Essential tremor—a neurodegenerative disorder associated with cognitive defects?

Neuropsychology and Movement Disorders

Neuropsychology is important in differential diagnosis, treatment planning, surgical work-up, and support of patients with movement disorders and their families. The cognitive profiles of several movement disorders are reviewed here. The authors also review relevant neuropsychologic literature related to neurosurgic intervention and cognitive-enhancing medication for patients with movement disorders.

Dynamic functional changes upon thalamotomy in essential tremor depend on baseline brain morphometry

Patients with drug-resistant essential tremor (ET) may undergo Gamma Knife stereotactic radiosurgical thalamotomy (SRS-T), where the ventro-intermediate nucleus of the thalamus (Vim) is lesioned by focused beams of gamma radiations to induce clinical improvement. Here, we studied SRS-T impacts on left Vim dynamic functional connectivity (dFC, n = 23 ET patients scanned before and 1 year after intervention), and on surface-based morphometric brain features (n = 34 patients, including those from dFC analysis). In matched healthy controls (HCs), three dFC states were extracted from resting-state functional MRI data. In ET patients, state 1 spatial stability increased upon SRS-T (F1,22 = 19.13, p = 0.004). More frequent expression of state 3 over state 1 before SRS-T correlated with greater clinical recovery in a way that depended on the MR signature volume (t6 = 4.6, p = 0.004). Lower pre-intervention spatial variability in state 3 expression also did (t6 = - 4.24, p = 0.005) and interacted with the presence of familial ET so that these patients improved less (t6 = 4.14, p = 0.006). ET morphometric profiles showed significantly lower similarity to HCs in 13 regions upon SRS-T (z ≤ - 3.66, p ≤ 0.022), and a joint analysis revealed that before thalamotomy, morphometric similarity and states 2/3 mean spatial similarity to HCs were anticorrelated, a relationship that disappeared upon SRS-T (z ≥ 4.39, p < 0.001). Our results show that left Vim functional dynamics directly relates to upper limb tremor lowering upon intervention, while morphometry instead has a supporting role in reshaping such dynamics.

Harmaline toxicity on dorsal striatal neurons and its role in tremor

Harmaline is one of the β-carboline derivative compounds that is widely distributed in the food chain and human tissues. Harmine, a dehydrogenated form of harmaline, appeared to have a higher concentration in the brain, and appeared to be elevated in essential tremor (ET) and Parkinson's disease. Exogenous harmaline exposure in high concentration has myriad consequences, including inducing tremor, and causing neurodegeneration of Purkinje cells in the cerebellum. Harmaline-induced tremor is an established animal model for human ET, but its underlying mechanism is still controversial. One hypothesis posits that the inferior olive-cerebellum pathway is involved, and CaV3.1 T-type Ca2+ channel is a critical target of action. However, accumulating evidence indicates that tremor can be generated without disturbing T-type channels. This implies that additional neural circuits or molecular targets are involved. Using in vitro slice Ca2+-imaging and patch clamping, we demonstrated that harmaline reduced intracellular Ca2+ and suppressed depolarization-induced spiking activity of medium spiny striatal neurons (MSN), and this effect of harmaline can be partially attenuated by sulpiride (5 µM). In addition, the frequencies of spontaneous excitatory post-synaptic currents (sEPSCs) on MSNs were also significantly attenuated. Furthermore, the induced tremor in C57BL/6 J mice by harmaline injections (i.p. 12.5-18 mg/kg) was also shown to be attenuated by sulpiride (20 mg/kg). This series of experiments suggests that the dorsal striatum is a site of harmaline toxic action and might contribute to tremor generation. The findings also provide evidence that D2 signaling might be a part of the mechanism underlying essential tremor.

Wearable Accelerometer and Gyroscope Sensors for Estimating the Severity of Essential Tremor

BACKGROUND

Several validated clinical scales measure the severity of essential tremor (ET). Their assessments are subjective and can depend on familiarity and training with scoring systems.

METHOD

We propose a multi-modal sensing using a wearable inertial measurement unit for estimating scores on the Fahn-Tolosa-Marin tremor rating scale (FTM) and determine the classification accuracy within the tremor type. 17 ET participants and 18 healthy controls were recruited for the study. Two movement disorder neurologists who were blinded to prior clinical information viewed video recordings and scored the FTM. Participants drew a guided Archimedes spiral while wearing an inertial measurement unit placed at the mid-point between the lateral epicondyle of the humerus and the anatomical snuff box. Acceleration and gyroscope recordings were analyzed. The ratio of the power spectral density between frequency bands 0.5-4 Hz and 4-12 Hz, and the sum of power spectrum density over the entire spectrum of 2-74 Hz, for both accelerometer and gyroscope data, were computed. FTM was estimated using regression model and classification using SVM was validated using the leave-one-out method.

RESULTS

Regression analysis showed a moderate to good correlation when individual features were used, while correlation was high ([Formula: see text] = 0.818) when suitable features of the gyro and accelerometer were combined. The accuracy for two-class classification of the combined features using SVM was 91.42% while for four-class it was 68.57%.

CONCLUSION

Potential applications of this novel wearable sensing method using a wearable Inertial Measurement Unit (IMU) include monitoring of ET and clinical trials of new treatments for the disorder.

Neuropsychological assessment protocol in an ongoing randomized controlled trial on posterior subthalamic area vs. ventral intermediate nucleus deep brain stimulation for essential tremor

Objective

Patients with essential tremor (ET) may experience cognitive-affective impairment. Deep brain stimulation (DBS) of different targets, such as the ventral intermediate nucleus (VIM) of the thalamus or the posterior subthalamic area (PSA), has been shown to be beneficial for refractory ET. However, there is little evidence regarding the possible neuropsychological effects of PSA-DBS on patients with ET, and there are few studies comparing it with VIM-DBS in this population.In this study, we aim to present the evaluation protocol and neuropsychological battery as used in an ongoing trial of DBS for ET comparing the already mentioned targets.

Methods

As part of a randomized, double-blind, crossover clinical trial comparing the effectiveness and safety of PSA-DBS vs. VIM-DBS, 11 patients with refractory ET will undergo a multi-domain neuropsychological battery assessment. This will include a pre-/post-implantation assessment (3 months after the stimulation of each target and 6 months after an open stage of DBS on the most optimal target).

Conclusion

Evidence on the neuropsychological effects of DBS in patients with refractory ET is very scarce, particularly in lesser-explored targets such as PSA. This study could contribute significantly in this field, particularly on pre-procedure safety analysis for tailored patient/technique selection, and to complete the safety analysis of the procedure. Moreover, if proven useful, this proposed neuropsychological assessment protocol could be extensible to other surgical therapies for ET.

