Rest and other types of tremor in adult-onset primary dystonia

Comparing Essential Tremor with and without Soft Dystonic Signs and Tremor Combined with Dystonia: The TITAN Study

BACKGROUND

Tremor disorders remain as clinical diagnoses and the rate of misdiagnosis between the commonest non-parkinsonian tremors is relatively high.

OBJECTIVES

To compare the clinical features of Essential Tremor without other features (pure ET), ET plus soft dystonic signs (ET + DS), and tremor combined with dystonia (TwD).

METHODS

We compared the clinical features of patients with pure ET, ET + DS, and TwD enrolled in The ITAlian tremor Network (TITAN). Linear regression models were performed to determine factors associated with health status and quality of life.

RESULTS

Three-hundred-eighty-three patients were included. Sex distribution was significantly different between the groups with males being more represented in pure ET and females in TwD. The initial site of tremor was different between the groups with about 40% of TwD having head tremor and ET + DS unilateral upper limb tremor at onset. This pattern mirrored the distribution of overt dystonia and soft dystonic signs at examination. Sensory trick, task-specificity, and position-dependence were more common, but not exclusive, to TwD. Pure ET patients showed the lowest degree of alcohol responsiveness and ET + DS the highest. Midline tremor was more commonly encountered and more severe in TwD than in the other groups. Regression analyses demonstrated that tremor severity, sex, age, and to a lesser degree the variable "group", independently predicted health status and quality of life, suggesting the existence of other determinants beyond tremor.

CONCLUSIONS

Pure ET and TwD manifest with a phenotypic overlap, which calls for the identification of diagnostic biomarkers. ET + DS shared features with both syndromes, suggesting intra-group heterogeneity.

Bedside clinical assessment of patients with common upper limb tremor and algorithmic approach

The diagnostic approach for patients with tremor is challenging due to the complex and overlapping phenotypes among tremor syndromes. The first step in the evaluation of tremor is to identify the tremulous movement and exclude the tremor mimics. The second step is to classify the tremor syndrome based on the characteristics of tremor from historical clues and focused examination (Axis 1). Comprehensive tremor examinations involve the assessment of tremor in different conditions (rest, action or mixed, position or task-specific), distribution of tremor (upper limb, lower limb, head, jaw), positive signs for functional tremor (FT) if suspected (distractibility, entrainment, co-contraction), and associated neurological signs including parkinsonism, dystonic posture, cerebellar/brainstem signs, neuropathy, and cognitive impairment. A pivotal feature in this step is to determine any distinct feature of a specific isolated or combined tremor syndrome. In this review, we propose an algorithm to assess upper limb tremors. Ancillary testing should be performed if clinical evaluation is unclear. The choice of investigation depends on the types of tremors considered to narrow down the spectrum of etiology (Axis 2). Laboratory blood tests are considered for acute onset and acute worsening of tremors, while structural neuroimaging is indicated in unilateral tremors with acute onset, nonclassical presentations, and a combination of neurological symptoms. Neurophysiological study is an important tool that aids in distinguishing between tremor and myoclonus, etiology of tremor and document specific signs of FT. Treatment is mainly symptomatic based depending on the etiology of the tremor and the patient's disabilities.

Epidemiologic Disparities and Challenges in Non-parkinsonian Tremor Disorders Research: A Scoping Review Emphasizing the Indian Context

Non-parkinsonian tremors represent a heterogeneous spectrum of movement disorders where knowledge gaps persist regarding epidemiology, pathophysiology, and clinical burden. This scoping review aimed to systematically consolidate literature on these disorders in India across the domains of prevalence, biological mechanisms, psychiatric comorbidity, disability impact, and quality of life. A systematic search was undertaken across databases to identify studies on non-parkinsonian tremors in India. Extracted data were synthesized descriptively under themes spanning reported prevalence estimates and variability, proposed biological processes, psychiatric symptom rates, stigma perceptions, and quality-of-life deficits. Methodological appraisal was undertaken. Twenty-nine studies reported prevalence estimates displaying wide variability from 0.09% to 22% for essential tremor, partly attributable to definitional inconsistencies. Proposed pathologic processes centered on cerebellar dysfunction, neurotransmitter disturbances, and genetic risks. Nine studies revealed variable anxiety (6.8%-90%) and depression (3.4%-60%) rates among essential tremor patients, while two indicated perceived stigma. Five studies unanimously concurred significant quality of life impairment in essential tremors. Evidence of dystonic tremor, functional tremor, and other tremors was limited. This review exposed critical knowledge gaps and methodological limitations, while systematically evaluating the Indian literature on non-parkinsonian tremors concerning epidemiology, mechanisms, and clinical burden. Large-scale collaborative research applying standardized diagnostic criteria is imperative to determine contemporary prevalence statistics and comprehensively characterize the multifaceted disability footprint to inform patient-centric models optimizing diagnosis and holistic care.

Clinical correlates of "pure" essential tremor: the TITAN study

Background

To date, there are no large studies delineating the clinical correlates of "pure" essential tremor (ET) according to its new definition.

Methods

From the ITAlian tremor Network (TITAN) database, we extracted data from patients with a diagnosis of "pure" ET and excluded those with other tremor classifications, including ET-plus, focal, and task-specific tremor, which were formerly considered parts of the ET spectrum.

Results

Out of 653 subjects recruited in the TITAN study by January 2022, the data of 208 (31.8%) "pure" ET patients (86M/122F) were analyzed. The distribution of age at onset was found to be bimodal. The proportion of familial cases by the age-at-onset class of 20 years showed significant differences, with sporadic cases representing the large majority of the class with an age at onset above 60 years. Patients with a positive family history of tremor had a younger onset and were more likely to have leg involvement than sporadic patients despite a similar disease duration. Early-onset and late-onset cases were different in terms of tremor distribution at onset and tremor severity, likely as a function of longer disease duration, yet without differences in terms of quality of life, which suggests a relatively benign progression. Treatment patterns and outcomes revealed that up to 40% of the sample was unsatisfied with the current pharmacological options.

Discussion

The findings reported in the study provide new insights, especially with regard to a possible inversed sex distribution, and to the genetic backgrounds of "pure" ET, given that familial cases were evenly distributed across age-at-onset classes of 20 years. Deep clinical profiling of "pure" ET, for instance, according to age at onset, might increase the clinical value of this syndrome in identifying pathogenetic hypotheses and therapeutic strategies.

Dystonia and tremor: Do they have a shared biology?

