Non-motor symptoms in essential tremor: A review of the current data and state of the field

REM sleep behavior disorder and Prodromal Parkinson's Disease in patients with Essential Tremor

Several studies suggested the presence of non-motor symptoms in Essential Tremor (ET), including REM sleep behavioral disorder (RBD). RBD is an essential criterion for Prodromal Parkinson's Disease (PPD), suggesting a link between ET and PD. Our objective was to assess the prevalence and features of ET patients with RBD and PDD. RBD was diagnosed by questionnaire screening, followed by polysomnography. PPD risk factors and prodromic markers were assessed with a structured protocol. Patients were characterized regarding tremor features. ET patients with RBD (ET-RBD) and PPD (ET-PPD) were compared to patients without RBD (ET-nonRBD) and without PPD (ET-nonPPD), respectively. ET-RBD patients were also compared with a group of isolated RBD (iRBD) regarding PPD features. We assessed a total of 64 ET patients. Five (8.3 %) and 4 (6.3 %) had criteria for RBD and PPD, respectively. ET-RBD patients did not differ from ET-nonRBD except for a higher prevalence of PPD. There were no significant differences between ET-RBD and iRBD (n = 12) groups. ET-PPD had a higher prevalence of positive DaT-Scans and RBD compared to ET-nonPPD. Three ET-RBD patients had PPD and 3 ET-PPD had RBD. Both RBD and PPD are more frequent in ET patients than in general aged population but not related with specific tremor features. ET-RBD patients did not differ significantly from iRBD patients, a group prone to develop PD. These data suggest a link between ET and PD and are in accordance with studies showing an increase incidence of lewy-body pathology and PD in ET populations.

Nabiximols (NBX) suppresses tremor in a rat Harmaline model of essential tremor

BACKGROUND

Essential tremor (ET) is one of the most prevalent movement disorders; despite this, there remains an unmet need for novel therapies. The treatment of rats with harmaline modulates the rhythmicity of inferior olivary neurons, resulting in generalized tremor with a frequency of 9-12 Hz in rats, comparable to that of human ET (4-12 Hz).

PURPOSE

Interestingly, cannabinoids reduce tremor, therefore we have assessed the cannabinoid nabiximols (NBX; marketed as Sativex) a complex botanical drug mixture, in the harmaline-rat model of ET.

METHOD

We tested the effects of acute (single dose) and subchronic (10 days) treatment of NBX (at 5.2, 10.4 and 20.8 mg kg-1 p.o.) administered prior to harmaline and acute NBX (20.8 mg kg-1) administered post-harmaline in male SD rats. Propranolol (20 mg kg-1 i.p.) was used as a positive control. Observed Scoring (OS) was carried out prior to placement in a tremor-monitoring apparatus for the calculation of Tremor Index (TI) and Motion Power Percentage (MPP).

RESULTS

Acute and subchronic NBX significantly attenuated harmaline-induced tremor at 10.4 and 20.8 mg kg-1, respectively, for each parameter (OS, TI, and MPP) when administered pre-harmaline as did propranolol (20 mg kg-1). NBX did not attenuate harmaline-induced tremor when administered post-harmaline.

CONCLUSIONS

These data suggest efficacy of acute and subchronic NBX to reduce tremors, based on OS, TI and MPP readouts if administered prior to harmaline. These data are the first to indicate the preclinical effects of an oral botanical cannabinoid formulation, NBX, in an animal model of ET.

Cognitive-motor interference in people with essential tremor

Adapting to different environments throughout daily activities requires flexibility in allocating attention. Compromised dual-tasking can hinder mobility, increase fall risk, and decrease functional independence in patients with essential tremor, who exhibit both mobility and cognitive impairments. We evaluated motor and cognitive dual-task effects and task prioritization in 15 people with Essential Tremor (ET) and 15 age-matched people without ET during a standard and more challenging water-carry TUG. Task-specific interference was evaluated by calculating motor and cognitive dual-task effects, whereas task prioritization was assessed by contrasting the cognitive dual-task effect with the motor dual-task effect. The simultaneous performance of two tasks did not differentially impact motor or cognitive performance in either group, and both groups prioritized cognitive task performance in standard and water-carry TUG assessments. This study enhances our understanding of motor-cognitive interactions in individuals with essential tremor. These insights could lead to patient-centered approaches to therapy to improve functional performance in dynamic daily environments.

Insight into the Relationship Between Motor and Cognitive Symptoms in Essential Tremor

Essential tremor (ET) is a heterogeneous disorder characterized by bilateral upper limbs action tremor and, possibly, neurological signs of uncertain significance, including voluntary movement abnormalities and cognitive disturbances, i.e., the so-called 'soft' signs configuring the ET-plus definition. While motor and cognitive disturbances often coexist in ET, their interrelationship remains largely unexplored. Here we aim to further investigate the relationship between motor symptoms, objectively assessed through kinematic analysis, and cognitive dysfunctions in ET. Seventy ET patients underwent clinical examination, as well as kinematic recordings of tremor and finger tapping and a thorough cognitive assessment. We then tested clinic-demographic and kinematic differences between patients with and without cognitive abnormalities, i.e., with mild cognitive impairment (MCI). Correlation analysis served to explore potential associations between kinematic and cognitive data. Forty-three ET patients (61.42%) had MCI. ET-MCI patients exhibited reduced movement velocity during finger tapping compared to those with normal cognition (p < 0.001). Lower movement velocity during finger tapping was associated with poorer cognitive performance. Namely, we observed a correlation between movement velocity and performance on the Babcock Story Immediate and Delayed Recall Test (r = 0.52 and r = 0.45, both p < 0.001), as well as the interference memory task at 10 and 30 s (r = 0.3, p = 0.008 and r = 0.2, p = 0.03). In this study, we have provided data for a better pathophysiological interpretation of motor and cognitive signs in ET, including the role played by the cerebellum or extra-cerebellar areas, which possibly underpin both signs.

Sleep and circadian rhythm dysfunctions in movement disorders beyond Parkinson's disease and atypical parkinsonisms

PURPOSE OF REVIEW

This review aimed to comprehensively outline sleep and circadian rhythm abnormalities in hyperkinetic movement disorders beyond Parkinson's disease and atypical parkinsonisms, including tremor, dystonia, choreiform movements, tics, and ataxia disorders.

RECENT FINDINGS

Insomnia, poor sleep quality, and excessive daytime sleepiness (EDS) are commonly reported in essential tremor, Wilson's disease, tics or Tourette's syndrome, and spinocerebellar ataxia (SCA). REM sleep behavior disorder (RBD) have been observed in Wilson's disease and SCA. A combination of REM and non-REM parasomnias, along with nocturnal stridor with the initiation of sleep and re-entering after awakening, are characterized by undifferentiated Non-REM and poorly structured N2 in anti-IgLON5 disease. Restless legs syndrome (RLS) has been reported commonly in SCAs. Sleep-related dyskinesia has been reported in ADCY5-related disease and GNAO1-related movement disorder.

SUMMARY

Sleep problems can manifest as a result of movement disorders, either through direct motor disturbances or secondary nonmotor symptoms. Medication effects must be considered, as certain medications for movement disorders can exacerbate or alleviate sleep disturbances. Distinguishing sleep problems in some diseases might involve pathognomonic symptoms and signs, aiding in the diagnosis of movement disorders.

