Clinical characteristics of patients with essential tremor or essential tremor plus

Determinants of clinical and neurophysiological features in essential tremor and essential tremor plus

The 2018 Movement Disorder Society classification introduced essential tremor plus (ETP) as a category for patients with essential tremor (ET) accompanied by additional features of uncertain significance. While earlier studies have characterized clinical features of ETP, the factors that characterize the phenotypic expression of ETP remain unclear. We prospectively evaluated 70 consecutive patients with ET or ETP. Clinical and neurophysiological assessments included tremor severity (Clinical Rating Scale for Tremor, CRST), cognitive functions (Addenbrooke's Cognitive Examination Revised, ACE-R), and accelerometric analysis. Statistical analyses examined between-group differences and factors influencing tremor characteristics. The prevalence of ETP (61%) exceeded that of ET. Among ETP patients, 77% exhibited two or more additional motor and/or cognitive features. Compared to ET patients, ETP patients demonstrated significantly higher tremor severity, lower tremor frequency, older age at assessment and onset, and poorer cognitive function, despite comparable disease duration. The accelerometric analysis revealed similar tremor patterns in both groups with quantitative differences in tremor amplitude and frequency. The propensity score matching and multiple regression analyses suggested that tremor severity and frequency are more influenced by age than by disease duration or diagnostic classification of ET/ETP. ACE-R score and the presence of resting tremor were also significant predictors of tremor severity. ETP represents a heterogeneous population with diverse neurological features, and age is likely a key determinant of severity and phenotypic expression. Comprehensive analysis is needed to identify other factors that may determine phenotype and treatment responsiveness.

Higher Prevalence of Common Neurological Soft Signs in Essential Tremor With Midline Distribution: A Multicenter Cohort Study

BACKGROUND AND PURPOSE

Essential tremor with a midline distribution (Mid-ET) may represent a distinct subtype of essential tremor (ET) that primarily affects midline structures, often indicating advanced disease stage and increased severity. Recent studies have highlighted the complexity of Mid-ET, but research on neurological soft signs (NSS) in Mid-ET remains insufficient.

METHODS

The patients with ET included in this cross-sectional study were divided into two subgroups based on whether or not the ET had a midline distribution: Mid-ET and No-Mid-ET. Comparative analyses were performed to assess clinical features and NSS prevalence in these subgroups.

RESULTS

Among 1,160 patients, 567 (48.9%) were Mid-ET and 593 (51.1%) were No-Mid-ET. The prevalence rates of head, face (including the jaw), and voice tremors were 31.9%, 23.0%, and 25.8%, respectively. In Mid-ET, tremor often affects multiple midline structures simultaneously. In the entire cohort, 24.7%, 16.6%, and 7.6% of patients exhibited tremors in one, two, and three midline structures, respectively. The prevalence of common NSS, including mild cognitive impairment, impaired tandem gait, and questionable dystonic posturing, was significantly higher in the Mid-ET than the No-Mid-ET subgroup (all p<0.001). Furthermore, we found that female sex (p<0.001), olfactory dysfunction (p=0.003), and questionable dystonic posturing (p=0.004) were associated with Mid-ET.

CONCLUSIONS

Mid-ET and No-Mid-ET presented significant clinical differences. The presence of questionable dystonic posturing may contribute to the distinct characteristics of Mid-ET, suggesting the presence of pathophysiological differences between the subgroups. Further investigations are warranted to determine the potential pathophysiological link between NSS and Mid-ET.

Polysomnographic Evaluation of Sleep Disorders in Essential Tremor and Essential Tremor Plus: A Comparison With Healthy Controls

OBJECTIVE

To explore sleep patterns in individuals with essential tremor (ET) and essential tremor plus (ET-Plus) compared with healthy controls and assess differences between ET and ET-Plus, given the lack of established polysomnography (PSG) data on these groups and the potential for sleep disturbances to serve as clinical markers.