Dystonia and tremor are the two most commonly encountered hyperkinetic movement disorders encountered in clinical practice. While there has been substantial progress in the research on these two disorders, there also exists a lot of gray areas. Entities such as dystonic tremor and tremor associated with dystonia occupy a major portion of the "gray zone". In addition, there is a marked clinical heterogeneity and overlap of several clinical and epidemiological features among dystonia and tremor. These facts raise the possibility that dystonia and tremor could be having shared biology. In this chapter, we revisit critical aspects of this possibility that may have important clinical and research implications in the future. We comprehensively review the points in favor and against the theory that dystonia and tremor have shared biology from clinical, epidemiological, genetic and neuroimaging studies.

Tremor is associated with familial clustering of dystonia

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Diagnostic Uncertainties in Tremor

The approach and diagnosis of patients with tremor may be challenging for clinicians. According to the most recent consensus statement by the Task Force on Tremor of the International Parkinson Movement Disorder Society, the differentiation between action (i.e., kinetic, postural, intention), resting, and other task- and position-specific tremors is crucial to this goal. In addition, patients with tremor must be carefully examined for other relevant features, including the topography of the tremor, since it can involve different body areas and possibly associate with neurological signs of uncertain significance. Following the characterization of major clinical features, it may be useful to define, whenever possible, a particular tremor syndrome and to narrow down the spectrum of possible etiologies. First, it is important to distinguish between physiological and pathological tremor, and, in the latter case, to differentiate between the underlying pathological conditions. A correct approach to tremor is particularly relevant for appropriate referral, counseling, prognosis definition, and therapeutic management of patients. The purpose of this review is to outline the possible diagnostic uncertainties that may be encountered in clinical practice in the approach to patients with tremor. In addition to an emphasis on a clinical approach, this review discusses the important ancillary role of neurophysiology and innovative technologies, neuroimaging, and genetics in the diagnostic process.

Treatment of Dystonic Tremor of the Upper Limbs: A Single-Center Retrospective Study

Tremor is part of the phenomenological spectrum of dystonia. Treatments available for tremor in dystonia are oral medications (OM), botulinum neurotoxin (BoNT), and brain surgery (deep brain stimulation or thalamotomy). There is limited knowledge regarding the outcome of different treatment options, and evidence is especially scarce for the tremor of the upper limbs occurring in people with dystonia. In this single-center retrospective study, we evaluated the outcome of different treatments in a cohort of people with upper limb dystonic tremors. Demographic, clinical, and treatment data were analyzed. Dropout rates and side effects were specifically assessed, as well as the 7-point patient-completed clinical global impression scale (p-CGI-S, 1: very much improved; 7: very much worse) as outcome measures. A total of 47 subjects (46.8% female) with dystonic tremor, tremor associated with dystonia, or task-specific tremor were included, with a median age at onset of 58 years (7-86). A total of 31 subjects were treated with OM, 31 with BoNT, and 7 with surgery. Dropout rates with OM were 74.2% due to either lack of efficacy (n = 10) or side effects (n = 13). A total of 7 patients treated with BoNT (22.6%) had mild weakness, causing dropout in 2. P-CGI-S was ≤3 (improvement) in 39% with OM, compared to 92% with BoNT and 100% with surgery. These findings suggest good symptom control of the tremor of the upper limb in dystonia with BoNT and surgery, with higher rates of dropout and side effects with OM. Randomized controlled studies are needed to confirm our findings and provide further insight into better selecting suitable patients for BoNT or brain surgery.

Essential tremor plus rest tremor: current concepts and controversies

Since the initial description of Essential Tremor (ET), the entity of ET with rest tremor has proven to be a controversial concept. Some authors argued it could be a late manifestation of ET, others suggested it could be a variant of ET, yet others suggested it could represent a transitional state between ET and Parkinson's disease. The novel tremor classification has proposed the construct of ET-plus to differentiate patients with rest tremor from pure ET. However, there is no clarity of what ET-plus rest tremor represents. With the aim of shedding light on this controversial entity, we have, therefore, systematically reviewed all clinical, electrophysiological, imaging and anatomopathological studies indexed in the Medline database published both before and after the new tremor classification and involving patients with ET-plus rest tremor. Forty-four studies involving 4028 patients were included in this review and analyzed in detail by means of descriptive statistics. The results of the current review suggest that ET-plus rest tremor is a heterogenous group of conditions: thus, rest tremor might represent a late feature of ET, might reflect a different disorder with higher age at onset and lower dependance on genetic susceptibility than ET, might suggest the development of Parkinson's disease or might indicate a misdiagnosis of ET. The reviewed lines of evidence refuse recent claims arguing against the construct of ET-plus, which should be viewed as a syndrome with different possible underpinnings, and highlights methodological issues to be solved in future research.

Dystonia, chorea, hemiballismus and other dyskinesias

Hyperkinesias are heterogeneous involuntary movements that significantly differ in terms of clinical and semeiological manifestations, including rhythm, regularity, speed, duration, and other factors that determine their appearance or suppression. Hyperkinesias are due to complex, variable, and largely undefined pathophysiological mechanisms that may involve different brain areas. In this chapter, we specifically focus on dystonia, chorea and hemiballismus, and other dyskinesias, specifically, levodopa-induced, tardive, and cranial dyskinesia. We address the role of neurophysiological studies aimed at explaining the pathophysiology of these conditions. We mainly refer to human studies using surface and invasive in-depth recordings, as well as spinal, brainstem, and transcortical reflexology and non-invasive brain stimulation techniques. We discuss the extent to which the neurophysiological abnormalities observed in hyperkinesias may be explained by pathophysiological models. We highlight the most relevant issues that deserve future research efforts. The potential role of neurophysiological assessment in the clinical context of hyperkinesia is also discussed.

The Italian tremor Network (TITAN): rationale, design and preliminary findings

INTRODUCTION

The recently released classification has revised the nosology of tremor, defining essential tremor (ET) as a syndrome and fueling an enlightened debate about some newly conceptualized entities such as ET-plus. As a result, precise information of demographics, clinical features, and about the natural history of these conditions are lacking.

METHODS

The ITAlian tremor Network (TITAN) is a multicenter data collection platform, the aim of which is to prospectively assess, according to a standardized protocol, the phenomenology and natural history of tremor syndromes.

RESULTS

In the first year of activity, 679 patients have been recruited. The frequency of tremor syndromes varied from 32% of ET and 41% of ET-plus to less than 3% of rare forms, including focal tremors (2.30%), task-specific tremors (1.38%), isolated rest tremor (0.61%), and orthostatic tremor (0.61%). Patients with ET-plus were older and had a higher age at onset than ET, but a shorter disease duration, which might suggest that ET-plus is not a disease stage of ET. Familial aggregation of tremor and movement disorders was present in up to 60% of ET cases and in about 40% of patients with tremor combined with dystonia. The body site of tremor onset was different between tremor syndromes, with head tremor being most commonly, but not uniquely, associated with dystonia.