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.

Neurologic comorbidity in psychiatric inpatients: evidence from neurologic consultations in a Spanish center

INTRODUCTION

The presence of psychiatric comorbidity in some neurological disorders is common. A bi-directional influence between some psychiatric and neurological disorders has been discussed, but not widely studied. There is an absence of literature on the typology and rates of neurology consultations in different types of psychiatric inpatients.

MATERIALS AND METHODS

Cross-sectional study based on real world data on patients who had a neurological consultation during hospitalization on a psychiatric ward.

RESULTS

The most frequent reasons for visits to neurologists in our study were cluster 'Epilepsy/other types of non-epileptic seizures' (n = 177, 36.44%), followed by cluster 'Movement disorders' (n = 77, 20.48%), 'Cognitive disorder' (n = 69, 18.35%), and finally cluster 'Neuropathy' (n = 21, 5.59%). The most frequent type of psychiatric patient who required neurologic consultation presented a psychotic disorder (n = 100, 26.60%), follow by problem behavior (n = 82, 21.81%), bipolar disorder (n = 78, 20.78%), depressive disorder (n = 42, 11.17%) and autism spectrum disorder (n = 20, 5.32%). We found a statistically significant relationship between (problem behavior and intellectual disability) and neurologic consultation for epilepsy/other types of non-epileptic seizures, and between (depressive disorder, bipolar disorder, autism spectrum disorder and intellectual disability) and neurologic consultation for movement disorders.

CONCLUSIONS

This is the first study in the literature which analyzes the rates and typology of neurologic consultations in people hospitalized with psychiatric disorders. A deep knowledge of epilepsy, movement disorders and cognitive disorders should be required for health professionals to treat psychiatric inpatients appropriately. Patients with particular psychiatric disorders seem to require a higher number of neurologic consultations than others during their hospitalization.

Exploring serum α‑synuclein and its autoantibodies in essential tremor: implications for diagnosis and symptom correlations

There is no definite biomarker for confirming the diagnosis of essential tremor (ET) or differentiating it from other diseases, particularly Parkinson's disease. The present study aimed to investigate the serum levels of the α-synuclein protein (α-syn) and its autoantibodies in patients with ET compared with healthy controls and its relation to motor and non-motor symptoms in patients with ET. Serum α-syn and its autoantibodies were measured in 32 patients with ET and 32 age- and sex-matched controls. Both groups were assessed using the non-motor symptoms scale, MoCA, Beck Depression Inventory, Hamilton Anxiety Rating Scale, and the Short Form 36 Health Survey Questionnaire. Tremor was assessed using the Fahn-Tolosa-Marin Tremor Rating Scale. The serum α-syn concentration in patients with ET was significantly lower than that in healthy controls (P<0.001), with a positive predictive value of 0.81 and a negative predictive value of 0.75, while the serum anti-a-syn autoantibody concentration was not significantly different between the two groups. There were no correlations between serum α-syn or its autoantibodies and patients' clinical characteristics. Furthermore, patients with ET had worse cognitive impairment, depression, anxiety, non-motor symptoms and quality of life. The serum α-syn concentration was lower in patients with ET than in controls, with favorable predictive values, suggesting that it could serve as a biomarker for ET diagnosis.

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.

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.

Stereotactic radiosurgery in the treatment of essential tremor - a systematic review

Introduction

Essential tremor (ET) is the most common movement disorder in adults, with an estimated incidence of up to 1% of the population and 5% of people older than 65 years of age. ET is manifested primarily by bilateral postural and kinetic tremor of the upper limbs with or without neurological symptoms and cognitive deficits. ET disrupts daily tasks and significantly lowers quality of life. Currently available medications alone are often insufficient to control severe symptoms. Several surgical treatment options are available, including stereotactic radiosurgery (SRS)-a minimally invasive treatment option aimed at relieving and controlling tremors.

Methods

We conducted a systematic review of the scientific literature on the use of SRS in the treatment of ET using PubMed, Scopus, Web of Science, Cochrane, ScienceDirect, and ClinicalTrials.gov registry and adhered to the PRISMA guidelines.

Results

The results obtained confirm the high efficacy and safety of the SRS procedure in treating drug-resistant intention tremor. The study results present high response rate reaching 80% and achievement of manual task improvement, lessening of the tremor and increase in the quality of life of the majority of the operated patients. The method also stands out for its favorable balance between efficiency and cost.

Disscusion

Stereotactic radiosurgery is a favourable, safe, efficient and cost-effective method in treatment of the essential tremor. Ongoing research is crucial to refine patient selection criteria for this procedure and further improve the effectiveness of the technique.

Sleep problems as predictors of cognitive decline in essential tremor: A prospective longitudinal cohort study

BACKGROUND

There is growing evidence that essential tremor (ET) patients are at high risk of cognitive impairment. Predictors of cognitive impairment have not been studied extensively. There is evidence from cross-sectional studies that sleep dysregulation is associated with cognitive dysfunction in ET, but longitudinal studies of the impact of sleep disruption on cognitive change have not been conducted. We investigated the extent to which sleep problems predict cognitive change in patients with ET.

METHODS

ET cases enrolled in a prospective, longitudinal study of cognitive performance. Sleep quality was assessed using the Pittsburg Sleep Quality Index (PSQI). Cognitive abilities across five domains (memory, executive function, attention, language, and visuospatial ability), and a global cognitive score (mean of the domains) were extracted from an extensive neuropsychological assessment. Generalized estimated equations were used to examine the association between baseline sleep problems and cognitive changes over three follow-up assessments each spaced 18 months apart.

RESULTS

The 188 non-demented ET cases had a mean age of 77.7 ± 9.5 years. Longer sleep latency was associated with longitudinal decline in executive function (p = 0.038), and marginally with longitudinal decline in global cognitive performance (p = 0.075). After excluding 29 cases with mild cognitive impairment, results were similar.

CONCLUSION

Cognitively healthy people with ET who have longer sleep latency had greater declines in executive function during prospective follow-up. Early detection of, and possibly intervention for, abnormal sleep latency may protect against certain aspects of cognitive decline in ET patients.

The Effects of Remote Signal Transmission and Recording on Acoustical Measures of Simulated Essential Vocal Tremor: Considerations for Remote Treatment Research and Telepractice

PURPOSE

Studies on medical and behavioral interventions for essential vocal tremor (EVT) have shown inconsistent effects on acoustical and perceptual outcome measures across studies and across participants. Remote acoustical and perceptual assessments might facilitate studies with larger samples of participants and repeated measures that could clarify treatment effects and identify optimal treatment candidates. Furthermore, remote acoustical and perceptual assessment might allow clinicians to monitor clients' treatment responses and optimize treatment approaches during telepractice. Thus, the purpose of this study was to evaluate the accuracy of remote signal transmission and recording for acoustical and perceptual assessment of EVT.

METHOD

Simulations of EVT were produced using a computational model and were recorded using local and remote procedures to represent client- and clinician-end recordings respectively. Acoustical analyses measured the extent and rate of fundamental frequency (fo) and intensity modulation to represent vocal tremor severity and the cepstral peak prominence (CPPS) to represent voice quality. The data were analyzed using repeated measures analysis of variance (ANOVA) with recording as the within-subjects factor and sex of the computational model as the between-subjects factor.

