How Common is Essential Tremor? Update on the Worldwide Prevalence of Essential Tremor

Essential Tremor

This JAMA Insights discusses the diagnostic evaluation and treatment, including pharmacological, nonpharmacological, and surgical options, of essential tremor.

Distinguishing essential tremor from Parkinson's disease: clinical and experimental tools

INTRODUCTION

Essential tremor (ET) and Parkinson's disease (PD) are the most common causes of tremor and the most prevalent movement disorders, with overlapping clinical features that can lead to diagnostic challenges, especially in the early stages.

AREAS COVERED

In the present paper, the authors review the clinical and experimental studies and emphasized the major aspects to differentiate between ET and PD, with particular attention to cardinal phenomenological features of these two conditions. Ancillary and experimental techniques, including neurophysiology, neuroimaging, fluid biomarker evaluation, and innovative methods, are also discussed for their role in differential diagnosis between ET and PD. Special attention is given to investigations and tools applicable in the early stages of the diseases, when the differential diagnosis between the two conditions is more challenging. Furthermore, the authors discuss knowledge gaps and unsolved issues in the field.

EXPERT OPINION

Distinguishing ET and PD is crucial for prognostic purposes and appropriate treatment. Additionally, accurate diagnosis is critical for optimizing clinical and experimental research on pathophysiology and innovative therapies. In a few years, integrated technologies could enable accurate, reliable diagnosis from early disease stages or prodromal stages in at-risk populations, but further research combining different techniques is needed.

Safety and Efficacy of Staged, Bilateral Focused Ultrasound Thalamotomy in Essential Tremor: An Open-Label Clinical Trial

Importance

Unilateral magnetic resonance-guided focused ultrasound ablation of ventralis intermedius nucleus of the thalamus for essential tremor reduces tremor on 1 side, but untreated contralateral or midline symptoms remain limiting for some patients. Historically, bilateral lesioning produced unacceptable risks and was supplanted by deep brain stimulation; increasing acceptance of unilateral focused ultrasound lesioning has led to interest in a bilateral option.

Objective

To evaluate the safety and efficacy of staged, bilateral focused ultrasound thalamotomy.

Design, Setting, and Participants

This prospective, open-label, multicenter trial treated patients with essential tremor from July 2020 to October 2021, with a 12-month follow-up, at 7 US academic medical centers. Of 62 enrolled patients who had undergone unilateral focused ultrasound thalamotomy at least 9 months prior to enrollment, 11 were excluded and 51 were treated. Eligibility criteria included patient age (22 years and older), medication refractory, tremor severity (Clinical Rating Scale for Tremor [CRST] part A score ≥2 for postural or kinetic tremor), and functional disability (CRST part C score ≥2 in any category).

Intervention

A focused ultrasound system interfaced with magnetic resonance imaging allowed real-time alignment of thermography maps with anatomy. Subthreshold sonications allowed target interrogation for efficacy and off-target effects before creating an ablation.

Main Outcomes and Measures

Tremor/motor score (CRST parts A and B) at 3 months for the treated side after treatment was the primary outcome measure, and secondary assessments for efficacy and safety continued to 12 months.

Results

The mean (SD) population age was 73 (13.9) years, and 44 participants (86.3%) were male. The mean (SD) tremor/motor score improved from 17.4 (5.4; 95% CI, 15.9-18.9) to 6.4 (5.3; 95% CI, 4.9 to 7.9) at 3 months (66% improvement in CRST parts A and B scores; 95% CI, 59.8-72.2; P < .001). There was significant improvement in mean (SD) postural tremor (from 2.5 [0.8]; 95% CI, 2.3 to 2.7 to 0.6 [0.9]; 95% CI, 0.3 to 0.8; P < .001) and mean (SD) disability score (from 10.3 [4.7]; 95% CI, 9.0-11.6 to 2.2 [2.8]; 95% CI, 1.4-2.9; P < .001). Twelve participants developed mild (study-defined) ataxia, which persisted in 6 participants at 12 months. Adverse events (159 of 188 [85%] mild, 25 of 188 [13%] moderate, and 1 severe urinary tract infection) reported most commonly included numbness/tingling (n = 17 total; n = 8 at 12 months), dysarthria (n = 15 total; n = 7 at 12 months), ataxia (n = 12 total; n = 6 at 12 months), unsteadiness/imbalance (n = 10 total; n = 0 at 12 months), and taste disturbance (n = 7 total; n = 3 at 12 months). Speech difficulty, including phonation, articulation, and dysphagia, were generally mild (rated as not clinically significant, no participants with worsening in all 3 measures) and transient.

Conclusions and Relevance

Staged, bilateral focused ultrasound thalamotomy significantly reduced tremor severity and functional disability scores. Adverse events for speech, swallowing, and ataxia were mostly mild and transient.

Trial Registration

ClinicalTrials.gov Identifier NCT04112381.

Subjective and Objective Day-to-Day Performance Measures of People with Essential Tremor

This paper aims to map the daily functional characteristics of people diagnosed with essential tremor (ET) based on their subjective self-reports. In addition, we provide objective measurements of a cup-drinking task. This study involved 20 participants diagnosed with ET who completed the Columbia University Assessment of Disability in Essential Tremor (CADET) questionnaire that included five additional tasks related to digital equipment operation we wrote. Participants also described task-performance modifications they implemented. To create objective personal performance profiles, they performed a cup-drinking task while being monitored using a sensor measurement system. The CADET's subjective self-report results indicate that the most prevalent tasks participants reported as having difficulty with or requiring modifications were writing, threading a needle, carrying a cup, using a spoon, pouring, and taking a photo or video on a mobile phone. Analysis of participants' modifications revealed that holding the object with two hands or with one hand supporting the other were the most prevalent types. No significant correlation was found between the CADET total scores and the cup drinking objective measures. Capturing patients' perspectives on their functional disability, alongside objective performance measures, is envisioned to contribute to the development of custom-tailored interventions aligned with individual profiles, i.e., patient-based/smart healthcare.

Assessing ChatGPT Ability to Answer Frequently Asked Questions About Essential Tremor

Background

Large-language models (LLMs) driven by artificial intelligence allow people to engage in direct conversations about their health. The accuracy and readability of the answers provided by ChatGPT, the most famous LLM, about Essential Tremor (ET), one of the commonest movement disorders, have not yet been evaluated.

Methods

Answers given by ChatGPT to 10 questions about ET were evaluated by 5 professionals and 15 laypeople with a score ranging from 1 (poor) to 5 (excellent) in terms of clarity, relevance, accuracy (only for professionals), comprehensiveness, and overall value of the response. We further calculated the readability of the answers.

Results

ChatGPT answers received relatively positive evaluations, with median scores ranging between 4 and 5, by both groups and independently from the type of question. However, there was only moderate agreement between raters, especially in the group of professionals. Moreover, readability levels were poor for all examined answers.

Discussion

ChatGPT provided relatively accurate and relevant answers, with some variability as judged by the group of professionals suggesting that the degree of literacy about ET has influenced the ratings and, indirectly, that the quality of information provided in clinical practice is also variable. Moreover, the readability of the answer provided by ChatGPT was found to be poor. LLMs will likely play a significant role in the future; therefore, health-related content generated by these tools should be monitored.

Disparities in the treatment of movement disorders using deep brain stimulation

OBJECTIVE

Deep brain stimulation (DBS) is a well-established treatment for Parkinson's disease (PD) and essential tremor (ET). Although the prevalence of PD and ET can vary by sex and race, little is known about the accessibility of neurosurgical treatments for these conditions. In this nationwide study, the authors aimed to characterize trends in the use of DBS for the treatment of PD and ET and to identify disparities in the neurosurgical treatment of these diseases based on ethnic, racial, sex, insurance, income, hospital, and geographic factors.

METHODS

Using the dates January 1, 2012, to December 31, 2019, the authors queried the National Inpatient Sample database for all discharges with an ICD-9 or ICD-10 diagnosis of PD or ET. Among these discharges, the DBS rates were reported for each subgroup of race, ethnicity, and sex. To develop national estimates, all analyses were weighted.

