under multiple motion scenarios with the participation of an ET-diagnosed volunteer.

Predictors of thermal response and lesion size in patients undergoing magnetic resonance-guided focused ultrasound thalamotomy

Magnetic resonance-guided focused ultrasound (MRgFUS) is being increasingly utilized in the treatment of movement disorders such as essential tremor (ET) and Parkinson's disease (PD). Whilst skull density ratio (SDR) has previously been correlated with achieving lesional temperature rises, other patient factors such as brain and cerebrospinal fluid (CSF) volume have not previously been investigated. We aimed to investigate the effect of brain and CSF volumes on lesional temperature rises, as well as the effect of brain and CSF volumes and SDR on post-treatment lesion sizes. Fifty-four consecutive patients were studied with patient and treatment-related variables collected along with post-treatment lesion sizes. Linear regression analysis identified that SDR alone was associated with lesional temperatures. Both SDR and brain atrophy were associated with post-treatment lesion sizes on linear regression analysis. On multiple linear regression analysis SDR was significantly associated with post-treatment lesion size, and the association between brain atrophy and lesion sizes approached significance, a finding that warrants further investigation.

Voxel-Based Morphometry of Cerebellar Lobules in Essential Tremor

BACKGROUND

The extent of neurodegeneration underlying essential tremor (ET) remains a matter of debate. Despite various extents of cerebellar atrophy on structural magnetic resonance imaging (MRI), previous studies have shown substantial heterogeneity and included a limited number of patients. Novel automated pipelines allow detailed segmentation of cerebellar lobules based on structural MRI.

OBJECTIVE

To compare the volumes of cerebellar lobules in ET patients with those in healthy controls (HCs) using an automated segmentation pipeline.

METHODS

Structural MRI scans of ET patients eligible for deep brain stimulation (n = 55) and of age-matched and gender-matched HCs (n = 55, from the IXI database) were segmented using the automated CEREbellum Segmentation pipeline. Lobule-specific volume differences between the ET and HC groups were evaluated using a general linear model corrected for multiple tests.

RESULTS

Total brain tissue volumes did not differ between the ET and HC groups. ET patients demonstrated reduced volumes of lobules I-II, left Crus II, left VIIB, and an increased volume of right X when compared with the HC group.

CONCLUSION

A large cohort of ET patients demonstrated subtle signs of decreased cerebellar lobule volumes. These findings oppose the hypothesis of localized atrophy in cerebellar motor areas in ET, but not the possibility of cerebellar pathophysiology in ET. Prospective investigations using alternative neuroimaging modalities may further elucidate the pathophysiology of ET and provide insights into diagnostic and therapeutic approaches.

Tapping the Potential of Multimodal Non-invasive Brain Stimulation to Elucidate the Pathophysiology of Movement Disorders

This mini-review provides a detailed outline of studies that have used multimodal approaches in non-invasive brain stimulation to investigate the pathophysiology of the three common movement disorders, namely, essential tremor, Parkinson’s disease, and dystonia. Using specific search terms and filters in the PubMed^® database, we finally shortlisted 27 studies in total that were relevant to this review. While two-thirds (Brittain et al., 2013) of these studies were performed on Parkinson’s disease patients, we could find only three studies that were conducted in patients with essential tremor. We clearly show that although multimodal non-invasive brain stimulation holds immense potential in unraveling the physiological mechanisms that are disrupted in movement disorders, the technical challenges and pitfalls of combining these methods may hinder their widespread application by movement disorder specialists. A multidisciplinary team with clinical and technical expertise may be crucial in reaping the fullest benefits from such novel multimodal approaches.