METHODS

We conducted a prospective cross-sectional study at National Institute of Mental Health and Neurosciences, Bengaluru, from November 2021 to August 2023 on 45 patients (26 ET, 19 ET-Plus) and 45 controls. Tremor severity was assessed using The Essential Tremor Rating Assessment Scale (TETRAS) and Fahn-Tolosa-Marin Clinical Rating Scale (FTMRS). Sleep symptoms were assessed via the Epworth Sleepiness Scale, Pittsburgh Sleep Quality Index, Mayo Sleep Questionnaire, restless legs syndrome questionnaire, Berlin questionnaire, Generalized Anxiety Disorder Scale 7, and Patient Health Questionnaire-9. All patients and controls underwent overnight video PSG. Sleep scoring was manually performed by a trained sleep research technician and the first author following the American Academy of Sleep Medicine (2017) guidelines, with data analyzed using R studio.

RESULTS

Compared with ET-Plus patients, ET patients had a younger onset age (46.8±11.1 years versus 30.8±16.7 years, respectively). Compared with ET patients, ET-Plus patients had higher TETRAS and FTMRS scores (p<0.005). Compared with controls, both ET patients and ET-Plus patients presented poorer sleep quality, excessive daytime sleepiness, rapid eye movement (REM) sleep behavior disorder, and restless legs syndrome symptoms. PSG findings supported these clinical observations, showing an elevated apnea‒hypopnea index, reduced total sleep time, prolonged REM latency, decreased sleep efficiency, increased N1 stage duration, and reduced N2/N3 durations and percentages in patients versus controls.

CONCLUSION

The study highlights significant sleep architecture abnormalities in both ET and ET-Plus patients compared with healthy controls, with no differences between the ET groups.

Long-Term Outcomes of Patients with Pre-Existing Essential Tremor After SARS-CoV-2 Infection

BACKGROUND/OBJECTIVES

Although COVID-19 has been linked to worse outcomes in patients with neurological disorders, its impact on those with essential tremor (ET) remains unclear. To investigate clinical outcomes of ET patients with and without COVID-19 three and a half years post-pandemic.

METHODS

1074 ET patients were evaluated in this retrospective study in the Montefiore Health System from January 2016 to July 2023. Comparisons between ET patients with and without a positive SARS-CoV-2 polymerase chain reaction test were made. Outcomes included post-index date major adverse cardiovascular events (MACEs), new-onset sleep disturbances, fatigue, dyspnea, first-time fall, new-onset anxiety, new-onset depression, headache, new-onset imbalance, new-onset mild cognitive impairment, and all-cause mortality, adjusted hazard ratios (aHR) adjusting for covariates were calculated.

RESULTS

ET patients with COVID-19 had higher prevalence of pre-existing type-2 diabetes, depression, and anxiety compared to ET patients without COVID-19. COVID-19 was significantly associated with higher risk of MACEs, (aHR = 2.39 [1.49, 3.82]), new-onset sleep disturbance, (aHR = 2.12 [1.44, 3.13]), fatigue, (aHR = 1.83 [1.27, 2.65]), dyspnea, (aHR = 1.98 [1.40, 2.80]), first-time fall, (aHR = 4.76 [2.24, 10.14]), new-onset anxiety, (aHR = 3.66 [2.02, 6.64]), and new-onset depression, (aHR = 2.38 [1.20, 4.70]). COVID-19 was not associated with all-cause mortality.

CONCLUSIONS

In patients with ET, COVID-19 significantly increases the risk of several long-term adverse health outcomes, but not mortality.

Essential Tremor and Essential Tremor Plus Are Essentially Similar Electrophysiologically

BACKGROUND

The merits of classifying the heterogeneous group of essential tremors into essential tremor (ET) and essential tremor plus (ETP) are debated.

OBJECTIVES

We studied the electrophysiological and spiral characteristics of tremor in ET and ETP.

METHODS

We reviewed standardized videos from a tremor database and clinically classified patients into ET, ETP, or dystonic tremor (DT). The following variables were derived from combined tri-axial accelerometry-surface electromyography (EMG)-peak frequency, total power, peak power, full width half maximum, tremor stability index and EMG-coherence. We analyzed hand-drawn spirals to derive mean deviation, tremor variability, inter-, and intra-loop widths. We compared these variables among the groups.