CONCLUSIONS

The TITAN study is anticipated to provide clinically relevant prospective information about the clinical correlates of different tremor syndromes and their specific outcomes and might serve as a basis for future etiological, pathophysiological, and therapeutic research.

A Case Report of Baclofen- and Clozapine-Induced Dyskinesia: A Movement Disorder

Movement disorder is a broad term comprising multiple disorders which result in either an excess or a paucity of voluntary and involuntary movements. There are numerous pieces of literature on drug-induced dyskinesia, although the exact mechanism underlying this phenomenon is yet to be understood. Drug-induced movement disorder is a complex and often neglected clinical presentation. There are various interactions of drugs with the dopaminergic, GABAergic, and serotonergic pathways in the body that seem to be the foundation, leading to these movement disorders. Further research and clinical trials are required to understand this clinical entity. Here we present a case report of GABAergic baclofen and an anti-dopaminergic clozapine-induced atypical case of dyskinesia, a severe form of movement disorder in a 69-year-old-male with a past medical history of physiologic tremor and neuropathic pain.

Clinical features, pathophysiology, treatment, and controversies of tremor in dystonia

Dystonia and tremor frequently co-occur. In some cases, they have shared biological mechanisms, while in others dystonia and tremor are two comorbid conditions. The term "dystonic tremor" is used to describe tremor in those who have dystonia. Two mutually exclusive definitions of "dystonic tremor" were proposed. According to one definition, dystonic tremor is the tremor in the dystonic body part. An alternate definition of dystonic tremor entails irregular and jerky oscillations that have saw tooth appearance with or without overt dystonia. This paper outlines the differences in two definitions of dystonic tremor and identifies their limitations. Given the diverse views defining "dystonic tremor", this paper will use the term "tremor in dystonia". In addition, we will outline different ways to separate the subtypes of tremor in dystonia. Then we will discuss pathophysiological mechanisms derived from the objective measures and single neuron physiology analyses of tremor in dystonia. This article is part of the Special Issue "Tremor" edited by Daniel D. Truong, Mark Hallett, and Aasef Shaikh.

Deep brain stimulation for arm tremor: A randomized trial comparing two targets

OBJECTIVE

Deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) effectively suppresses arm tremor. Uncontrolled studies suggest the posterior subthalamic area (PSA) may be superior. We compared the intra-individual efficacy of VIM- versus PSA-DBS on tremor suppression and arm function.

METHODS

We performed a randomized, double-blind, crossover trial at Oslo University Hospital in patients (18-80 years) with isolated or combined action tremor affecting at least one arm. Four-contact DBS leads were implanted (bi- or unilaterally) with a trajectory to cover the VIM (upper two contacts) and PSA (lower two contacts). Patients were randomized (1:1 ratio) post-surgery to: Group 1, VIM-stimulation months 0-3 (period 1), then PSA-stimulation months 4-6 (period 2); Group 2, PSA-stimulation first, then VIM-stimulation. Primary endpoint was the difference in improvement from baseline to the end of the VIM- versus PSA-period in the sum of the dominant arm tremor scores of the Fahn-Tolosa-Marin Tremor Rating Scale (FTMTRS), items 5/6 + 10-14.

RESULTS

Forty-five patients were randomized to Group 1 (n = 23) or 2 (n = 22). In the primary endpoint per-protocol analysis (mixed model, n = 40), mean difference in the sum FTMTRS score improvement for the dominant arm was -2.65 points (95% CI -4.33 to -0.97; p = 0.002). The difference in favour of PSA stimulation was highly significant in period 2, but not period 1.

INTERPRETATION

Our randomized trial demonstrated that PSA stimulation provided superior tremor suppression compared with VIM stimulation. A period effect reducing tremor for up to three months in both groups was most likely attributed to a post-surgery stun effect. This article is protected by copyright. All rights reserved.

Bayesian Interpretation of Essential Tremor Plus

Essential tremor (ET) plus is a new tremor classification that was introduced in 2018 by a task force of the International Parkinson and Movement Disorder Society. Patients with ET plus meet the criteria for ET but have one or more additional systemic or neurologic signs of uncertain significance or relevance to tremor (“soft signs”). Soft signs are not sufficient to diagnose another tremor syndrome or movement disorder, and soft signs in ET plus are known to have poor interrater reliability and low diagnostic sensitivity and specificity. Therefore, the clinical significance of ET plus must be interpreted probabilistically when judging whether a patient is more likely to have ET or a combined tremor syndrome, such as dystonic tremor. Such a probabilistic interpretation is possible with Bayesian analysis. This review presents a Bayesian analysis of ET plus in patients suspected of having ET versus a dystonic tremor syndrome, which is the most common differential diagnosis in patients referred for ET. Bayesian analysis of soft signs provides an estimate of the probability that a patient with possible ET is more likely to have an alternative diagnosis. ET plus is a distinct tremor classification and should not be viewed as a subtype of ET. ET plus covers a more-comprehensive phenotyping of people with possible ET, and the clinical interpretation of ET plus is enhanced with Bayesian analysis of associated soft signs.

Cerebello-thalamic activity drives an abnormal motor network into dystonic tremor

Dystonic tremor syndromes are highly burdensome and treatment is often inadequate. This is partly due to poor understanding of the underlying pathophysiology. Several lines of research suggest involvement of the cerebello-thalamo-cortical circuit and the basal ganglia in dystonic tremor syndromes, but their role is unclear. Here we aimed to investigate the contribution of the cerebello-thalamo-cortical circuit and the basal ganglia to the pathophysiology of dystonic tremor syndrome, by directly linking tremor fluctuations to cerebral activity during scanning. In 27 patients with dystonic tremor syndrome (dystonic tremor: n = 23; tremor associated with dystonia: n = 4), we used concurrent accelerometery and functional MRI during a posture holding task that evoked tremor, alternated with rest. Using multiple regression analyses, we separated tremor-related activity from brain activity related to (voluntary) posture holding. Using dynamic causal modelling, we tested for altered effective connectivity between tremor-related brain regions as a function of tremor amplitude fluctuations. Finally, we compared grey matter volume between patients (n = 27) and matched controls (n = 27). We found tremor-related activity in sensorimotor regions of the bilateral cerebellum, contralateral posterior and anterior ventral lateral nuclei of the thalamus (VLp and VLa), contralateral primary motor cortex (hand area), contralateral pallidum, and the bilateral frontal cortex (laterality with respect to the tremor). Grey matter volume was increased in patients compared to controls in the portion of contralateral thalamus also showing tremor-related activity, as well as in bilateral medial and left lateral primary motor cortex, where no tremor-related activity was present. Effective connectivity analyses showed that inter-regional coupling in the cerebello-thalamic pathway, as well as the thalamic self-connection, were strengthened as a function of increasing tremor power. These findings indicate that the pathophysiology of dystonic tremor syndromes involves functional and structural changes in the cerebello-thalamo-cortical circuit and pallidum. Deficient input from the cerebellum towards the thalamo-cortical circuit, together with hypertrophy of the thalamus, may play a key role in the generation of dystonic tremor syndrome.