A Study on the Essential and Parkinson’s Arm Tremor Classification

In this article, the challenge of discriminating between essential and Parkinson’s tremor is addressed. Although a variety of methods have been proposed for diagnosing the severity of these highly occurring tremor types, their rapid and effective identification, especially in their early stages, proves particularly difficult and complicated due to their wide range of causes and similarity of symptoms. To this goal, a clinical analysis was performed, where a number of volunteers including essential and Parkinson’s tremor-diagnosed patients underwent a series of pre-defined motion patterns, during which a wearable sensing setup was used to measure their lower arm tremor characteristics from multiple selected points. Extracted features from the acquired accelerometer signals were used to train classification algorithms, including decision trees, discriminant analysis, support vector machine (SVM), K-nearest neighbor (KNN) and ensemble learning algorithms, for providing a comparative study and evaluating the potential of utilizing machine learning to accurately discriminate among different tremor types. Overall, SVM related classifiers proved to be the most successful in terms of classifying between Parkinson’s, essential and no tremor diagnosed with percentages reaching up to 100% for a single accelerometer measurement at the metacarpal area. In general and in motion while holding an object position, Coarse Gaussian SVM classifier reached 82.62% accuracy.

Comparison between deep brain stimulation and magnetic resonance-guided focused ultrasound in the treatment of essential tremor: a systematic review and pooled analysis of functional outcomes

The current gold standard surgical treatment for medication-resistant essential tremor (ET) is deep brain stimulation (DBS). However, recent advances in technologies have led to the development of incisionless techniques, such as magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy. The authors perform a systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement to compare unilateral MRgFUS thalamotomy to unilateral and bilateral DBS in the treatment of ET in terms of tremor severity and quality of life improvement. PubMed, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials and SCOPUS databases were searched. 45 eligible articles, published between 1990 and 2019, were retrieved. 1202 patients were treated with DBS and 477 were treated with MRgFUS thalamotomy. Postoperative tremor improvement was greater following DBS than MRgFUS thalamotomy (p<0.001). A subgroup analysis was carried out stratifying by treatment laterality: bilateral DBS was significantly superior to both MRgFUS and unilateral DBS (p<0.001), but no significant difference was recorded between MRgFUS and unilateral DBS (p<0.198). Postoperative quality of life improvement was significantly greater following MRgFUS thalamotomy than DBS (p<0.001). Complications were differently distributed among the two groups (p<0.001). Persistent complications were significantly more common in the MRgFUS group (p=0.042). While bilateral DBS proves superior to unilateral MRgFUS thalamotomy in the treatment of ET, a subgroup analysis suggests that treatment laterality is the most significant determinant of tremor improvement, thus highlighting the importance of future investigations on bilateral staged MRgFUS thalamotomy.

Frequency-dependent spike-pattern changes in motor cortex during thalamic deep brain stimulation

The cerebellar-receiving area of the motor thalamus is the primary anatomical target for treating essential tremor with deep brain stimulation (DBS). Although neuroimaging studies have shown that higher stimulation frequencies in this target correlate with increased cortical metabolic activity, less is known about the cellular-level functional changes that occur in the primary motor cortex (M1) with thalamic stimulation and how these changes depend on the frequency of DBS. In this study, we used a preclinical animal model of DBS to collect single-unit spike recordings in M1 before, during, and after DBS targeting the cerebellar-receiving area of the motor thalamus (VPLo, nucleus ventralis posterior lateralis pars oralis). The effects of VPLo-DBS on M1 spike rates, interspike interval entropy, and peristimulus phase-locking were compared across stimulus pulse train frequencies ranging from 10 to 130 Hz. Although VPLo-DBS modulated the spike rates of 20-50% of individual M1 cells in a frequency-dependent manner, the population-level average spike rate only weakly depended on stimulation frequency. In contrast, the population-level entropy measure showed a pronounced decrease with high-frequency stimulation, caused by a subpopulation of cells that exhibited strong phase-locking and general spike-pattern regularization. Contrarily, low-frequency stimulation induced an entropy increase (spike-pattern disordering) in a relatively large portion of the recorded population, which diminished with higher stimulation frequencies. These results also suggest that changes in phase-locking and spike-pattern entropy are not necessarily equivalent pattern phenomena, but rather that they should both be weighed when quantifying stimulation-induced spike-pattern changes.NEW & NOTEWORTHY The network mechanisms of thalamic deep brain stimulation (DBS) are not well understood at the cellular level. This study investigated the neuronal firing rate and pattern changes in the motor cortex resulting from stimulation of the cerebellar-receiving area of the motor thalamus. We showed that there is a nonintuitive relationship between general entropy-based spike-pattern measures and phase-locked regularization to DBS.