RESULTS

There was a significant main effect of recording on the rate of fo modulation and significant interactions of recording and sex for the extent of intensity modulation, rate of intensity modulation, and CPPS. Posthoc pairwise comparisons and analysis of effect size indicated that recording procedures had the largest effect on the extent of intensity modulation for male simulations, the rate of intensity modulation for male and female simulations, and the CPPS for male and female simulations. Despite having disabled all known software and computer audio enhancing options and having stable ethernet connections, there was inconsistent attenuation of signal amplitude in remote recordings that was most problematic for samples with a breathy voice quality but also affected samples with typical and pressed voice qualities.

CONCLUSIONS

Acoustical measures that correlate to perception of vocal tremor and voice quality were altered by remote signal transmission and recording. In particular, signal transmission and recording in Zoom altered time-based estimates of intensity modulation and CPPS with male and female simulations of EVT and magnitude-based estimates of intensity modulation with male simulations of EVT. In contrast, signal transmission and recording in Zoom minimally altered time- and magnitude-based estimates of fo modulation with male and female simulations of EVT. Therefore, acoustical and perceptual assessments of EVT should be performed using audio recordings that are collected locally on the participant- or client-end, particularly when measuring modulation of intensity and CPP or estimating vocal tremor severity and voice quality. Development of procedures for collecting local audio recordings in remote settings may expand data collection for treatment research and enhance telepractice.

The cognitive profile of essential tremor on the Repeatable Battery for the Assessment of Neuropsychological Status

Objective: Essential tremor (ET), while defined by progressive motor symptoms, is increasingly associated with cognitive impairments (e.g. attention, memory, and executive functions). This study characterizes the cognitive profile of individuals with ET on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), a commonly-used neuropsychological screening measure. Method: Seventy-seven individuals (mean age: 70.6, 34% female) diagnosed with ET and being considered for surgical/procedural intervention were recruited from a Movement Disorders Clinic. All participants completed the RBANS, Grooved Pegboard Test (GPB), and Fahn, Tolosa, Marin Tremor Scale (FTMTS) in the clinical evaluation of their tremor. Results: One-sample t-tests found Immediate Memory, Language, Attention, and Total Scale Index scores to be significantly lower than the expected population mean (p < .05). List Learning, Semantic Fluency, Coding, and List Recall subtests were significantly lower and Picture Naming was significantly higher than the expected population mean (p < .05). GPB scores were correlated with the Attention Index as well as List Learning and Coding subtests. FTMTS Severity was correlated with the Coding subtest and FTMTS Disability was correlated with the Figure Recall subtest. Conclusions: Results support prior literature indicating cognitive weaknesses in those with ET. Individuals with ET had poorer global cognitive abilities, with specific decrements in Immediate Memory, Attention, and Language. Notably, the Attention Index and Coding subtest were most affected by motor functioning. Cognitive screening measures, like the RBANS, can efficiently identify strengths and weaknesses in individuals with ET seeking surgical/procedural interventions.

A prospective cohort study of familial versus sporadic essential tremor cases: Do clinical features evolve differently across time?

BACKGROUND

Although essential tremor (ET) is often divided into familial and sporadic cases, few data compare the evolution of clinical features in these groups over time. Leveraging data from a prospective, longitudinal study, we present analyses of the evolution of a broad range of cognitive, motor (i.e., tremor, tandem gait) and other features (e.g., disability) of ET.

METHODS

Sixty-six familial and 23 sporadic ET cases completed in-home evaluations at baseline and 18, 36, and 54-month follow-ups. Assessments included detailed neuropsychological testing and videotaped neurological examinations. Analyses compared the longitudinal course of 16 clinical features in familial and sporadic cases.

RESULTS

Baseline mean age was 75.2 ± 8.8 years and mean observation period was 4.7 ± 0.3 years. Tremor onset age was lower and childhood onset more common in familial than sporadic cases (p's = 0.02). Longitudinal analyses revealed no significant differences between clinical features displayed by familial and sporadic cases, or differences between the patterns of change in clinical features observed in these groups across time. Sporadic cases' daily activity skills declined significantly, whereas familial cases' did not, p's = 0.04 and 0.34, respectively; however, this finding was non-significant when controlling for false discovery rate. Several additional non-significant trends were noted.

CONCLUSION

Familial and sporadic ET cases differed in onset age, and in the prevalence of childhood tremor onset. Although a number of interesting trends were observed, no significant differences in the evolution of clinical features over time in patients with and without a family history of ET were revealed.

Recognition subtests of the Repeatable Battery for the Assessment of Neuropsychological Status: evidence for a cortical vs. subcortical distinction

INTRODUCTION

Within clinical neuropsychology, a classic diagnostic distinction is made between cortical and subcortical disorders, especially based on their memory profiles. Typically, this is based on the comparison of recall and recognition trials, where individuals with cortical conditions do not tend to benefit (i.e., score well) on recognition trials and individuals with subcortical conditions do. Although the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) is a widely used brief cognitive battery, there is a lack of evidence to support this measure's utility in distinguishing between the memory profiles of these conditions.

METHOD

Thirty-six mild Alzheimer's disease (AD), 55 Parkinson's disease (PD), and 105 essential tremor (ET) participants (N = 196) were administered the RBANS with additional Story and Figure Recognition subtests. Group differences on recall and recognition scores (Total Correct, Hits or True Positives, False Positive Errors, and discriminability index) were examined across the three groups, while controlling for the influence of age and gender.

RESULTS

As expected, individuals with AD had poorer recognition scores compared to the other clinical groups across tasks (all p-values < .05), while the ET sample largely performed comparably to the PD sample. With the exception of comparable Figure Recognition and Recall in the PD sample, all groups exhibited significantly greater recognition Hit performance compared to Recall (all p-values < .05).

CONCLUSIONS

The group differences in performance across RBANS recognition subtests suggest support for traditional "cortical" and "subcortical" profiles. However, all groups, including the mild AD sample, demonstrated a benefit from recognition cues compared to free recall. Overall, these findings support the inclusion of the newly developed Story and Figure Recognition subtests in future clinical practice and research endeavors.

Structural brain differences in essential tremor and Parkinson's disease deep brain stimulation patients

BACKGROUND

Essential tremor (ET) and Parkinson's disease (PD) are the most common tremor disorders and are common indications for deep brain stimulation (DBS). In some patients, PD and ET symptoms overlap and diagnosis can be challenging based on clinical criteria alone. The objective of this study was to identify structural brain differences between PD and ET DBS patients to help differentiate these disorders and improve our understanding of the different brain regions involved in these pathologic processes.

METHODS

We included ET and PD patients scheduled to undergo DBS surgery in this observational study. Patients underwent 3T brain MRI while under general anesthesia as part of their procedure. Cortical thicknesses and subcortical volumes were quantified from T1-weighted images using automated multi-atlas segmentation. We used logistic regression analysis to identify brain regions associated with diagnosis of ET or PD.

RESULTS

149 ET and 265 PD patients were included. Smaller volumes in the pallidum and thalamus and reduced thickness in the anterior orbital gyrus, lateral orbital gyrus, and medial precentral gyrus were associated with greater odds of ET diagnosis. Conversely, reduced volumes in the caudate, amygdala, putamen, and basal forebrain, and reduced thickness in the orbital part of the inferior frontal gyrus, supramarginal gyrus, and posterior cingulate were associated with greater odds of PD diagnosis.