Predictive modeling of spread in adult-onset isolated dystonia: Key properties and effect of tremor inclusion

BACKGROUND AND PURPOSE

Several clinical and demographic factors relate to anatomic spread of adult-onset isolated dystonia, but a predictive model is still lacking. The aims of this study were: (i) to develop and validate a predictive model of anatomic spread of adult-onset isolated dystonia; and (ii) to evaluate whether presence of tremor associated with dystonia influences model predictions of spread.

METHODS

Adult-onset isolated dystonia participants with focal onset from the Dystonia Coalition Natural History Project database were included. We developed two prediction models, one with dystonia as sole disease manifestation ("dystonia-only") and one accepting dystonia OR tremor in any body part as disease manifestations ("dystonia OR tremor"). Demographic and clinical predictors were selected based on previous evidence, clinical plausibility of association with spread, or both. We used logistic regressions and evaluated model discrimination and calibration. Internal validation was carried out based on bootstrapping.

RESULTS

Both predictive models showed an area under the curve of 0.65 (95% confidence intervals 0.62-0.70 and 0.62-0.69, respectively) and good calibration after internal validation. In both models, onset of dystonia in body regions other than the neck, older age, depression and history of neck trauma were predictors of spread.

CONCLUSIONS

This predictive modeling of spread in adult-onset isolated dystonia based on accessible predictors (demographic and clinical) can be easily implemented to inform individuals' risk of spread. Because tremor did not influence prediction of spread, our results support the argument that tremor is a part of the dystonia syndrome, and not an independent or coincidental disorder.

Approach to Tremor Disorders

Tremor disorders are diverse and complex. Historical clues and examination features play a major role in diagnosing these disorders, but diagnosis can be challenging due to phenotypic overlap. Ancillary testing, such as neuroimaging or laboratory testing, is driven by the history and examination, and should be performed particularly when there are other neurological or systemic manifestations. The pathophysiology of tremor is not entirely understood, but likely involves multiple networks along with the cerebello-thalamo-cortical pathways. Treatment options include medications, botulinum toxin, surgery, and nonpharmacologic interventions utilizing physical and occupational therapies and assistive devices. Further work is needed in developing accurate diagnostic tests and better treatment options for tremor disorders.

Effect of Botulinum Toxin on Non-Motor Symptoms in Cervical Dystonia

Patients with cervical dystonia (CD) may display non-motor symptoms, including psychiatric disturbances, pain, and sleep disorders. Intramuscular injection of botulinum toxin type A (BoNT-A) is the most efficacious treatment for motor symptoms in CD, but little is known about its effects on non-motor manifestations. The aim of the present study was to longitudinally assess BoNT-A’s effects on CD non-motor symptoms and to investigate the relationship between BoNT-A-induced motor and non-motor changes. Forty-five patients with CD participated in the study. Patients underwent a clinical assessment that included the administration of standardized clinical scales assessing dystonic symptoms, psychiatric disturbances, pain, sleep disturbances, and disability. Clinical assessment was performed before and one and three months after BoNT-A injection. BoNT-A induced a significant improvement in dystonic symptoms, as well as in psychiatric disturbances, pain, and disability. Conversely, sleep disorders were unaffected by BoNT-A treatment. Motor and non-motor BoNT-A-induced changes showed a similar time course, but motor improvement did not correlate with non-motor changes after BoNT-A. Non-motor symptom changes after BoNT-A treatment are a complex phenomenon and are at least partially independent from motor symptom improvement.

Tremor Syndromes: An Updated Review

Tremor is the most commonly encountered movement disorder in clinical practice. A wide range of pathologies may manifest with tremor either as a presenting or predominant symptom. Considering the marked etiological and phenomenological heterogeneity, it would be desirable to develop a classification of tremors that reflects their underlying pathophysiology. The tremor task force of the International Parkinson Disease and Movement Disorders Society has worked toward this goal and proposed a new classification system. This system has remained a prime topic of scientific communications on tremor in recent times. The new classification is based on two axes: 1. based on the clinical features, history, and tremor characteristics and 2. based on the etiology of tremor. In this article, we discuss the key aspects of the new classification, review various tremor syndromes, highlight some of the controversies in the field of tremor, and share the potential future perspectives.

Assessment of Botulinum Neurotoxin Injection for Dystonic Hand Tremor: A Randomized Clinical Trial

Importance

There is an unmet need for safe and efficacious treatments for upper-extremity dystonic tremor (DT). To date, only uncontrolled retrospective case series have reported the effect of botulinum neurotoxin (BoNT) injections on upper-extremity DT.

Objective

To assess the effect of BoNT injections on tremor in patients with upper-extremity DT.

Design, Setting, and Participants

In this placebo-controlled, parallel-group randomized clinical trial, 30 adult patients with upper-extremity DT treated at a movement disorder clinic in a tertiary care university hospital were randomized in a 1:1 ratio to BoNT or saline injection, 0.9%, using a computer-generated randomization sequence. Randomization was masked using opaque envelopes. The participant, injector, outcome assessor, and statistician were blinded to the randomization. Participants were recruited between November 20, 2018, and December 12, 2019, and the last follow-up was completed in March 2020.

Interventions

Participants received electromyographically guided intramuscular injections of BoNT or placebo into the tremulous muscles of the upper extremity. Injection patterns and doses were individualized according to tremor phenomenologic findings.

Main Outcomes and Measures

The primary outcome was the total score on the Fahn-Tolosa-Marin Tremor Rating Scale 6 weeks after the intervention. Outcomes were assessed at baseline, 6 weeks, and 12 weeks. All patients were offered open-label BoNT injections after 12 weeks and reassessed 6 weeks later.