Telemedicine for Hyperkinetic Movement Disorders

Telemedicine is the use of electronic communication technology to facilitate healthcare between distant providers and patients. In addition to synchronous video conferencing, asynchronous video transfer has been used to support care for neurology patients.

There is a growing literature on using telemedicine in movement disorders, with the most common focus on Parkinson’s disease. There is accumulating evidence for videoconferencing to diagnose and treat patients with hyperkinetic movement disorders and to support providers in remote underserviced areas. Cognitive testing has been shown to be feasible remotely. Genetic counseling and other counseling-based therapeutic interventions have also successfully performed in hyperkinetic movement disorders.

We use a problem-based approach to review the current evidence for the use of telemedicine in various hyperkinetic movement disorders. This Viewpoint attempts to identify possible telemedicine solutions as well as discussing unmet needs and future directions.

Excitatory Amino Acid Transporters in Physiology and Disorders of the Central Nervous System

Excitatory amino acid transporters (EAATs) encompass a class of five transporters with distinct expression in neurons and glia of the central nervous system (CNS). EAATs are mainly recognized for their role in uptake of the amino acid glutamate, the major excitatory neurotransmitter. EAATs-mediated clearance of glutamate released by neurons is vital to maintain proper glutamatergic signalling and to prevent toxic accumulation of this amino acid in the extracellular space. In addition, some EAATs also act as chloride channels or mediate the uptake of cysteine, required to produce the reactive oxygen speciesscavenger glutathione. Given their central role in glutamate homeostasis in the brain, as well as their additional activities, it comes as no surprise that EAAT dysfunctions have been implicated in numerous acute or chronic diseases of the CNS, including ischemic stroke and epilepsy, cerebellar ataxias, amyotrophic lateral sclerosis, Alzheimer’s disease and Huntington’s disease. Here we review the studies in cellular and animal models, as well as in humans that highlight the roles of EAATs in the pathogenesis of these devastating disorders. We also discuss the mechanisms regulating EAATs expression and intracellular trafficking and new exciting possibilities to modulate EAATs and to provide neuroprotection in course of pathologies affecting the CNS.

A Phase 2, Randomized, Double-Blind, Placebo-Controlled Trial of CX-8998, a Selective Modulator of the T-Type Calcium Channel in Inadequately Treated Moderate to Severe Essential Tremor: T-CALM Study Design and Methodology for Efficacy Endpoint and Digital Biomarker Selection

Background: Essential tremor (ET) is a common, progressive neurological syndrome with bilateral upper-limb dysfunction of at least 3-year duration, with or without tremor in other body locations. This disorder has a negative impact on daily function and quality of life. A single oral therapy has been approved by FDA for ET. Off-label pharmacotherapies have inadequate efficacy and poor tolerability with high rates of patient dissatisfaction and discontinuation. Safe and efficacious pharmacotherapies are urgently needed to decrease tremor and improve daily living. T-CALM (Tremor-CAv3 modulation) protocol is designed to assess safety and efficacy of CX-8998, a selective modulator of the T-type calcium channel, for ET therapy.

