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.

Sensory processing in the auditory and olfactory domains is normal in laryngeal dystonia

Abnormal sensory discriminatory processing has been implicated as an endophenotypic marker of isolated dystonia. However, the extent of alterations across the different sensory domains and their commonality in different forms of dystonia are unclear. Based on the previous findings of abnormal temporal but not spatial discrimination in patients with laryngeal dystonia, we investigated sensory processing in the auditory and olfactory domains as potentially additional contributors to the disorder pathophysiology. We tested auditory temporal discrimination and olfactory function, including odor identification, threshold, and discrimination, in 102 laryngeal dystonia patients and 44 healthy controls, using dichotically presented pure tones and the extended Sniffin' Sticks smell test protocol, respectively. Statistical significance was assessed using analysis of variance with non-parametric bootstrapping. Patients had a lower mean auditory temporal discrimination threshold, with abnormal values found in three patients. Hyposmia was found in 64 patients and anosmia in 2 patients. However, there were no statistically significant differences in either auditory temporal discrimination threshold or olfactory identification, threshold, and discrimination between the groups. A significant positive relationship was found between olfactory threshold and disorder severity based on the Burke-Fahn-Marsden dystonia rating scale. Our findings demonstrate that, contrary to altered visual temporal discrimination, auditory temporal discrimination and olfactory function are likely not candidate endophenotypic markers of laryngeal dystonia.

Botulinum toxin for motor disorders

Botulinum neurotoxins are a group of biological toxins produced by the gram-negative bacteria Clostridium botulinum. After intramuscular injection, they produce dose-related muscle relaxation, which has proven useful in the treatment of a large number of motor and movement disorders. In this chapter, we discuss the utility of botulinum toxin treatment in three major and common medical conditions related to the dysfunction of the motor system, namely dystonia, tremor, and spasticity. A summary of the existing literature is provided along with different techniques of injection including those recommended by the authors.

Brain Connectivity in Dystonia: Evidence from Magnetoencephalography

Magnetoencephalography (MEG) detects synchronized activity within a neuronal network by measuring the magnetic field changes generated by intracellular current flow. Using MEG data, we can quantify brain region networks with similar frequency, phase, or amplitude of activity and thereby identify patterns of functional connectivity seen with specific disorders or disease states. In this review, we examine and summarize MEG-based literature on functional networks in dystonias. Specifically, we inspect literature evaluating the pathogenesis of focal hand dystonia, cervical dystonia, embouchure dystonia, the effects of sensory tricks, treatment with botulinum toxin and deep brain stimulation, and rehabilitation approaches. This review additionally highlights how MEG has potential for application to clinical care of patients with dystonia.

Dystonia in individuals with spastic cerebral palsy and isolated periventricular leukomalacia

AIM

To determine the prevalence of dystonia in individuals with periventricular leukomalacia (PVL) and spastic cerebral palsy (CP), but without basal ganglia and thalamic injury (BGTI) on brain magnetic resonance imaging (MRI).

METHOD

This was a retrospective study of individuals with spastic CP and PVL on MRI evaluated between 2005 and 2018 in a CP center. Individuals with non-PVL brain lesions on MRI, including BGTI, were excluded. Dystonia was assessed via blinded review of neurological exam videos by pediatric movement disorders specialists.

RESULTS

Eighty-five participants (45 males, 40 females; mean age at videotaping 12 years [standard deviation 5 years 6 months], range 4-26 years) met inclusion and exclusion criteria. Of these participants, 50 (59%) displayed dystonia in their exam videos. The most common locations of dystonia were the fingers and hip adductors. The prevalence of dystonia was unaffected by the gestational age or severity of PVL, and was affected by Gross Motor Function Classification System level.

INTERPRETATION

Dystonia is common in individuals with spastic CP and PVL, even without BGTI on MRI. Our findings suggest vigilance for dystonia in individuals with spastic CP should remain high, even without MRI evidence of BGTI.

WHAT THIS PAPER ADDS

Individuals with spastic cerebral palsy and isolated periventricular leukomalacia on magnetic resonance imaging commonly display dystonia. Common sites of dystonia are in the fingers and hip adductors.

Synaptic Dysfunction in Dystonia: Update From Experimental Models

Dystonia, the third most common movement disorder, refers to a heterogeneous group of neurological diseases characterized by involuntary, sustained or intermittent muscle contractions resulting in repetitive twisting movements and abnormal postures. In the last few years, several studies on animal models helped expand our knowledge of the molecular mechanisms underlying dystonia. These findings have reinforced the notion that the synaptic alterations found mainly in the basal ganglia and cerebellum, including the abnormal neurotransmitters signalling, receptor trafficking and synaptic plasticity, are a common hallmark of different forms of dystonia. In this review, we focus on the major contribution provided by rodent models of DYT-TOR1A, DYT-THAP1, DYT-GNAL, DYT/ PARK-GCH1, DYT/PARK-TH and DYT-SGCE dystonia, which reveal that an abnormal motor network and synaptic dysfunction represent key elements in the pathophysiology of dystonia.