RESULTS

We recruited 72 participants (81.9% male) with mean age 47.7 ± 16.1 years and Fahn-Tolosa-Marin Tremor Rating Scale total score 31.1 ± 14.1. Patients with ET were younger (P = 0.014) and had less severe tremor (P = 0.020) compared to ETP and DT. In ETP group, 48.6% had subtle dystonia. Peak frequency was greater in ETP (7.3 ± 0.3 Hz) compared to DT (6.1 ± 0.4 Hz; P = 0.024). Peak power was greater in ETP and DT for postural tremor. Rest tremor was recordable on accelerometry in 26.7% of ET. Other variables were similar among the groups.

CONCLUSION

Electrophysiological evaluation revealed postural tremor of frequency 6 to 7 Hz in ET, ETP, and DT with subtle differences more severe tremor in ETP and DT, and higher frequency in ETP compared to DT. Our findings suggest a similar tremor oscillator in these conditions, supporting the view that these entities are part of a spectrum of tremor disorders, rather than distinct etiological entities.

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.

The Spectrum of Non-Parkinsonian Tremor: A Registry at a Tertiary Care Teaching Institute

Background

Tremors other than those associated with Parkinson's disease (non-parkinsonian tremor) are commonly observed in clinical settings. However, their frequency and clinical characteristics have rarely been reported.

Objectives

To classify non-parkinsonian tremors based on the consensus statement on the classification of tremors, from the task force of the International Parkinson and Movement Disorder Society published in 2018.

Methods

A prospective registry at a tertiary care teaching institute.

Results

A total of 475 patients with non-parkinsonian tremors were recruited for the study. 67.57% (n = 321) of our patients were male and a family history of tremor was present in 20.84% (n = 99) of patients. Dystonic tremor (DT) was the most common non-parkinsonian tremor (33.26%). 27.78% of patients fulfilled the new classification criteria for essential tremor, with 13.47% classified as pure ET (ET) and 14.31% exhibiting neurological soft signs, leading to the classification of ET plus (ETP). Patients with ETP had more family history (57.35%) [vs DT (26.48%, p = 0.00004) and ET (10.93%, p = 0.00003], longer duration of disease [mean ± standard deviation (SD) = 9.53 ± 8.64 years] [vs DT (5.60 ± 5.93, p = 0.0003) and ET (6.38 ± 5.97, p = 0.01) years], and more severe tremor as measured by the essential tremor rating assessment scale total score [mean ± SD = 27.42 ± 11.70] [vs DT (23.50 ± 8.62, p = 0.007) and ET (22.12 ± 8.19, p = 0.007)] compared with patients with DT and ET.

Conclusions

DT was the most common cause of non-parkinsonian tremor in our registry followed by essential tremor syndrome. ETP was more common than ET.

Age and Sex Affect Essential Tremor (ET) Plus: Clinical Heterogeneity in ET Based on the National Survey in China

The new term essential tremor (ET) plus was proposed in the 2018 tremor consensus criteria. The National Survey of Essential Tremor Plus in China, a large multicenter registry study, aimed to evaluate the clinical features of pure ET and ET plus and explore possible factors related to ET plus. All patients with ET underwent neurological examination and neuropsychological assessment at 17 clinical sites. The diagnosis was made according to the 2018 consensus criteria. Clinicodemographic characteristics were analyzed. A total of 1160 patients were included, including 546 patients with pure ET and 614 patients with ET plus. The proportion of females was significantly higher in the ET plus than that in the pure ET (P = 0.001). The age at onset (AAO) of pure ET showed a bimodal distribution, with peaks in the 2nd and 5th decades. However, the AAO of the ET plus group demonstrated a skewed distribution, with a single peak in the 6th decade. Female sex (OR=1.645, P<0.001), older age (OR=1.023, P<0.001), lower educational level (OR=0.934, P<0.001), head tremor (OR=1.457, P<0.001), and higher the Tremor Research Group Essential Tremor Rating Assessment Scale (TETRAS)-II scores (OR=1.134, P<0.001) were significantly associated with ET plus. Old age and female sex may contribute to ET plus development. Pure ET showed a bimodal distribution for AAO, whereas ET plus showed a unimodal distribution. It remains unclear whether pure ET and ET plus are merely different stages of a single disease or represent distinct disease entities.