CONCLUSIONS

These findings identify structural brain differences between PD and ET patients. These results expand our understanding of the different brain regions involved in these disorders and suggest that structural MRI may help to differentiate patients with these two disorders.

Cognitive impairment in essential tremor assessed by the cerebellar cognitive affective syndrome scale

Background

Essential tremor (ET) is a movement disorder characterized by cerebellar neurodegenerative changes. ET is also associated with non-motor symptoms including cognitive impairment. The neuropsychologic profile of a patient with ET could relate to cerebellar cognitive affective syndrome (CCAS).

Objective

This study aimed to assess the prevalence of cognitive impairment in patients with ET and identify whether the cognitive impairment in ET corresponds to a CCAS.

Methods

Cognitive functions were evaluated with the CCAS-Scale (CCAS-S) in 20 patients with ET and 20 controls matched for age, sex, and level of education. The results of the CCAS-S were compared between patients and controls. The underlying determinant of CCAS inpatients with ET was identified through the correlation between the results of the CCAS-S and age at onset of symptoms, disease duration, and the Essential Tremor Rating Assessment Scale (TETRAS).

Results

On a group level, ET patients performed significantly worse than matched controls. In total, 13 individuals with ET had a definite CCAS (CCAS-S failed items ≥ 3). ASO and TETRAS scores significantly correlated with CCAS-S performances in ET patients.

Conclusion

CCAS is highly prevalent in patients with ET which supports the cerebellar pathophysiology of associated cognitive impairment and supports a more systematic use of the CCAS-S to cognitively assessed patients with ET.

Is Hearing Loss a Risk Factor for Idiopathic Parkinson's Disease? An English Longitudinal Study of Ageing Analysis

Observations that hearing loss is a substantial risk factor for dementia may be accounted for by a common pathology. Mitochondrial oxidative stress and alterations in α-synuclein pathology may be common pathology candidates. Crucially, these candidate pathologies are implicated in Parkinson's disease (PD). Consequently, hearing loss may be a risk factor for PD. Subsequently, this prospective cohort study of the English Longitudinal Study of Ageing examines whether hearing loss is a risk factor for PD longitudinally. Participants reporting self-reported hearing capabilities and no PD diagnosis prior to entry (n = 14,340) were used. A joint longitudinal and survival model showed that during a median follow up of 10 years (SD = 4.67 years) increased PD risk (p < 0.001), but not self-reported hearing capability (p = 0.402). Additionally, an exploratory binary logistic regression modelling the influence of hearing loss identified using a screening test (n = 4812) on incident PD indicated that neither moderate (p = 0.794), nor moderately severe/severe hearing loss (p = 0.5210), increased PD risk, compared with normal hearing. Whilst discrepancies with prior literature may suggest a neurological link between hearing loss and PD, further large-scale analyses using clinically derived hearing loss are needed.

Associations between cognitive function and a range of significant life events in an elderly essential tremor cohort study

BACKGROUND

Although essential tremor (ET) is associated with cognitive decline, we know little about how specific cognitive changes predict significant events in patients' lives. We examined the relations of attention, executive function, language, memory, and visuospatial performance to the occurrence of near falls, falls, walking aid use, home health aide use, non-independent living and hospitalizations within a prospective, longitudinal study of ET cases. We expected executive function and memory to be most strongly associated with these events.

METHODS

131 ET cases (mean age at baseline = 76.4 ± 9.4 years; 109 normal cognition; 17 mild cognitive impairment, 5 demented) completed questionnaires (clinical history and occurrence of life events) and a battery of neuropsychological tests at baseline and at 18, 36, and 54 months. We assessed associations between cognitive functioning and outcomes via regression equations.

RESULTS

Cases with lower baseline levels of executive function reported more near falls, p < 0.006, and were more likely to use a walking aid, p < 0.03, odds ratio (OR) = 2.89 during the follow-up period, than were other cases. Decline in executive function was associated with home health aide use during follow-up, p < 0.04, OR = 3.34. Baseline visuospatial performance also bore a marginally significant association with non-independent living arrangements during follow-up, p < 0.06, OR = 2.13. These effects were independent of age and tremor severity.

CONCLUSION

These data establish the important role that cognitive decline, and executive function specifically, play in the experiences of ET patients. Moreover, these associations are of sufficient magnitude to have significant clinical implications.

[Essential tremor: are we just splitting hairs? Non-motor symptoms and essential tremor-plus]

INTRODUCTION

The existence of non-motor symptoms in essential tremor (ET) and the appearance of a new condition, ET-plus, are two controversial issues.

AIMS

To offer a review of the current status of these two topics.

DEVELOPMENT

We performed an analysis of the studies conducted on non-motor symptoms in ET and of the articles for and against the use of the term ET-plus.

CONCLUSIONS

Non-motor symptoms have gained increased recognition as a feature accompanying ET. Several studies have documented its presence compared to matched controls. It is not clear, however, whether these non-motor symptoms would be part of the spectrum of ET symptoms (a primary phenomenon) or whether they would be symptoms that appear as a consequence of the physical or psychological disability produced by the clinical signs and symptoms of ET itself (a secondary phenomenon). For the time being, their evaluation and treatment are not included within the standard assessment of patients with ET. In view of the heterogeneous phenotype, the term ET-plus aims to improve phenotypic homogeneity for genetic or therapeutic studies. Yet, there is no pathological basis, and epidemiological, genetic and therapeutic research studies have numerous drawbacks. In the absence of clear objective biomarkers, distinguishing between ET and ET-plus by clinical distinction alone is very complex. We should be cautious about using new terms that are not yet backed by sound scientific evidence.

Longitudinal study of clinical and neurophysiological features in essential tremor

BACKGROUND AND PURPOSE

Essential tremor (ET) is a common and heterogeneous disorder characterized by postural/kinetic tremor of the upper limbs and other body segments and by non-motor symptoms, including cognitive and psychiatric abnormalities. Only a limited number of longitudinal studies have comprehensively and simultaneously investigated motor and non-motor symptom progression in ET. Possible soft signs that configure the ET-plus diagnosis are also under-investigated in follow-up studies. We aimed to longitudinally investigate the progression of ET manifestations by means of clinical and neurophysiological evaluation.

METHODS

Thirty-seven ET patients underwent evaluation at baseline (T0) and at follow-up (T1; mean interval ± SD = 39.89 ± 9.83 months). The assessment included the clinical and kinematic evaluation of tremor and voluntary movement execution, as well as the investigation of cognitive and psychiatric disorders.

RESULTS

A higher percentage of patients showed tremor in multiple body segments and rest tremor at T1 as compared to T0 (all p-values < 0.01). At T1, the kinematic analysis revealed reduced finger-tapping movement amplitude and velocity as compared to T0 (both p-values < 0.001). The prevalence of cognitive and psychiatric disorders did not change between T0 and T1. Female sex, absence of family history, and rest tremor at baseline were identified as predictive factors of worse disease progression.

