Alleviating manoeuvres (sensory tricks) in cervical dystonia

Cerebral-Cerebellar Cortical Activity and Connectivity Underlying Sensory Trick in Cervical Dystonia

OBJECTIVE

The objective of this study was to investigate the activity and connectivity of cerebral and cerebellar cortices underlying the sensory trick (ST) effects in patients with cervical dystonia (CD), using electroencephalography (EEG).

METHODS

We recruited 15 CD patients who exhibited clinically effective ST and 15 healthy controls (HCs) who mimicked the ST maneuver. EEG signals and multiple-channel electromyography (EMG) were recorded simultaneously during resting and acting stages. EEG source analysis and functional connectivity were performed. To account for the effects of sensory processing, we calculated relative power changes as the difference in power spectral density between resting and the maneuver execution.

RESULTS

ST induced a decrease in low gamma (30-50 Hz) spectral power in the primary sensory and cerebellar cortices, which remained lower than in HCs during the maintenance period. Compared with HCs, patients exhibited consistently strengthened connectivity within the sensorimotor network during the maintenance period, particularly in the primary sensory-sensorimotor cerebellum connection.

INTERPRETATION

The application of ST resulted in altered cortical excitability and functional connectivity regulated by gamma oscillation in CD patients, suggesting that this effect cannot be solely attributed to motor components. The cerebellum may play important roles in mediating the ST effects.

Therapeutic Benefit of Sensory Trick in Cervical Dystonia

Background

Sensory tricks (STs) are voluntary maneuvers that dampen the abnormal movement in cervical dystonia (CD).

Objectives

To investigate the effect of ST on CD severity and treatment.

Methods

Data on 1039 individuals with a modified Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) score were extracted from the CD Patient Registry for Observation of OnabotulinumtoxinA (onabotA) Efficacy study. Univariate and multivariate models evaluated the direct and indirect impact of ST on CD severity and treatment, while controlling for confounds.

Results

Complete ST was associated with a 10% lower mean onabotA dose. Absence of complete ST was associated with a higher onabotA dose after controlling for dystonia severity (OR = 1.37, P = 0.04). ST moderated the relationship between dystonia severity and toxin dose (β = -0.16, P = 0.02).

Conclusions

ST is related to lower CD severity and toxin dose. It may have a direct effect on lowering toxin dose, independent of CD severity.

Isolated Cervical Dystonia: Diagnosis and Classification

This document presents a consensus on the diagnosis and classification of isolated cervical dystonia (iCD) with a review of proposed terminology. The International Parkinson and Movement Disorder Society Dystonia Study Group convened a panel of experts to review the main clinical and diagnostic issues related to iCD and to arrive at a consensus on diagnostic criteria and classification. These criteria are intended for use in clinical research, but also may be used to guide clinical practice. The benchmark is expert clinical observation and evaluation. The criteria aim to systematize the use of terminology as well as the diagnostic process, to make it reproducible across centers and applicable by expert and non-expert clinicians. Although motor abnormalities remain central, increasing recognition has been given to nonmotor manifestations, which are incorporated into the current criteria. Three iCD presentations are described in some detail: idiopathic (focal or segmental) iCD, genetic iCD, and acquired iCD. The relationship between iCD and isolated head tremor is also reviewed. Recognition of idiopathic iCD has two levels of certainty, definite or probable, supported by specific diagnostic criteria. Although a probable diagnosis is appropriate for clinical practice, a higher diagnostic level may be required for specific research studies. The consensus retains elements proven valuable in previous criteria and omits aspects that are no longer justified, thereby encapsulating diagnosis according to current knowledge. As understanding of iCD expands, these criteria will need continuous revision to accommodate new advances. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Botox (onabotulinumtoxinA) mechanism of action

Studies in the 1920s found that botulinum neurotoxin type A (BoNT/A) inhibited the activity of motor and parasympathetic nerve endings, confirmed several decades later to be due to decreased acetylcholine release. The 1970s were marked by studies of cellular mechanisms aided by use of neutralizing antibodies as pharmacologic tools: BoNT/A disappeared from accessibility to neutralizing antibodies within minutes, although it took several hours for onset of muscle weakness. The multi-step mechanism was experimentally confirmed and is now recognized to consist broadly of binding to nerve terminals, internalization, and lysis or cleavage of a protein (SNAP-25: synaptosomal associated protein-25 kDa) that is part of the SNARE (Soluble NSF Attachment protein REceptor) complex needed for synaptic vesicle docking and fusion. Clinical use of the BoNT/A product onabotulinumtoxinA was based on its ability to reduce muscle contractions via inhibition of acetylcholine from motor terminals. Sensory mechanisms of onabotulinumtoxinA have now been identified, supporting its successful treatment of chronic migraine and urgency in overactive bladder. Exploration into migraine mechanisms led to anatomical studies documenting pain fibers that send axons through sutures of the skull to outside the head-a potential route by which extracranial injections could affect intracranial processes. Several clinical studies have also identified benefits of onabotulinumtoxinA in major depression, which have been attributed to central responses induced by feedback from facial muscle and skin movement. Overall, the history of BoNT/A is distinguished by basic science studies that stimulated clinical use and, conversely, clinical observations that spurred basic research into novel mechanisms of action.

Physiology of dystonia: Human studies

In this chapter, we discuss neurophysiological techniques that have been used in the study of dystonia. We examine traditional disease models such as inhibition and excessive plasticity and review the evidence that these play a causal role in pathophysiology. We then review the evidence for sensory and peripheral influences within pathophysiology and look at an emergent literature that tries to probe how oscillatory brain activity may be linked to dystonia pathophysiology.