Results

A total of 48 adult patients with a diagnosis of brachial dystonia with DT were screened. Fifteen were ineligible and 3 refused consent; therefore, 30 patients (mean [SD] age, 46.0 [18.6] years; 26 [86.7%] male) were recruited, with 15 randomized to receive BoNT and 15 to receive placebo. In the intention-to-treat group, the Fahn-Tolosa-Marin Tremor Rating Scale total score was significantly lower in the BoNT group at 6 weeks (adjusted mean difference, -10.9; 95% CI, -15.4 to -6.5; P < .001) and 12 weeks (adjusted mean difference, -5.7; 95% CI, -11.0 to -0.5; P = .03). More participants in the BoNT group reported global improvement on the Global Impression of Change (PGIC) assessment (PGIC 1, 2, and 3: BoNT: 4 [26.7%], 6 [40.0%], and 5 [33.3%]; placebo: 5 [33.3%], 10 [66.7%], and 0, respectively; P = .047). Subjective hand weakness (BoNT: 6 [40.0%]; placebo: 4 [28.6%], P = .52) and dynamometer-assessed grip strength (mean difference, -0.2 log10[kgf/m2]2/Hz-Hz; 95% CI, -0.9 to 0.4 log10[kgf/m2]2/Hz-Hz; P = .45) were similar in both groups.

Conclusions and Relevance

In this randomized clinical trial, botulinum neurotoxin injections were superior to placebo in reducing tremor severity in upper-extremity DT. An individualized approach to muscle selection and dosing was beneficial without unacceptable adverse effects.

Trial Registration

Clinical Trials Registry of India (http://ctri.nic.in) Identifier: CTRI/2018/02/011721.

Dystonia and Tremor: A Cross-Sectional Study of the Dystonia Coalition Cohort

OBJECTIVE

To assess the clinical manifestations and predictors of different types of tremors in individuals with different types of isolated dystonia.

METHODS

Clinical manifestations of tremor were assessed in a multicenter, international cross-sectional, cohort study of 2,362 individuals with all types of isolated dystonia (focal, segmental, multifocal, and generalized) recruited through the Dystonia Coalition.

RESULTS

Methodical and standardized assessments of all participants in this cohort revealed the overall prevalence of any type of tremor was 53.3%. The prevalence of dystonic tremor varied from 36.9% to 48.4%, depending on criteria used to define it. To identify the factors associated with tremors in dystonia, the data were analyzed by generalized linear modeling and cluster analyses. Generalized linear modeling indicated 2 of the strongest factors associated with tremor included body region affected by dystonia and recruitment center. Tremor was also associated with severity of dystonia and duration of dystonia, but not with sex or race. The cluster analysis distinguished 8 subgroups within the whole cohort; defined largely by body region with dystonia, and secondarily by other clinical characteristics.

CONCLUSION

The large number of cases evaluated by an international team of movement disorder experts facilitated the dissection of several important factors that influence the apparent prevalence and phenomenology of tremor in dystonia. These results are valuable for understanding the many differences reported in prior studies, and for guiding future studies of the nosology of tremor and dystonia.

Motor and Sensory Features of Cervical Dystonia Subtypes: Data From the Italian Dystonia Registry

Introduction: Cervical dystonia (CD) is one of the most common forms of adult-onset isolated dystonia. Recently, CD has been classified according to the site of onset and spread, in different clinical subgroups, that may represent different clinical entities or pathophysiologic subtypes. In order to support this hypothesis, in this study we have evaluated whether different subgroups of CD, that clinically differ for site of onset and spread, also imply different sensorimotor features.

Methods: Clinical and demographic data from 842 patients with CD from the Italian Dystonia Registry were examined. Motor features (head tremor and tremor elsewhere) and sensory features (sensory trick and neck pain) were investigated. We analyzed possible associations between motor and sensory features in CD subgroups [focal neck onset, no spread (FNO-NS); focal neck onset, segmental spread (FNO-SS); focal onset elsewhere with segmental spread to neck (FOE-SS); segmental neck involvement without spread (SNI)].

Results: In FNO-NS, FOE-SS, and SNI subgroups, head tremor was associated with the presence of tremor elsewhere. Sensory trick was associated with pain in patients with FNO-NS and with head tremor in patients with FNO-SS.

Conclusion: The frequent association between head tremor and tremor elsewhere may suggest a common pathophysiological mechanism. Two mechanisms may be hypothesized for sensory trick: a gating mechanism attempting to reduce pain and a sensorimotor mechanism attempting to control tremor.

Systematic clinical approach for diagnosing upper limb tremor

Tremor is the most common movement disorder worldwide, but diagnosis is challenging. In 2018, the task force on tremor of the International Parkinson and Movement Disorder Society published a consensus statement that proposes a tremor classification along two independent axes: a clinical tremor syndrome and its underlying aetiology. In line with this statement, we here propose a stepwise diagnostic approach that leads to the correct clinical and aetiological classification of upper limb tremor. We also describe the typical clinical signs of each clinical tremor syndrome. A key feature of our algorithm is the distinction between isolated and combined tremor syndromes, in which tremor is accompanied by bradykinesia, cerebellar signs, dystonia, peripheral neuropathy or brainstem signs. This distinction subsequently informs the selection of appropriate diagnostic tests, such as neurophysiology, laboratory testing, structural and dopaminergic imaging and genetic testing. We highlight treatable metabolic causes of tremor, as well as drugs and toxins that can provoke tremor. The stepwise approach facilitates appropriate diagnostic testing and avoids unnecessary investigations. We expect that the approach offered in this article will reduce diagnostic uncertainty and increase the diagnostic yield in patients with tremor.

Tremor in Idiopathic Cervical Dystonia - Possible Implications for Botulinum Toxin Treatment Considering the Col-Cap Classification

Background

Tremor is an important phenotypic feature of dystonia. Using the new concept (Col-Cap) of classification we examined the frequency of tremor in cervical dystonia (CD) patients, their main subtypes and muscles injected.

Methods

In this large study conducted at multiple movement disorder centres in Europe and India, between January and June 2019, we examined 293 patients with idiopathic CD who were all treated with botulinum toxin (BTX).

Results

The dystonic head tremor (DHT+) was present in 57.6 % of CD patients and they had a significantly longer duration of symptoms than patients without head tremor (DHT-). In DHT+ patients torticaput was the most common subtype and the majority (63.3%) had one or two subtypes only. There was no significant difference between the number of unilateral injections for any of the muscles in the DHT+ and DHT- groups, while the number of patients receiving bilateral injections in splenius capitis (78 vs 25; p = 0.00001), sternocleidomastoid (31 vs 6; p = 0.0005), trapezius (28 vs 9; p = 0.01), and obliquus capitis inferior (15 vs 2; p = 0.008) were significantly more in the DHT+ group. The mean doses of all three types of BTX/A were not significantly different between the two groups.

Conclusions

The frequency of head tremor was 57.6% in our CD patients and torticaput was the most common dystonic subtype associated with tremor. Simple forms of CD seemed more likely associated with head tremor, than complex forms of CD. Most of the DHT+ patients received bilateral injections. The use of 'Col-Cap' classification was helpful in the identification of muscles likely to be involved in tremor in CD patients.