RESULTS

Among 2,517,639 discharges with PD, 29,820 (1.2%) received DBS, and among 652,935 discharges with ET, 11,885 (1.8%) received DBS. Amid the PD cases, Black patients (n = 405 [0.2%], OR 0.16, 95% CI 0.12-0.20) were less likely than White patients (n = 23,975 [1.2%]) to receive DBS treatment, as were Hispanic patients (n = 1965 [1.1%], OR 0.76, 95% CI 0.65-0.88), whereas Asian/Pacific Islander patients (n = 855 [1.5%]) did not statistically differ from White patients. Amid the ET cases, Black (n = 230 [0.8%], OR 0.39, 95% CI 0.27-0.56), Hispanic (n = 215 [1.0%], OR 0.39, 95% CI 0.28-0.55), and Asian/Pacific Islander (n = 55 [1.0%], OR 0.51, 95% CI 0.28-0.93) patients were less likely than White patients (n = 10,440 [1.9%]) to receive DBS. Females were less likely than males to receive DBS for PD (OR 0.69, p < 0.0001) or ET (OR 0.70, p < 0.0001).

CONCLUSIONS

The authors describe significant racial and sex-based differences in the utilization of DBS for the treatment of PD and ET. Further research is required to ascertain the causes of these disparities, as well as any differences in access to specialty neurosurgical care and referral for neuromodulation approaches.

Motor Output Variability in Movement Disorders: Insights From Essential Tremor

Findings on individuals with essential tremor suggest that tremor (within-trial movement unsteadiness) and inconsistency (trial-to-trial movement variance) stem from distinct pathologies and affect function uniquely. Nonetheless, the intricacies of inconsistency in movement disorders remain largely unexplored, as exemplified in ataxia where inconsistency below healthy levels is associated with greater pathology. We advocate for clinical assessments that quantify both tremor and inconsistency.

Essential Tremor: Update of Therapeutic Strategies

In the last decades there has been progress in the treatment of essential tremor (TE) especially in the surgical field and to a lesser extent in the pharmacological field. We carry out a review of the currently available treatments. The first intervention is the use of non-pharmacological and non-surgical strategies (general advice, occupational therapy, speech therapy, psychotherapy). With discrete advances, the pharmacological treatment is not very satisfactory. Only 30-60% of patients have a positive response, and in these the anti-tremor effectiveness is 40-60%. The first-line drugs are still propranolol and primidone. In cases with severe tremor we will consider a surgical option, the method of choice being thalamotomy using high-intensity focused ultrasound. In the future we must continue to study the pathophysiology of TE, develop drugs specifically designed for TE and improve the technology of available invasive techniques.

Subjective Sleep Disturbance and Lewy Pathology: Data from a Cohort of Essential Tremor Brain Donors

INTRODUCTION

Sleep disturbances have been associated with essential tremor (ET). However, their pathophysiological underpinnings remain unknown. In this exploratory study, we examined the association between subjective sleep disturbances and the presence of Lewy pathology (LP) on postmortem brain examination in ET cases.

METHODS

Fifty-two ET cases enrolled in a prospective, longitudinal study were assessed over an average period of 42 months. Cases completed the Pittsburgh Sleep Quality Index (PSQI), which yields seven component scores (e.g., sleep quality, sleep latency). For each component score, we calculated the difference between the last score and the baseline score. Brains were harvested at death. Each had a complete neuropathological assessment, including extensive α-synuclein immunostaining. We examined the associations between baseline PSQI scores and the change in PSQI scores (last - first), and LP on postmortem brain examination.

RESULTS

ET cases had a mean baseline age of 87.1 ± 4.8 years. LP was observed in 12 (23.1%) of 52 cases; in 7 of these 12, LP was observed in the locus coeruleus (LC). Change in time needed to fall asleep (last - first sleep latency component score) was associated with presence of LP on postmortem brain examination - greater increase in sleep latency was associated with higher odds of LP (odds ratio = 2.98, p = 0.02). The greatest increase in sleep latency was observed in cases with LP in the LC (p = 0.04).

CONCLUSION

In ET cases, increases in sleep latency over time could be a marker of underlying LP, especially in the LC.

Pathologically based criteria to distinguish essential tremor from controls: analyses of the human cerebellum

OBJECTIVE

Essential tremor is among the most prevalent neurological diseases. Diagnosis is based entirely on neurological evaluation. Historically, there were few postmortem brain studies, hindering attempts to develop pathologically based criteria to distinguish essential tremor from control brains. However, an intensive effort to bank essential tremor brains over recent years has resulted in postmortem studies involving >200 brains, which have identified numerous degenerative changes in the essential tremor cerebellar cortex. Although essential tremor and controls have been compared with respect to individual metrics of pathology, there has been no overarching analysis to derive a combination of metrics to distinguish essential tremor from controls. We asked whether there is a constellation of pathological findings that separates essential tremor from controls, and how well that constellation performs.

METHODS

Analyses included 100 essential tremor brains from the essential tremor centralized brain repository and 50 control brains. A standard tissue block from the cerebellar cortex was used to quantify 11 metrics of pathological change. Three supervised classification algorithms were investigated, with data divided into training and validation samples.

RESULTS

Using three different algorithms, we illustrate the ability to correctly predict a diagnosis of essential tremor, with sensitivity and specificity >87%, and in the majority of situations, >90%. We also provide a web-based application that uses these metric values, and based on specified cutoffs, determines the likely diagnosis.

INTERPRETATION

These analyses set the stage for use of pathologically based criteria to distinguish clinically diagnosed essential tremor cases from controls, at the time of postmortem.

Serum Neurofilament Light-Chain Concentrations in Essential Tremor: a Case-Control Study

Essential tremor (ET) is a common neurological disorder, with clinical and pathophysiological links to the cerebellum. Inquiries into the etiology, pathophysiology, and nosology of ET stand to benefit from the identification of disease biomarkers. Serum neurofilament light chain (NfL) has emerged as a novel signature of conditions in which neuronal injury reflects an outcome of the ongoing disease process. We sought to investigate the concentrations of NfL in ET patients and healthy controls. In this case-control study, our powered study population of 41 ET patients and 40 age-matched healthy controls underwent clinical assessments and measurement of serum NfL concentration using Simoa technology. Serum NfL was elevated in ET patients - mean log-transformed serum NfL concentration = 1.23 ± 0.19 (95% confidence interval [CI] = 1.17-1.29) vs. 1.08 ± 0.15 (95% CI = 1.03-1.13), p = 0.0002. This difference persisted after accounting for age, sex and Montreal Cognitive Assessment score in a multiple linear regression model (p = 0.002) and in an age-matched sample subset of 35 ET cases and 35 controls (p = 0.006). There was no association between tremor severity and serum NfL levels (p = 0.73). In this sample of ET patients and controls, serum NfL concentrations were significantly higher in ET. Studies in additional cohorts of ET cases would be of value in attempting to replicate these results and assessing diagnostic utility.

Decreased Synaptic Vesicle Glycoprotein 2A Binding in the Human Postmortem Essential Tremor Cerebellum: Evidence of Reduction in Synaptic Density

OBJECTIVE

Despite being one of the most prevalent neurological diseases, the pathophysiology of essential tremor (ET) is not fully understood. Neuropathological studies have identified numerous degenerative changes in the cerebellum of ET patients, however. These data align with considerable clinical and neurophysiological data linking ET to the cerebellum. While neuroimaging studies have variably shown mild atrophy in the cerebellum, marked atrophy is not a clear feature of the cerebellum in ET and a search for a more suitable neuroimaging signature of neurodegeneration is in order. Postmortem studies in ET have examined different neuropathological alterations in the cerebellum, but as of yet have not focused on measures of generalized synaptic markers. This pilot study focuses on synaptic vesicle glycoprotein 2A (SV2A), a protein expressed in practically all synapses in the brain, as a measure of synaptic density in postmortem ET cases.

METHODS

The current study utilized autoradiography with the SV2A radioligand [18F]SDM-16 to assess synaptic density in the cerebellar cortex and dentate nucleus in three ET cases and three age-matched controls.

RESULTS

Using [18F]SDM-16, SV2A was 53% and 46% lower in the cerebellar cortex and dentate nucleus, respectively, in ET cases compared to age-matched controls.

CONCLUSION

In this pilot study, using in vitro SV2A autoradiography, we have observed significantly lower synaptic density in the cerebellar cortex and dentate nucleus of ET cases. Future research could expand on our sample size and focus on in vivo imaging in ET to explore whether SV2A imaging could serve as a much-needed disease biomarker.