Dystonias: Clinical Recognition and the Role of Additional Diagnostic Testing

Dystonia is the third most common movement disorder, characterized by abnormal, frequently twisting postures related to co-contraction of agonist and antagonist muscles. Diagnosis is challenging. We provide a comprehensive appraisal of the epidemiology and an approach to the phenomenology and classification of dystonia, based on the clinical characteristics and underlying etiology of dystonia syndromes. We discuss the features of common idiopathic and genetic forms of dystonia, diagnostic challenges, and dystonia mimics. Appropriate workup is based on the age of symptom onset, rate of progression, whether dystonia is isolated or combined with another movement disorder or complex neurological and other organ system eatures. Based on these features, we discuss when imaging and genetic should be considered. We discuss the multidisciplinary treatment of dystonia, including rehabilitation and treatment principles according to the etiology, including when pathogenesis-direct treatment is available, oral pharmacological therapy, chemodenervation with botulinum toxin injections, deep brain stimulation and other surgical therapies, and future directions.

Secondary dystonia following parenchymal brain tumors

BACKGROUND

Secondary dystonia has been associated with diverse etiologies. Dystonia associated with brain tumors has not been well characterized.

OBJECTIVES

To characterize dystonia and relationship with parenchymal brain tumors.

METHODS

We present six patients (1.03%) with dystonia related to parenchymal brain tumors, among 580 screened cases.

RESULTS

Contralateral hemidystonia was observed in four cases, followed by focal limb (n = 1) and cervical dystonia (n = 1). Dystonia presented during the phase of tumor growth in four cases, and following tumor treatment in two, one case had re-emergent dystonia. Tumors were low-grade (WHO I or II) and located in the basal ganglia (n = 3), cortical areas (n = 2), thalamus (n = 1) and cerebral peduncle (n = 1).

CONCLUSIONS

Secondary dystonia may be caused by brain tumors in diverse locations including basal ganglia, cortex and thalamus. It may be the presenting symptom of brain tumor or follow surgical resection combined with ancillary therapy.

Cortical mechanisms of sensory trick in cervical dystonia

Patients with cervical dystonia (CD) often show an improvement in dystonic posture after sensory trick (ST), though the mechanisms underlying ST remain unclear. In this study, we aimed to investigate the effects of ST on cortical activity in patients with CD and to explore the contribution of motor and sensory components to ST mechanisms. To this purpose, we studied 15 CD patients with clinically effective ST, 17 without ST, and 14 healthy controls (HCs) who mimicked the ST. We used electroencephalographic (EEG) recordings and electromyography (EMG) data from bilateral sternocleidomastoid (SCM) muscles. We compared ST-related EEG spectral changes from sensorimotor and posterior parietal areas and EMG power changes between groups. To better understand the contribution of motor and sensory components to ST, we tested EEG and EMG correlates of three different conditions mimicking ST, the first without skin touch ("no touch" condition), the second without voluntary movements ("passive" condition), and finally without arm movements ("examiner touch" condition). Results showed ST-related alpha desynchronization in the sensorimotor cortex and theta desynchronization in the sensorimotor and posterior parietal cortex. Both spectral changes were more significant during maneuver execution in CD patients with ST than in CD patients without ST and HCs who mimicked the ST. Differently, the "no touch", "passive", or "examiner touch" conditions did not show significant differences in EEG or EMG changes determined by ST execution/mimicking between CD patients with or without ST. A higher desynchronization within alpha and theta bands in the sensorimotor and posterior parietal areas correlated with a more significant activity decrease in the contralateral SCM muscle, Findings from this study suggest that ST-related changes in the activity of sensorimotor and posterior parietal areas may restore dystonic posture and that both motor and sensory components contribute to the ST effect.

Role of supplementary motor area in cervical dystonia and sensory tricks

Sensory trick is a characteristic feature of cervical dystonia (CD), where a light touch on the area adjacent to the dystonia temporarily improves symptoms. Clinical benefit from sensory tricks can be observed before tactile contact is made or even by imagination. The supplementary motor area (SMA) may dynamically interact with the sensorimotor network and other brain regions during sensory tricks in patients with CD. In this study, we examined the functional connectivity of the SMA at rest and during sensory trick performance and imagination in CD patients compared to healthy controls using functional magnetic resonance imaging. The functional connectivity between the SMA and left intraparietal sulcus (IPS) region was lower in CD patients at rest and it increased with sensory trick imagination and performance. SMA-right cerebellum connectivity also increased with sensory trick imagination in CD patients, while it decreased in healthy controls. In CD patients, SMA connectivity increased in the brain regions involved in sensorimotor integration during sensory trick performance and imagination. Our study results showed a crucial role of SMA in sensorimotor processing during sensory trick performance and imagination and suggest the IPS as a novel potential therapeutic target for brain modulation.

Evaluation of outcome of different neurosurgical modalities in management of cervical dystonia

Background

Cervical dystonia is the most common form of focal dystonia and is managed by multiple modalities including repeated botulinum toxin injections, in addition to medical treatment with anticholinergics, muscle relaxants, and physiotherapy. However, surgical interventions could be beneficial in otherwise refractory patients. This study aims to report our experience in the neurosurgical management of cervical dystonia and evaluate patient outcomes using reliable outcome scores for the assessment of patients with cervical dystonia and possible complications. This case series study was conducted on 19 patients with cervical dystonia of different etiologies who underwent surgical management [ten patients underwent selective peripheral denervation, five patients underwent pallidotomy, and four patients underwent bilateral globus pallidus internus (GPi) deep brain stimulation (DBS)] in the period between July 2018 and June 2021 at Ain Shams University Hospitals, Cairo, Egypt. With the assessment of surgical outcomes using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) and the Tsui scale 6 months postoperatively.

Results

Surgical management of patients with cervical dystonia of either primary or secondary etiology was associated with significant improvement in head and neck postures after 6 months without major complications associated with the different surgical procedures. The mean improvement in total TWSTRS and Tsui scores were 51.2% and 64.8%, respectively, compared with preoperative scores, while the mean improvement in the TWSTRS subscales (severity, disability, and pain) were 40.2%, 66.9%, and 58.3%, respectively.