Visuomotor Adaptation Deficits in Patients with Essential Tremor

Essential tremor (ET) is a progressive movement disorder whose pathophysiology is not fully understood. Current evidence supports the view that the cerebellum is critically involved in the genesis of the tremor in ET. However, it is still unknown whether cerebellar dysfunction affects not only the control of current movements but also the prediction of future movements through dynamic adaptation toward a changed environment. Here, we tested the capacity of 28 patients with ET to adapt in a visuomotor adaptation task known to depend on intact cerebellar function. We found specific impairments in that task compared to age-matched healthy controls. Adaptation to the visual perturbation was disrupted in ET patients, while de-adaptation, the phase after abrupt removal of the perturbation, developed similarly to control subjects. Baseline tremor-independent motor performance was as well similar to healthy controls, indicating that adaptation deficits in ET patients were not rooted in an inability to perform goal-directed movements. There was no association between clinical severity scores of ET and early visuomotor adaptation abilities. These results provide further evidence that the cerebellum is dysfunctional in ET.

Exploring the heterogeneous morphometric data in essential tremor with probabilistic modelling

Essential tremor (ET) is a prevalent movement disorder characterized by marked clinical heterogeneity. Here, we explored the morphometric underpinnings of this cross-subject variability on a cohort of 34 patients with right-dominant drug-resistant ET and 29 matched healthy controls (HCs). For each brain region, group-wise morphometric data was modelled by a multivariate Gaussian to account for morphometric features' (co)variance. No group differences were found in terms of mean values, highlighting the limits of more basic group comparison approaches. Variance in surface area was higher in ET in the left lingual and caudal anterior cingulate cortices, while variance in mean curvature was lower in the right superior temporal cortex and pars triangularis, left supramarginal gyrus and bilateral paracentral gyrus. Heterogeneity further extended to the right putamen, for which a mixture of two Gaussians fitted the ET data better than a single one. Partial Least Squares analysis revealed the rich clinical relevance of the ET population's heterogeneity: first, increased head tremor and longer symptoms' duration were accompanied by broadly lower cortical gyrification. Second, more severe upper limb tremor and impairments in daily life activities characterized the patients whose morphometric profiles were more atypical compared to the average ET population, irrespective of the exact nature of the alterations. Our results provide candidate morphometric substrates for two different types of clinical variability in ET. They also demonstrate the importance of relying on analytical approaches that can efficiently handle multivariate data and enable to test more sophisticated hypotheses regarding its organization.

Morphometric features of drug-resistant essential tremor and recovery after stereotactic radiosurgical thalamotomy

Essential tremor (ET) is the most common movement disorder. Its neural underpinnings remain unclear. Here, we quantified structural covariance between cortical thickness (CT), surface area (SA), and mean curvature (MC) estimates in patients with ET before and 1 year after ventro-intermediate nucleus stereotactic radiosurgical thalamotomy, and contrasted the observed patterns with those from matched healthy controls. For SA, complex rearrangements within a network of motion-related brain areas characterized patients with ET. This was complemented by MC alterations revolving around the left middle temporal cortex and the disappearance of positive-valued covariance across both modalities in the right fusiform gyrus. Recovery following thalamotomy involved MC readjustments in frontal brain centers, the amygdala, and the insula, capturing nonmotor characteristics of the disease. The appearance of negative-valued CT covariance between the left parahippocampal gyrus and hippocampus was another recovery mechanism involving high-level visual areas. This was complemented by the appearance of negative-valued CT/MC covariance, and positive-valued SA/MC covariance, in the right inferior temporal cortex and bilateral fusiform gyrus. Our results demonstrate that different morphometric properties provide complementary information to understand ET, and that their statistical cross-dependences are also valuable. They pinpoint several anatomical features of the disease and highlight routes of recovery following thalamotomy.

Genomics as a Clinical Decision Support Tool for Identifying and Addressing Modifiable Causes of Cognitive Decline and Improving Outcomes: Proof of Concept Support for This Personalized Medicine Strategy

The landscape of therapeutics for mild cognitive impairment and dementia is quite limited. While many single-agent trials of pharmaceuticals have been conducted, these trials have repeatedly been unable to show improvement in cognition. It is hypothesized that because Alzheimer’s, like many other chronic illnesses, is not a monogenic illness, but is instead caused by the downstream effects of an individual’s genetic variants interacting with each other, the environment, and lifestyle, that improving outcomes will require a personalized, precision medicine approach. This approach requires identifying and then addressing contributing genomic and other factors specific to each individual in a simultaneous fashion. Until recently, the utility of genomics as part of clinical decision-making for Alzheimer’s and cognitive decline has been limited by the lack of availability of a genomic platform designed specifically to evaluate factors contributing to cognitive decline and how to respond to these factors The clinical decision support (CDS) platform used in the cases presented focuses on common variants that relate to topics including, but not limited to brain inflammation, amyloid processing, nutrient carriers, brain ischemia, oxidative stress, and detoxification pathways. Potential interventions based on the scientific literature were included in the CDS, but the final decision on what interventions to apply were chosen by each patient’s physician. Interventions included supplements with “generally regarded as safe (GRAS)” rating, along with targeted diet and lifestyle modifications. We hypothesize that a personalized genomically targeted approach can improve outcomes for individuals with mild cognitive impairment who are at high risk of Alzheimer’s. The cases presented in this report represent a subset of cases from three physicians’ offices and are meant to provide initial proof of concept data demonstrating the efficacy of this method and provide support for this hypothesis. These patients were at elevated risk for Alzheimer’s due to their apolipoprotein E ε4 status. While further prospective and controlled trials need to be done, initial case reports are encouraging and lend support to this hypothesis of the benefit of a genomically targeted personalized medicine approach to improve outcomes in individuals with cognitive decline who are at high risk for Alzheimer’s.

Is essential tremor a degenerative or an electrical disorder? Electrical disorder

Essential tremor (ET) is one of the most common movement disorders, yet we do not have a complete understanding of its pathophysiology. From a phenomenology standpoint, ET is an isolated tremor syndrome of bilateral upper limb action tremor with or without tremor in other body locations. ET is a pathological tremor that arises from excessive oscillation in the central motor network. The tremor network comprises of multiple brain regions including the inferior olive, cerebellum, thalamus, and motor cortex, and there is evidence that a dynamic oscillatory disturbance within this network leads to tremor. ET is a chronic disorder, and the natural history shows a slow progression of tremor intensity with age. There are reported data suggesting that ET follows the disease model of a neurodegenerative disorder, however whether ET is a degenerative or electrical disorder has been a subject of debate. In this chapter, we will review cumulative evidence that ET as a syndrome is a fundamentally electric disorder. The etiology is likely heterogenous and may not be primarily neurodegenerative.

Association of Essential Tremor With Dementia and Affective Disorders: A Meta-Analysis

Background

The dementia and affective disorders are common non-motor features in patients with essential tremor (ET). However, the relationship of ET with cognitive impairments and affective disorders remains controversial. This meta-analysis aimed to analyze the association of ET with dementia and affective disorders.

Methods

Original studies published from January 1999 to October 2019 were systematically searched from the database of Medline (OvidSP), EMBASE (OvidSP), and the Cochrane Central Register of Controlled Trials. Pooled standard mean difference (SMD, random effect model), odds ratios (ORs), relative risk (RR), and 95% CI were calculated.