Methods/Design: T-CALM is a phase 2, proof of concept, randomized, double-blind, placebo-controlled trial. Titrated doses of CX-8998 to 10 mg BID or placebo will be administered for 28 days to moderate to severe ET patients who are inadequately treated with existing therapies. The primary endpoint will be change from baseline to day 28 of The Essential Tremor Rating Assessment Performance Subscale (TETRAS-PS). Secondary efficacy endpoints for clinician and patient perception of daily function will include TETRAS Activity of Daily Living (ADL), Quality of Life in Essential Tremor Questionnaire (QUEST), Clinical Global Impression-Improvement (CGI-I), Patient Global Impression of Change (PGIC), and Goal Attainment Scale (GAS). Kinesia One, Kinesia 360, and iMotor will biometrically evaluate motor function and tremor amplitude. Safety will be assessed by adverse events, physical and neurological exams and laboratory tests. Sample size of 43 patients per group is estimated to have 90% power to detect a 5.5-point difference between CX-8998 and placebo for TETRAS-PS. Efficacy analyses will be performed with covariance (ANCOVA) and 2-sided test at 0.05 significance level.

Discussion: T-CALM has a unique design with physician rating scales, patient-focused questionnaires and scales and objective motor measurements to assess clinically meaningful and congruent efficacy. Patient perception of ET debilitation and therapy with CX-8998 will be key findings. Overall goal of T-CALM is generation of safety and efficacy data to support a go, no-go decision to further develop CX-8998 for ET. Design of T-CALM may guide future clinical studies of ET pharmacotherapies.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT03101241

Impact of skull density ratio on efficacy and safety of magnetic resonance-guided focused ultrasound treatment of essential tremor

OBJECTIVE

Skull density ratio (SDR) assesses the transparency of the skull to ultrasound. Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy in essential tremor (ET) patients with a lower SDR may be less effective, and the risk for complications may be increased. To address these questions, the authors analyzed clinical outcomes of MRgFUS thalamotomy based on SDRs.

METHODS

In 189 patients, 3 outcomes were correlated with SDRs. Efficacy was based on improvement in Clinical Rating Scale for Tremor (CRST) scores 1 year after MRgFUS. Procedural efficiency was determined by the ease of achieving a peak voxel temperature of 54°C. Safety was based on the rate of the most severe procedure-related adverse event. SDRs were categorized at thresholds of 0.45 and 0.40, selected based on published criteria.

RESULTS

Of 189 patients, 53 (28%) had an SDR < 0.45 and 20 (11%) had an SDR < 0.40. There was no significant difference in improvement in CRST scores between those with an SDR ≥ 0.45 (58% ± 24%), 0.40 ≤ SDR < 0.45 (i.e., SDR ≥ 0.40 but < 0.45) (63% ± 27%), and SDR < 0.40 (49% ± 28%; p = 0.0744). Target temperature was achieved more often in those with an SDR ≥ 0.45 (p < 0.001). Rates of adverse events were lower in the groups with an SDR < 0.45 (p = 0.013), with no severe adverse events in these groups.

CONCLUSIONS

MRgFUS treatment of ET can be effectively and safely performed in patients with an SDR < 0.45 and an SDR < 0.40, although the procedure is more efficient when SDR ≥ 0.45.

Tensometric tremorography in high-precision medical diagnostic systems

BACKGROUND

The objective of the study was to develop a system for the precision diagnostics of pathologies of motor brain regions based on tensometric measurement and to explore its diagnostic capabilities.

MATERIALS AND METHODS

Tremor is a syndrome that indicates the abnormal state of the central nervous system, primarily in the motor brain regions. Analysis of tremor parameters provides significant information about the changes in the body motion control and can be used as an objective index of the central nervous system state. Existing methods are aimed at the analysis of visible tremor based on the use of different sensors. We suggest an alternative approach based on the use of a tensometric system performing tremor measurements when the tremor appears on the background of voluntary isometric efforts. The key advantage of our approach is that it allows to determine the tremor before its visible manifestation. In the article, we describe hardware implementation of our tremor analysis system.

RESULTS

In the article, we represent the new methodology and the original equipment based on the control of isometric effort. Isometric effort formed by a patient is controlled with the use of a feedback system on the patient's monitor. We evaluated the performance of our equipment with more than 400 healthy volunteers and patients with various pathologies of the central nervous system motor regions, and the results of the investigations, allowing to identify tremor parameters typical for parkinsonism, are represented in our article.