Conclusion

Cervical dystonia patients in whom non-surgical options have failed to alleviate their symptoms can be managed surgically leading to significant improvements with minimal adverse effects. However, surgical treatment should be tailored according to several factors including but not limited to the etiology, pattern of dystonic activity, and comorbidities. Therefore, management should be tailored to achieve long-term improvement with minimal risk of complications.

‘Tricked’ sensory trick: a geste antagoniste in functional dystonia

A sensory trick, or geste antagoniste, is a manoeuvre used by patients with dystonia to ameliorate their dystonic movements or posturing. Typically, a sensory trick is a confirmatory clue indicating an organic nature of the dystonia. In this report, we present an extremely rare case of a sensory trick in a patient with functional dystonia.

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.

Sports-Related Dystonia

Background

Task-specific dystonia (TSD) is a form of focal dystonia that occurs in the context of the performance of selective, highly skilled, often repetitive, motor activity. TSD may be apparent during certain tasks such as writing, playing musical instruments, or other activities requiring fine motor control, but may also occur during certain sports, and maybe detrimental to professional athletes' careers. Therefore, sports physicians and movement disorder neurologists need to be aware of the presentation and phenomenology of sports-related dystonia (SRD), the topic of this review.

Methods

A broad PubMed search using a wide range of keywords and combinations was done in October 2021 to identify suitable articles for this review.

Results

Most of the publications are on yips in golfers and on runners' dystonia. Other sports in which SRD has been reported are ice skating, tennis, table tennis, pistol shooting, petanque, baseball, and billiards.

Discussion

Yips, which may affect up to half of the golfers and rarely athletes in other sports (e.g., baseball, cricket, basketball, speed skating, gymnastics) seems to be a multi-factorial form of TSD that is particularly troublesome in highly skilled professional golfers. Runners' dystonia, affecting the foot, leg, and hip (in decreasing order), may evolve into more generalized and less specific dystonia. The pathophysiologic mechanisms of SRD are not well understood. Botulinum toxin has been reported to alleviate dystonia in golfers', runners', and other forms of SRD. Future studies should utilize neurophysiologic, imaging, and other techniques to elucidate mechanisms of this underrecognized group of movement disorders.

Comparing Brain Functional Activities in Patients With Blepharospasm and Dry Eye Disease Measured With Resting-State fMRI

Background: Blepharospasm (BSP) and dry eye disease (DED) are clinically common diseases characterized by an increased blinking rate. A sustained eyelid muscle activity may alter the cortical sensorimotor concordance and lead to secondary functional changes. This study aimed to explore the central mechanism of BSP by assessing brain functional differences between the two groups and comparing them with healthy controls.

Methods: In this study, 25 patients with BSP, 22 patients with DED, and 23 healthy controls underwent resting-state functional magnetic resonance imaging (fMRI) scan. The amplitude of low-frequency fluctuations (ALFF) was applied to analyze the imaging data.

Results: Analysis of covariance (ANCOVA) revealed widespread differences in ALFF across the three groups. In comparison with healthy controls, patients with BSP showed abnormal ALFF in the sensorimotor integration related-brain regions, including the bilateral supplementary motor area (SMA), left cerebellar Crus I, left fusiform gyrus, bilateral superior medial prefrontal cortex (MPFC), and right superior frontal gyrus (SFG). In comparison with patients with DED, patients with BSP exhibited a significantly increased ALFF in the left cerebellar Crus I and left SMA. ALFF in the left fusiform gyrus/cerebellar Crus I was positively correlated with symptomatic severity of BSP.

Conclusions: Our results reveal that the distinctive changes in the brain function in patients with BSP are different from those in patients with DED and healthy controls. The results further emphasize the primary role of sensorimotor integration in the pathophysiology of BSP.

Sensory tricks modulate corticocortical and corticomuscular connectivity in cervical dystonia

OBJECTIVE

To examine interactions between cortical areas and between cortical areas and muscles during sensory tricks in cervical dystonia (CD).

METHODS

Thirteen CD patients and thirteen age-matched healthy controls performed forewarned reaction time tasks, sensory tricks, and two tasks replicating aspects of the tricks (moving necks/arms). Control subjects mimicked sensory tricks. Corticocortical and corticomuscular coherence values were calculated from surface electrodes placed over motor, premotor, and sensory cortical areas and dystonic muscles.

RESULTS

During initial preparation (after the warning stimulus), the only between-task difference was found in the γ-band corticocortical coherence (higher during tricks than during voluntary neck movements). With movements (before/after the imperative stimulus), the γ-band coherence of CD patients significantly increased during tricks but decreased during voluntary movements, while opposite trends were observed in healthy subjects. Additionally, the α- and β-band coherence decreased in healthy subjects during movements. Between the two patient subgroups (typical vs. forcible tricks), only those with typical tricks showed significant decrease in corticomuscular coherence during tricks.

CONCLUSIONS

Observed changes in the corticocortical coherence suggest that sensory tricks improve cortical function, which reduces corticomuscular connectivity and the dystonia.

SIGNIFICANCE

We demonstrated that sensory tricks fundamentally affect sensorimotor integration in CD, both in movement preparation and execution.