Results

Compared with the Non-ET group, patients with ET had significantly lower Mini-Mental State Examination (MMSE) score (SMD, −1.16; 95% CI, −1.75 to −0.58; p = 0.0001) and had significantly higher depressive and anxiety symptoms scale score (SMD, 0.55; 95% CI, 0.22–0.87; p = 0.0009). The OR for dementia and affective disorders in individuals with ET compared with individuals without ET was 2.49 (95% CI, 2.17–2.85, p &lt; 0.00001). While there was no significant difference in Montreal Cognitive Assessment (MoCA) score between ET and Non-ET groups (SMD, −0.52; 95% CI, −0.16 to 0.13; p = 0.23), there was a significant difference in the risk of mortality between ET and Non-ET groups (RR = 4.69, 95% CI, 2.18–10.07).

Conclusion

The non-motor symptoms should not be neglected among patients with ET. However, the causal relationship between ET and dementia, depression, and anxiety is unclear.

Essential tremor

Essential tremor (ET) is one of the most common movement disorders, with a reported >60 million affected individuals worldwide. The definition and underlying pathophysiology of ET are contentious. Patients present primarily with motor features such as postural and action tremors, but may also have other non-motor features, including cognitive impairment and neuropsychiatric symptoms. Genetics account for most of the ET risk but environmental factors may also be involved. However, the variable penetrance and challenges in validating data make gene-environment analysis difficult. Structural changes in cerebellar Purkinje cells and neighbouring neuronal populations have been observed in post-mortem studies, and other studies have found GABAergic dysfunction and dysregulation of the cerebellar-thalamic-cortical circuitry. Commonly prescribed medications include propranolol and primidone. Deep brain stimulation and ultrasound thalamotomy are surgical options in patients with medically intractable ET. Further research in post-mortem studies, and animal and cell-based models may help identify new pathophysiological clues and therapeutic targets and, together with advances in omics and machine learning, may facilitate the development of precision medicine for patients with ET.

Patient-specific effects on sonication heating efficiency during magnetic resonance-guided focused ultrasound thalamotomy

PURPOSE

During magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy for refractory tremor, high temperatures must be achieved and sustained for tissue necrosis. We assessed the impact of both patient-specific as well as procedure-related factors on the efficiency of acoustic energy transfer, or heating efficiency (HE).

METHODS

Retrospective analysis of 92 consecutive patients (857 sonications) with essential tremor or tremor-dominant Parkinson's disease treated at a single institution. Temperature elevations at the target were measured for each sonication with MR thermometry. HE of each sonication was defined as the ratio of peak temperature elevation and the delivered energy. HE was analyzed with respect to patient skull features (area, thickness, skull density ratio [SDR]), computed from CT scans, as well as demographic and clinical variables (age, sex, diagnosis, and duration of symptoms).

RESULTS

Across the full range of sonication energies that can be delivered with current devices (up to 36 kJ), average sonication HE was diminished in patients with lower SDR. In individual subjects, there was a progressive loss in HE as sonication energy was titrated up throughout the course of treatment, with a more rapid decline in patients with higher SDR. This energy-dependent loss in HE was not related to procedural factors, namely, the number of previous sonications, or the cumulative energy deposited during previous sonications. In contrast to SDR, neither skull area nor thickness was an independent predictor of average HE or the rate of its decline with increasing energies. In 11% of patients, all of whom with SDR < 0.45, sonication HE fell below the threshold to reach 54°C even with delivery of maximum energy. In contrast, temperatures ≥ 50°C could be obtained in all but one patient.

CONCLUSIONS

SDR is predictive of sonication HE, and determines patient-specific limits on the magnitude of temperature elevation that can be achieved with current devices. These data inform strategies for predictable lesioning in MRgFUS thalamotomy.

Essential Tremor Within the Broader Context of Other Forms of Cerebellar Degeneration

Essential tremor (ET) has recently been reconceptualized by many as a degenerative disease of the cerebellum. Until now, though, there has been no attempt to frame it within the context of these diseases. Here, we compare the clinical and postmortem features of ET with other cerebellar degenerations, thereby placing it within the broader context of these diseases. Action tremor is the hallmark feature of ET. Although often underreported in the spinocerebellar ataxias (SCAs), action tremors occur, and it is noteworthy that in SCA12 and 15, they are highly prevalent, often severe, and can be the earliest disease manifestation, resulting in an initial diagnosis of ET in many cases. Intention tremor, sometimes referred to as "cerebellar tremor," is a common feature of ET and many SCAs. Other features of cerebellar dysfunction, gait ataxia and eye motion abnormalities, are seen to a mild degree in ET and more markedly in SCAs. Several SCAs (e.g., SCA5, 6, 14, and 15), like ET, follow a milder and more protracted disease course. In ET, numerous postmortem changes have been localized to the cerebellum and are largely confined to the cerebellar cortex, preserving the cerebellar nuclei. Purkinje cell loss is modest. Similarly, in SCA3, 12, and 15, Purkinje cell loss is limited, and in SCA12 and 15, there is preservation of cerebellar nuclei and relative sparing of other central nervous system regions. Both clinically and pathologically, there are numerous similarities and intersection points between ET and other disorders of cerebellar degeneration.

Analysis of Fine Motor Skills in Essential Tremor: Combining Neuroimaging and Handwriting Biomarkers for Early Management

Essential tremor (ET) is a highly prevalent neurological disorder characterized by action-induced tremors involving the hand, voice, head, and/or face. Importantly, hand tremor is present in nearly all forms of ET, resulting in impaired fine motor skills and diminished quality of life. To advance early diagnostic approaches for ET, automated handwriting tasks and magnetic resonance imaging (MRI) offer an opportunity to develop early essential clinical biomarkers. In this study, we present a novel approach for the early clinical diagnosis and monitoring of ET based on integrating handwriting and neuroimaging analysis. We demonstrate how the analysis of fine motor skills, as measured by an automated Archimedes' spiral task, is correlated with neuroimaging biomarkers for ET. Together, we present a novel modeling approach that can serve as a complementary and promising support tool for the clinical diagnosis of ET and a large range of tremors.

Phenotypic Features of Isolated Essential Tremor, Essential Tremor Plus, and Essential Tremor-Parkinson's Disease in a Movement Disorders Clinic

Background:

Patients with essential tremor were initially considered to have isolated tremor, but additional motor and non-motor features have been increasingly recognized. The term “essential tremor plus” was adopted by the Task Force on Tremor of the International Parkinson and Movement Disorder Society to describe essential tremor patients with additional neurologic signs.

Objectives:

To characterize essential tremor patients and their phenotypes in a movement disorders clinic population in the context of the new tremor classification.

Methods:

Demographic, clinical, historical, treatment, and diagnostic data were retrospectively collected on 300 patients diagnosed by movement disorder experts with essential tremor. Patients were classified as having essential tremor, essential tremor plus, or essential tremor-Parkinson’s disease combination, and features between these groups were compared.