Does essential tremor increase risk of cognitive impairment and dementia? Yes

Essential Tremor (ET), by definition, is a disorder of movement. Yet over the years, epidemiologic, clinical, pathologic, and neuroimaging studies have converged to reveal a cognitive side of ET. The cognitive symptoms in ET are heterogeneous and are likely to reflect heterogeneous underlying mechanisms. In this chapter, we review and synthesize a diverse set of studies from both population-based settings to cohorts with more detailed investigations into cognition to consider the various mechanisms by which cognitive symptoms may emerge in a subset of individuals with ET. As part of our analysis, we consider questions surrounding ET diagnosis and the possibility of comorbid disease as potential factors that, upon closer examination, appear to strengthen the argument in favor of ET as a risk factor for dementia. Importantly, we also consider the clinical relevance of cognitive impairment in ET. While ET is not universally characterized by significant cognitive deficits, the data from epidemiological, cognitive, neuroimaging, and postmortem neuropathologic studies converge to reveal an increased risk for cognitive impairment and dementia among individuals with ET. We conclude by offering directions for future research, and a neurocognitive framework with which to consider existing findings and to use in the design of novel studies dedicated to clarifying the basis, nature, and course of cognitive impairments in ET.

The differences in clinical characteristics and natural history between essential tremor and essential tremor plus

The diverse clinical manifestation of essential tremor (ET) has led to the question whether the different phenotypes may affect the clinical outcome and progression. This study aimed to estimate the clinical characteristics and natural history of ET and ET-plus. A total of 221 patients with ET were included, 117 (52.9%) reclassified as ET and 104 (47.1%) as ET-plus. Patients with ET-plus were significantly older in age at onset (P < 0.001); had a higher frequency of cranial tremors (P < 0.001), neurological comorbidities (P < 0.001) and psychiatric comorbidities (P = 0.025); more tremor progression (P < 0.001); and poorer response to medical treatment (P < 0.001) compared to ET patients. Regression analysis revealed that late-onset tremor (OR 11.02, 95% CI 2.79-43.53), neurological comorbidities (OR 3.38, 95% CI 1.56-7.31), psychiatric comorbidities (OR 4.29, 95% CI 1.48-12.44), cranial tremors (OR 2.10, 95% CI 1.02-4.30), and poor response to medical treatment (OR 3.67, 95% CI 1.87-7.19) were associated with ET-plus diagnosis. ET and ET-plus differ in the age of onset, tremor distribution, comorbidities, treatment response rate, and progression. Identifying the ET phenotypes may increase the clinical value in therapeutic strategies and clinical research in the future.

Is essential tremor a family of diseases or a syndrome? A syndrome

In a consensus statement, a task force of the "International Parkinson and Movement Disorder Society" (IPMDS) has recently proposed a two axes classification for tremor: axis I (clinical manifestations) and axis II (etiology). In the axis, I, the clinical features of tremor in a given patient are specified in terms of medical history, tremor characteristics, associated signs, and laboratory tests for some tremors leading to the discovery of axis 2 etiologies. Based on axis I sign and symptoms a specific clinical syndrome is diagnosed which have been categorized as isolated tremor syndrome (a syndrome consisting only of tremor) and combined tremor syndrome (consisting of tremor and other systemic or neurological signs). The IPMDS task force defined essential tremor as an isolated tremor syndrome of bilateral upper limb action tremor of at least 3years duration with or without a tremor in other locations (e.g., head, voice or lower limbs) in absence of other neurological signs, such as dystonia, ataxia, or parkinsonism. Patients with neurological signs of uncertain significance (such as impaired tandem gait, questionable dystonic posturing, or memory impairment) are classified as essential tremor plus. In this paper, the author will make the argument that essential tremor is a syndrome with multiple causes.