Oromandibular Dystonia: A Clinical Examination of 2,020 Cases

Objective: The goal of this study is to better characterize the phenotypic heterogeneity of oromandibular dystonia (OMD) for the purpose of facilitating early diagnosis. Methods: First, we provide a comprehensive summary of the literature encompassing 1,121 cases. Next, we describe the clinical features of 727 OMD subjects enrolled by the Dystonia Coalition (DC), an international multicenter cohort. Finally, we summarize clinical features and treatment outcomes from cross-sectional analysis of 172 OMD subjects from two expert centers. Results: In all cohorts, typical age at onset was in the 50s and 70% of cases were female. The Dystonia Coalition cohort revealed perioral musculature was involved most commonly (85%), followed by jaw (61%) and tongue (17%). OMD more commonly appeared as part of a segmental dystonia (43%), and less commonly focal (39%) or generalized (10%). OMD was found to be associated with impaired quality of life, independent of disease severity. On average, social anxiety (LSA score: 33 ± 28) was more common than depression (BDI II score: 9.7 ± 7.8). In the expert center cohorts, botulinum toxin injections improved symptom severity by more than 50% in ~80% of subjects, regardless of etiology. Conclusions: This comprehensive description of OMD cases has revealed novel insights into the most common OMD phenotypes, pattern of dystonia distribution, associated psychiatric disturbances, and effect on QoL. We hope these findings will improve clinical recognition to aid in timely diagnosis and inform treatment strategies.

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.

Long-term efficacy and safety of botulinum toxin treatment for cervical dystonia: a critical reappraisal

Introduction: Botulinum toxin (BoNT) injections represent the gold standard treatment for cervical dystonia (CD). Different types of BoNT have been used for the treatment of CD, but only two serotypes, BoNT type A (BoNT-A) and type B (BoNT-B), have been approved by regulatory agencies. Efficacy and safety of BoNT have been well documented by many short-term studies, but the longterm effects have been investigated only relatively recently.Areas covered: In the present review, we aimed to critically reappraise the existing evidence on the long-term efficacy and safety of BoNT treatment in CD. The examined studies mainly explored BoNT-A serotypes. Only a few studies examined the long-term effects of BoNT-B serotypes, and only one head-to-head comparison between BoNT-A and BoNT-B was found. BoNT was consistently reported to be an effective and safe treatment for CD patients, with good outcomes and a few adverse events in the long-term. However about a third of patients still drop out from the treatment during a long-term follow-up.Expert opinion: We conclude that BoNT is safe and effective in the long-term treatment of patients with CD. Additional studies are needed to further explore patients real-life experiences and perspectives to better understand the long-term outcomes and reasons for discontinuation of treatment.

Does Raising the Arms Modify Head Tremor Severity in Cervical Dystonia?

Background:

A defining characteristic of dystonia is its position-dependence. In cervical dystonia (CD), sensory tricks ameliorate head tremor (HT). But it remains unknown whether raising the arms alone has the same impact.

Methods:

We analyzed data collected from patients enrolled by the Dystonia Coalition. For 120 patients with HT, we assessed how raising their arms without touching their head changed their HT severity.

Results:

Forty-eight out of 120 patients exhibited changes in HT severity when raising their arms. These patients were more likely to exhibit decreases in HT severity (N = 35) than increases (N = 13, χ² (1, N = 48) = 10.1, p = 0.002). Demographic factors and sensory trick efficacy were not significant predictors of whether HT severity changed when raising their arms.

Discussion:

Raising the arms without touching the head is a posture that can reduce HT severity in some CD patients. Our results extend the concept of position-dependent motor symptoms in CD to include the position of the arms.

Highlights

Head tremor (HT) is a prevalent symptom of cervical dystonia (CD) that can often be disabling. This study demonstrates that raising the arms without touching the head is a posture that can reduce HT severity in some CD patients. Our findings also identify a novel form of position-dependence in CD.

Sensory trick effect in craniofacial dystonia as one of the possible impacts of wearing face masks during the COVID-19 pandemic

BACKGROUND

The report of a patient with blepharospasm during the COVID-19 pandemic suggested a potential ameliorating effect of wearing a face mask.

OBJECTIVE

We prospectively evaluated a possible symptom change through wearing a face mask in all consecutive patients with craniofacial hyperkinesias in our botulinum toxin outpatient treatment cohort.

METHODS

Patients with craniofacial hyperkinesia were asked to rate changes of symptoms between - 2 (markedly worsened), - 1 (slightly worsened), 0 (no change), + 1 (slightly improved) and + 2 (markedly improved).

RESULTS

Of 101 patients (19 with blepharospasm [BSP], 54 with cervical dystonia [CD], 6 with oromandibular dystonia [OMD], and 22 with hemifacial spasm [HFS]) 81 (80%) rated no symptom change, 11 (11%) symptom improvement, and 9 (9%) symptom worsening. Improvements in 9 of the 82 dystonia patients (BSP, CD, OMD) consisted of a perceived decrease in dystonic activity. 33% of dystonia patients had previously noticed or used a sensory trick. Its presence turned out to be a significant predictor of improvement during mask wearing. Deteriorations were attributed from all patients to disturbing effects of the mask interacting with facial muscle overactivity. Improvements in HSF patients were attributed to the symptom-hiding nature of the mask and not to an effect on the spasm activity itself.

CONCLUSIONS

Wearing a face mask did not affect self-perceived symptoms in 80% of patients with craniofacial hyperkinesis. 11% of patients reported an improvement, which occurred as sensory trick in dystonia patients and as a concealment of a stigmatizing facial expression in patients with HSF.

The Dystonia Coalition: A Multicenter Network for Clinical and Translational Studies

Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal postures, repetitive movements, or both. Research in dystonia has been challenged by several factors. First, dystonia is uncommon. Dystonia is not a single disorder but a family of heterogenous disorders with varied clinical manifestations and different causes. The different subtypes may be seen by providers in different clinical specialties including neurology, ophthalmology, otolaryngology, and others. These issues have made it difficult for any single center to recruit large numbers of subjects with specific types of dystonia for research studies in a timely manner. The Dystonia Coalition is a consortium of investigators that was established to address these challenges. Since 2009, the Dystonia Coalition has encouraged collaboration by engaging 56 sites across North America, Europe, Asia, and Australia. Its emphasis on collaboration has facilitated establishment of international consensus for the definition and classification of all dystonias, diagnostic criteria for specific subtypes of dystonia, standardized evaluation strategies, development of clinimetrically sound measurement tools, and large multicenter studies that document the phenotypic heterogeneity and evolution of specific types of dystonia.