Prevalence of and Annual Conversion Rates to Mild Cognitive Impairment and Dementia: Prospective, Longitudinal Study of an Essential Tremor Cohort

OBJECTIVE

Despite recent attention to cognitive impairment in essential tremor, few studies examine rates of conversion to diagnoses of mild cognitive impairment and dementia. Development of dementia in essential tremor is associated with loss of functional ability and a doubling of mortality rate. This prospective, longitudinal study comprehensively reports the prevalence and incidence of, and the annual rates of conversion to, mild cognitive impairment and dementia in an essential tremor cohort.

METHODS

Patients underwent detailed cognitive assessments and were assigned diagnoses of normal cognition, mild cognitive impairment, or dementia. There were 222 patients at baseline (mean age = 79.3 ± 9.7 years), and 177 patients participated in follow-up evaluations at 18, 36, 54, and 72 months (mean years of observation = 5.1 ± 1.7). Data were compared to those of historical controls and Parkinson disease patients.

RESULTS

The cumulative prevalence of dementia and average annual conversion rate of mild cognitive impairment to dementia were 18.5% and 12.2%, nearly three times higher than rates in the general population, and approximately one half the magnitude of those reported for Parkinson disease patients. The cumulative prevalence of mild cognitive impairment (26.6%) was almost double that of the general population, but less than that in Parkinson disease populations.

INTERPRETATION

We present the most complete exposition of the longitudinal trajectory of cognitive impairment in an essential tremor cohort yet presented. The prevalence of and conversion rates to dementia in essential tremor fall between those associated with the natural course of aging and the more pronounced rates observed in Parkinson disease. ANN NEUROL 2024;95:1193-1204.

Evaluation and Management of Tremor

Tremor is a commonly encountered condition in the primary care setting and can manifest at rest, with action, or both. Common causes include Parkinson disease, essential tremor, and drug-induced tremor. In this article, the authors discuss how to examine a patient with tremor and which features of the history and examination can help clue the provider in to the appropriate diagnosis. They also review treatments for varying types of tremor and when referral to a neurologist may be necessary.

Updates in essential tremor

Essential tremor (ET) is one of the most common tremor disorders and can be disabling in its affect on daily activities. There have been major breakthroughs in the treatment of tremor and ET is the subject of important ongoing research. This review will present recent advancements in the epidemiology, genetics, pathophysiology, diagnosis, comorbidities, and imaging of ET. Current and future treatment options in the management of ET will also be reviewed. The need for continued innovation and scientific inquiry to address the unmet needs of persons of ET will be highlighted.

Sustained reduction of essential tremor with low-power non-thermal transcranial focused ultrasound stimulations in humans

BACKGROUND

Transcranial ultrasound stimulation (TUS) is a non-invasive brain stimulation technique; when skull aberrations are compensated for, this technique allows, with millimetric accuracy, circumvention of the invasive surgical procedure associated with deep brain stimulation (DBS) and the limited spatial specificity of transcranial magnetic stimulation.

OBJECTIVE

/hypothesis: We hypothesize that MR-guided low-power TUS can induce a sustained decrease of tremor power in patients suffering from medically refractive essential tremor.

METHODS

The dominant hand only was targeted, and two anatomical sites were sonicated in this exploratory study: the ventral intermediate nucleus of the thalamus (VIM) and the dentato-rubro-thalamic tract (DRT). Patients (N = 9) were equipped with MR-compatible accelerometers attached to their hands to monitor their tremor in real-time during TUS.

RESULTS

VIM neurostimulations followed by a low-duty cycle (5 %) DRT stimulation induced a substantial decrease in the tremor power in four patients, with a minimum of 89.9 % reduction when compared with the baseline power a few minutes after the DRT stimulation. The only patient stimulated in the VIM only and with a low duty cycle (5 %) also experienced a sustained reduction of the tremor (up to 93.4 %). Four patients (N = 4) did not respond. The temperature at target was 37.2 ± 1.4 °C compared to 36.8 ± 1.4 °C for a 3 cm away control point.

CONCLUSIONS

MR-guided low power TUS can induce a substantial and sustained decrease of tremor power. Follow-up studies need to be conducted to reproduce the effect and better to understand the variability of the response amongst patients. MR thermometry during neurostimulations showed no significant thermal rise, supporting a mechanical effect.

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.

Accessibility and Ease of Use in Neuromodulation Devices

BACKGROUND

The utilization of neuromodulation therapy continues to grow as therapeutic indications expand. These conditions often present with comorbid physical, visual, and auditory impairments. Patients with disabilities in these categories may have difficulty operating their devices. Thus, reviewing the accessibility and inclusive design of neuromodulation devices is imperative to ensure equal access for patients of all ability levels. To date, the literature provides little insight into this topic.

MATERIALS AND METHODS

Manufacturers of Food and Drug Administration-approved neuromodulation devices in the United States completed our electronic survey to assess neuromodulation device features, universal/inclusive design guidelines, and methods used to make the device accessible to patients with disabilities.

RESULTS

We assessed 11 devices from seven manufacturers. Of those, there were six spinal cord, two peripheral nerve, and three deep brain stimulators. Of all respondents, 91% used universal inclusive design guidelines. Of the studied devices, 91% have an interface that uses visual feedback, and 82% have an interface that uses auditory feedback. All surveyed devices were reported to have an interface that requires physical handling.

DISCUSSION

Our study found that most devices incorporate auditory signals, buttons with raised indentations, speech commands, or other useful features to assist those with visual disabilities. Visual interfaces may be sufficient for a patient with hearing impairment to use all the surveyed devices. However, dual sensory impairment presents a significant limitation in all devices surveyed. Furthermore, the biggest barrier to using neuromodulation devices was physical impairment because all surveyed devices require physical handling.

CONCLUSIONS

Manufacturers have awareness of universal inclusive design principles. However, our study was unable to find a device that is accessible to all users regardless of ability. As such, it is critical to involve universal design principles to ensure that inclusive devices are available to improve patient adherence, treatment efficacy, and outcomes.

Cerebellar and thalamic connector hubs facilitate the involvement of visual and cognitive networks in essential tremor

INTRODUCTION

Connector hubs are specialized brain regions that connect multiple brain networks and therefore have the potential to affect the functions of multiple systems. This study aims to examine the involvement of connector hub regions in essential tremor.

METHODS

We examined whole-brain functional connectivity alterations across multiple brain networks in 27 patients with essential tremor and 27 age- and sex-matched healthy controls to identify affected hub regions using a network metric called functional connectivity overlap ratio estimated from resting-state functional MRI. We also evaluated the relationships of affected hubs with cognitive and tremor scores in all patients and with motor function improvement scores in 15 patients who underwent postoperative follow-up evaluations after focused ultrasound thalamotomy.

RESULTS

We have identified affected connector hubs in the cerebellum and thalamus. Specifically, the dentate nucleus in the cerebellum and the dorsomedial thalamus exhibited more extensive connections with the sensorimotor network in patients. Moreover, the connections of the thalamic pulvinar with the visual network were also significantly widespread in the patient group. The connections of these connector hub regions with cognitive networks were negatively associated (FDR q < 0.05) with cognitive, tremor, and motor function improvement scores.

CONCLUSION

In patients with essential tremor, connector hub regions within the cerebellum and thalamus exhibited widespread functional connections with sensorimotor and visual networks, leading to alternative pathways outside the classical tremor axis. Their connections with cognitive networks also affect patients' cognitive function.

Editorial for "Alteration of White Matter Connectivity for MR-Guided Focused Ultrasound in the Treatment of Essential Tremor"

Level of Evidence

5

Technical Efficacy Stage

3

A Randomized Phase 2 KINETIC Trial Evaluating SAGE-324/BIIB124 in Individuals with Essential Tremor

BACKGROUND

SAGE-324/BIIB124 is an investigational positive allosteric modulator of GABAA receptors.

OBJECTIVE

KINETIC (NCT04305275), a double-blind, randomized, placebo-controlled, phase 2 study, evaluated SAGE-324/BIIB124 in individuals with essential tremor (ET).

METHODS

Individuals aged 18 to 80 years were randomly assigned 1:1 to orally receive 60 mg of SAGE-324/BIIB124 or placebo once daily for 28 days. The primary endpoint was change from baseline in The Essential Tremor Rating Assessment Scale-Performance Subscale (TETRAS-PS) Item 4 (upper-limb tremor) at day 29 with SAGE-324/BIIB124 versus placebo.