Results:

Of the 300 patients, 20.7% were classified as isolated essential tremor, 53.3% as essential tremor plus, and 26.0% as essential tremor-Parkinson’s disease. There was no significant difference in the duration of tremor symptoms. Essential tremor plus patients were more likely to have dystonia, tandem gait abnormalities, head tremor and greater tremor severity. Essential tremor-Parkinson’s disease patients were more likely to have RBD symptoms. There was no significant difference in cognitive impairment between essential tremor plus and essential tremor-Parkinson’s disease patients.

Conclusions:

Additional motor and non-motor features, including parkinsonism, are common in patients with essential tremor. Further studies are needed to clarify essential tremor phenotypes and to provide insights into possible subtypes.

Highlights:

300 patients with essential tremor from a movement disorders clinic were re-classified based on the Movement Disorder Society Consensus Statement on the Classification of Tremors. Additional motor and non-motor features, including parkinsonism, were common, and only 20.7% of patients remained classified as isolated essential tremor.

Orthostatic Hypotension in Elderly Patients with Essential Tremor

PURPOSE

Essential tremor (ET) is the most common movement disorder in which dysautonomia symptoms can be present. We aimed to evaluate the presence of orthostatic hypotension (OH) and its relationship with the clinical features.

PATIENTS AND METHODS

Forty-four elderly patients with ET and 118 healthy elderly controls were included. OH was assessed via the head-up tilt table test and defined, according to the change in position, as a drop of at least 20 mmHg in systolic blood pressure and/or 10 mmHg in diastolic blood pressure. Tremor severity was evaluated using the Fahn-Tolosa-Marin Tremor Rating (FTMTR) Scale. All patients underwent geriatric comprehensive assessment.

RESULTS

There were no differences between the controls and patients with ET regarding age and gender. The mean age was 72.8±6.1, the mean disease duration 19.1±13.5 years and the mean FTMTR score was 30.9±17.1 in patients with ET. The frequency of OH at the 1st minute in patients with ET was higher than in controls (31.8% vs 17.8%, p=0.046). Furthermore, the frequency of jaw tremor in patients with OH was higher than in those without OH (35.7% vs 6.7%, p=0.025). About 28.6% of ET patients with OH had orthostatic symptoms.

CONCLUSION

We demonstrated that ET patients, particularly those with jaw tremors, had OH and that most of them were asymptomatic. Therefore, in order to protect patients from complications related to OH, it would be appropriate to evaluate OH in the follow-up and treatment of elderly patients with ET.

Association between positive history of essential tremor and disease progression in patients with Parkinson's disease

This study aimed to explore the effect of pre-existing essential tremor (ET) history on the disease progression of Parkinson’s disease (PD). We recruited and followed-up a group of PD patients from March 2009 to July 2020. The ET history of each patient was obtained by retrospective interviews or past medical records. Cox proportional hazards models with inverse probability of treatment weighting (IPTW) were used to estimate the hazard ratio (HR) with 95% confidence intervals (CIs). Of 785 patients who completed the followed-up visits, 61 patients (7.8%) reported a history of pre-existing ET. Cox regression models after IPTW indicated that the positive ET history in patients with PD was protective against time to United PD Rating Scale III 14-point increase (HR = 0.301, 95% CI = 0.134–0.678, P = 0.004), time to akinesia and rigidity 8-point increase (HR = 0.417, 95% CI = 0.218–0.796, P = 0.008), time to conversion to Hoehn and Yahr stage 3 (HR = 0.356, 95% CI = 0.131–0.969, P = 0.043), time to develop dyskinesia (HR = 0.160, 95% CI = 0.037–0.698, P = 0.015), and time to Montreal Cognitive Assessment 3-point decrease (HR = 0.389, 95% CI = 0.160–0.946, P = 0.037), but had no relationship with time to tremor 4-point increase (HR = 1.638, 95% CI = 0.822–3.266, P = 0.161) and time to death (HR = 0.713, 95% CI = 0.219–2.319, P = 0.574). Our study indicated that ET history in patients with PD is associated with a benign prognosis with slower motor and non-motor progression.

Classification of Parkinson's disease and essential tremor based on balance and gait characteristics from wearable motion sensors via machine learning techniques: a data-driven approach

BACKGROUND

Parkinson's disease (PD) and essential tremor (ET) are movement disorders that can have similar clinical characteristics including tremor and gait difficulty. These disorders can be misdiagnosed leading to delay in appropriate treatment. The aim of the study was to determine whether balance and gait variables obtained with wearable inertial motion sensors can be utilized to differentiate between PD and ET using machine learning. Additionally, we compared classification performances of several machine learning models.

METHODS

This retrospective study included balance and gait variables collected during the instrumented stand and walk test from people with PD (n = 524) and with ET (n = 43). Performance of several machine learning techniques including neural networks, support vector machine, k-nearest neighbor, decision tree, random forest, and gradient boosting, were compared with a dummy model or logistic regression using F1-scores.

RESULTS

Machine learning models classified PD and ET based on balance and gait characteristics better than the dummy model (F1-score = 0.48) or logistic regression (F1-score = 0.53). The highest F1-score was 0.61 of neural network, followed by 0.59 of gradient boosting, 0.56 of random forest, 0.55 of support vector machine, 0.53 of decision tree, and 0.49 of k-nearest neighbor.

CONCLUSIONS

This study demonstrated the utility of machine learning models to classify different movement disorders based on balance and gait characteristics collected from wearable sensors. Future studies using a well-balanced data set are needed to confirm the potential clinical utility of machine learning models to discern between PD and ET.

Prodromal Markers of Parkinson's Disease in Patients With Essential Tremor

Background: Essential tremor (ET) is manifested as an isolated syndrome of bilateral upper limb action tremor. Parkinson's disease (PD) is the second most common neurodegenerative disease, with typical motor symptoms of bradykinesia, rigidity, and resting tremor. ET-PD describes the new-onset of PD in ET patients. Recently, numerous studies on epidemiology, genetics, pathology, clinical features, and neuroimaging studies are challenging the idea that ET is an isolated disease, suggesting that patients with ET have the tendency to develop PD. Methods: In this review article, we collected recent findings that reveal prodromal markers of PD in patients with ET. Results: Substantia nigra hyperechogenicity serves as a prodromal marker for predicting the development of PD in patients with ET and provides a reference for therapeutic strategies. Additional potential markers include other neuroimaging, clinical features, heart rate, and genetics, whereas others lack sufficient evidence. Conclusion: In consideration of the limited research of PD in patients with ET, we are still far from revealing the prodromal markers. However, from the existing follow-up studies on ET patients, Substantia nigra hyperechogenicity may enable further exploration of the relationship between ET and PD and the search for pathogenesis-based therapies.

Essential tremor: the most common form of cerebellar degeneration?