Functional neurological disorder: Extending the diagnosis to other disorders, and proposing an alternate disease term—Attentionally-modifiable disorder

BACKGROUND: The term “functional neurological disorder,” or “FND,” applies to disorders whose occurrence of neurological symptoms fluctuate with the patient’s attention to them. However, many other disorders that are not called “FND” nonetheless can also follow this pattern. Consequently, guidelines are unclear for diagnosing “FND.” OBJECTIVE: To review the neurological conditions that follow this pattern, but which have not so far been termed “FND,” to understand their overlap with conditions that have been termed “FND,” and to discuss the rationale for why FND has not been diagnosed for them. METHOD: A systematic review of the PubMed literature registry using the terms “fluctuation,” “inconsistency,” or “attention” did not yield much in the way of these candidate disorders. Consequently, this review instead relied on the author’s personal library of peer-reviewed studies of disorders that have resembled FND but which were not termed this way, due to his longstanding interest in this problem. Consequently, this approach was not systematic and was subjective regarding disease inclusion. RESULTS: This review identified numerous, diverse conditions that generally involve fluctuating neurological symptoms that can vary with the person’s attention to them, but which have not been called “FND.” The literature was unclear for reasons for not referring to “FND” in these instances. CONCLUSION: Most likely because of historical biases, the use of the term “FND” has been unnecessarily restricted. Because at its core FND is an attentionally-influenced disorder that can respond well to behavioral treatments, the field of neurological rehabilitation could benefit by extending the range of conditions that could be considered as “FND” and referred for similar behavioral treatments. Because the term “FND” has been viewed unfavorably by some patients and clinical practitioners and whose treatment is not implied, the alternative term attentionally-modifiable disorder is proposed.

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.

"ET Plus": Instability of the Diagnosis During Prospective Longitudinal Follow-up of Essential Tremor Cases

Background: A recent consensus statement introduced the term "ET plus". Although investigators have quantified the prevalence of ET plus in cross-sectional studies, patients with ET plus have not been tracked longitudinally; hence, there is no understanding of its stability over time. Methods: We present prospective, longitudinal phenotypic data on an ET cohort that was followed regularly at 18-month intervals (T1, T2, T3, T4) for up to 64 months. We assigned an ET or ET plus diagnosis to each case at each time interval. Results: There were 201 participants at baseline. The proportion with ET plus increased from 58.7% at baseline to 72.1% at T4 (p = 0.046). Of 172 (85.6%) who received a diagnosis of ET plus at one or more time intervals, the diagnosis was unstable (e.g., with reversion) in 62 (36.0%). We also assessed the stability of the clinical features of ET plus. Rest tremor was the most unstable clinical feature of ET plus; it was present in 59 participants, among whom it reverted from present to absent in 23 (39.0%). By contrast, for "memory impairment" (i.e., either mild cognitive impairment or dementia), the proportion who reverted from present to absent was only 21.3%. Conclusion: These data support our two a priori hypotheses: (1) the prevalence of ET plus would increase progressively, as it likely represents a more advanced stage of ET, and (2) the ET plus diagnosis would not be stable over time, as cases would fluctuate with respect to their phenotypic features and their assigned diagnoses.

DTI for brain targeting: Diffusion weighted imaging fiber tractography-Assisted deep brain stimulation

Fiber tractography assisted Deep Brain Stimulation (DBS) has been performed by different groups for more than 10 years to now. Groups around the world have adapted initial approaches to currently embrace the fiber tractography technology mainly for treating tremor (DBS and lesions), psychiatric indications (OCD and major depression) and pain (DBS). Despite the advantages of directly visualizing the target structure, the technology is demanding and is vulnerable to inaccuracies especially since it is performed on individual level. In this contribution, we will focus on tremor and psychiatric indications, and will show future applications of sophisticated tractography applications for subthalamic nucleus (STN) DBS surgery and stimulation steering as an example.

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.

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

Background:

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

Objectives:

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

Methods:

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

Results:

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

Conclusions:

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

Highlights:

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

Sleep Disorders in Patients with Essential Tremor

PURPOSE OF THE REVIEW

Patients diagnosed with essential tremor (ET) report frequent sleep complaints. This review focuses on the main findings of studies addressing sleep features in patients diagnosed with ET, updating previously reported information. Bad quality of sleep and excessive daytime somnolence are very frequent in patients with ET, although the effects of the drugs used for the therapy of ET could contribute to these complaints. REM sleep behavior disorder, restless legs, insomnia, and nocturia are frequent complaints as well. There is a lack of studies addressing polysomnographic features of ET.