Rest tremor in dystonia: epidemiology, differential diagnosis, and pathophysiology

BACKGROUND

The most common type of tremor reported in dystonia patients is postural and kinetic. There is uncertainty regarding the prevalence of rest tremor in dystonia.

OBJECTIVE

This review focuses on the clinical and neurophysiological features of rest tremor in dystonia, its differential diagnosis, and methods to distinguish it from other rest tremor syndromes.

METHODS

A PubMed search was done, and the available literature identified. Bibliography of the available literature was reviewed for relevant references.

RESULTS

Rest tremor in dystonia has been reported with a variable frequency of 1.81-12.05%. The most common body distribution is arm, and it tends to be asymmetric. Most of the affected patients have multifocal and segmental dystonia. Rest tremor is a late-onset phenomenon associated with severe and spreading dystonia. Clinically, it is difficult to distinguish rest tremor in dystonia from other rest tremor syndromes based on tremor characteristics; however, other neurological signs can provide clues to differentiate these syndromes. Surface electromyography and other neurophysiological tests can help differentiate the various rest tremor syndromes.

CONCLUSION

Rest tremor in dystonia can be differentiated from other rest tremor syndromes based on neurophysiological techniques. There is some evidence to suggest that SWEDDs could be a form of dystonic tremor, but further studies are required to clarify this diagnostic dilemma. Data regarding the treatment of rest tremor in dystonia are virtually nonexistent, and there is an urgent need for prospective studies focusing its medical management and to know the surgical targets.

Network-level connectivity is a critical feature distinguishing dystonic tremor and essential tremor

Dystonia is a movement disorder characterized by involuntary muscle co-contractions that give rise to disabling movements and postures. A recent expert consensus labelled the incidence of tremor as a core feature of dystonia that can affect body regions both symptomatic and asymptomatic to dystonic features. We are only beginning to understand the neural network-level signatures that relate to clinical features of dystonic tremor. At the same time, clinical features of dystonic tremor can resemble that of essential tremor and present a diagnostic confound for clinicians. Here, we examined network-level functional activation and connectivity in patients with dystonic tremor and essential tremor. The dystonic tremor group included primarily cervical dystonia patients with dystonic head tremor and the majority had additional upper-limb tremor. The experimental paradigm included a precision grip-force task wherein online visual feedback related to force was manipulated across high and low spatial feedback levels. Prior work using this paradigm in essential tremor patients produced exacerbation of grip-force tremor and associated changes in functional activation. As such, we directly compared the effect of visual feedback on grip-force tremor and associated functional network-level activation and connectivity between dystonic tremor and essential tremor patient cohorts to better understand disease-specific mechanisms. Increased visual feedback similarly exacerbated force tremor during the grip-force task in dystonic tremor and essential tremor cohorts. Patients with dystonic tremor and essential tremor were characterized by distinct functional activation abnormalities in cortical regions but not in the cerebellum. We examined seed-based functional connectivity from the sensorimotor cortex, globus pallidus internus, ventral intermediate thalamic nucleus, and dentate nucleus, and observed abnormal functional connectivity networks in dystonic tremor and essential tremor groups relative to controls. However, the effects were far more widespread in the dystonic tremor group as changes in functional connectivity were revealed across cortical, subcortical, and cerebellar regions independent of the seed location. A unique pattern for dystonic tremor included widespread reductions in functional connectivity compared to essential tremor within higher-level cortical, basal ganglia, and cerebellar regions. Importantly, a receiver operating characteristic determined that functional connectivity z-scores were able to classify dystonic tremor and essential tremor with 89% area under the curve, whereas combining functional connectivity with force tremor yielded 94%. These findings point to network-level connectivity as an important feature that differs substantially between dystonic tremor and essential tremor and should be further explored in implementing appropriate diagnostic and therapeutic strategies.

The Prevalence of Dystonic Tremor and Tremor Associated with Dystonia in Patients with Cervical Dystonia

The link between dystonia and tremor has been known for decades, but the question of whether they are two separate illnesses or just different manifestations of one disease with the same pathophysiological background remains unanswered. We distinguish two types of tremor in dystonia: dystonic tremor (DT), which appears on the body part affected by dystonia, and tremor associated with dystonia (TAWD), which appears in locations where the dystonia does not occur. In this study, the frequency of occurrence of different forms of tremor was determined by clinical examination in a group of adult-onset isolated cervical dystonia (CD) patients treated with regular local injections of botulinum toxin A in our department. In total, 120 patients were included in the study, of which 70 (58.3%) had DT of the head. TAWD was, in all 14 cases (11.7%), observed on the upper limbs, in the form of static or intentional tremor. The aim of this study was to point out the presence of TAWD as one of the clinical signs of CD. DT occurred in more than half of the patients and appears to be a relatively common part of the clinical picture in patients with CD.

Revisiting the Clinical Phenomenology of "Cerebellar Tremor": Beyond the Intention Tremor

Tremor is an involuntary, rhythmic, oscillatory movement of a body part. It is a central feature of a range of diseases resulting from pathological changes in the cerebellum. Interestingly, in modern times, the terms "cerebellar tremor" and "intention tremor" are often used synonymously and interchangeably. However, "cerebellar tremor" (i.e., tremors of cerebellar origin) do not always present exclusively as intention tremor. In this article, we comprehensively revisit the clinical phenomenology of tremors observed in various diseases that are based in the cerebellum. By this, we mean diseases for which the cerebellum and its various connections are often seen as playing a central and defining role. These include spinocerebellar ataxias, essential tremor, orthostatic tremor, dystonia, acute cerebellitis, cerebellar tumors, paraneoplastic cerebellar degeneration, and cerebellar strokes. The theme of this article is to highlight, through published data available in the current literature, that the clinical phenomenology of tremor of cerebellar origin is heterogeneous, and it extends beyond that of intention tremor to include postural tremors, kinetic tremor, rest tremor, and orthostatic tremor. This heterogeneity is consistent with the seminal work of Gordon Holmes, in which he described a variety of tremors aside from intention tremor in the setting of cerebellar lesions. In the end, it would seem that the notion that intention tremor is the sole signature of cerebellar lesions is an over-simplification and is not correct. Future studies are warranted to identify and further characterize the heterogeneity of tremors arising from the various cerebellar etiologies.

Temporal discrimination is altered in patients with isolated asymmetric and jerky upper limb tremor

BACKGROUND

Unilateral or very asymmetric upper limb tremors with a jerky appearance are poorly investigated. Their clinical classification is an unsolved problem because their classification as essential tremor versus dystonic tremor is uncertain. To avoid misclassification as essential tremor or premature classification as dystonic tremor, the term indeterminate tremor was suggested.