Contemporary functional neuroanatomy and pathophysiology of dystonia

Dystonia is a disabling movement disorder characterized by abnormal postures or patterned and repetitive movements due to co-contraction of muscles in proximity to muscles desired for a certain movement. Important and well-established pathophysiological concepts are the impairment of sensorimotor integration, a loss of inhibitory control on several levels of the central nervous system and changes in synaptic plasticity. These mechanisms collectively contribute to an impairment of the gating function of the basal ganglia which results in an insufficient suppression of noisy activity and an excessive activation of cortical areas. In addition to this traditional view, a plethora of animal, genetic, imaging and electrophysiological studies highlight the role of the (1) cerebellum, (2) the cerebello-thalamic connection and (3) the functional interplay between basal ganglia and the cerebellum in the pathophysiology of dystonia. Another emerging topic is the better understanding of the microarchitecture of the striatum and its implications for dystonia. The striosomes are of particular interest as they likely control the dopamine release via inhibitory striato-nigral projections. Striosomal dysfunction has been implicated in hyperkinetic movement disorders including dystonia. This review will provide a comprehensive overview about the current understanding of the functional neuroanatomy and pathophysiology of dystonia and aims to move the traditional view of a ‘basal ganglia disorder’ to a network perspective with a dynamic interplay between cortex, basal ganglia, thalamus, brainstem and cerebellum.

Neurobiological mechanisms associated with antipsychotic drug-induced dystonia

Dystonia is by far the most intrusive and invalidating extrapyramidal side effect of potent classical antipsychotic drugs. Antipsychotic drug-induced dystonia is classified in both acute and tardive forms. The incidence of drug-induced dystonia is associated with the affinity to inhibitory dopamine D2 receptors. Particularly acute dystonia can be treated with anticholinergic drugs, but the tardive form may also respond to such antimuscarinic treatment, which contrasts their effects in tardive dyskinesia. Combining knowledge of the pathophysiology of primary focal dystonia with the anatomical and pharmacological organization of the extrapyramidal system may shed some light on the mechanism of antipsychotic drug-induced dystonia. A suitable hypothesis is derived from the understanding that focal dystonia may be due to a faulty processing of somatosensory input, so leading to inappropriate execution of well-trained motor programmes. Neuroplastic alterations of the sensitivity of extrapyramidal medium-sized spiny projection neurons to stimulation, which are induced by the training of specific complex movements, lead to the sophisticated execution of these motor plans. The sudden and non-selective disinhibition of indirect pathway medium-sized spiny projection neurons by blocking dopamine D2 receptors may distort this process. Shutting down the widespread influence of tonically active giant cholinergic interneurons on all medium-sized spiny projection neurons by blocking muscarinic receptors may result in a reduction of the influence of extrapyramidal cortical-striatal-thalamic-cortical regulation. Furthermore, striatal cholinergic interneurons have an important role to play in integrating cerebellar input with the output of cerebral cortex, and are also targeted by dopaminergic nigrostriatal fibres affecting dopamine D2 receptors.

It's tricky: Rating alleviating maneuvers in cervical dystonia

OBJECTIVES

To investigate hypothesized sources of error when quantifying the effect of the sensory trick in cervical dystonia (CD) with the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS-2), test strategies to mitigate them, and provide guidance for future research on the sensory trick.

METHODS

Previous analyses suggested the sensory trick (or "alleviating maneuver", AM) item be removed from the TWSTRS-2 because of its poor clinimetric properties. We hypothesized three sources of clinimetric weakness for rating the AM: 1) whether patients were given sufficient time to demonstrate their AM; 2) whether patients' CD was sufficiently severe for detecting AM efficacy; and 3) whether raters were inadvertently rating the item in reverse of scale instructions. We tested these hypotheses with video recordings and TWSTRS-2 ratings by one "site rater" and a panel of five "video raters" for each of 185 Dystonia Coalition patients with isolated CD.

RESULTS

Of 185 patients, 23 (12%) were not permitted sufficient testing time to exhibit an AM, 23 (12%) had baseline CD too mild to allow confident rating of AM effect, and 1 site- and 1 video-rater each rated the AM item with a reverse scoring convention. When these confounds were eliminated in step-wise fashion, the item's clinimetric properties improved.

CONCLUSIONS

The AM's efficacy can contribute to measuring CD motor severity by addressing identified sources of error during its assessment and rating. Given the AM's sensitive diagnostic and potential pathophysiologic significance, we also provide guidance on modifications to how AMs can be assessed in future CD research.

Plasticity and dystonia: a hypothesis shrouded in variability

Studying plasticity mechanisms with Professor John Rothwell was a shared highlight of our careers. In this article, we discuss non-invasive brain stimulation techniques which aim to induce and quantify plasticity, the mechanisms and nature of their inherent variability and use such observations to review the idea that excessive and abnormal plasticity is a pathophysiological substrate of dystonia. We have tried to define the tone of our review by a couple of Professor John Rothwell's many inspiring characteristics; his endless curiosity to refine knowledge and disease models by scientific exploration and his wise yet humble readiness to revise scientific doctrines when the evidence is supportive. We conclude that high variability of response to non-invasive brain stimulation plasticity protocols significantly clouds the interpretation of historical findings in dystonia research. There is an opportunity to wipe the slate clean of assumptions and armed with an informative literature in health, re-evaluate whether excessive plasticity has a causal role in the pathophysiology of dystonia.

The Dystonias

PURPOSE OF REVIEW

This article provides a summary of the state of the art in the diagnosis, classification, etiologies, and treatment of dystonia.