RESULTS

Between May 2020 and February 2021, 69 U.S. participants were randomly assigned to receive SAGE-324/BIIB124 (n = 34) or placebo (n = 35). There was a significant reduction from baseline in TETRAS-PS Item 4 at day 29 with SAGE-324/BIIB124 versus placebo (least squares mean [standard error]: -2.31 [0.401] vs. -1.24 [0.349], P = 0.0491). The most common treatment-emergent adverse events included somnolence, dizziness, fatigue, and balance disorder.

CONCLUSION

These results support further development of SAGE-324/BIIB124 for potential ET treatment. © 2024 Sage Therapeutics, Inc and The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Evaluating Postural Transition Movement Performance in Individuals with Essential Tremor via the Instrumented Timed Up and Go

Flexibility in performing various movements like standing, walking, and turning is crucial for navigating dynamic environments in daily life. Individuals with essential tremor often experience movement difficulties that can affect these postural transitions, limiting mobility and independence. Yet, little research has examined the performance of postural transitions in people with essential tremor. Therefore, we assessed postural transition performance using two versions of the timed up and go test: the standard version and a more complex water-carry version. We examined the total duration of the standard and water-carry timed up and go in 15 people with and 15 people without essential tremor. We also compared the time taken for each phase (sit-to-stand phase, straight-line walk phase, stand-to-sit phase) and the turning velocity between groups. Our findings revealed decreased performance across all phases of standard and water-carry timed up and go assessments. Further, both ET and non-ET groups exhibited reduced performance during the water-carry timed up and go compared to the standard timed up and go. Evaluating specific phases of the timed up and go offers valuable insights into functional movement performance in essential tremor, permitting more tailored therapeutic interventions to improve functional performance during activities of daily living.

Neuronal Intranuclear Inclusion Disease with NOTCH2NLC GGC Repeat Expansion: A Systematic Review and Challenges of Phenotypic Characterization

Neuronal intranuclear inclusion disease (NIID) is a highly clinically heterogeneous neurodegenerative disorder primarily attributed to abnormal GGC repeat expansions in the NOTCH2NLC gene. This study aims to comprehensively explore its phenotypic characteristics and genotype-phenotype correlation. A literature search was conducted in PubMed, Embase, and the Cochrane Library from September 1, 2019, to December 31, 2022, encompassing reported NIID cases confirmed by pathogenic NOTCH2NLC mutations. Linear regressions and trend analyses were performed. Analyzing 635 cases from 85 included studies revealed that familial cases exhibited significantly larger GGC repeat expansions than sporadic cases (p < 0.001), and this frequency significantly increased with expanding GGC repeats (p trend < 0.001). Age at onset (AAO) showed a negative correlation with GGC repeat expansions (p < 0.001). The predominant initial symptoms included tremor (31.70%), cognitive impairment (14.12%), and muscle weakness (10.66%). The decreased or absent tendon reflex (DTR/ATR) emerged as a notable clinical indicator of NIID due to its high prevalence. U-fiber was observed in 79.11% of patients, particularly prominent in paroxysmal disease-dominant (87.50%) and dementia-dominant cases (81.08%). Peripheral neuropathy-dominant cases exhibited larger GGC repeat expansions (median = 123.00) and an earlier AAO (median = 33.00) than other phenotypes. Moreover, a significant genetic anticipation of 3.5 years was observed (p = 0.039). This study provides a comprehensive and up-to-date compilation of genotypic and phenotypic information on NIID since the identification of the causative gene NOTCH2NLC. We contribute a novel diagnostic framework for NIID to support clinical practice.

Reduced Bergmann glial process terminations and lateral appendages in essential tremor

OBJECTIVE

Postmortem examination of the essential tremor cerebellum has revealed a variety of pathological changes centered in and around Purkinje cells. Studies have predominantly focused on cerebellar neuronal connections. Bergmann glial morphology has not yet been studied in essential tremor. Among their many roles, Bergmann glia in the cerebellar cortex ensheath Purkinje cell synapses and provide neuroprotection. Specifically, the complex radial processes and lateral appendages of Bergmann glia are structural domains that modulate Purkinje cell synaptic transmission. In this study, we investigate whether Bergmann glia morphology is altered in the essential tremor cerebellum.

METHODS

We applied the Golgi-Kopsch method and used computerized three-dimensional cell reconstruction to visualize Bergmann glia in the postmortem cerebellum of 34 cases and 17 controls. We quantified morphology of terminal structures (number of terminations and lateral appendage density) and morphology of radial processes (total process length, branch length, branch order, and branch volume) in each glial cell. We quantified number of branches and volume as well.

RESULTS

Essential tremor cases had a 31.9% decrease in process terminations and a 35.7% decrease in lateral appendage density in Bergmann glia. Total process length and branch length did not differ between essential tremor cases and controls. We found also a reduction in number of secondary and tertiary branches and tertiary branches volume.

INTERPRETATION

These findings suggest that Bergmann glia in essential tremor cases have more alterations in their terminal structures, with a relative preservation of radial processes, and highlight a potential role for these astrocytes in the disease pathophysiology.

Postural tremor and sexual chromosome aneuploidies: case report and review of literature

PURPOSE

To examine the link between tremor and sex chromosome abnormalities, emphasizing the necessity of comprehensive physical examination.

CASE DESCRIPTION

An 18-year-old man exhibited an isolated action tremor in both hands. Despite having no familial history of tremors and no identifiable secondary causes, his tall stature and learning difficulties suggested a genetic origin. His karyotype confirmed the diagnosis of Jacob's syndrome (XYY syndrome). Therapies with primidone and propranolol were ineffective for his tremor.

CONCLUSIONS

Tremor can be caused by various conditions, and aneuploidies might often be overlooked as a cause. They should be considered in young patients with concrete phenotypes and negative familiar history of tremors. Karyotyping is a cost-effective diagnostic tool crucial for genetic counselling. Common treatments for tremors often yield unsatisfactory results in these cases.

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.

Vestibular reflexes in essential tremor: abnormalities of ocular and cervical vestibular-evoked myogenic potentials are associated with the cerebellum and brainstem involvement

This study utilized cervical vestibular-evoked myogenic potentials tests (cVEMP) and ocular vestibular-evoked myogenic potentials tests (oVEMP) to investigate the vestibulocollic and vestibuloocular reflex arcs and to evaluate cerebellar and brainstem involvement) in essential tremor (ET). Eighteen cases with ET and 16 age- and gender-matched healthy control subjects (HCS) were included in the present study. Otoscopic and neurologic examinations were performed on all participants, and both cervical and ocular VEMP tests were performed. Pathological cVEMP results were increased in the ET group (64.7%) compared to the HCS (41,2%; p > 0.05). The latencies of P1 and N1 waves were shorter in the ET group than in HCS (p = 0.01 and p = 0.001). Pathological oVEMP responses were significantly higher in the ET group (72.2%) compared to the HCS (37.5%; p = 0.01). There was no statistically significant difference in oVEMP N1-P1 latencies between groups (p > 0.05). Because the ET group had high pathological responses to the oVEMP, but not the cVEMP, the upper brainstem pathways may be more affected by ET.

Gene Expression Analysis of Laser-Captured Purkinje Cells in the Essential Tremor Cerebellum

Essential tremor (ET) is a common, progressive neurological disease characterized by an 8-12-Hz kinetic tremor. Despite its high prevalence, the patho-mechanisms of tremor in ET are not fully known. Through comprehensive studies in postmortem brains, we identified major morphological changes in the ET cerebellum that reflect cellular damage in Purkinje cells (PCs), suggesting that PC damage is central to ET pathogenesis. We previously performed a transcriptome analysis in ET cerebellar cortex, identifying candidate genes and several dysregulated pathways. To directly target PCs, we purified RNA from PCs isolated by laser capture microdissection and performed the first ever PC-specific RNA-sequencing analysis in ET versus controls. Frozen postmortem cerebellar cortex from 24 ETs and 16 controls underwent laser capture microdissection, obtaining ≥2000 PCs per sample. RNA transcriptome was analyzed via differential gene expression, principal component analysis (PCA), and gene set enrichment analyses (GSEA). We identified 36 differentially expressed genes, encompassing multiple cellular processes. Some ET (13/24) had greater dysregulation of these genes and segregated from most controls and remaining ETs in PCA. Characterization of genes/pathways enriched in this PCA and GSEA identified multiple pathway dysregulations in ET, including RNA processing/splicing, synapse organization/ion transport, and oxidative stress/inflammation. Furthermore, a different set of pathways characterized marked heterogeneity among ET patients. Our data indicate a range of possible mechanisms for the pathogenesis of ET. Significant heterogeneity among ET combined with dysregulation of multiple cellular processes supports the notion that ET is a family of disorders rather than one disease entity.