CONCLUSION

Testing of the system confirmed its high diagnostic validity and reliability, high sensitivity, simplicity and high speed of information processing. The approach based on tensometric measurements is very promising for the diagnostics of Parkinson disease and dysfunctions of a central nervous system.

A method for characterizing essential tremor from the shoulder to the wrist

BACKGROUND

Despite the pervasive and devastating effect of Essential Tremor (ET), the distribution of ET throughout the upper limb is unknown. We developed a method for characterizing the distribution of ET and performed a preliminary characterization in a small number of subjects with ET.

METHODS

Using orientation sensors and inverse kinematics, we measured tremor in each of the seven major degrees of freedom (DOF) from the shoulder to the wrist while ten patients with mild ET assumed 16 different postures. We described the tremor in each DOF in terms of power spectral density measures and investigated how tremor varied between DOF, postures, gravitational torques, and repetitions.

FINDINGS

Our method successfully resulted in tremor measures in each DOF, allowing one to compare tremor between DOF and determine the distribution of tremor throughout the upper limb, including how the distribution changes with posture. In our small number of subjects, we found that the amount of power in the frequency band associated with ET (4-12Hz) was lowest in the shoulder and greatest in the wrist. Similarly, the existence and amplitude of peaks in this band increased from proximal to distal. Although the amount of tremor differed significantly between postures, we did not find any clear patterns with changes in posture or gravitational torque.

INTERPRETATION

This method can be used to characterize the distribution of tremor throughout the upper limb. Our preliminary characterization suggests that the amount of tremor increases in a proximal-distal manner.

Botulinum Toxin Type A Injections as Monotherapy for Upper Limb Essential Tremor Using Kinematics

Background:There is a significant need for a targeted therapy for essential tremor (ET), as medications have not been developed specifically for ET, and the ones prescribed are often not well-tolerated, so that many patients remain untreated. Recent work has shown that, unlike previous experience, kinematically guided individualized botulinum toxin type A (BoNT-A) injections provide benefit along with minimal weakness. Ours is the first long-term (96-week) safety and efficacy study of BoNT-A as monotherapy for ET using kinematically driven injection parameters.Methods:Ten ET patients were administered six serial BoNT-A treatments every 16 weeks and were assessed at 6 weeks following treatment. During each study visit, the Fahn–Tolosa–Marin (FTM) scale, the Unified Parkinson’s Disease Rating Scale, and the Quality of Life for Essential Tremor Questionnaire (QUEST) were administered along with kinematic assessment of the treated limb. Participants performed scripted tasks with motion sensors placed over each arm joint. Dosing patterns were determined using the movement disorder neurologist’s interpretation of muscles contributing to the kinematically analyzed upper limb tremor biomechanics.Results:There was a 33.8% (p<0.05) functional improvement (FTM part C) and a 39.8% (p<0.0005) improvement in QUEST score at week 96 compared to pretreatment scores at week 0. Although there was a 44.6% (p<0.0005) non-dose-dependent reduction in maximal grip strength, only 2 participants complained of mild weakness. Following the fourth serial treatment, mean action tremor score was reduced by 62.9% (p=0.001) in the treated and by 44.4% (p=0.03) in the untreated arm at week 96 compared to week 48.Conclusions:Individualized BoNT-A dosing patterns to each individual’s tremor biomechanics provided an effective monotherapy for ET as function improved without functionally limiting muscle weakness.

Effects of chronic alcohol consumption on long-term outcomes of thalamic deep brain stimulation for essential tremor