CONCLUSIONS

ET progression is characterized by the spread of tremor in multiple body segments and by the emergence of soft signs. We also identified possible predictors of disease worsening. The results contribute to a better understanding of ET classification and pathophysiology.

Noninvasive neuroimaging provides evidence for deterioration of the glymphatic system in Parkinson's disease relative to essential tremor

INTRODUCTION

Growing evidence has demonstrated dysfunction of the glymphatic system in α-synucleinopathy and related diseases. In this study, we aimed to use diffusion tensor image analysis along the perivascular space (DTI-ALPS) and MRI-visible enlarged perivascular spaces (EPVS) to evaluate glymphatic system function quantitatively and qualitatively and its relationship to clinical scores of disease severity in Parkinson's disease (PD) and essential tremor (ET).

METHODS

Overall, 124 patients with PD, 74 with ET, and 106 healthy controls (HC) were enrolled. Two trained neurologists performed quantitative calculations of ALPS on DTI and visual ratings of EPVS on T2-weighted images in the centrum semiovale (CSO), basal ganglia (BG), midbrain, and cerebellum.

RESULTS

The ALPS index was lower in patients with PD than in patients with ET (p < 0.001) and HC (p < 0.001). Similarly, patients with PD showed a more severe EPVS burden in the CSO, BG, and midbrain compared to ET and HC. Moreover, the ALPS index was negatively correlated with disease severity in the PD subgroups; however, it did not differ within the ET subgroup. No differences in ALPS or EPVS were observed between the ET and HC groups.

CONCLUSION

In conclusion, DTI-ALPS and EPVS both provide neuroimaging evidence of glymphatic system dysfunction in PD, which further supports that PD is an α-synucleinopathy disease, while ET is a cerebellar dysfunction-related disease.

Prevalence and risk factors for abnormal tandem gait in patients with essential tremor syndrome: A cross-sectional study in Southwest China

Objectives

Patients with essential tremor (ET) syndrome have more prevalent and more serious gait and balance impairments than healthy controls. In this cross-sectional study, we explored whether balance impairments are associated with falls as well as more pronounced non-motor symptoms in patients with ET syndrome.

Methods

We assessed the tandem gait (TG) test, as well as falls or near-falls that occurred over the previous year. Non-motor symptoms-including cognitive deficits, psychological and sleep disorders-were evaluated. In univariate analyses, statistical significance was corrected for multiple comparisons using the Benjamini-Hochberg method. Multiple logistic regression was utilized to evaluate the risk factors of poor TG performance in patients with ET syndrome.

Results

A total of 358 patients with ET syndrome were divided into the abnormal TG (a-TG) and normal TG (n-TG) groups based on their performances in the TG test. We revealed that 47.2% of patients with ET syndrome had a-TG. The patients with a-TG were older, were more likely female, and were more likely present with cranial tremors and falls or near-falls (all adjusted P < 0.01). The patients with a-TG had significantly lower Mini-Mental Status Examination scores, as well as significantly higher Hamilton Depression/Anxiety Rating Scale and Pittsburgh Sleep Quality Index scores. Multiple logistic regression analysis demonstrated that female sex (OR 1.913, 95% CI: 1.180-3.103), age (OR 1.050, 95% CI: 1.032-1.068), cranial tremor scores (OR 1.299, 95% CI: 1.095-1.542), a history of falls or near-falls (OR 2.952, 95% CI: 1.558-5.594), and the presence of depressive symptoms (OR 1.679, 95% CI: 1.034-2.726) were associated with the occurrence of a-TG in patients with ET syndrome.

Conclusion

TG abnormalities may be a predictor of fall risk in patients with ET syndrome and are associated with non-motor symptoms, especially depression.

Challenging functional connectivity data: machine learning application on essential tremor recognition

BACKGROUND AND AIMS

This paper aimed to investigate the usefulness of applying machine learning on resting-state fMRI connectivity data to recognize the pattern of functional changes in essential tremor (ET), a disease characterized by slight brain abnormalities, often difficult to detect using univariate analysis.

METHODS

We trained a support vector machine with a radial kernel on the mean signals extracted by 14 brain networks obtained from resting-state fMRI scans of 18 ET and 19 healthy control (CTRL) subjects. Classification performance between pathological and control subjects was evaluated using a tenfold cross-validation. Recursive feature elimination was performed to rank the importance of the extracted features. Moreover, univariate analysis using Mann-Whitney U test was also performed.

RESULTS

The machine learning algorithm achieved an AUC of 0.75, with four networks (language, primary visual, cerebellum, and attention), which have an essential role in ET pathophysiology, being selected as the most important features for classification. By contrast, the univariate analysis was not able to find significant results among these two conditions.

CONCLUSION

The machine learning approach identifies the changes in functional connectivity of ET patients, representing a promising instrument to discriminate specific pathological conditions and find novel functional biomarkers in resting-state fMRI studies.

Non-Persistence of Tremorolytic Effect of Perampanel in Essential Tremor: Real-World Experience with 50 Patients

Background

We describe our experience of using perampanel to treat essential tremor (ET) over 12 months.

Methods

We enrolled 50 ET patients in an open-label trial. Perampanel was titrated to 4 mg/day as adjuvant therapy. The main outcome measures were baseline, +1, +3, +6, and + 12 month scores of the Tremor Clinical Rating Scale (TCRS) and the Glass scale (GS).

Results

Twenty patients withdrew because of adverse effects. At +1 month, 27 of 30 patients improved: 68% reduction in both TCRS 1 + 2 (P < 0.001) and TCRS 3 (P < 0.001); TCRS 4 + 1.8 and GS 1.1 point reduction. By +12 months non-persistence of therapeutic effect occurred in 70% of patients: the mean reduction in TCRS 1 + 2 was 33% (P = 0.03), TCRS 3 (0.04), TCRS 4 + 0.8, GS 0.2 points reduction.

Conclusions

We report important peramapanel acute tremorolytic effects, but poor tolerance to adverse effects and a non-sustained therapeutic effect in most patients.

Upper Limb Function but Not Proprioception is Impaired in Essential Tremor: A Between-Groups Study and Causal Mediation Analysis

Background

Essential tremor (ET) is characterized by abnormal oscillatory muscle activity and cerebellar involvement, factors that can lead to proprioceptive deficits, especially in active tasks. The present study aimed to quantify the severity of proprioceptive deficits in people with ET and estimate how these contribute to functional impairments.

Methods

Upper limb sensory, proprioceptive and motor function was assessed inindividuals with ET (n = 20) and healthy individuals (n = 22). To measure proprioceptive ability, participants discriminated the width of grasped objects and the weight of objects liftedwith the wrist extensors. Causal mediation analysis was used to estimate the extentthat impairments in upper limb function in ET was mediated by proprioceptive ability.

Results

Participants with ET had impaired upper limb function in all outcomes, and had greater postural and kinetic tremor. There were no differences between groups in proprioceptive discrimination of width (between-group mean difference [95% CI]: 0.32 mm [-0.23 to 0.87 mm]) or weight (-1.12 g [-7.31 to 5.07 g]). Causal mediation analysis showed the effect of ET on upper limb function was not mediated by proprioceptive ability.

Conclusions

Upper limb function but not proprioception was impaired in ET. The effect of ET on motor function was not mediated by proprioception. These results indicate that the central nervous system of people with ET is able to accommodate mild to moderate tremor in active proprioceptive tasks that rely primarily on afferent signals from muscle spindles.