Background

The degenerative cerebellar ataxias comprise a large and heterogeneous group of neurological diseases whose hallmark clinical feature is ataxia, and which are accompanied, to variable degrees, by other features that are attributable to cerebellar dysfunction. Essential tremor (ET) is an exceptionally common neurological disease whose primary motor feature is action tremor, although patients often manifest intention tremor, mild gait ataxia and several other features of cerebellar dysfunction.

Main Body

In this paper, we review the abundant evidence derived from clinical, neuroimaging and postmortem studies, linking ET to cerebellar dysfunction. Furthermore, we review the combination of clinical, natural history and postmortem features suggesting that ET is neurodegenerative. We then compare the prevalence of ET (400 – 900 cases per 100,000) to that of the other cerebellar degenerations (ranging from <0.5 – 9 cases per 100,000, and in composite likely to be on the order of 20 cases per 100,000) and conclude that ET is 20 to 45 times more prevalent than all other forms of cerebellar degeneration combined.

Conclusion

Given the data we present, it is logical to conclude that ET is, by far, the most common form of cerebellar degeneration.

Quantitative Separation of Tremor and Ataxia in Essential Tremor

OBJECTIVE

This study addresses an important problem in neurology, distinguishing tremor and ataxia using quantitative methods. Specifically, we aimed to quantitatively separate dysmetria, a cardinal sign of ataxia, from tremor in essential tremor (ET).

METHODS

In Experiment 1, we compared 19 participants diagnosed with ET undergoing thalamic deep brain stimulation (DBS; ET_DBS ) to 19 healthy controls (HC). We quantified tremor during postural tasks using accelerometry and dysmetria with fast, reverse-at-target goal-directed movements. To ensure that endpoint accuracy was unaffected by tremor, we quantified dysmetria in selected trials manifesting a smooth trajectory to the endpoint. Finally, we manipulated tremor amplitude by switching DBS ON and OFF to examine its effect on dysmetria. In Experiment 2, we compared 10 ET participants with 10 HC to determine whether we could identify and distinguish dysmetria from tremor in non-DBS ET.

RESULTS

Three findings suggest that we can quantify dysmetria independently of tremor in ET. First, ET_DBS and ET exhibited greater dysmetria than HC and dysmetria did not correlate with tremor (R²  < 0.01). Second, even for trials with tremor-free trajectories to the target, ET exhibited greater dysmetria than HC (p < 0.01). Third, activating DBS reduced tremor (p < 0.01) but had no effect on dysmetria (p > 0.2).

INTERPRETATION

We demonstrate that dysmetria can be quantified independently of tremor using fast, reverse-at-target goal-directed movements. These results have important implications for the understanding of ET and other cerebellar and tremor disorders. Future research should examine the neurophysiological mechanisms underlying each symptom and characterize their independent contribution to disability. ANN NEUROL 2020;88:375-387.

Aberrant global and local efficiency of the executive subnetwork in essential tremor

This study aims to use probabilistic tractography to ascertain the global (GE) and local efficiency (LE) of the executive subnetwork in essential tremor (ET). Significantly lower GE of the whole executive subnetwork and lower LE of the left rostral middle frontal gyrus, frontal pole, inferior frontal gyrus, bilateral anterior cingulate cortex, and medial orbitofrontal cortex. These results imply ineffective and inadequate communication of the executive subnetwork, and may be causally associated with the executive dysfunction observed in ET.

Expansion of GGC repeat in the human-specific NOTCH2NLC gene is associated with essential tremor

Essential tremor is one of the most common movement disorders. Despite its high prevalence and heritability, the genetic aetiology of essential tremor remains elusive. Up to now, only a few genes/loci have been identified, but these genes have not been replicated in other essential tremor families or cohorts. Here we report a genetic study in a cohort of 197 Chinese pedigrees clinically diagnosed with essential tremor. Using a comprehensive strategy combining linkage analysis, whole-exome sequencing, long-read whole-genome sequencing, repeat-primed polymerase chain reaction and GC-rich polymerase chain reaction, we identified an abnormal GGC repeat expansion in the 5′ region of the NOTCH2NLC gene that co-segregated with disease in 11 essential tremor families (5.58%) from our cohort. Clinically, probands that had an abnormal GGC repeat expansion were found to have more severe tremor phenotypes, lower activities of daily living ability. Obvious genetic anticipation was also detected in these 11 essential tremor-positive families. These results indicate that abnormal GGC repeat expansion in the 5′ region of NOTCH2NLC gene is associated with essential tremor, and provide strong evidence that essential tremor is a family of diseases with high clinical and genetic heterogeneities.

Enfeeblement in Essential Tremor: Development and Validation of a New Psychometric Measure

INTRODUCTION

Despite a growing body of knowledge regarding essential tremor (ET), past studies have fallen short in capturing the full impact of ET on patients and caregivers. We propose enfeeblement (i.e., having the qualities of being prematurely old, helpless, or debilitated) as a novel clinical outcome measure in ET. Due to the lack of enfeeblement scales for ET in the literature, we developed and validated an enfeeblement scale for ET.

METHODS

The Essential Tremor Enfeeblement Survey (ETES) consists of eight 5-point Likert-type scale questions and is designed to be a caregiver-reported outcome.

RESULTS

Enfeeblement scores showed a floor effect of 15.3%, no ceiling effects, and demonstrated good overall test-retest reliability (intraclass correlation coefficient = 0.73), favorable internal consistency (Cronbach α coefficient = 0.92) and good convergent validity.

CONCLUSION

The ETES has robust properties. Aside from future studies of enfeeblement in ET, enfeeblement should be explored more broadly as a psychometric measure across other neurological disorders.

Abnormal hippocampal subfields are associated with cognitive impairment in Essential Tremor

Multi-domain cognitive impairment (CI) has been frequently described in patients with essential tremor (ET). However, the exact neuroanatomical basis for this impairment is uncertain. This study aims to ascertain the role of the hippocampal formation in cognitive impairment in ET. Forty patients with ET and 40 age, gender and education matched healthy controls (HC) were enrolled. Cognition was assessed using a structured neuropsychological battery and patients were categorized as ET with CI (ETCI) and ET without CI (ETNCI). Automatic segmentation of hippocampal subfields was performed using FreeSurfer 6.0. The obtained volumes were correlated with scores of neuropsychological tests. Significant atrophy of the left subiculum, CA4, granule-cell layer of dentate gyrus, right molecular layer, and hypertrophy of bilateral parasubiculum, right hippocampus-amygdala-transition-area, bilateral hippocampal tail (HT) and widening of right hippocampal fissure was observed in ET. Trends toward atrophy of right subiculum, and widening of left HF was also observed. Comparison of HC and ETCI revealed atrophy of right subiculum, hypertrophy of bilateral parasubiculum, HT, and widening of left HF. ETCI showed a trend toward widening of right HF. ETNCI had isolated left parasubicular hypertrophy and in comparison, to ETNCI the ETCI subgroup had atrophy of bilateral fimbria. Significant correlations were observed between the volumes of HT, HF, fimbria and scores of tests for executive function, working and verbal memory. Patients with ET have significant volumetric abnormalities of several hippocampal subfields and these abnormalities may be important contributors for some forms of cognitive impairment observed in ET.