Comparison of Motion Grading in 1,000 Patients by First- and Second-Generation HR-pQCT: A Propensity Score Matched Cohort Study

In-vivo bone microstructure measured by high-resolution peripheral quantitative computed tomography (HR-pQCT) is gaining importance in research and clinical practice. Second-generation HR-pQCT (XCT2) shows improved image quality and shorter measurement duration compared to the first generation (XCT1). Predicting and understanding the occurrence of motion artifacts is crucial for clinical practice. We retrospectively analyzed data from HR-pQCT measurements at the distal radius and tibia of 1,000 patients (aged 20 to 89) evenly distributed between both generations of HR-pQCT. Motion artifacts were graded between 1 (no motion) and 5 (severe motion), with grades greater 3 considered unusable. Additionally, baseline characteristics and patients' muscle performance and balance were measured. Various group comparisons between the two generations of HR-pQCT and regression analyses between patient characteristics and motion grading were performed. The study groups of XCT1 and XCT2 did not differ by age (XCT1: 64.9 vs. XCT2: 63.8 years, p = 0.136), sex (both 74.5% females, p > 0.999), or BMI (both 24.2 kg/m2, p = 0.911) after propensity score matching. XCT2 scans exhibited significantly lower motion grading in both extremities compared to XCT1 (Radius: p < 0.001; Tibia: p = 0.002). In XCT2 motion-corrupted scans were more than halved at the radius (XCT1: 35.3% vs. XCT2: 15.5%, p < 0.001), and at the tibia the frequency of best image quality scans was increased (XCT1: 50.2% vs. XCT2: 63.7%, p < 0.001). The strongest independent predictor for motion-corrupted images is the occurrence of high motion grading at the other scanning site during the same consultation. The association between high motion grading in one scan and a corresponding high motion grading in another scan within the same session suggests a non-resting patient. Additionally, aged, female, and patients with smaller stature tend towards higher motion grading, requiring special attention to a correct extremity fixation.

Active contact proximity to the cerebellothalamic tract predicts initial therapeutic current requirement with DBS for ET: an application of 7T MRI

Objective

To characterize how the proximity of deep brain stimulation (DBS) active contact locations relative to the cerebellothalamic tract (CTT) affect clinical outcomes in patients with essential tremor (ET).

Background

DBS is an effective treatment for refractory ET. However, the role of the CTT in mediating the effect of DBS for ET is not well characterized. 7-Tesla (T) MRI-derived tractography provides a means to measure the distance between the active contact and the CTT more precisely.

Methods

A retrospective review was conducted of 12 brain hemispheres in 7 patients at a single center who underwent 7T MRI prior to ventral intermediate nucleus (VIM) DBS lead placement for ET following failed medical management. 7T-derived diffusion tractography imaging was used to identify the CTT and was merged with the post-operative CT to calculate the Euclidean distance from the active contact to the CTT. We collected optimized stimulation parameters at initial programing, 1- and 2-year follow up, as well as a baseline and postoperative Fahn-Tolosa-Marin (FTM) scores.

Results

The therapeutic DBS current mean (SD) across implants was 1.8 mA (1.8) at initial programming, 2.5 mA (0.6) at 1 year, and 2.9 mA (1.1) at 2-year follow up. Proximity of the clinically-optimized active contact to the CTT was 3.1 mm (1.2), which correlated with lower current requirements at the time of initial programming (R2 = 0.458, p = 0.009), but not at the 1- and 2-year follow up visits. Subjects achieved mean (SD) improvement in tremor control of 77.9% (14.5) at mean follow-up time of 22.2 (18.9) months. Active contact distance to the CTT did not predict post-operative tremor control at the time of the longer term clinical follow up (R2 = -0.073, p = 0.58).

Conclusion

Active DBS contact proximity to the CTT was associated with lower therapeutic current requirement following DBS surgery for ET, but therapeutic current was increased over time. Distance to CTT did not predict the need for increased current over time, or longer term post-operative tremor control in this cohort. Further study is needed to characterize the role of the CTT in long-term DBS outcomes.

Mapping Essential Tremor to a Common Brain Network Using Functional Connectivity Analysis

BACKGROUND AND OBJECTIVES

The cerebello-thalamo-cortical circuit plays a critical role in essential tremor (ET). However, abnormalities have been reported in multiple brain regions outside this circuit, leading to inconsistent characterization of ET pathophysiology. Here, we test whether these mixed findings in ET localize to a common functional network and whether this network has therapeutic relevance.

METHODS

We conducted a systematic literature search to identify studies reporting structural or metabolic brain abnormalities in ET. We then used 'coordinate network mapping,' which leverages a normative connectome (n = 1,000) of resting-state fMRI data to identify regions commonly connected to findings across all studies. To assess whether these regions may be relevant for the treatment of ET, we compared our network with a therapeutic network derived from lesions that relieved ET. Finally, we investigated whether the functional connectivity of this ET symptom network is abnormal in an independent cohort of patients with ET as compared with healthy controls.

RESULTS

Structural and metabolic brain abnormalities in ET were located in heterogeneous regions throughout the brain. However, these coordinates were connected to a common functional brain network, including the cerebellum, thalamus, motor cortex, precuneus, inferior parietal lobe, and insula. The cerebellum was identified as the hub of this network because it was the only brain region that was both functionally connected to the findings of over 90% of studies and significantly different in connectivity compared with a control data set of other movement disorders. This network was strikingly similar to the therapeutic network derived from lesions improving ET, with key regions aligning in the thalamus and cerebellum. Furthermore, positive functional connectivity between the cerebellar network hub and the sensorimotor cortices was significantly reduced in patients with ET compared with healthy controls, and connectivity within this network was correlated with tremor severity and cognitive functioning.

DISCUSSION

These findings suggest that the cerebellum is the central hub of a network commonly connected to structural and metabolic abnormalities in ET. This network may have therapeutic utility in refining and informing new targets for neuromodulation of ET.

Physiological Recordings of the Cerebellum in Movement Disorders

The cerebellum plays an important role in movement disorders, specifically in symptoms of ataxia, tremor, and dystonia. Understanding the physiological signals of the cerebellum contributes to insights into the pathophysiology of these movement disorders and holds promise in advancing therapeutic development. Non-invasive techniques such as electroencephalogram and magnetoencephalogram can record neural signals with high temporal resolution at the millisecond level, which is uniquely suitable to interrogate cerebellar physiology. These techniques have recently been implemented to study cerebellar physiology in healthy subjects as well as individuals with movement disorders. In the present review, we focus on the current understanding of cerebellar physiology using these techniques to study movement disorders.

Damping TENS-Induced Essential Tremor Symptoms in Activities of Daily Living Using the TuMove Wrist Exoskeleton

Essential Tremor (ET) is the most frequent movement disorder in adults. Upper-limb exoskeletons are a promising solution to alleviate ET symptoms. We propose a novel wrist exoskeleton for tremor damping. The TuMove exoskeleton is light-weight, portable, easy to use, and designed for ADLs and activities requiring hand dexterity. We validated the effectiveness of our exoskeleton by inducing forearm tremors using TENS on 5 healthy subjects. Our results show that wrist ranges are generally kept in most of the ROM needed in ADLs. The damping system reduced more than 30% of the tremor's angular velocity during drinking and pouring tasks. Furthermore, the completion time of the Archimedes spiral was decreased by 2.76 seconds (13.0%) and for the 9-Hole-Peg-Test by 2.77 seconds (11.8 %), indicating a performance improvement in dexterity tasks.