Differential contributions of depression, apathy, and anxiety to neuropsychological performance in Parkinson's disease versus essential tremor

INTRODUCTION

Mood symptoms are common features of Parkinson's disease (PD) and essential tremor (ET) and have been linked to worse cognition. The goals of the present study were to compare the severity of anxiety, apathy, and depressive symptoms in PD, ET, and healthy controls (HC) and to examine differential relationships between mood and cognition.

METHOD

Older adults with idiopathic PD (N = 448), ET (N = 128), or HC (N = 136) completed a multi-domain neuropsychological assessment consisting of memory, executive function, and attention/working memory domains. Participants also completed self-reported mood measures. Between-group differences in mood and cognition were assessed, and hierarchical regression models were conducted to examine relationships between mood and cognition in each group.

RESULTS

Relative to the HC group, the PD and ET groups reported more mood symptoms and scored lower across all cognitive measures. There were no differences between the two movement disorder groups. Mood variables explained 3.9-13.7% of the total variance in cognitive domains, varying by disease group. For PD, apathy was the only unique predictor of executive function (β = -.114, p = .05), and trait anxiety was the only unique predictor of attention/working memory (β = -.188, p < .05). For ET, there were no unique predictors, though the overall models significantly predicted performance in the executive function and attention/working memory domains.

CONCLUSIONS

In a large cohort of ET and PD, we observed that the two groups had similar self-reported mood symptoms. Mood symptoms were differentially associated with cognition in PD versus ET. In PD, increased apathy was associated with worse executive function and higher trait anxiety predicted worse attention/working memory. For ET, there were no unique predictors, though the overall mood symptom severity was related to cognition. Our study highlights the importance of considering the relationship between mood and neuropsychological performance in individuals with movement disorders.

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

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

Essential tremor patients experience significant burden beyond tremor: A systematic literature review

Background

Essential tremor (ET) is among the most common movement disorders in adults. While ET is diagnosed and primarily characterized by the presence of tremor, it also can impact cognition, sleep, mood, and motor functioning more broadly. The manifestations of ET can have various consequences, including difficulty with activities of daily living (ADL), embarrassment, and overall decline in health-related quality of life, which have not been fully explored in prior studies.

Objective

We performed a systematic literature review to comprehensively characterize the burden experienced by patients with ET from the clinical and humanistic perspectives, focusing on outcomes beyond tremor.

Methods

This systematic literature review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Searches in PubMed, Embase, and Cochrane Library identified original, observational studies of the clinical and humanistic burden in adult patients with ET published in English between 2010 and 2020. Studies assessing epidemiology, treatment patterns, or disease management were excluded. Search results were screened according to pre-determined eligibility criteria. Data from included studies were collected, independently verified, and qualitatively synthesized.

Results

Following the screening of 2,303 records and 145 full-text articles, 39 studies were identified. There was significant heterogeneity in study designs, statistical approaches, and patient cohorts across the included studies. Patients with ET in these studies exhibited more severe disabilities and reduced independence compared to healthy individuals, and they often struggled to perform ADL and relied on caregivers for physical and emotional support. Patients also experienced various issues with movement and balance, increased risk of falls, depression, anxiety, poor sleep quality, and psychosocial consequences including embarrassment, apathy, and enfeeblement.

Conclusion

A systematic literature review of non-tremor manifestations and/or consequences of ET identified far-reaching negative impacts on patients' ability to function independently and revealed accompanying psychosocial effects, including social fear and embarrassment. The reduced function and psychosocial deficits observed in patients with ET result in significant clinical and humanistic burdens, decreasing quality of life. Future studies should evaluate this condition beyond the tremor itself to provide an improved understanding of the multi-dimensional burden of the disease, thereby highlighting the need to diagnose and appropriately manage patients with ET.

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.

Graph Theoretical Analysis of Structural Covariance Reveals the Relevance of Visuospatial and Attentional Areas in Essential Tremor Recovery After Stereotactic Radiosurgical Thalamotomy

Essential tremor (ET) is the most common movement disorder. Its pathophysiology is only partially understood. Here, we leveraged graph theoretical analysis on structural covariance patterns quantified from morphometric estimates for cortical thickness, surface area, and mean curvature in patients with ET before and one year after (to account for delayed clinical effect) ventro-intermediate nucleus (Vim) stereotactic radiosurgical thalamotomy. We further contrasted the observed patterns with those from matched healthy controls (HCs). Significant group differences at the level of individual morphometric properties were specific to mean curvature and the post-/pre-thalamotomy contrast, evidencing brain plasticity at the level of the targeted left thalamus, and of low-level visual, high-level visuospatial and attentional areas implicated in the dorsal visual stream. The introduction of cross-correlational analysis across pairs of morphometric properties strengthened the presence of dorsal visual stream readjustments following thalamotomy, as cortical thickness in the right lingual gyrus, bilateral rostral middle frontal gyrus, and left pre-central gyrus was interrelated with mean curvature in the rest of the brain. Overall, our results position mean curvature as the most relevant morphometric feature to understand brain plasticity in drug-resistant ET patients following Vim thalamotomy. They also highlight the importance of examining not only individual features, but also their interactions, to gain insight into the routes of recovery following intervention.

Topologically Disrupted Gray Matter Networks in Drug-Naïve Essential Tremor Patients With Poor Sleep Quality

Background

Sleep disturbances are widespread among patients with essential tremor (ET) and may have adverse effects on patients' quality of life. However, the pathophysiology underlying poor quality of sleep (QoS) in patients with ET remains unclear. Our study aimed to identify gray matter (GM) network alterations in the topological properties of structural MRI related to QoS in patients with ET.

Method

We enrolled 45 ET patients with poor QoS (SleET), 59 ET patients with normal QoS (NorET), and 66 healthy controls (HC), and they all underwent a three-dimensional T1-weighted MRI scan. We used a graph-theoretical approach to investigate the topological organization of GM morphological networks, and individual morphological brain networks were constructed according to the interregional similarity of GM volume distributions. Furthermore, we performed network-based statistics, and partial correlation analyses between topographic features and clinical characteristics were conducted.

Results

Global network organization was disrupted in patients with ET. Compared with the NorET group, the SleET group exhibited disrupted topological GM network organization with a shift toward randomization. Moreover, they showed altered nodal centralities in mainly the frontal, temporal, parietal, and cerebellar lobes. Morphological connection alterations within the default mode network (DMN), salience, and basal ganglia networks were observed in the SleET group and were generally more extensive than those in the NorET and HC groups. Alterations within the cerebello-thalamo-(cortical) network were only detected in the SleET group. The nodal degree of the left thalamus was negatively correlated with the Fahn-Tolosa-Marin Tremor Rating Scale score (r = −0.354, p =0.027).

Conclusion

Our findings suggest that potential complex interactions underlie tremor and sleep disruptions in patients with ET. Disruptions within the DMN and the cerebello-thalamo-(cortical) network may have a broader impact on sleep quality in patients with ET. Our results offer valuable insight into the neural mechanisms underlying poor QoS in patients with ET.