Mind the gaps: What we don't know about cognitive impairment in essential tremor

INTRODUCTION

Although the hallmark feature of essential tremor (ET) is tremor, there is growing appreciation that cognitive impairment also occurs, including increased prevalence of mild cognitive impairment (MCI) and increased prevalence and incidence of dementia. With emerging knowledge of ET-cognitive impairment, come fundamental questions regarding its course, bases, predictors and clinical outcomes. Studies in the general population and in Parkinson's disease (PD), a related movement disorder, offer a starting point from which to begin filling these clinically important knowledge gaps.

METHODS

A PubMed search (June 2018) identified articles for this review.

RESULTS

Much of our knowledge of cognitive impairment in ET is of the static condition (e.g., prevalence of cognitive impairment in ET), with nearly no information on its bases, predictors and dynamics (i.e., course, and clinical outcomes). In PD, where such data have been published, rates of cognitive decline and conversion to MCI/dementia are higher than in the general population. Predictors of cognitive change in PD and the general population have also been identified, yet they only partially overlap one another.

CONCLUSION

The predictors and dynamics of cognitive impairment have been investigated fairly extensively in the general population, to a somewhat lesser extent in PD, and are emerging only now in ET. We suggest that longitudinal studies specific to ET are needed, and we outline variables to be considered in these investigations. Increased knowledge of ET-cognitive impairment will facilitate meaningful counseling of patients and their families.

Phenotypic Variability of Essential Tremor Based on the Age at Onset

Background: Essential tremor (ET) is reported to have a bimodal distribution of age at onset (AAO) with phenotypic variability based on the AAO. This study aims to explore the distribution of AAO based on mathematical modeling and ascertain the differences, if any, in the clinical features of groups. Methods: A chart review was conducted for 252 patients with ET diagnosed based on the Consensus statement of the Movement Disorder Society on Tremor. Finite mixture modeling was performed to identify groups of the cohort based on the AAO. Results: Three groups were defined: early onset (EO): AAO ≤ 22 years, n = 63, intermediate onset (IO): 23 ≤ AAO ≤ 35 years, n = 43, and late onset (LO): AAO ≥ 36 years, n = 146. There were no significant differences related to family history or responsiveness to alcohol. The EO group had significantly higher prevalence of upper limb and lower limb tremor. Head tremor and voice tremor was more prevalent in the IO and LO groups. Cerebellar signs showed a significant increase with an increase in AAO. Conclusions: ET shows significant phenotypic variability based on the AAO. Patients with an early AAO are more likely to develop an appendicular tremor, whereas the probability of axial tremor and cerebellar signs increases with increasing AAO.

What Predicts Mortality in Essential Tremor? A Prospective, Longitudinal Study of Elders

Objective: Essential tremor (ET) is among the most common neurologic diseases. Although in the past it was considered a benign condition, recent research has demonstrated increased risk of mortality. To date, however, no studies have examined predictors of mortality in ET.

Methods: In a longitudinal, prospective study of 141 elders with ET, we used Cox proportional-hazards models to estimate hazard ratios (HRs) for death.

Results: The mean baseline age was 81.1 ± 8.8 years. During the follow-up interval, 27 (19.1%) died. Average time from baseline to death was 12.3 ± 8.7 months (range = 0.3–31.2). In univariate Cox regression models, older age (HR = 1.16, p < 0.001), lower Montreal Cognitive Assessment score (HR = 0.88, p = 0.004), higher Clinical Dementia Rating (CDR) score (HR = 4.53, p < 0.001), higher score on the Geriatric Depression scale (GDS) (HR = 1.07, p = 0.048), less balance confidence (HR = 0.98, p = 0.006), more falls (HR = 1.11, p = 0.003), and more tandem mis-steps (HR = 1.53, p = 0.004) were associated with increased risk of mortality. In the final multivariate Cox model, older age (HR = 1.14, p = 0.005), higher CDR score (HR = 3.80, p = 0.002) and higher GDS (HR = 1.11, p = 0.01) were independently associated with increased risk of mortality.

Conclusions: This study highlights several independent predictors of mortality in elderly ET; clinicians should consider screening for depressive symptoms, assessing cognition and tracking CDR scores, and assessing balance while evaluating patients with ET.

Essential tremor

Essential tremor (ET) is one of the most common neurologic disorders, and genetic factors are thought to contribute significantly to disease etiology. There has been a relative lack of progress in understanding the genetic etiology of ET. This could reflect a number of factors, including the presence of substantial phenotypic and genotypic heterogeneity. Thus, a meticulous approach to phenotyping is important for genetic research. A lack of standardized phenotyping across studies and patient centers likely has contributed to the relative lack of success of genomewide association studies in ET. To dissect the genetic architecture of ET, whole-genome sequencing will likely be of value. This will allow specific hypotheses about the mode of inheritance and genetic architecture to be tested. A number of approaches still remain unexplored in ET genetics, including the contribution of copy number variants, uncommon moderate-effect alleles, rare variant large-effect alleles (including Mendelian and complex/polygenic modes of inheritance), de novo and gonadal mosaicism, epigenetic changes, and noncoding variation.

Probable REM-Sleep Behavior Disorder and Dysautonomic Symptoms in Essential Tremor

Background

Non-motor symptoms can be present in essential tremor (ET). We intend to assess the frequency of rapid eye movement (REM) sleep behavior disorder (RBD) and dysautonomic symptoms in ET patients and evaluate the differences between patients with ET and RBD (ET-RBD and ET without RBD [ET-nonRBD]).

Methods

All ET patients were contacted by telephone. Autonomic symptoms were assessed using the Scales for Outcomes in Parkinson's Disease-Autonomic (SCOPA-AUT) questionnaire, and RBD symptoms with the RBD screening questionnaire (RBDSQ) using ≥5 as a cut-off for probable RBD (pRBD).

Results

From 92 ET patients contacted, 53 (55% female) were included. The mean age at assessment was 73.6±19 years, and the average disease duration was 19.9±17.3 years. Fourteen patients (26.4%) had pRBD and 52 (98.1%) reported at least one autonomic symptom, the most prevalent being urinary symptoms (96%). The ET-RBD group had higher SCOPA-total and thermoregulatory scores than ET-nonRBD patients (13.9±9.6 vs. 7.7±5.1, p=0.017 and 2.5±2.0 vs. 0.9±1.6, p=0.001). There were no other differences between groups.

Discussion

Our results suggest that pRBD is common in ET, and its presence is associated with dysautonomic symptoms. As these symptoms are known to be prodromal symptoms of Parkinson's disease (PD), we question if this patient subgroup has a higher risk of developing a synucleinopathy.

Is there a Premotor Phase of Essential Tremor?