OBJECTIVES

The aim of this study was to characterize this tremor subgroup electrophysiologically and evaluate whether diagnostically meaningful electrophysiological differences exist compared to patients with essential tremor and dystonic tremor.

METHODS

We enrolled 29 healthy subjects and 64 patients with tremor: 26 with dystonic tremor, 23 with essential tremor, and 15 patients with upper limb tremor resembling essential tremor but was unusually asymmetric and jerky (indeterminate tremor). We investigated the somatosensory temporal discrimination threshold, the short-interval intracortical inhibition, and the cortical plasticity by paired associative stimulation.

RESULTS

Somatosensory temporal discrimination threshold was significantly increased in patients with dystonic tremor and indeterminate tremor, but it was normal in the essential tremor patients and healthy controls. Significant differences in short-interval intracortical inhibition and paired associative stimulation were not found among the three patient groups and controls.

CONCLUSION

These results indicate that indeterminate tremor, as defined in this study, shares electrophysiological similarities with dystonic tremor rather than essential tremor. Therefore, we propose that indeterminate tremor should be considered as a separate clinical entity from essential tremor and that it might be dystonic in nature. Somatosensory temporal discrimination appears to be a useful tool in tremor classification. © 2019 International Parkinson and Movement Disorder Society.

[The new tremor classification of the International Parkinson and Movement Disorder Society : Update on frequent tremors]

Tremor is one of the most frequent movement disorders. The recently published new classification of the Movement Disorder Society separates the clinical description of tremor syndromes as so-called axis 1 symptom constellations from the etiologies of tremor (axis 2). The same tremor syndromes can therefore be combined with different causes and vice versa. The terminology used in this classification is precisely defined and thereby also the necessary language for medical communication. Frequent tremor syndromes, such as enhanced physiologic tremor, dystonic and parkinsonian tremor as well as focal tremors and task and position-specific tremors are discussed with respect to the phenomenology, and current therapy.

Recent advances in understanding and managing dystonia

Within the field of movement disorders, the conceptual understanding of dystonia has continued to evolve. Clinical advances have included improvements in recognition of certain features of dystonia, such as tremor, and understanding of phenotypic spectrums in the genetic dystonias and dystonia terminology and classification. Progress has also been made in the understanding of underlying biological processes which characterize dystonia from discoveries using approaches such as neurophysiology, functional imaging, genetics, and animal models. Important advances include the role of the cerebellum in dystonia, the concept of dystonia as an aberrant brain network disorder, additional evidence supporting the concept of dystonia endophenotypes, and new insights into psychogenic dystonia. These discoveries have begun to shape treatment approaches as, in parallel, important new treatment modalities, including magnetic resonance imaging-guided focused ultrasound, have emerged and existing interventions such as deep brain stimulation have been further refined. In this review, these topics are explored and discussed.

Tremor

Tremor is a phenomenon observed in a broad spectrum of diseases with different pathophysiologies. While patients with tremor may not complain in the clinic of symptoms of imbalance, gait difficulties, or falls, laboratory research studies using quantitative analysis of gait and posture and neurophysiologic techniques have demonstrated impaired gait and balance across a variety of tremor etiologies. These findings have been supported by careful epidemiologic studies assessing symptoms of imbalance. Imaging and neurophysiologic studies have identified cerebellar networks as important mediators of tremor, and therefore a likely common site of dysfunction to explain the phenomenologic overlap between impaired postural and gait control with tremor. Further understanding of these mechanisms and networks is of crucial importance in the development of new treatments, particularly surgical or minimally invasive lesional therapies.

The Anatomical Basis for Dystonia: The Motor Network Model

Background

The dystonias include a clinically and etiologically very diverse group of disorders. There are both degenerative and non-degenerative subtypes resulting from genetic or acquired causes. Traditionally, all dystonias have been viewed as disorders of the basal ganglia. However, there has been increasing appreciation for involvement of other brain regions including the cerebellum, thalamus, midbrain, and cortex. Much of the early evidence for these other brain regions has come from studies of animals, but multiple recent studies have been done with humans, in an effort to confirm or refute involvement of these other regions. The purpose of this article is to review the new evidence from animals and humans regarding the motor network model, and to address the issues important to translational neuroscience.

Methods

The English literature was reviewed for articles relating to the neuroanatomical basis for various types of dystonia in both animals and humans.

Results

There is evidence from both animals and humans that multiple brain regions play an important role in various types of dystonia. The most direct evidence for specific brain regions comes from animal studies using pharmacological, lesion, or genetic methods. In these studies, experimental manipulations of specific brain regions provide direct evidence for involvement of the basal ganglia, cerebellum, thalamus and other regions. Additional evidence also comes from human studies using neuropathological, neuroimaging, non-invasive brain stimulation, and surgical interventions. In these studies, the evidence is less conclusive, because discriminating the regions that cause dystonia from those that reflect secondary responses to abnormal movements is more challenging.

Discussion

Overall, the evidence from both animals and humans suggests that different regions may play important roles in different subtypes of dystonia. The evidence so far provides strong support for the motor network model. There are obvious challenges, but also advantages, of attempting to translate knowledge gained from animals into a more complete understanding of human dystonia and novel therapeutic strategies.

Tremor in Dystonia: A Cross-sectional Study from India

Background

Tremor is an important phenotypic motor feature in dystonia, but there is limited literature regarding its prevalence and phenomenology.

Methods

This cross-sectional study included 90 patients with adult-onset, isolated dystonia from a tertiary care movement disorder center in India. Patients were assessed for tremor in the head and in different body parts. Surface electromyography studies of tremor were recorded of the involved limb in different positions.

Results

Tremor was present in 41 patients (45.55%) who had dystonia, including 21 of 41 patients (51.21%) with cervical dystonia, 15 of 34 (44.11%) with limb dystonia, and 5 of 15 (33.33%) with cranial dystonia. Significantly later age at presentation (47.19 ± 14.55 years vs. 40.39 ± 13.74 years; P = 0.012) and longer disease duration (5.11 ± 5.85 years vs. 2.60 ± 2.57 years; P = 0.004) were observed in patients with versus without tremor. Upper limb tremor was present in 33 patients, head tremor was present in 14, and leg tremor was present in 2. Tremor was present in 17 of 25 patients (68%) with segmental dystonia and in 6 of 9 (66.66%) with multifocal dystonia. Tremor was least frequent in patients with focal dystonia (18 of 56 patients; 32.14%).

Conclusions

Tremor was common (>45%) in patients with primary adult-onset dystonia. Patients who had tremor were older and had a longer duration of symptoms. Patients with segmental and multifocal dystonia had more tremor than those with focal dystonia. In contrast to some other studies, the current patients had more upper limb tremor than head tremor, and a combination of dystonic tremor and tremor associated with dystonia was more common than isolated dystonic tremor.