Medication Status and Related Factors in Essential Tremor Patients: A Cross-Sectional Study in China

INTRODUCTION

Essential tremor (ET) is one of the most common movement disorders. Oral drugs play a crucial role in treating ET, with various available options such as propranolol, primidone, and topiramate. However, the medication status and related factors among Chinese ET patients are unknown yet.

METHODS

This study used the baseline data from the National Survey of Essential Tremor Plus in China cohort. ET patients with information related to medication intake were included. Medication patients were defined as patients who were taking medication at the time of the survey. We further defined recommended medication users according to Chinese guideline recommendations and clinical knowledge. We used mean and standard deviation (SD), median and interquartile range (IQR), or frequencies and percentages when appropriate for descriptive analysis. We used multivariate logistic regression analyses to explore factors related to medication intake in all ET patients and in recommended medication users.

RESULTS

Of 1,153 included ET participants, 207 (18.0%) took medication. Arotinolol (115, 55.6%) and propranolol (63, 30.4%) were the top 2 used medicines. Patients with middle school education (odds ratio 0.57, 95% confidence interval 0.39-0.83), college or higher level education (0.46, 0.28-0.76), and late-onset ET (LO-ET) (0.38, 0.23-0.63) were less likely to take medication. Patients with intention tremor (1.90, 1.38-2.62), every 10-unit increase in age (1.10, 1.00-1.21), Tremor Research Group Essential Tremor Rating Assessment Scale (TETRAS) Part 1 (1.63, 1.37-1.93), and TETRAS Part 2 (1.81, 1.48-2.22) were more likely to take medication. Among 332 recommended medication users, only 104 (31.3%) took medicine. The associations of LO-ET (0.36, 0.17-0.75), intention tremor (2.27, 1.35-3.81), TETRAS Part 1 (1.52, 1.09-2.13), and TETRAS Part 2 (1.59, 1.15-2.20) with medication were similar to all ET patients.

CONCLUSION

The proportion of medication intake is low among both all ET patients and recommended medication users. The top 2 commonly used medications among all ET patients are arotinolol and propranolol. Influencing factors of medication intake are different between all ET patients and recommended medication users. Clinicians are suggested to provide counseling and education on ET medication to promote medication intake.

Defective cerebellar ryanodine receptor type 1 and endoplasmic reticulum calcium 'leak' in tremor pathophysiology

Essential Tremor (ET) is a prevalent neurological disease characterized by an 8-10 Hz action tremor. Molecular mechanisms of ET remain poorly understood. Clinical data suggest the importance of the cerebellum in disease pathophysiology, and pathological studies indicate Purkinje Cells (PCs) incur damage. Our recent cerebellar cortex and PC-specific transcriptome studies identified alterations in calcium (Ca2+) signaling pathways that included ryanodine receptor type 1 (RyR1) in ET. RyR1 is an intracellular Ca2+ release channel located on the Endoplasmic Reticulum (ER), and in cerebellum is predominantly expressed in PCs. Under stress conditions, RyR1 undergoes several post-translational modifications (protein kinase A [PKA] phosphorylation, oxidation, nitrosylation), coupled with depletion of the channel-stabilizing binding partner calstabin1, which collectively characterize a "leaky channel" biochemical signature. In this study, we found markedly increased PKA phosphorylation at the RyR1-S2844 site, increased RyR1 oxidation and nitrosylation, and calstabin1 depletion from the RyR1 complex in postmortem ET cerebellum. Decreased calstabin1-RyR1-binding affinity correlated with loss of PCs and climbing fiber-PC synapses in ET. This 'leaky' RyR1 signature was not seen in control or Parkinson's disease cerebellum. Microsomes from postmortem cerebellum demonstrated excessive ER Ca2+ leak in ET vs. controls, attenuated by channel stabilization. We further studied the role of RyR1 in tremor using a mouse model harboring a RyR1 point mutation that mimics constitutive site-specific PKA phosphorylation (RyR1-S2844D). RyR1-S2844D homozygous mice develop a 10 Hz action tremor and robust abnormal oscillatory activity in cerebellar physiological recordings. Intra-cerebellar microinfusion of RyR1 agonist or antagonist, respectively, increased or decreased tremor amplitude in RyR1-S2844D mice, supporting a direct role of cerebellar RyR1 leakiness for tremor generation. Treating RyR1-S2844D mice with a novel RyR1 channel-stabilizing compound, Rycal, effectively dampened cerebellar oscillatory activity, suppressed tremor, and normalized cerebellar RyR1-calstabin1 binding. These data collectively support that stress-associated ER Ca2+ leak via RyR1 may contribute to tremor pathophysiology.

Can the Montreal Cognitive Assessment and Mini-Mental State Examination detect cognitive decline in elderly patients with essential tremor?

Objective Given the association between essential tremor (ET) and higher rates of cognitive decline, assessing this decline is an important element of research and clinical care. The Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA) are two broad, brief measures that are widely used to monitor cognitive impairment in various neurological disorders. We sought to determine the relative ability of the MoCA and the MMSE to detect cognitive decline in elderly patients with ET. Methods We administered a neuropsychological battery to an ET cohort every 18 months over 4.5 years. We defined the gold standard for change in cognition as the change in neuropsychological test scores over consecutive evaluations and applied the Reliable Change Method to detect meaningful increases/decreases in test scores. We performed receiver operating characteristics (ROC) analysis to quantify the area under the curve (AUC) and compare the ability of the MoCA and the MMSE to detect cognitive decline. Results The AUCs for the MoCA and the MMSE did not differ significantly at any interval or when all intervals were pooled for analysis. Across all intervals, the ability of the MoCA and the MMSE to detect cognitive decline was consistently fair or poor. Conclusions We found that the ability of the MoCA and the MMSE to detect cognitive decline in ET patients over 18-month intervals is inadequate. Unchanged scores on the MoCA and the MMSE in ET over time should be approached with caution. We propose that these screening tools should be supplemented with additional neuropsychological tests.

Gamma Knife Thalamotomy for Essential Tremor: A Retrospective Analysis

BACKGROUND

Gamma knife (GK) thalamotomy has been used as a treatment option for essential tremor (ET). Numerous studies on GK use in ET treatment have reported more varied responses and complication rates.

METHODS

Data from 27 patients with ET who underwent GK thalamotomy were retrospectively analyzed. The Fahn-Tolosa-Marin Clinical Rating Scale for Tremor, handwriting, and spiral drawing were evaluated. Postoperative adverse events and magnetic resonance imaging findings were also evaluated.

RESULTS

The mean age at GK thalamotomy was 78.1 ± 4.2 years. The mean follow-up period was 32.5 ± 19.4 months. The preoperative postural tremor, handwriting, and spiral drawing scores were 3.4 ± 0.6, 3.3 ± 1.0, and 3.2 ± 0.8, respectively, all of which showed significant improvements to 1.5 ± 1.2 (55.9% improvement, P < 0.001), 1.4 ± 1.1 (57.6% improvement, P < 0.001), and 1.6 ± 1.3 (50% improvement, P < 0.001), respectively, at the available final follow-up evaluations. Three patients presented with no improvement in tremor. Six patients presented with adverse effects, including complete hemiparesis, foot weakness, dysarthria, dysphagia, lip numbness, and finger numbness, at the final follow-up period. Two patients presented with serious complications, including complete hemiparesis due to massive widespread edema and chronic encapsulated expanding hematoma. One patient died of aspiration pneumonia following severe dysphagia secondary to chronic encapsulated expanding hematoma.

CONCLUSIONS

GK thalamotomy is an efficient procedure for treating ET. Careful treatment planning is necessary to reduce complication rates. The prediction of radiation complications will increase the safety and effectiveness of GK treatment.

A Novel KCNN2 Variant in a Family with Essential Tremor Plus: Clinical Characteristics and In Silico Analysis

BACKGROUND

Essential tremor (ET) is one of the more common movement disorders. Current diagnosis is solely based on clinical findings. ET appears to be inherited in an autosomal dominant pattern. Several loci on specific chromosomes have been studied by linkage analysis, but the causes of essential tremor are still unknown in many patients. Genetic studies described the association of several genes with familial ET. However, they were found only in distinct families, suggesting that some can be private pathogenic variants.

AIM OF THE STUDY

to characterize the phenotype of an Italian family with ET and identify the genetic variant associated.