The prevalence of essential tremor (ET) is about 4% above 40years of age. Chronic alcohol consumption is present in around 20% of patients with ET. Our objective was to identify whether chronic alcohol consumption was associated with a negative effect on tremor outcome after thalamic deep brain stimulation (DBS) in ET patients. We conducted a retrospective chart review, from January 2005 to December 2012, from which 23 patients who had ventral intermediate nucleus (Vim)-DBS surgery for ET were identified. Seven patients had a positive history of chronic alcohol consumption. We defined as chronic alcohol users those patients with a habit of drinking alcohol every day in order to suppress tremor. In the overall group of 23 patients, there was a reduction in the median tremor score from 8 pre-operatively, to 1 post-operatively (p<0.0001). The alcohol consumers group experienced a reduction in the median tremor score from 6 pre-operatively to 0 post-operatively (p=0.03). The non-alcohol consumers group had a reduction in the median tremor score from 8 pre-operatively to 1.7 post-operatively (p<0.0001). Both groups of patients experienced significant benefit from thalamic DBS. A larger study may reveal statistically significant differences between subgroups.

Slowed saccades and increased square wave jerks in essential tremor

BACKGROUND

Eye movements in essential tremor (ET) are poorly described and may present useful information on the underlying pathophysiology of the disorder.

METHODS

Sixty patients with ET, including 15 de novo untreated patients, and 60 age-matched controls constitute the study population. A video-based eye tracker was used to assess binocular eye position. Oculomotor function was assessed while subjects followed random horizontally and vertically step-displaced targets.

RESULTS

For all reflexive saccades, latencies were increased in ET subjects by a mean of 16.3% (p<0.01). Saccades showed reduced peak velocities with a lengthy, wavering velocity plateau, followed by slowed decelerations. For larger 30°+ saccades, peak velocities were decreased by a mean of 25.2% (p<0.01) and durations increased by 31.8% (p<0.01). The frequency of square wave jerks (SWJs) in patients was more than triple that of controls (p<0.0001). Despite frequent interruptions by SWJs, fixations were otherwise stable and indistinguishable from controls (root mean square [RMS] velocity, p = 0.324). The abnormal eye movement parameters were independent of disease duration, tremor severity, and medication therapy.

DISCUSSION

In contrast to normally swift onset and efficient acceleration/deceleration movements, saccades in ET are characterized by abnormally prolonged latencies and slowed velocity profiles. Although ET subjects maintain highly stable fixations, they are interrupted by increased numbers of SWJs. This study reveals novel oculomotor deficits in ET, which are distinct from the eye movement dysfunction of other movement disorders, supporting a role for eye tracking to assist in the differential diagnoses of not only atypical, but also more common movement disorders.

Chiropractic management of essential tremor and migraine: a case report

OBJECTIVE

The purpose of this case report is to describe the chiropractic management of a 39-year-old woman with essential tremors and migraine headaches.

CLINICAL FEATURES

A 39-year-old woman presented with essential tremors and migraine headaches, which occurred 2 to 3 times per week. The essential tremor was diagnosed in 2000, and migraine headaches with aura were diagnosed when she was 10. Both diagnoses were made by her general medical practitioner. Previous treatments for migraine included propranolol, isometheptene, dichloralphenazone, acetaminophen, sumatriptan, and over-the-counter pain relievers.

INTERVENTION AND OUTCOME

The patient received high-velocity, low-amplitude chiropractic spinal manipulation to her upper cervical spine using the Blair Upper Cervical chiropractic technique protocol. There was improvement in her tremors and migraine headaches following her initial chiropractic treatment, with a sustained improvement after 4 months of care.

CONCLUSION

This case study demonstrated improvement in a woman with essential tremors and migraine headaches. This suggests the need for more research to examine how upper cervical specific chiropractic care may help mitigate tremors and migraine headaches.

Essential tremor, the cerebellum, and motor timing: towards integrating them into one complex entity