Vitamin D Receptor and Binding Protein Gene Variants in Patients with Essential Tremor

Several studies have shown an association between some variants in the vitamin D receptor (VDR) and the GC vitamin D binding protein (GC) genes with the risk for Parkinson's disease or other neurological disorders. VDR rs2228570 has shown an association with essential tremor (ET) in a previous study. The aim of this study is to look for the association between several common variants in these genes and the risk for ET. We genotyped 272 patients diagnosed with familial ET and 272 age-matched controls using specific TaqMan assays for VDR rs2228570, VDR rs731236, VDR rs7975232, VDR rs739837, VDR rs78783628, GC rs7041, and GC rs4588 single nucleotide variants (SNVs). We found an association between GC rs7041 SNV and ET using recessive, codominant, and allelic models. Despite our results did not find an association between VDR rs2228570 and ET, the pooled data with those by a previous report suggest this association under recessive, codominant, and allelic models. None of the SNVs studied was related to the age at onset of tremor in ET patients. Data from the current study suggest an association between GC rs7041 and VDR rs2228570 SNVs and ET risk.

Disrupted Brain Functional Network Topology in Essential Tremor Patients With Poor Sleep Quality

Sleep disturbances, especially poor quality of sleep (QoS), are common among essential tremor (ET) patients and may have adverse effects on their quality of life, but the etiology driving the poor QoS in these individuals remains inadequately understood. Few data are available on the neuroimaging alterations of ET with poor QoS. Thirty-eight ET patients with poor QoS (SleET), 48 ET patients with normal QoS (NorET), and 80 healthy controls (HCs) participated in this study. All subjects underwent a 3.0-T magnetic resonance imaging (MRI) scan for resting-state functional MRI data collection. Then, the whole-brain functional connectome was constructed by thresholding the partial correlation matrices of 116 brain regions. Graph theory and network-based statistical analyses were performed. We used a non-parametric permutation test for group comparisons of topological metrics. Partial correlation analyses between the topographical features and clinical characteristics were conducted. The SleET and NorET groups exhibited decreased clustering coefficients, global efficiency, and local efficiency and increased the characteristic path length. Both of these groups also showed reduced nodal degree and nodal efficiency in the left superior dorsolateral frontal gyrus, superior frontal medial gyrus (SFGmed), posterior cingulate gyrus (PCG), lingual gyrus, superior occipital gyrus, right middle occipital gyrus, and right fusiform gyrus. The SleET group additionally presented reduced nodal degrees and nodal efficiency in the right SFGmed relative to the NorET and HC groups, and nodal efficiency in the right SFGmed was negatively correlated with the Pittsburgh Sleep Quality Index score. The observed impaired topographical organizations of functional brain networks within the central executive network (CEN), default mode network (DMN), and visual network serve to further our knowledge of the complex interactions between tremor and sleep, adding to our understanding of the underlying neural mechanisms of ET with poor QoS.

Is essential tremor a degenerative disorder or an electric disorder? Degenerative disorder

Essential tremor (ET) is a highly prevalent neurologic disease and is the most common of the many tremor disorders. ET is a progressive condition with marked clinical heterogeneity, associated with a spectrum of both motor and non-motor features. However, its disease mechanisms remain poorly understood. Much debate has centered on whether ET should be considered a degenerative disorder, with underlying pathological changes in brain causing progressive disease manifestations, or an electric disorder, with overactivity of intrinsically oscillatory motor networks that occur without underlying structural brain abnormalities. Converging data from clinical, neuroimaging and pathological studies in ET now provide considerable evidence for the neurodegenerative hypothesis. A major turning point in this debate is that rigorous tissue-based studies have recently identified a series of structural changes in the ET cerebellum. Most of these pathological changes are centered on the Purkinje cell and connected neuronal populations, which can result in partial loss of Purkinje cells and circuitry reorganizations that would disturb cerebellar function. There is significant overlap in clinical and pathological features of ET with other disorders of cerebellar degeneration, and an increased risk of developing other degenerative diseases in ET. The combined implication of these studies is that ET could be degenerative. The evidence in support of the degenerative hypothesis is presented.

The Pathophysiology and Treatment of Essential Tremor: The Role of Adenosine and Dopamine Receptors in Animal Models

Essential tremor (ET) is one of the most common neurological disorders that often affects people in the prime of their lives, leading to a significant reduction in their quality of life, gradually making them unable to independently perform the simplest activities. Here we show that current ET pharmacotherapy often does not sufficiently alleviate disease symptoms and is completely ineffective in more than 30% of patients. At present, deep brain stimulation of the motor thalamus is the most effective ET treatment. However, like any brain surgery, it can cause many undesirable side effects; thus, it is only performed in patients with an advanced disease who are not responsive to drugs. Therefore, it seems extremely important to look for new strategies for treating ET. The purpose of this review is to summarize the current knowledge on the pathomechanism of ET based on studies in animal models of the disease, as well as to present and discuss the results of research available to date on various substances affecting dopamine (mainly D3) or adenosine A1 receptors, which, due to their ability to modulate harmaline-induced tremor, may provide the basis for the development of new potential therapies for ET in the future.

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.

Identifying Depressed Essential Tremor Using Resting-State Voxel-Wise Global Brain Connectivity: A Multivariate Pattern Analysis

Background and Objective: Although depression is one of the most common non-motor symptoms in essential tremor (ET), its pathogenesis and diagnosis biomarker are still unknown. Recently, machine learning multivariate pattern analysis (MVPA) combined with connectivity mapping of resting-state fMRI has provided a promising way to identify patients with depressed ET at the individual level and help to reveal the brain network pathogenesis of depression in patients with ET.

Methods: Based on global brain connectivity (GBC) mapping from 41 depressed ET, 49 non-depressed ET, 45 primary depression, and 43 healthy controls (HCs), multiclass Gaussian process classification (GPC) and binary support vector machine (SVM) algorithms were used to identify patients with depressed ET from non-depressed ET, primary depression, and HCs, and the accuracy and permutation tests were used to assess the classification performance.

Results: While the total accuracy (40.45%) of four-class GPC was poor, the four-class GPC could discriminate depressed ET from non-depressed ET, primary depression, and HCs with a sensitivity of 70.73% (P < 0.001). At the same time, the sensitivity of using binary SVM to discriminate depressed ET from non-depressed ET, primary depression, and HCs was 73.17, 80.49, and 75.61%, respectively (P < 0.001). The significant discriminative features were mainly located in cerebellar-motor-prefrontal cortex circuits (P < 0.001), and a further correlation analysis showed that the GBC values of significant discriminative features in the right middle prefrontal gyrus, bilateral cerebellum VI, and Crus 1 were correlated with clinical depression severity in patients with depressed ET.

Conclusion: Our findings demonstrated that GBC mapping combined with machine learning MVPA could be used to identify patients with depressed ET, and the GBC changes in cerebellar-prefrontal cortex circuits not only posed as the significant discriminative features but also helped to understand the network pathogenesis underlying depression in patients with ET.

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.