Thalamic Deep Brain Stimulation in Essential Tremor Plus Is as Effective as in Essential Tremor

The new essential tremor (ET) classification defined ET-plus (ET-p) as an ET subgroup with additional neurological signs besides action tremor. While deep brain stimulation (DBS) is effective in ET, there are no studies specifically addressing DBS effects in ET-p. 44 patients with medication-refractory ET and thalamic/subthalamic DBS implanted at our center were postoperatively classified into ET and ET-p according to preoperative documentation. Tremor suppression with DBS (stimulation ON vs. preoperative baseline and vs. stimulation OFF), measured via the Fahn–Tolosa–Marin tremor rating scale (TRS), stimulation parameters, and the location of active contacts were compared between patients classified as ET and ET-p. TRS scores at baseline were higher in ET-p. ET-p patients showed comparable tremor reduction as patients with ET, albeit higher stimulation parameters were needed in ET-p. Active electrode contacts were located more dorsally in ET-p of uncertain reason. Our data show that DBS is similarly effective in ET-p compared to ET. TRS scores were higher in ET-p preoperatively, and higher stimulation parameters were needed for tremor reduction compared to ET. The latter may be related to a more dorsal location of active electrode contacts in the ET-p group of this cohort. Prospective studies are warranted to investigate DBS in ET-p further.

Do We Belittle Essential Tremor by Calling It a Syndrome Rather Than a Disease? No

A task force of the International Parkinson and Movement Disorder Society (MDS) recently published a tremor classification scheme that is based on the nosologic principle of two primary axes for classifying an illness: clinical manifestations (Axis 1) and etiology (Axis 2). An Axis 1 clinical syndrome is a recurring group of clinical symptoms, signs (physical findings), and possibly laboratory results that suggests the presence of at least one underlying Axis 2 etiology. Syndromes must be defined and used consistently to be of value in finding specific etiologies and effective treatments. The MDS task force concluded that essential tremor is a common neurological syndrome that has never been defined consistently by clinicians and researchers. The MDS task force defined essential tremor as a syndrome of bilateral upper limb action tremor of at least 3 years duration, with or without tremor in other locations (e.g., head, voice, or lower limbs), in the absence of other neurological signs (e.g., dystonia, parkinsonism, myoclonus, ataxia, peripheral neuropathy, and cognitive impairment). Deviations from this definition should not be labeled as essential tremor. Patients with additional questionably-abnormal signs or with signs of uncertain relevance to tremor are classified as essential tremor plus. The MDS classification scheme encourages a thorough unbiased phenotyping of patients with tremor, with no assumptions of etiology, pathology, pathophysiology, or relationship to other neurological disorders. The etiologies, pathology, and clinical course of essential tremor are too heterogeneous for this syndrome to be viewed as a disease or a family of diseases.

The Problem of Questionable Dystonia in the Diagnosis of 'Essential Tremor-Plus'

In a recent consensus statement on tremor, the task force of the International Parkinson and Movement Disorder Society proposed a new term, ‘essential tremor-plus (ET-plus)’ which includes patients with the characteristics of essential tremor (ET) and additional soft neurological signs of uncertain significance such as questionable dystonic posturing. The clinical interpretation of questionable dystonia has been left to the investigator. The consensus statement also stated that the ET-plus syndrome does not include other clearly defined syndromes like dystonic tremor. However, the boundary between questionable dystonia and definite dystonia is not distinct leading to diagnostic uncertainty in a clinical setting. A similar case may be classified as ET-plus by one observer and dystonic tremor by another. Following the new definition, many studies have reclassified their ET cohort, and they have highlighted the problem of defining questionable dystonia in the diagnosis of ET plus. ET-plus is likely to be a mixture of patients that actually have dystonia and those that don’t, and clinically all we can do is to be suspicious that there might be dystonia. For example, it is not clear whether we should consider spooning and index finger pointing as a sign of questionable or definite dystonia. There are major research and possible therapeutic implications of questionable dystonia in the diagnosis of ET-plus. The concept of ET-plus is extremely difficult to implement without definite guidelines. The resolution will need a biomarker such as physiology or imaging.