Essential tremor (ET) is the most common movement disorder in humans. It is characterized by a postural and kinetic tremor most commonly affecting the forearms and hands. Isolated head tremor has been found in 1-10% of patients, suggesting that ET may be a composite of several phenotypes. The exact pathophysiology of ET is still unknown. ET has been repeatedly shown as a disorder of mild cerebellar degeneration, particularly in postmortem studies. Clinical observations, electrophysiological, volumetric and functional imaging studies all reinforce the fact that the cerebellum is involved in the generation of ET. However, crucial debate exists as to whether ET is a neurodegenerative disease. Data suggesting that it is neurodegenerative include postmortem findings of pathological abnormalities in the brainstem and cerebellum, white matter changes on diffusion tensor imaging, and clinical studies demonstrating an association with cognitive and gait changes. There is also conflicting evidence against ET as a neurodegenerative disease: the improvement of gait abnormalities with ethanol administration, lack of gray matter volume loss on voxel-based morphometry, failure to confirm the prominent presence of Lewy bodies in the locus ceruleus, and other pathological findings. To clarify this issue, future research is needed to describe the mechanism of cellular changes in the ET brain and to understand the order in which they occur. The cerebellum has been shown to be involved in the timing of movement and sensation, acting as an internal timing system that provides the temporal representation of salient events spanning hundreds of milliseconds. It has been reported that cerebellar timing function is altered in patients with ET, showing an increased variability of rhythmic hand movements as well as diminished performance during predictive motor timing task. Based on current knowledge and observations, we argue that ET is essentially linked with cerebellar degeneration, or at least cerebellar dysfunction, together with disturbance of motor timing. We explain the context of our current understanding on this topic, highlighting possible clinical consequences for patients suffering from ET and future research directions.

Essential tremor with ubiquitinated intranuclear inclusions and cerebellar degeneration

Background: Essential tremor (ET), a progressive, age-associated disease, is one of the most common neurological disorders. Yet until recently, there had been few postmortem examinations so that the full range of pathological changes associated with this disease has not been catalogued. Objectives: We report a patient with ET who had a pattern of pathological change which to our knowledge has not previously been reported in ET or another neurological disease. Methods: Clinical-pathological case report. Results: The patient had adult-onset, non-familial, kinetic arm tremor that gradually worsened. Voice and head tremors were also present. The clinical diagnosis was ET. She died at age 102. On postmortem examination, there was severe segmental loss of Purkinje cells, Bergmann gliosis and numerous torpedoes in the cerebellum. The other outstanding change was the presence of neurons in the cerebral cortex and hippocampus that contained an ubiquitinated, nuclear inclusion. These inclusions were not detected in Luxol fast blue/hematoxylin and eosin-stained sections. Conclusions: This ET patient had a pattern of pathological change that has not been reported previously. This case further reinforces the view that ET is likely to be a heterogeneous family of degenerative diseases whose underlying pathological anatomy involves the cerebellum.

Improved spatial targeting with directionally segmented deep brain stimulation leads for treating essential tremor

Deep brain stimulation (DBS) in the ventral intermediate nucleus of thalamus (Vim) is known to exert a therapeutic effect on postural and kinetic tremor in patients with essential tremor (ET). For DBS leads implanted near the caudal border of Vim, however, there is an increased likelihood that one will also induce paresthesia side-effects by stimulating neurons within the sensory pathway of the ventral caudal (Vc) nucleus of thalamus. The aim of this computational study was to (1) investigate the neuronal pathways modulated by therapeutic, sub-therapeutic and paresthesia-inducing DBS settings in three patients with ET and (2) determine how much better an outcome could have been achieved had these patients been implanted with a DBS lead containing directionally segmented electrodes (dDBS). Multi-compartment neuron models of the thalamocortical, cerebellothalamic and medial lemniscal pathways were first simulated in the context of patient-specific anatomies, lead placements and programming parameters from three ET patients who had been implanted with Medtronic 3389 DBS leads. The models showed that in these patients, complete suppression of tremor was associated most closely with activating an average of 62% of the cerebellothalamic afferent input into Vim (n = 10), while persistent paresthesias were associated with activating 35% of the medial lemniscal tract input into Vc thalamus (n = 12). The dDBS lead design demonstrated superior targeting of the cerebello-thalamo-cortical pathway, especially in cases of misaligned DBS leads. Given the close proximity of Vim to Vc thalamus, the models suggest that dDBS will enable clinicians to more effectively sculpt current through and around thalamus in order to achieve a more consistent therapeutic effect without inducing side-effects.