BACKGROUND

Essential tremor (ET) is the most common tremor disorder. In addition to its hallmark feature, kinetic tremor of the upper limbs, patients may have a number of non-motor symptoms and signs (NMS). Several lines of evidence suggest that ET is a neurodegenerative disorder and certain NMS may antedate the onset of tremor. This article comprehensively reviews the evidence for the existence of a "premotor phase" of ET, and discusses plausible biological explanations and implications.

METHODS

A PubMed search in May 2017 identified articles for this review.

RESULTS

The existence of a premotor phase of ET gains support primarily from longitudinal data. In individuals who develop incident ET, baseline (i.e., premotor) evaluations reveal greater cognitive dysfunction, a faster rate of cognitive decline, and the presence of a protective effect of education against dementia. In addition, baseline evaluations also reveal more self-reported depression, antidepressant medication use, and shorter sleep duration in individuals who eventually develop incident ET. In cross-sectional studies, certain personality traits and NMS (e.g., olfactory dysfunction) also suggest the existence of a premotor phase.

DISCUSSION

There is preliminary evidence supporting the existence of a premotor phase of ET. The mechanisms are unclear; however, the presence of Lewy bodies in some ET brains in autopsy studies and involvement of multiple neural networks in ET as evident from the neuroimaging studies, are possible contributors. Most evidence is from a longitudinal cohort (Neurological Disorders of Central Spain: NEDICES); additional longitudinal studies are warranted to gain better insights into the premotor phase of ET.

Mild Cognitive Impairment Subtypes in a Cohort of Elderly Essential Tremor Cases

OBJECTIVES

Individuals with essential tremor (ET) exhibit a range of cognitive deficits generally conceptualized as "dysexecutive" or "fronto-subcortical," and thought to reflect disrupted cortico-cerebellar networks. In light of emerging evidence that ET increases risk for Alzheimer's disease (AD), it is critical to more closely examine the nature of specific cognitive deficits in ET, with particular attention to amnestic deficits that may signal early AD.

METHODS

We performed a cross-sectional analysis of baseline data from 128 ET cases (age 80.4±9.5 years) enrolled in a longitudinal, clinical-pathological study. Cases underwent a comprehensive battery of motor-free neuropsychological tests and a functional assessment to inform clinical diagnoses of normal cognition (ET-NC), mild cognitive impairment (MCI) (ET-MCI), or dementia (ET-D). ET-MCI was subdivided into subtypes including: amnestic single-domain (a-MCI), amnestic multi-domain (a-MCI+), non-amnestic single-domain (na-MCI), or non-amnestic multi-domain (na-MCI+).

RESULTS

Ninety-one (71.1%) cases were ET-NC, 24 (18.8%) were ET-MCI, and 13 (10.2%) were ET-D. Within MCI, the a-MCI+ subtype was the most common (13/24; 54.2%) followed by a-MCI (4/24; 16.7%), na-MCI+ (4/24; 16.7%), and na-MCI (3/24; 12.5%). Cases with amnestic MCI demonstrated lower recognition memory Z-scores (-2.4±1.7) than non-amnestic groups (-0.9±1.2) (p=.042).

CONCLUSIONS

Amnestic MCI, defined by impaired memory recall but associated with lower memory storage scores, was the most frequent MCI subtype in our study. Such impairment has not been explicitly discussed in the context of ET and may be an early hallmark of AD. Results have implications for the prognosis of specific cognitive deficits in ET. (JINS, 2017, 23, 390-399).

Increased risk of essential tremor in migraine: A population-based retrospective cohort study

Purpose

To examine the long-term risk of essential tremor (ET) in migraine.

Methods

Using population-based administrative data from a subset of the National Health Insurance Research Database (NHIRD) of Taiwan, we identified 22,696 newly diagnosed migraineurs (mean age 44.5 years) and a matched migraine-free cohort of 90,784 individuals in the period 2000–2008. Multivariable Cox proportional hazards regression analysis was conducted for assessing the ET risk for the migraine cohort compared to the migraine-free cohort.

Results

After adjusting for covariates, the migraine cohort had a 1.83-fold increased risk (95% CI 1.50–2.23) of subsequent ET in comparison to the migraine-free cohort (8.97 vs. 4.81 per 10,000 person-years). In the subgroup analysis, patients with migraine were associated with higher risks of ET, regardless of gender, age or the existence of comorbidities.

Conclusion

Our findings demonstrated an association between migraine and ET, suggesting a possible shared pathophysiology underpinning both disorders.

Self-reported physical activity in essential tremor: Relationship with tremor, balance, and cognitive function

BACKGROUND

Physical inactivity may be the result of medical comorbidities. Inactivity itself may also lead to important health consequences, especially in older patients. Essential tremor (ET) patients may have a variety of physical and cognitive problems that could detrimentally impact on level of physical activity. Yet, to our knowledge, there have been no studies of physical activity in these patients.

METHODS

Self-reported physical activity was assessed using the Physical Activity Scale for the Elderly (PASE) in 100 ET cases (mean age 80.5years) enrolled in a clinical study. Additional clinical measures were the total tremor score, Montreal Cognitive Assessment (MOCA) score and number of steps taken off of the straight line during tandem gait (a measure of balance).

RESULTS

Lower PASE score was associated with older age, more tandem gait difficulty, higher total tremor score and lower MOCA score (all p<0.05). In a linear regression model that included total tremor score, MOCA score, number of steps off of the straight line during tandem gait, and age, higher total tremor score (p=0.046) and more steps off of the straight line during tandem gait (p=0.014) were independently associated with reductions in physical activity.

CONCLUSIONS

Several of the motor features of ET (tremor and imbalance) are independently associated with reductions in level of physical activity.

Time reproduction deficits in essential tremor patients

BACKGROUND

Although motor symptoms predominate in essential tremor, increasing evidence indicates additional cognitive deficits. According to the pivotal role of cognitive functioning for temporal information processing and acknowledging the relevance of temporal information processing for movement coordination, we investigated whether essential tremor patients exhibit time reproduction deficits.

METHODS

A total of 24 essential tremor patients and 24 healthy controls performed sub- and suprasecond visual duration reproduction tasks of 500 to 900 milliseconds and 1.6 to 2.4 seconds, respectively. To differentiate deficient time processing from motor or other cognitive dysfunctions, the average temporal reproduction errors were correlated with tremor severity, immediate and delayed word-list recall performance, and verbal fluency.

RESULTS

Essential tremor patients significantly underreproduced sub- and suprasecond time intervals longer than 800 milliseconds. Moreover, time compression correlated significantly with semantic verbal fluency and word-list retrieval performance, but not with tremor severity.

CONCLUSION

Data suggest impaired temporal processing in essential tremor, corroborating evidence for specific cognitive deficits. © 2016 International Parkinson and Movement Disorder Society.

Plasma insulin-like growth factor 1 is associated with cognitive impairment in Parkinson's disease

OBJECTIVE

The aim of this study was to test plasma insulin-like growth factor 1 (IGF-1) change in Parkinson's disease (PD) and essential tremor (ET), and assess the association of plasma IGF-1 level with motor and nonmotor symptoms in PD and ET.