NOTCH2NLC-related repeat expansion disorders: an expanding group of neurodegenerative disorders

The NOTCH2NLC gene 5' untranslated region (UTR) GGC repeat expansion mutations were identified as a genetic contributor of neuronal intranuclear inclusion disease (NIID) in 2019. Since then, the number of reported cases with NOTCH2NLC GGC repeat expansion in Asian and European populations has increased rapidly, indicating that the expanded mutation not only leads to the onset or progression of the NIID, but also may play an important role in multiple progressive neurological disorders, including Parkinson's disease, essential tremor, multiple system atrophy, Alzheimer's disease, frontotemporal dementia, amyotrophic lateral sclerosis, leukoencephalopathy, and oculopharyngodistal myopathy type 3. Nevertheless, the underlying pathogenic mechanism of the NOTCH2NLC 5' UTR region GGC repeat expansion in these disorders remains largely unknown. This review aims to present recent breakthroughs on this mutation and improve our knowledge of a newly defined spectrum of disease: NOTCH2NLC-related repeat expansion disorder.

Mild cognitive impairment, dementia and risk of mortality in essential tremor: A longitudinal prospective study of elders

BACKGROUND

There is evidence that the risk of mortality is increased in patients with essential tremor (ET), however, there are few longitudinal, prospective data on the predictors of mortality in ET. There is also evidence that ET is associated with cognitive impairment; yet, it is unknown whether this is associated with elevated risk of mortality.

METHODS

In a longitudinal, prospective study of 194 elders with ET, an extensive neuropsychological test battery was performed at three time points: baseline, 18 months, and 36 months, and cognitive diagnoses (normal, mild cognitive impairment [MCI], and dementia) were assigned during consensus conferences. We used Cox proportional hazards models to estimate hazard ratios (HR) for death.

RESULTS

The mean baseline age was 79.1 ± 9.7 years. During follow-up, 52 (26.8%) died. In initial univariate models, a variety of baseline factors were associated with increased risk of mortality, including demographic variables (i.e., older age), cognitive variables and gait and balance variables. In the final multivariate Cox model, baseline dementia (HR = 2.66, p = 0.006), older baseline age (HR = 1.18, p < 0.001), and more reported falls at baseline (HR = 1.10, p < 0.001) were independently associated with increased risk of mortality. Amnestic MCI was marginally associated with increased risk of mortality (HR = 1.93, p = 0.08) in primary analyses and significantly (p < 0.05) in several sensitivity analyses.

CONCLUSIONS

In this longitudinal, prospective study, baseline dementia resulted in a 2- to 3-times increase in risk of mortality in ET, further highlighting the clinical significance of cognitive impairment, specifically dementia, in this population.

White Matter Hyperintensities Are Associated With Severity of Essential Tremor in the Elderly

Background: Essential tremor (ET) occurs with steeply increasing prevalence in the elderly, and apart from disease duration, age is independently associated with an increase of tremor amplitude and a decrease of frequency. White matter hyperintensities (WMHs) are a common finding in the elderly, and their role in the pathophysiology of ET is unknown. The aims of this study were to examine whether ET patients differ in their total or region-specific WMH volumes from healthy controls and to determine the impact of WMH on tremor characteristics. Methods: A total of 47 elderly ET patients with a mean age of 72 years and 39 age-matched healthy controls underwent a thorough clinical assessment and 3T MRI. Total WMH volumes were derived from T2-weighted fluid-attenuated inversion recovery (FLAIR) MR images. Additionally, region of interest-based WMH volumes for the Johns Hopkins University (JHU) white matter tracts and labels were calculated, and WMHs were assessed semiquantitatively using the Fazekas scale. Results: Essential tremor patients and healthy controls did not differ in their total or tract-specific WMH volumes or Fazekas scores. However, WMH volume was significantly positively correlated with tremor severity on the TETRAS scale, and there was a significant negative correlation with the mean accelerometric tremor frequency. In a multiple linear regression model including disease duration, age, and age-adjusted total WMH volume, only the WMH volume significantly predicted tremor severity, while age and disease duration were not significant. Conclusion: We found evidence for a direct association between WMH volume and tremor severity. If confirmed by larger studies, our findings could explain the well-known relation between age and tremor severity.

Genomic Markers for Essential Tremor

There are many reports suggesting an important role of genetic factors in the etiopathogenesis of essential tremor (ET), encouraging continuing the research for possible genetic markers. Linkage studies in families with ET have identified 4 genes/loci for familial ET, although the responsible gene(s) have not been identified. Genome-wide association studies (GWAS) described several variants in LINGO1, SLC1A2, STK32B, PPARGC1A, and CTNNA3, related with ET, but none of them have been confirmed in replication studies. In addition, the case-control association studies performed for candidate variants have not convincingly linked any gene with the risk for ET. Exome studies described the association of several genes with familial ET (FUS, HTRA2, TENM4, SORT1, SCN11A, NOTCH2NLC, NOS3, KCNS2, HAPLN4, USP46, CACNA1G, SLIT3, CCDC183, MMP10, and GPR151), but they were found only in singular families and, again, not found in other families or other populations, suggesting that some can be private polymorphisms. The search for responsible genes for ET is still ongoing.

Thalamic but Not Subthalamic Neuromodulation Simplifies Word Use in Spontaneous Language

Several investigations have shown language impairments following electrode implantation surgery for Deep Brain Stimulation (DBS) in movement disorders. The impact of the actual stimulation, however, differs between DBS targets with further deterioration in formal language tests induced by thalamic DBS in contrast to subtle improvement observed in subthalamic DBS. Here, we studied speech samples from interviews with participants treated with DBS of the thalamic ventral intermediate nucleus (VIM) for essential tremor (ET), or the subthalamic nucleus (STN) for Parkinson’s disease (PD), and healthy volunteers (each n = 13). We analyzed word frequency and the use of open and closed class words. Active DBS increased word frequency in case of VIM, but not STN stimulation. Further, relative to controls, both DBS groups produced fewer open class words. Whereas VIM DBS further decreased the proportion of open class words, it was increased by STN DBS. Thus, VIM DBS favors the use of relatively common words in spontaneous language, compatible with the idea of lexical simplification under thalamic stimulation. The absence or even partial reversal of these effects in patients receiving STN DBS is of interest with respect to biolinguistic concepts suggesting dichotomous thalamic vs. basal ganglia roles in language processing.

Sleep disorders in essential tremor: systematic review and meta-analysis

Sleep disorders are frequent in patients diagnosed with essential tremor (ET). The present review focuses on sleep disorders and the results of polysomnographic studies performed in patients with ET. For this purpose we performed a systematic review crossing the search term "essential tremor" with "sleep," "sleep disorders," "sleep disturbances" and "polysomnography," and with specific sleep disorders, according to the International Classification of the Sleep Disorders-Third Edition, using the PubMed, EMBASE, MEDLINE, and Web of Science Databases. The most frequent sleep problems reported by patients with ET were the bad quality of sleep and excessive daytime somnolence (the latter could be related to drugs commonly used for the treatment of ET). Probable rapid eye movement sleep behavior disorder, coexistent restless legs syndrome, insomnia, and nocturia were not infrequent complaints, while the presence of other sleep disorders in patients with ET was restricted to anecdotal reports or not described. Meta-analyses of previous reports showed that patients with ET (according to the PRISMA and MOOSE guidelines) showed higher scores in the Pittsburgh Sleep Quality Index and the Epworth Sleepiness Scale than controls and lower scores than those of patients diagnosed with Parkinson's disease. Studies using polysomnography in patients with ET are scarce and do not permit to establish valid conclusions regarding polysomnographic features in this disorder.