Sustained Medication Reduction Following Unilateral VIM Thalamic Stimulation for Essential Tremor

BACKGROUND

Deep brain stimulation (DBS) is an increasingly utilized therapeutic modality for the management of medication refractory essential tremor (ET). The aim of this study was to determine whether DBS allowed for anti-tremor medication reduction within the year after the procedure was performed.

METHODS

We conducted a retrospective chart review and telephone interviews on 34 consecutive patients who had been diagnosed with ET, and who had undergone unilateral DBS surgery.

RESULTS

Of the 34 patients in our cohort, 31 patients (91%) completely stopped all anti-tremor medications either before surgery (21 patients, 62%) or in the year following DBS surgery (10 patients, 29%). Patients who discontinued tremor medications before DBS surgery did so because their tremors either became refractory to anti-tremor medication, or they developed adverse events to tremor medications. Patients who stopped tremor medications after DBS surgery did so due to sufficient tremor control. Only three patients (9%) who were taking tremor medications at the time of surgery continued the use of a beta-blocker post-operatively for the purpose of hypertension management in all cases.

DISCUSSION

The data from this study indicate that medication cessation is common following unilateral DBS for ET.

Motor map reliability and aging: a TMS/fMRI study

This study compared the reliability of motor maps over 3 sessions from both neuronavigated transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) data between younger and older adults. Seven younger (ages 19-31) and seven older (ages 64-76) adults participated in three joint TMS/fMRI assessment sessions separated by 7 or 14 days. Sessions involved mapping of the right first dorsal interosseous muscle using single-pulse TMS immediately followed by block-design fMRI scanning involving volitional right-hand index finger to thumb oppositional squeeze. Intersession reliability of map volume, evaluated by intraclass correlation and Jaccard Coefficient between testing sessions, was more consistent for younger adults in both fMRI and TMS. A positive correlation was evidenced between fMRI and TMS map volumes and Jaccard Coefficients indicating spatial consistency across sessions between the two measures. Comparisons of map reliability between age groups showed that younger adults have more stable motor maps in both fMRI and TMS. fMRI and TMS maps show consistency across modalities. Future interpretation of motor maps should attempt to account for potential increased variability of such mapping in older age groups. Despite these age group differences in reliability, fMRI and TMS appear to offer consistent and complementary information about cortical representation of the first dorsal interosseous muscle.

The effects of TPA023, a GABAAα2,3 subtype-selective partial agonist, on essential tremor in comparison to alcohol

Essential tremor (ET) is a relatively frequent neurological disorder that responds in some patients to gamma-aminobutyric acid A (GABA(A)) agonists such as the benzodiazepines. Partial subtype-selective GABA(A) agonists may have an improved side effect profile compared to non-selective GABA(A) agonists. However, it is unknown which GABA(A) subtypes are involved in the therapeutic effects of benzodiazepines in ET. The effects of 2 mg TPA023, a GABA(A) α2,3 subtype-selective partial agonist, on ET were compared to the effects of a stable alcohol level (0.6 g/L) and placebo in nine patients with ET. Tremor evaluation included laboratory accelerometry and a performance-based scale. Additional measurements were performed to evaluate other effects on the central nervous system (CNS). Alcohol significantly diminished tremor symptoms in the postural and kinetic condition, as assessed by laboratory accelerometry, but the performance-based rating scale was unaffected. Tremor was also reduced after TPA023 treatment in the kinetic condition, albeit not significantly. Additionally, TPA023 decreased saccadic peak velocity, while alcohol decreased subjective feelings of alertness. This study showed that alcohol reduced maximum tremor power, as assessed by laboratory accelerometry, unlike TPA023, which decreased tremor symptoms to some extent but not significantly. This study showed that treatment with an α2,3 subunit-selective GABA(A) partial agonist was less effective than a stable level of alcohol in reducing ET symptoms. These results provide no support for a therapeutic role of TPA023 in the suppression of ET symptoms.