METHODS

Plasma IGF-1 was measured in 100 PD patients, 40 ET patients, and 76 healthy controls. Motor and nonmotor symptoms were assessed by different scales. Spearman correlation test and linear logistic model were used to analyze the correlation of plasma IGF-1 with motor and nonmotor symptoms of PD and ET.

RESULTS

The plasma IGF-1 level was significantly increased in PD compared to healthy controls and ET patients. In addition, low plasma IGF-1 was correlated with low Mini-Mental State Examination (MMSE) scores in PD patients. However, no correlation was found between plasma IGF-1 and MMSE scores in ET patients.

CONCLUSION

Plasma IGF-1 increased significantly in PD but remained unchanged in ET. A low plasma IGF-1 level was associated with poor cognitive performance in PD but not in ET patients.

Selective attentional deficit in essential tremor: Evidence from the attention network test

INTRODUCTION

The traditional view of essential tremor (ET) as a monosymptomatic and benign disorder has been reconsidered after patients with ET have been shown to experience cognitive deficits that are also related to attention. The Attention Network Test (ANT) is a rapid, widely used test to measure the efficiency of three attentional networks, i.e. alerting, orienting and executive, by evaluating reaction times (RTs) in response to visual stimuli. The aim of this study was to investigate attentional functioning in ET patients by means of the ANT.

METHODS

21 non-demented patients with ET and 21 age- and sex-matched healthy controls performed the ANT.

RESULTS

RT was significantly longer in ET patients than in controls (p < 0.001). Moreover, a significant difference in alerting and executive efficiency (p = 0.003 and p = 0.01 respectively) was found between groups, while the difference in the orienting efficiency only bordered on significance.

CONCLUSION

Our results point to a difficulty in the alerting and executive domains of attention in ET patients, probably owing to a dysfunction in the cerebello-thalamo-cortical loop. These selective attentional deficits are not related to clinical motor symptoms, contributing to shed further light on the clinical picture of ET.

A comparison between rate of nonmotor symptom development in essential tremor and Parkinson's disease

In the last decade our perspective on essential tremor (ET) as a pure motor system disorder has begun to change. By virtue of recent studies of nonmotor symptoms (NMSs) that are used to characterize Parkinson's disease (PD), these symptoms have also been added to the definition of ET. There is increasing evidence to suggest that ET might not be as benign and monosymptomatic as we previously thought. The aim of this study was to evaluate nonmotor symptoms in ET, and to compare them with PD. We studied 37 ET and 23 PD patients. Tremor rate was evaluated using the Fahn-Tolosa-Marin tremor rating scale (FTM-TRS) in ET patients. The patients with PD were scored for motor symptoms using the unified Parkinson's disease rating scale (UPDRS)-III and the Hoehn-Yahr scale. Cognitive functions were assessed with the Montreal Cognitive Assessment (MoCA) test. NMSs were evaluated with the nonmotor symptoms questionnaire (NMSQuest). In the ET group, the most common NMSs were forgetting things, feeling sad, nocturia, urgency, and difficulty concentrating. The mean NMSQuest score was 8.43 ± 4.14 in the ET group and 14.06 ± 5.44 in the PD group (p value <0.001). However, except for 12 items in NMSQuest, in comparing items one by one there was no statistical difference between them. The mean MoCA total score was 17.81 ± 4.56 in the ET group and 17.08 ± 4.08 in the PD group (p value 0.675). There were no significant differences in MoCA subgroup scores. Evaluation of nonmotor symptoms in ET may help us to understand this emerging definition of ET. This study contributes evidence toward this new concept.

Accumulation of amyloid-β in the cerebellar cortex of essential tremor patients

The accumulation of insoluble amyloid-beta (Aβ) peptides is associated with neurodegenerative disorders, such as Alzheimer's disease (AD). As essential tremor (ET) could involve neurodegenerative processes in the cerebellum, we quantified soluble and insoluble Aβ in cerebellar cortices from patients diagnosed with ET (n=9), compared to Controls (n=16) or individuals with Parkinson's disease (n=10). Although ante-mortem cognitive performance was not documented, all individuals included had the diagnosis of AD ruled out by a neuropathologist. ELISA-determined concentrations of insoluble Aβ42 in ET patients displayed a bimodal distribution, with a median 246-fold higher than in Controls (P<0.01, Kruskal-Wallis). Higher Aβ42 concentrations were measured in the parietal cortex of the same ET patients, compared to Controls (107-fold median increase, P<0.01, Kruskal-Wallis), but similar phosphorylated tau levels were detected. The rise in cerebellar insoluble Aβ42 concentrations is not associated to APP expression and processing or the ApoE4 status. However, Aβ42 levels in ET individuals were correlated with cerebellar insoluble phosphorylated tau (r(2)=0.71, P=0.005), unphosphorylated neurofilament heavy chain (NF-H; r(2)=0.50, P=0.030) and Lingo-1 (r(2)=0.73, P=0.007), indicative of a generalized neurodegenerative process involving the cerebellum. Our results suggest prevalent accumulations of insoluble Aβ42 in the cerebellum of ET, but not in age-matched PD. Whether this anomaly plays a role in ET symptoms warrants further investigations.

Poorer Cognitive Performance in Patients with Essential Tremor-Parkinson's Disease vs. Patients with Parkinson's Disease

Background

Patients with essential tremor (ET) seem to be at increased risk of developing Parkinson’s disease (PD). Surprisingly, little has been written about this clinical entity, ET-PD. Cognitive dysfunction is a well-known feature of PD, and can also be an issue in patients with ET. Whether the presence of the combined diagnosis, ET-PD, is associated with additive cognitive effects as compared with PD has not been studied.

Methods

Thirty ET-PD patients and 53 age-matched PD patients were enrolled in a clinical-epidemiological study. Two cognitive screens, the Telephone Interview for Cognitive Status (TICS, score = 0–41) and Folstein Mini-Mental State Examination (MMSE; range 0–30), were administered.

Results

The MMSE score was lower in ET-PD than PD [26.5 ± 3.1 (median 28.0) vs. 28.4 ± 2.2 (median 29.0), p = 0.001]. The TICS score was lower in ET-PD than PD [31.7 ± 3.9 (32.0) vs. 35.0 ± 2.0 (35.0), p < 0.001]. Subscores of these tests that related to orientation (p < 0.001), language (p < 0.001), and working memory (p = 0.001) were lower in ET-PD than PD, whereas the delayed memory subscore was only marginally lower in ET-PD than PD (p = 0.06), and the two groups did not differ with respect to the motor/construction subscore (p = 0.22). Both global cognitive scores were inversely correlated with disease duration (for MMSE score, Spearman’s r = −0.46, p < 0.001; for TICS score, Spearman’s r = −0.53, p < 0.001).

Conclusion

The combined diagnosis, ET-PD, seemed to be associated with additive cognitive effects as compared with PD alone.