METHODS

Clinical and genetic examinations were performed. Genetic testing was done with whole-exome sequencing (WES) using the Illumina platform. Bidirectional capillary Sanger sequencing was used to investigate the presence of variant in all affected members of the family. In silico prediction of pathogenicity was used to study the effect of gene variants on protein structure.

RESULTS

The proband was a 15-year-old boy. The patient was the first of two children of a non-consanguineous couple. Family history was remarkable for tremor in the mother line. His mother suffered from bilateral upper extremity kinetic tremors (since she was 20 years old), anxiety, and depression. Other relatives referred bilateral upper extremity tremors. In the index case, WES analysis performed supposing a dominant mode of inheritance, identified a novel heterozygous missense variant in potassium calcium-activated channel subfamily N member 2 (KCNN2) (NM_021614.3: c.1145G>A, p.Gly382Asp). In the pedigree investigation, all carriers of the gene variant had ET and showed variable expressivity, the elder symptomatic relative showing cognitive impairment and hallucinations in the last decade, in addition to tremor since a young age. The amino acid residue #382 is located in a transmembrane region and in silico analysis suggested a causative role for the variant. Modelling of the mutant protein structure showed that the variant causes a clash in the protein structure. Therefore, the variant could cause a conformational change that alters the ability of the protein in the modulation of ion channels Conclusions: The KCNN2 gene variant identified could be associated with ET. The variant could modify a voltage-independent potassium channel activated by intracellular calcium.

Cognitive Performance as a Function of MAPT Haplotype: A Prospective Longitudinal Study of an Essential Tremor Cohort

Background

Cognitive impairment is a feature of essential tremor (ET). There are no studies of the genetic drivers of this association. We examined whether the microtubule-associated protein tau (MAPT) H1 haplotype is associated with cognitive performance in ET.

Methods

ET cases genotyped for the MAPT H1 and H2 haplotypes completed a battery of neuropsychological tests at baseline and four follow-up evaluations. Chi-square, t-tests, and analyses of covariance examined associations between the presence of the MAPT H1 haplotype, cognitive diagnoses of normal, mild cognitive impairment (MCI), and dementia, and performance in specific cognitive domains.

Results

We observed no evidence of cognitive differences as a function of the presence of the MAPT H1 haplotype. Specifically, cases with (n = 57) and without (n = 42) this haplotype did not differ with respect to the prevalence of diagnoses of MCI or dementia, p ≥ 0.87. Moreover, cases with vs without this haplotype did not differ in either the age or point in the disease course at which observed conversions to MCI or dementia occurred, p's ≥ 0.51. Finally, no haplotype-related differences were observed in performance in the cognitive domains of attention, executive function, language, memory, visuospatial or global ability, p's ≥ 0.21, or in changes in performance in these domains across time, p's ≥ 0.08.

Discussion

The study in an ET cohort revealed no influence of MAPT haplotypes on cognitive performance. This study serves as a valuable foundation for future studies to expand our understanding of the genetic drivers of cognitive impairment in ET.

Highlights

This study found no evidence of cognitive differences between individuals with and without the MAPT H1 haplotype. Our work provides a valuable foundation for future work to expand our knowledge of the genetic drivers of cognitive impairment in ET.

Odds of Medical Comorbidities in Essential Tremor: Retrospective Analysis of a Large Claims Database in the United States

INTRODUCTION

Essential tremor (ET) is the most common tremor disorder, estimated to affect 7 million individuals in the USA. There is little empirical evidence on comorbidities among this population beyond higher prevalence of brain-related and stress-related disorders. This study aims to examine differences in the prevalence of the 31 Elixhauser comorbidities among ET patients compared to statistically similar control patients.

METHODS

An extract from Optum's de-identified Clinformatics® Data Mart Database (CDM) from 2018 to 2019 of adults aged 40-80 years with at least one claim with an ET diagnosis was propensity score matched to controls. Logistic regression was used to generate doubly robust adjusted odds ratios for each of the 31 Elixhauser comorbidities.

RESULTS

In these analyses, ET patients had significantly greater adjusted odds of depression, alcohol abuse, and other neurological disorders, as well as chronic pulmonary disease, renal failure, hyperthyroidism, and cardiac arrhythmias relative to controls. They also had lower odds of uncomplicated diabetes, congestive heart failure, metastatic cancer, paralysis, peripheral vascular disease, and fluid and electrolyte disorders.

CONCLUSION

A number of recent studies, including our own, suggest that psychiatric, neurologic, and stress-related disorders may be more prevalent among ET patients than controls. Additional differences in the prevalence of a range of medical comorbidities have also been variably reported across studies, suggesting that some combination of these might be more prevalent. Further studies would be of value in sorting through these associations.

Tremor is associated with familial clustering of dystonia

INTRODUCTION

Dystonia is a movement disorder of variable etiology and clinical presentation and is accompanied by tremor in about 50% of cases. Monogenic causes in dystonia are rare, but also in the group of non-monogenic dystonias 10-30% of patients report a family history of dystonia. This points to a number of patients currently classified as idiopathic that have at least in part an underlying genetic contribution. The present study aims to identify clinical and demographic features associated with heritability of yet idiopathic dystonia.

METHODS

Seven hundred thirty-three datasets were obtained from the DysTract dystonia registry, patients with acquired dystonia or monogenic causes were excluded. Affected individuals were assigned to a familial and sporadic group, and clinical features were compared across these groups. Additionally, the history of movement disorders was also counted in family members.

RESULTS

18.2% of patients reported a family history of dystonia. Groups differed in age at onset, disease duration and presence of tremor on a descriptive level. Logistic regression analysis revealed that tremor was the only predictor for a positive family history of dystonia (OR 2.49, CI = 1.54-4.11, p < 0.001). Tremor turned out to be the most common movement disorder in available relatives of patients, and presence of tremor in relatives was associated with tremor in index patients (X²(1) = 16.2, p < 0.001).

CONCLUSIONS

Tremor is associated with an increased risk of familial clustering of dystonia and with a family history of tremor itself. This indicates a hereditable dystonia-tremor syndrome with a clinical spectrum ranging from tremor-predominant diseases to dystonia.

Global Epidemiology of Movement Disorders: Rare or Underdiagnosed?

In this manuscript, we review the epidemiology of movement disorders including Parkinson's disease (PD), atypical parkinsonism, essential tremor, dystonia, functional movement disorders, tic disorders, chorea, and ataxias. We emphasize age-, sex-, and geography-based incidence and prevalence, as well as notable trends including the rising incidence and prevalence of PD. Given the growing global interest in refining clinical diagnostic skills in recognizing movement disorders, we highlight some key epidemiological findings that may be of interest to clinicians and health systems tasked with diagnosing and managing the health of patients with movement disorders.

Histopathology of the cerebellar cortex in essential tremor and other neurodegenerative motor disorders: comparative analysis of 320 brains

In recent years, numerous morphologic changes have been identified in the essential tremor (ET) cerebellar cortex, distinguishing ET from control brains. These findings have not been fully contextualized within a broader degenerative disease spectrum, thus limiting their interpretability. Building off our prior study and now doubling the sample size, we conducted comparative analyses in a postmortem series of 320 brains on the severity and patterning of cerebellar cortex degenerative changes in ET (n = 100), other neurodegenerative disorders of the cerebellum [spinocerebellar ataxias (SCAs, n = 47, including 13 SCA3 and 34 SCA1, 2, 6, 7, 8, 14); Friedreich's ataxia (FA, n = 13); multiple system atrophy (MSA), n = 29], and other disorders that may involve the cerebellum [Parkinson's disease (PD), n = 62; dystonia, n = 19] versus controls (n = 50). We generated data on 37 quantitative morphologic metrics, grouped into 8 broad categories: Purkinje cell (PC) loss, heterotopic PCs, PC dendritic changes, PC axonal changes (torpedoes), PC axonal changes (other than torpedoes), PC axonal changes (torpedo-associated), basket cell axonal hypertrophy, and climbing fiber-PC synaptic changes. Principal component analysis of z scored raw data across all diagnoses (11,651 data items) revealed that diagnostic groups were not uniform with respect to pathology. Dystonia and PD each differed from controls in only 4/37 and 5/37 metrics, respectively, whereas ET differed in 21, FA in 10, SCA3 in 10, MSA in 21, and SCA1/2/6/7/8/14 in 27. Pathological changes were generally on the milder end of the degenerative spectrum in ET, FA and SCA3, and on the more severe end of that spectrum in SCA1/2/6/7/8/14. Comparative analyses across morphologic categories demonstrated differences in relative expression, defining distinctive patterns of changes in these groups. In summary, we present a robust and reproducible method that identifies somewhat distinctive signatures of degenerative changes in the cerebellar cortex that mark each of these disorders.