Paroxysmal movement disorders: Paroxysmal dyskinesia and episodic ataxia

Paroxysmal movement disorders have traditionally been classified into paroxysmal dyskinesia (PxD), which consists in attacks of involuntary movements (mainly dystonia and/or chorea) without loss of consciousness, and episodic ataxia (EA), which features spells of cerebellar dysfunction with or without interictal neurological manifestations. In this chapter, PxD will be discussed first according to the trigger-based classification, thus reviewing clinical, genetic, and molecular features of paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia, and paroxysmal exercise-induced dyskinesia. EA will be presented thereafter according to their designated gene or genetic locus. Clinicogenetic similarities among paroxysmal movement disorders have progressively emerged, which are herein highlighted along with growing evidence that their pathomechanisms overlap those of epilepsy and migraine. Advances in our comprehension of the biological pathways underlying paroxysmal movement disorders, which involve ion channels as well as proteins associated with the vesical synaptic cycle or implicated in neuronal energy metabolism, may represent the cornerstone for defining a shared pathophysiologic framework and developing target-specific therapies.

Dystonia in Childhood: How Insights from Paediatric Research Enrich the Network Theory of Dystonia

Dystonia is now widely accepted as a network disorder, with multiple brain regions and their interconnections playing a potential role in the pathophysiology. This model reconciles what could previously have been viewed as conflicting findings regarding the neuroanatomical and neurophysiological characteristics of the disorder, but there are still significant gaps in scientific understanding of the underlying pathophysiology. One of the greatest unmet challenges is to understand the network model of dystonia in the context of the developing brain. This article outlines how research in childhood dystonia supports and contributes to the network theory and highlights aspects where data from paediatric studies has revealed novel and unique physiological insights, with important implications for understanding dystonia across the lifespan.

Motor seizure semiology

Motor semiology is a major component of epilepsy evaluation, which provides essential information on seizure classification and helps in seizure localization. The typical motor seizures include tonic, clonic, tonic-clonic, myoclonic, atonic, epileptic spasms, automatisms, and hyperkinetic seizures. Compared to the "positive" motor signs, negative motor phenomena, for example, atonic seizures and Todd's paralysis are also crucial in seizure analysis. Several motor signs, for example, version, unilateral dystonia, figure 4 sign, M2e sign, and asymmetric clonic ending, are commonly observed and have significant clinical value in seizure localization. The purpose of this chapter is to review the localization value and pathophysiology associated with the well-defined motor seizure semiology using updated knowledge from intracranial electroencephalographic recordings, particularly stereoelectroencephalography.

Altered brain connectivity in hyperkinetic movement disorders: A review of resting-state fMRI

BACKGROUND

Hyperkinetic movement disorders (HMD) manifest as abnormal and uncontrollable movements. Despite reported involvement of several neural circuits, exact connectivity profiles remain elusive.

OBJECTIVES

Providing a comprehensive literature review of resting-state brain connectivity alterations using resting-state fMRI (rs-fMRI). We additionally discuss alterations from the perspective of brain networks, as well as correlations between connectivity and clinical measures.

METHODS

A systematic review was performed according to PRISMA guidelines and searching PubMed until October 2022. Rs-fMRI studies addressing ataxia, chorea, dystonia, myoclonus, tics, tremor, and functional movement disorders (FMD) were included. The standardized mean difference was used to summarize findings per region in the Automated Anatomical Labeling atlas for each phenotype. Furthermore, the activation likelihood estimation meta-analytic method was used to analyze convergence of significant between-group differences per phenotype. Finally, we conducted hierarchical cluster analysis to provide additional insights into commonalities and differences across HMD phenotypes.

RESULTS

Most articles concerned tremor (51), followed by dystonia (46), tics (19), chorea (12), myoclonus (11), FMD (11), and ataxia (8). Altered resting-state connectivity was found in several brain regions: in ataxia mainly cerebellar areas; for chorea, the caudate nucleus; for dystonia, sensorimotor and basal ganglia regions; for myoclonus, the thalamus and cingulate cortex; in tics, the basal ganglia, cerebellum, insula, and frontal cortex; for tremor, the cerebello-thalamo-cortical circuit; finally, in FMD, frontal, parietal, and cerebellar regions. Both decreased and increased connectivity were found for all HMD. Significant spatial convergence was found for dystonia, FMD, myoclonus, and tremor. Correlations between clinical measures and resting-state connectivity were frequently described.