RECENT FINDINGS

Although many different clinical manifestations of dystonia have been recognized for decades, it is only in the past 5 years that a broadly accepted approach has emerged for classifying them into specific subgroups. The new classification system aids clinical recognition and diagnosis by focusing on key clinical features that help distinguish the many subtypes. In the past few years, major advances have been made in the discovery of new genes as well as advances in our understanding of the biological processes involved. These advances have led to major changes in strategies for diagnosis of the inherited dystonias. An emerging trend is to move away from heavy reliance on the phenotype to target diagnostic testing toward a broader approach that involves large gene panels or whole exome sequencing.

SUMMARY

The dystonias are a large family of phenotypically and etiologically diverse disorders. The diagnosis of these disorders depends on clinical recognition of characteristic clinical features. Symptomatic treatments are useful for all forms of dystonia and include oral medications, botulinum toxins, and surgical procedures. Determination of etiology is becoming increasingly important because the number of disorders is growing and more specific and sometimes disease-modifying therapies now exist.

Laryngeal vibration as a non-invasive neuromodulation therapy for spasmodic dysphonia

Spasmodic dysphonia (SD) is an incurable focal dystonia of the larynx that impairs speech and communication. Vibro-tactile stimulation (VTS) alters afferent proprioceptive input to sensorimotor cortex that controls speech. This proof-of-concept study examined the effect of laryngeal VTS on speech quality and cortical activity in 13 SD participants who vocalized the vowel /a/ while receiving VTS for 29 minutes. In response to VTS, 9 participants (69%) exhibited a reduction of voice breaks and/or a meaningful increase in smoothed cepstral peak prominence, an acoustic measure of voice/speech quality. Symptom improvements persisted for 20 minutes past VTS. Application of VTS induced a significant suppression of theta band power over the left somatosensory-motor cortex and a significant rise of gamma rhythm over right somatosensory-motor cortex. Such suppression of theta oscillations is observed in patients with cervical dystonia who apply effective sensory tricks, suggesting that VTS in SD may activate a similar neurophysiological mechanism. Results of this feasibility study indicate that laryngeal VTS modulates neuronal synchronization over sensorimotor cortex, which can induce short-term improvements in voice quality. The effects of long-term VTS and its optimal dosage for treating voice symptoms in SD are still unknown and require further systematic study.

Sensory Tricks Are Associated with Higher Sleep-Related Quality of Life in Cervical Dystonia

Background

Sensory tricks are compensatory gestures that cervical dystonia (CD) patients use to reduce abnormal neck posture and movements. Although sensory tricks are common in CD, little is known about whether trick efficacy changes over time or has effect on quality of life.

Methods

We analyzed clinical data and video recordings from 188 patients with isolated CD. We calculated the duration of CD and assessed the Toronto Western Spasmodic Torticollis Rating Scales and the Cervical Dystonia Impact Profile (CDIP-58).

Results

A longer duration of CD corresponded to a less effective sensory trick (r(187) = 0.1901, p = 0.009). Patients who demonstrated more effective sensory tricks reported higher sleep-related quality of life than patients with less effective sensory tricks (r(187) = 0.1680, p = 0.0212). There were no significant relationships between the effectiveness of a sensory trick and the other aspects of quality of life as measured by the CDIP-58.

Discussion

Patients who have had CD longer had less effective sensory tricks consistent with patients’ verbal reports of previously having a trick that no longer works. Patients should be apprised of a wide variety of sensory tricks because their previous tricks may lose efficacy over time and because more effective tricks are associated with higher sleep-related quality of life.

Abnormal spontaneous neural activity of brain regions in patients with primary blepharospasm at rest

BACKGROUND

Primary blepharospasm (BSP) is characterized by excessive involuntary eyelid spasms without significant morphological brain abnormalities. Its neural bases remain unclear. Resting-state functional magnetic resonance imaging (rs-fMRI) is a powerful tool for exploring cerebral function mechanisms in BSP.

METHODS

Two subject groups (24 patients with BSP and 24 healthy controls) underwent rs-fMRI scans. The rs-fMRI images were analyzed using the regional homogeneity (ReHo) method to assess the local features of spontaneous brain activity. Correlation analysis was carried out to explore the relationship between the ReHo values of abnormal brain areas and clinical variables including illness duration, symptom severity, and depression/anxiety symptoms.

RESULTS

Relative to healthy controls, patients with BSP showed significantly decreased ReHo in the left superior temporal pole/left insula, left calcarine cortex, and bilateral superior medial frontal gyrus (mSFG), and increased ReHo in the bilateral supplementary motor area (SMA). There were no significant correlations between ReHo values in these brain regions and clinical variables in the patients.

CONCLUSIONS

Our results suggest that abnormal spontaneous brain activity in multiple brain regions not limited to the basal ganglia may be trait alterations in the patients, which provides more insights into the pathogenesis of BSP.

Alterations of Interhemispheric Functional Connectivity and Degree Centrality in Cervical Dystonia: A Resting-State fMRI Study

Background

Cervical dystonia (CD) is a neurological movement disorder characterized by involuntary head and neck movements and postures. Reports on microstructural and functional abnormalities in multiple brain regions not limited to the basal ganglia have been increasing in patients with CD. However, the neural bases of CD are unclear. This study is aimed at identifying cerebral functional abnormalities in CD by using resting-state functional magnetic resonance imaging (rs-fMRI).

Methods

Using rs-fMRI data, voxel-mirrored homotopic connectivity (VMHC) and degree centrality were used to compare the alterations of the rs-functional connectivity (FC) between 19 patients with CD and 21 healthy controls. Regions showing abnormal FCs from two measurements were the regions of interest for correlation analyses.

Results

Compared with healthy controls, patients with CD exhibited significantly decreased VMHC in the supplementary motor area (SMA), precuneus (PCu)/postcentral gyrus, and superior medial prefrontal cortex (MPFC). Significantly increased degree centrality in the right PCu and decreased degree centrality in the right lentiform nucleus and left ventral MPFC were observed in the patient group compared with the control group. Further correlation analyses showed that the VMHC values in the SMA were negatively correlated with dystonia severity.