Cerebellar α6GABAA Receptors as a Therapeutic Target for Essential Tremor: Proof-of-Concept Study with Ethanol and Pyrazoloquinolinones

Ethanol has been shown to suppress essential tremor (ET) in patients at low-to-moderate doses, but its mechanism(s) of action remain unknown. One of the ET hypotheses attributes the ET tremorgenesis to the over-activated firing of inferior olivary neurons, causing synchronic rhythmic firings of cerebellar Purkinje cells. Purkinje cells, however, also receive excitatory inputs from granule cells where the α6 subunit-containing GABAA receptors (α6GABAARs) are abundantly expressed. Since ethanol is a positive allosteric modulator (PAM) of α6GABAARs, such action may mediate its anti-tremor effect. Employing the harmaline-induced ET model in male ICR mice, we evaluated the possible anti-tremor effects of ethanol and α6GABAAR-selective pyrazoloquinolinone PAMs. The burrowing activity, an indicator of well-being in rodents, was measured concurrently. Ethanol significantly and dose-dependently attenuated action tremor at non-sedative doses (0.4-2.4 g/kg, i.p.). Propranolol and α6GABAAR-selective pyrazoloquinolinones also significantly suppressed tremor activity. Neither ethanol nor propranolol, but only pyrazoloquinolinones, restored burrowing activity in harmaline-treated mice. Importantly, intra-cerebellar micro-injection of furosemide (an α6GABAAR antagonist) had a trend of blocking the effect of pyrazoloquinolinone Compound 6 or ethanol on harmaline-induced tremor. In addition, the anti-tremor effects of Compound 6 and ethanol were synergistic. These results suggest that low doses of ethanol and α6GABAAR-selective PAMs can attenuate action tremor, at least partially by modulating cerebellar α6GABAARs. Thus, α6GABAARs are potential therapeutic targets for ET, and α6GABAAR-selective PAMs may be a potential mono- or add-on therapy.

Application of optimized convolutional neural networks for early aided diagnosis of essential tremor: Automatic handwriting recognition and feature analysis

Essential tremor (ET) is one of the most common neurological disorders, and its mainly clinical symptoms, including patient hand's kinetic tremor, dystonia, ataxia, etc., would influence the daily life of patients inordinately. Current ET diagnosis highly replies on the clinical evaluation and neurological examination, so the objective measurement indicators are particularly important in the auxiliary diagnosis of ET. In this research, the Archimedes spiral line freehand sketching samples without template assistance is collected and the Convolutional Neural Network (CNN) model of optimized structure is adopted to fully analyze the tremor, spacing of turns, shape, etc. shown in the handwriting samples of patients with ET, including the following main process: characteristics extraction, model visualization and subregional relevance evaluation. Dropout is used as a regularization technique in the network structure. The test group consisted of 50 patients with confirmed ET and the control group consisted of 40 healthy individuals. The main research objectives of this paper comprise two points: on the one hand, to achieve effective automatic classification of patients with ET and healthy controls using a scheme combining deep learning and simple hand mapping for the purpose of primary disease screening; on the other hand, to design sub-regional automatic classification experiments to demonstrate that Archimedean spiral hand drawings of patients with ET do have distinct local features, and to lay the experimental foundation for future hand drawing-based automatic aid for the identification of a variety of neurodegenerative diseases. Our model's average accuracy rate in test set reaches 89.3%, and average AUC is 0.972, with favorable stability and generalization performance. Besides, subregional characteristics recognition proofs that the spiral line samples of most of the patients with ET show more category-related characteristics in the local area of upper right, which provides evidences and theory update for predecessors' medical research.

Tremor assessment scales before, during and after MRgFUS for essential tremor - results, recommendations and implications

BACKGROUND

neurosurgical interventions such as MR-guided focused ultrasound (MRgFUS) are increasingly deployed for treatment of essential tremor.

OBJECTIVE

to make recommendations for monitoring treatment effects during and after MRgFUS based on our investigation of correlations between different scales of tremor severity.

METHODS

twenty-five clinical assessments were collected from thirteen patients before and after unilateral MRgFUS sequential lesioning of the thalamus and posterior subthalamic area for alleviating essential tremor. Scales included Bain Findley Spirography (BFS), Clinical Rating Scale for Tremor (CRST), Upper Extremity Total Tremor Score (UETTS) and Quality of Life of Essential Tremor (QUEST), and were documented at baseline, while lying in the scanner with stereotactic frame attached (BFS), and at 24-month follow-up.

RESULTS

the four different scales of tremor severity all correlated significantly. BFS and CRST showed a strong correlation of 0.833 (p < 0.001). BFS, UETTS and CRST correlated moderately with QUEST (ρ = 0.575-0.721, p < 0.001). BFS and UETTS correlated significantly with all CRST subparts, with the strongest correlation between UETTS and CRST part C (ρ = 0.831, p < 0.001). Moreover, BFS drawn sitting upright in an outpatient setting correlated with spirals drawn in a supine position on the scanner bed with the stereotactic frame attached.

CONCLUSION

we recommend a combination of BFS & UETTS for intraoperative assessment of awake essential tremor patients and BFS & QUEST for pre-operative and follow-up assessments, as these scale sets are quick and simple to collect and provide meaningful information whilst meeting the practical constraints of intraoperative assessment.

Limb positioning and magnitude of postural tremor ratings: A study of 100 essential tremor cases

BACKGROUND

Essential tremor (ET) is a highly prevalent movement disorder. As the diagnosis is purely clinical, it is important for clinicians to develop a reliable taxonomy of signs and symptoms of ET. Here, we investigate two common clinical maneuvers for determining the presence and severity of postural tremor in ET cases: the evaluation of tremor observed when arms are held in the outstretched and wing posture positions.

METHODS

Two movement disorders neurologists assessed tremor severity from videotaped neurological evaluations of 100 ET cases displaying outstretched and wing posture positions. These raters also completed a forced choice measure indicating whether upper limb tremor was more severe in the outstretched position, the wing posture position, or equivalent in the two positions.

RESULTS

Our raters judged tremor observed in the wing posture position to be more severe than tremor observed in the outstretched position (average ratings of 1.17 and 1.03, respectively, p's <0.05). This finding replicated across the two independent neurologists' ratings of tremor severity. Analyses of the forced choice measure revealed parallel results, with tremor observed in the wing posture position more often identified as more severe than tremor observed in the outstretched position (37.5% versus 14.5%, respectively, p < 0.05).

CONCLUSION

Our data reveal that ET cases generally display more severe upper limb tremor in the wing posture position than in the outstretched position. These findings having potential clinical and research implications, suggesting that postural tremor in ET may be more easily identified from observations of the wing posture than the outstretched position.

T-type calcium channels as therapeutic targets in essential tremor and Parkinson's disease

Neuronal action potential firing patterns are key components of healthy brain function. Importantly, restoring dysregulated neuronal firing patterns has the potential to be a promising strategy in the development of novel therapeutics for disorders of the central nervous system. Here, we review the pathophysiology of essential tremor and Parkinson's disease, the two most common movement disorders, with a focus on mechanisms underlying the genesis of abnormal firing patterns in the implicated neural circuits. Aberrant burst firing of neurons in the cerebello-thalamo-cortical and basal ganglia-thalamo-cortical circuits contribute to the clinical symptoms of essential tremor and Parkinson's disease, respectively, and T-type calcium channels play a key role in regulating this activity in both the disorders. Accordingly, modulating T-type calcium channel activity has received attention as a potentially promising therapeutic approach to normalize abnormal burst firing in these diseases. In this review, we explore the evidence supporting the theory that T-type calcium channel blockers can ameliorate the pathophysiologic mechanisms underlying essential tremor and Parkinson's disease, furthering the case for clinical investigation of these compounds. We conclude with key considerations for future investigational efforts, providing a critical framework for the development of much needed agents capable of targeting the dysfunctional circuitry underlying movement disorders such as essential tremor, Parkinson's disease, and beyond.