CONCLUSION

Key brain regions contributing to functional connectivity changes across HMD often overlap. Possible increases and decreases of functional connections of a specific region emphasize that HMD should be viewed as a network disorder. Despite the complex interplay of physiological and methodological factors, this review serves to gain insight in brain connectivity profiles across HMD phenotypes.

Motor and psychiatric features in idiopathic blepharospasm: A data-driven cluster analysis

INTRODUCTION

Idiopathic blepharospasm is a clinically heterogeneous dystonia also characterized by non motor symptoms.

METHODS

We used a k-means cluster analysis to assess 188 patients with idiopathic blepharospasm in order to identify relatively homogeneous subpopulations of patients, using a set of motor and psychiatric variables to generate the cluster solution.

RESULTS

Blepharospasm patients reached higher scores on scales assessing depressive- and anxiety-related disorders than healthy/disease controls. Cluster analysis suggested the existence of three groups of patients that differed by type of spasms, overall motor severity, and presence/severity of psychiatric problems. The greater severity of motor symptoms was observed in Group 1, the least severity in Group 3, while the severity of blepharospasm in Group 2 was between that observed in Groups 1 and 3. The three motor subtypes also differed by psychiatric features: the lowest severity of psychiatric symptoms was observed in the group with least severe motor symptoms (group 3), while the highest psychiatric severity scores were observed in group 2 that carried intermediate motor severity rather than in the group with more severe motor symptoms (group 1). The three groups did not differ by disease duration, age of onset, sex or other clinical features.

CONCLUSIONS

The present study suggests that blepharospasm patients may be classified in different subtypes according to the type of spasms, overall motor severity and presence/severity of depressive symptoms and anxiety.

Tardive Oromandibular Dystonia Induced by Trazodone: A Clinical Case and Management from the Perspective of the Dental Specialist

BACKGROUND

Tardive Oromandibular Dystonia is an iatrogenic drug-induced movement form of extrapyramidal symptoms associated primarily with chronic consumption of dopamine receptor blocking agents. Tardive symptoms attributable to selective serotonin reuptake inhibitors antidepressants are far less prevalent.

CLINICAL CASE

The authors will present a clinical case and management, from the dental specialist perspective, of a 55-year-old female patient who developed tardive oromandibular dystonia induced by Trazodone prescribed for sleep insomnia.

CONCLUSIONS

Trazodone-induced oromandibular dystonia is extremely rare. Early identification and assessment of tardive symptoms are imperative for successful treatment. Trazodone should be prescribed with caution in patients taking other medications with the potential to cause tardive syndromes.

Characterizing the temporal discrimination threshold in musician's dystonia

The temporal discrimination threshold (TDT) has been established as a biomarker of impaired temporal processing and endophenotype in various forms of focal dystonia patients, such as cervical dystonia, writer's cramp or blepharospasm. The role of TDT in musician's dystonia (MD) in contrast is less clear with preceding studies reporting inconclusive results. We therefore compared TDT between MD patients, healthy musicians and non-musician controls using a previously described visual, tactile, and visual-tactile paradigm. Additionally, we compared TDT of the dystonic and non-dystonic hand and fingers in MD patients and further characterized the biomarker regarding its potential influencing factors, i.e. musical activity, disease variables, and personality profiles. Repeated measures ANOVA and additional Bayesian analyses revealed lower TDT in healthy musicians compared to non-musicians. However, TDTs in MD patients did not differ from both healthy musicians and non-musicians, although pairwise Bayesian t-tests indicated weak evidence for group differences in both comparisons. Analyses of dystonic and non-dystonic hands and fingers revealed no differences. While in healthy musicians, age of first instrumental practice negatively correlated with visual-tactile TDTs, TDTs in MD patients did not correlate with measures of musical activity, disease variables or personality profiles. In conclusion, TDTs in MD patients cannot reliably be distinguished from healthy musicians and non-musicians and are neither influenced by dystonic manifestation, musical activity, disease variables nor personality profiles. Unlike other isolated focal dystonias, TDT seems not to be a reliable biomarker in MD.