Conclusion

Local abnormalities and interhemispheric interaction deficits in the sensorimotor network (SMA, postcentral gyrus, and PCu), default mode network (MPFC and PCu), and basal ganglia may be the key characteristics in the pathogenesis mechanism of CD.

Sensory trick in upper limb dystonia

INTRODUCTION

Sensory trick is a specific maneuver that temporarily improves dystonia that is usually observed in 44%-89% of patients with cranial-cervical dystonia and in 20% of patients with upper limb dystonia. This study aimed to assess the prevalence of sensory trick in a cohort of 37 patients with idiopathic adult-onset upper limb dystonia and to determine whether sensory trick can be a useful tool to distinguish dystonic and non-dystonic tremor.

METHODS

Thirty-seven right-handed patients with idiopathic upper limb dystonia and disturbed handwriting and 19 patients with non-dystonic action tremor in the upper limb causing writing disturbances participated into the study. Patients were asked to write a standard sentence twice, before and after applying a standardized sensory trick (gently grabbing right wrist with his left hand). Readability of the two sentences was assessed by three observers blinded to diagnosis.

RESULTS

Five/37 patients (13%) self-discovered ST over disease history, while performing the standardized trick maneuver improved handwriting in 14/37 patients (38%). Interobserver agreement on the effectiveness of sensory trick among the three observers yielded a kappa value of 0.86 (p < 0.0001). The standardized trick was effective in 8/19 patients with dystonic tremor (42%) and in 0/19 patients with non-dystonic tremor (p = 0.003).

CONCLUSION

The results of applying a standardized non-spontaneous trick demonstrated that, in upper limb dystonia, ST may be more frequent than usually observed. Effective sensory trick, when present, may be a hallmark of idiopathic dystonia. The lack of effective sensory trick may help to identify non dystonic upper limb tremor.

Selective sensory deafferentation induces structural and functional brain plasticity

Sensory-motor integration models have been proposed aiming to explain how the brain uses sensory information to guide and check the planning and execution of movements. Sensory neuronopathy (SN) is a peculiar disease characterized by exclusive, severe and widespread sensory loss. It is a valuable condition to investigate how sensory deafferentation impacts brain organization. We thus recruited patients with clinical and electrophysiological criteria for SN to perform structural and functional MRI analyses. We investigated volumetric changes in gray matter (GM) using anatomical images; the microstructure of WM within segmented regions of interest (ROI), via diffusion images; and brain activation related to a finger tapping task. All significant results were related to the long disease duration subgroup of patients. Structural analysis showed hypertrophy of the caudate nucleus, whereas the diffusion study identified reduction of fractional anisotropy values in ROIs located around the thalamus and the striatum. We also found differences regarding finger-tapping activation in the posterior parietal regions and in the medial areas of the cerebellum. Our results stress the role of the caudate nucleus over the other basal ganglia in the sensory-motor integration models, and suggest an inhibitory function of a recently discovered tract between the thalamus and the striatum. Overall, our findings confirm plasticity in the adult brain and open new avenues to design neurorehabilitation strategies.

Dystonia

Dystonia is a neurological condition characterized by abnormal involuntary movements or postures owing to sustained or intermittent muscle contractions. Dystonia can be the manifesting neurological sign of many disorders, either in isolation (isolated dystonia) or with additional signs (combined dystonia). The main focus of this Primer is forms of isolated dystonia of idiopathic or genetic aetiology. These disorders differ in manifestations and severity but can affect all age groups and lead to substantial disability and impaired quality of life. The discovery of genes underlying the mendelian forms of isolated or combined dystonia has led to a better understanding of its pathophysiology. In some of the most common genetic dystonias, such as those caused by TOR1A, THAP1, GCH1 and KMT2B mutations, and idiopathic dystonia, these mechanisms include abnormalities in transcriptional regulation, striatal dopaminergic signalling and synaptic plasticity and a loss of inhibition at neuronal circuits. The diagnosis of dystonia is largely based on clinical signs, and the diagnosis and aetiological definition of this disorder remain a challenge. Effective symptomatic treatments with pharmacological therapy (anticholinergics), intramuscular botulinum toxin injection and deep brain stimulation are available; however, future research will hopefully lead to reliable biomarkers, better treatments and cure of this disorder.

Sensory Trick in a Patient with Cervical Dystonia: Insights from Magnetoencephalography

BACKGROUND

The proposed mechanisms for the sensory trick include peripheral sensory feedback to aid in correcting abnormal posture or movement.

CASE REPORT

A 53-year-old woman with cervical dystonia underwent magnetoencephalography pre- and post-botulinum toxin injection and sensory trick, which was described as yawning. Study revealed connectivity between the left frontal and inferior frontal gyrus before yawning, which changed to the visual cortex and right middle frontal gyrus with yawning. Beta frequencies reduced and gamma frequencies increased after yawning.

DISCUSSION

The increase in gamma frequency bands may indicate increased GABAergic activity. Increase in connectivity in the right cerebellar region underscores the importance of cerebellum in pathogenesis of dystonia.