Nonmotor Symptoms in Essential Tremor and Other Tremor Disorders

Tremor, like dystonia, is a term used at the phenomenological, syndromic, and aetiopathological level. Parkinsonian, essential, and dystonic tremor are the three most common tremor diagnoses encountered in clinical practice. Investigation of nonmotor symptoms in essential tremor and dystonic tremor syndromes is significantly hampered by the lack of clear clinical diagnostic criteria for these groups at a syndromic level, and the absence of biomarkers which allow definitive diagnosis at an aetiopathological level. Much work is needed in clarifying the motor features of these disorders in order to allow delineation of the nonmotor features of the most common tremor syndromes. With this limitation in mind, this chapter reviews what is known about nonmotor symptoms in these two tremor types. The final sections deal with nonmotor symptoms observed in patients with lesional tremor, thankfully a much more clearly defined albeit less common group of patients.

Rest tremor revisited: Parkinson's disease and other disorders

Tremor is the most common movement disorder characterized by a rhythmical, involuntary oscillatory movement of a body part. Since distinct diseases can cause similar tremor manifestations and vice-versa, it is challenging to make an accurate diagnosis. This applies particularly for tremor at rest. This entity was only rarely studied in the past, although a multitude of clinical studies on prevalence and clinical features of tremor in Parkinson's disease (PD), essential tremor and dystonia, have been carried out. Monosymptomatic rest tremor has been further separated from tremor-dominated PD. Rest tremor is also found in dystonic tremor, essential tremor with a rest component, Holmes tremor and a few even rarer conditions. Dopamine transporter imaging and several electrophysiological methods provide additional clues for tremor differential diagnosis. New evidence from neuroimaging and electrophysiological studies has broadened our knowledge on the pathophysiology of Parkinsonian and non-Parkinsonian tremor. Large cohort studies are warranted in future to explore the nature course and biological basis of tremor in common tremor related disorders.

The essential tremor syndromes

PURPOSE OF REVIEW

Essential tremor has not been defined or used consistently in clinical diagnosis and research. Other monosymptomatic disorders are often referred to as essential tremor variants.

RECENT FINDINGS

There is now solid evidence that essential tremor, however defined, is a syndrome with multiple causes.

SUMMARY

A new tremor classification scheme is being developed by the International Parkinson and Movement Disorder Society Task Force on Tremor. In this scheme, tremor in the absence of other neurological signs is called isolated tremor, and tremor in combination with other signs is called combined tremor. Many isolated and combined tremor syndromes can be defined on the basis of commonly recurring or unique clinical symptoms and signs, including historical features (age at onset, family history, and temporal evolution) and tremor characteristics (body distribution, activation condition, associated features). Essential tremor, however defined, is simply a syndrome and not a specific disease. Essential tremor should be defined and used consistently, or this term should be abandoned. As essential tremor is an arbitrarily defined syndrome, it makes no sense to refer to other tremors as variants of essential tremor or essential tremor syndromes.

Clinical and demographic characteristics related to onset site and spread of cervical dystonia

BACKGROUND

Clinical characteristics of isolated idiopathic cervical dystonia such as onset site and spread to and from additional body regions have been addressed in single-site studies with limited data and incomplete or variable dissociation of focal and segmental subtypes. The objectives of this study were to characterize the clinical characteristics and demographics of isolated idiopathic cervical dystonia in the largest standardized multicenter cohort.

METHODS

The Dystonia Coalition, through a consortium of 37 recruiting sites in North America, Europe, and Australia, recruited 1477 participants with focal (60.7%) or segmental (39.3%) cervical dystonia on examination. Clinical and demographic characteristics were evaluated in terms of the body region of dystonia onset and spread.

RESULTS

Site of dystonia onset was: (1) focal neck only (78.5%), (2) focal onset elsewhere with later segmental spread to neck (13.3%), and (3) segmental onset with initial neck involvement (8.2%). Frequency of spread from focal cervical to segmental dystonia (22.8%) was consistent with prior reports, but frequency of segmental onset with initial neck involvement was substantially higher than the 3% previously reported. Cervical dystonia with focal neck onset, more than other subtypes, was associated with spread and tremor of any type. Sensory tricks were less frequent in cervical dystonia with segmental components, and segmental cervical onset occurred at an older age.

CONCLUSIONS

Subgroups had modest but significant differences in the clinical characteristics that may represent different clinical entities or pathophysiologic subtypes. These findings are critical for design and implementation of studies to describe, treat, or modify disease progression in idiopathic isolated cervical dystonia. © 2016 International Parkinson and Movement Disorder Society.

Understanding dystonia: diagnostic issues and how to overcome them

ABSTRACT The diagnosis and treatment of dystonia are challenging. This is likely due to gaps in the complete understanding of its pathophysiology, lack of animal models for translational studies, absence of a consistent pathological substrate and highly variable phenotypes and genotypes. The aim of this review article is to provide an overview of the clinical, neurophysiological and genetic features of dystonia that can help in the identification of this movement disorder, as well as in the differential diagnosis of the main forms of genetic dystonia. The variation of penetrance, age of onset, and topographic distribution of the disease in carriers of the same genetic mutation indicates that other factors – either genetic or environmental – might be involved in the development of symptoms. The growing knowledge of cell dysfunction in mutants may give insights into more effective therapeutic targets.

A Pilot Study of Botulinum Toxin for Jerky, Position-Specific, Upper Limb Action Tremor

BACKGROUND

We aimed to investigate the efficacy and safety of botulinum toxin (BT) injections for jerky action tremor of the upper limb.

METHODS

We performed an uncontrolled, prospective study of electromyography (EMG)-guided BT injections for jerky, position-specific, upper limb action tremor. The primary outcome was clinical global impression at 3-6 weeks after baseline.

RESULTS

Eight patients with jerky, position-specific action tremor involving the upper limb were consecutively recruited. After a median follow-up of 4.4 weeks (interquartile range [IQR] 3.6-6 weeks), four of them rated themselves as "improved" and two as "much improved." Five of these six subjects reported improvements in specific activities of daily living (bringing liquids to mouth, feeding, shaving, and dressing). Upper limb subscore of the Fahn-Tolosa-Marin Tremor Rating Scale (FTM) significantly decreased from 4.5 (4-6) to 3 (2-5) (p = 0.01).

DISCUSSION

This pilot, prospective cohort study suggests that EMG-guided BT injections may improve jerky, position-specific, upper limb action tremor. Placebo-controlled studies evaluating larger samples of patients are warranted to confirm these findings.