Perceptual decisions based on previously learned information are independent of dopaminergic tone

Both cognitive and motor symptoms in people with Parkinson's disease (PD) arise from either too little or too much dopamine (DA). Akinesia stems from DA neuronal cell loss, and dyskinesia often stems from an overdose of DA medication. Cognitive behaviors typically associated with frontal cortical function, such as working memory and task switching, are also affected by too little or too much DA in PD. Whether motor and cognitive circuits overlap in PD is unknown. In this article, we show that whereas motor performance improves in people with PD when on dopaminergic medication compared with off medication, perceptual decision-making based on previously learned information (priors) remains impaired whether on or off medications. To rule out effects of long-term DA treatment and dopaminergic neuronal loss such as occur in PD, we also tested a group of people with dopa-unresponsive focal dystonia, a disease that involves the basal ganglia, like PD, but has motor symptoms that are insensitive to dopamine treatment and is not thought to involve frontal cortical DA circuits, unlike PD. We found that people with focal dystonia showed intact perceptual decision-making performance but impaired use of priors in perceptual decision-making, similar to people with PD. Together, the results show a dissociation between motor and cognitive performance in people with PD and reveal a novel cognitive impairment, independent of sensory and motor impairment, in people with focal dystonia. The combined results from people with PD and people with focal dystonia provide mechanistic insights into the role of basal ganglia non-dopaminergic circuits in perceptual decision-making based on priors.

Postural control and the relation with cervical sensorimotor control in patients with idiopathic adult-onset cervical dystonia

Cervical dystonia (CD) is a movement disorder characterized by involuntary muscle contractions leading to an abnormal head posture or movements of the neck. Dysfunctions in somatosensory integration are present and previous data showed enlarged postural sway in stance. Postural control during quiet sitting and the correlation with cervical sensorimotor control were investigated. Postural control during quiet sitting was measured via body sway parameters in 23 patients with CD, regularly receiving botulinum toxin treatment and compared with 36 healthy controls. Amplitude and velocity of displacements of the center of pressure (CoP) were measured by two embedded force plates at 1000 Hz. Three samples of 30 s were recorded with the eyes open and closed. Disease-specific characteristics were obtained in all patients by the Tsui scale, Cervical Dystonia Impact Profile (CDIP-58) and Toronto Western Spasmodic Rating Scale (TWSTRS). Cervical sensorimotor control was assessed with an infrared Vicon system during a head repositioning task. Body sway amplitude and velocity were increased in patients with CD compared to healthy controls. CoP displacements were doubled in patients without head tremor and tripled in patients with a dystonic head tremor. Impairments in cervical sensorimotor control were correlated with larger CoP displacements (r_s ranged from 0.608 to 0.748). Postural control is impaired and correlates with dysfunction in cervical sensorimotor control in patients with CD. Treatment is currently focused on the cervical area. Further research towards the potential value of postural control exercises is recommended.

Disrupted superior collicular activity may reveal cervical dystonia disease pathomechanisms

Cervical dystonia is a common neurological movement disorder characterised by muscle contractions causing abnormal movements and postures affecting the head and neck. The neural networks underpinning this condition are incompletely understood. While animal models suggest a role for the superior colliculus in its pathophysiology, this link has yet to be established in humans. The present experiment was designed to test the hypothesis that disrupted superior collicular processing is evident in affected patients and in relatives harbouring a disease-specific endophenotype (abnormal temporal discrimination). The study participants were 16 cervical dystonia patients, 16 unaffected first-degree relatives with abnormal temporal discrimination, 16 unaffected first-degree relatives with normal temporal discrimination and 16 healthy controls. The response of participant’s superior colliculi to looming stimuli was assessed by functional magnetic resonance imaging. Cervical dystonia patients and relatives with abnormal temporal discrimination demonstrated (i) significantly reduced superior collicular activation for whole brain and region of interest analysis; (ii) a statistically significant negative correlation between temporal discrimination threshold and superior collicular peak values. Our results support the hypothesis that disrupted superior collicular processing is involved in the pathogenesis of cervical dystonia. These findings, which align with animal models of cervical dystonia, shed new light on pathomechanisms in humans.

The Effect of Botulinum Toxin on Network Connectivity in Cervical Dystonia: Lessons from Magnetoencephalography

BACKGROUND

Pharmacological management of cervical dystonia (CD) is considered to be symptomatic in effect, rather than targeting the underlying pathophysiology of the disease. Magnetoencephalography (MEG), a direct measure of neuronal activity, while accepted as a modality for pre-surgical mapping in epilepsy, has never been used to explore the effect of pharmacotherapy in movement disorders.

METHODS

Resting state MEG data were collected from patients with CD, pre- and post-botulinum toxin injections. All of these patients exhibited good clinical benefit with botulinum toxin. Resting state MEG data from four age- and gender-matched healthy controls with no neurological disorders were also collected.

RESULTS

Our exploratory study reveals a difference in coherence between controls and patients in the following regions: fronto-striatal, occipito-striatal, parieto-striatal, and striato-temporal networks. In these regions there is an increase after botulinum toxin. Specifically, increased coherence in the left putamen and right superior parietal gyrus was noticeable. Both intrahemispheric and interhemispheric networks were affected.

DISCUSSION

This is the first attempt to directly assess changes in functional connectivity with pharmacotherapy using MEG. Botulinum toxin might affect sensorimotor integration, leading to clinical benefit. The presence of increased interhemispheric coherence and intrahemispheric coherence points to the importance of global and local networks in the pathophysiology of dystonia.

Dystonia

INTRODUCTION

Dystonia is a clinically heterogeneous group of hyperkinetic movement disorders. Recent advances have provided a better understanding of these conditions with significant clinical impact.

SOURCES OF DATA

Peer reviewed journals and reviews. PubMed.gov.

AREAS OF AGREEMENT

A recent consensus classification, including the assessment of phenomenology and identification of the dystonia syndromes, has provided a helpful tool for the clinical assessment. New forms of monogenic dystonia have been recently identified.

AREAS OF CONTROVERSY

Despite recent advances in the understanding of dystonia, treatment remains symptomatic in most patients.

GROWING POINTS

Recent advances in genetics have provided a better understanding of the potential pathogenic mechanisms involved in dystonia. Deep brain stimulation has shown to improve focal and combined forms of dystonia and its indications are constantly expanding.

AREAS TIMELY FOR DEVELOPING RESEARCH

Growing understanding of the disease mechanisms involved will allow the development of targeted and disease-modifying therapies in the future.