Musicians Focal Dystonia: The Practitioner's Perspective on Psychological, Psychosocial, and Behavioural Risk Factors and Non-motor Symptoms

Musician's focal dystonia (MFD) is a painless, task-specific neurological movement disorder that impairs fine motor control when playing an instrument. The pathophysiology is not fully understood, and while the available treatment strategies can help with improving motor control, they are rarely able to fully and reliably rehabilitate playing skills. Recent studies suggest that apart from genetic factors, maladaptive neuroplasticity, and the repetitive nature of the instrumental technique, psychosocial, psychological, and behavioural factors might also play a role in the onset of MFD. However, the presence of some of these risk factors is supported primarily by anecdotal evidence, with only a few aspects examined empirically. To explore this area further, 14 semi-structured interviews were conducted with a convenience sample of practitioners (8 medical professionals and 6 musician-coaches) who frequently treated MFD sufferers. Throughout their career, these participants are estimated to have interacted with more than 2,000 musicians with MFD, creating a large, indirect sample. A detailed patient profile emerged from the data with three main components: 1) the negative impact of social environments, including traumatic experiences and low quality of instrumental teaching; 2) a perfectionist, anxious, overly sensitive, and acquiescent personality type; and 3) obsessive, controlling, and inadequate practice behaviours. Participants stated MFD needs to be treated holistically and that neglecting these aspects during treatment could jeopardise rehabilitation. Further objective, controlled research trials are needed to describe these factors in detail, quantify their potential impact as risk factors, and understand how they might hinder therapy.

A GLP1 receptor agonist diabetes drug ameliorates neurodegeneration in a mouse model of infantile neurometabolic disease

Infantile neuroaxonal dystrophy (INAD) is a rare paediatric neurodegenerative condition caused by mutations in the PLA2G6 gene, which is also the causative gene for PARK14-linked young adult-onset dystonia parkinsonism. INAD patients usually die within their first decade of life, and there are currently no effective treatments available. GLP1 receptor (GLP-1R) agonists are licensed for treating type 2 diabetes mellitus but have also demonstrated neuroprotective properties in a clinical trial for Parkinson's disease. Therefore, we evaluated the therapeutic efficacy of a new recently licensed GLP-1R agonist diabetes drug in a mouse model of INAD. Systemically administered high-dose semaglutide delivered weekly to juvenile INAD mice improved locomotor function and extended the lifespan. An investigation into the mechanisms underlying these therapeutic effects revealed that semaglutide significantly increased levels of key neuroprotective molecules while decreasing those involved in pro-neurodegenerative pathways. The expression of mediators in both the apoptotic and necroptotic pathways were also significantly reduced in semaglutide treated mice. A reduction of neuronal loss and neuroinflammation was observed. Finally, there was no obvious inflammatory response in wild-type mice associated with the repeated high doses of semaglutide used in this study.

Sex and gender differences in movement disorders: Parkinson's disease, essential tremor, dystonia and chorea

Sex and gender-based differences in epidemiology, clinical features and therapeutical responses are emerging in several movement disorders, even though they are still not widely recognized. In this chapter, we summarize the most relevant evidence concerning these differences in Parkinson's disease, essential tremor, dystonia and chorea. Indeed, both sex-related biological (hormonal levels fluctuations) and gender-related variables (socio-cultural and environmental factors) may differently impact symptoms manifestation and severity, phenotype and disease progression of movement disorders on men and women. Moreover, sex differences in treatment responses should be taken into account in any therapeutical planning. Physicians need to be aware of these major differences between men and women that will eventually have a major impact on better tailoring prevention, treatment, or even delaying progression of the most common movement disorders.

Transgenic Mice for the Translational Study of Neuropathic Pain and Dystonia

Murine models are fundamental in the study of clinical conditions and the development of new drugs and treatments. Transgenic technology has started to offer advantages in oncology, encompassing all research fields related to the study of painful syndromes. Knockout mice or mice overexpressing genes encoding for proteins linked to pain development and maintenance can be produced and pain models can be applied to transgenic mice to model the most disabling neurological conditions. Due to the association of movement disorders with sensitivity and pain processing, our group focused for the first time on the role of the torsinA gene GAG deletion—responsible for DYT1 dystonia—in baseline sensitivity and neuropathic responses. The aim of the present report are to review the complex network that exists between the chaperonine-like protein torsinA and the baseline sensitivity pattern—which are fundamental in neuropathic pain—and to point at its possible role in neurodegenerative diseases.

Movement disorders of the mouth: a review of the common phenomenologies

Movement disorders of the mouth encompass a spectrum of hyperactive movements involving the muscles of the orofacial complex. They are rare conditions and are described in the literature primarily in case reports originating from neurologists, psychiatrists, and the dental community. The focus of this review is to provide a phenomenological description of different oral motor disorders including oromandibular dystonia, orofacial dyskinesia and orolingual tremor, and to offer management strategies for optimal treatment based on the current literature. A literature search of full text studies using PubMed/Medline and Cochrane library combined with a manual search of the reference lists was conducted until June 2021. Results from this search included meta-analyses, systematic reviews, reviews, clinical studies, case series, and case reports published by neurologists, psychiatrists, dentists and oral and maxillofacial surgeons. Data garnered from these sources were used to provide an overview of most commonly encountered movement disorders of the mouth, aiding physicians in recognizing these rare conditions and in initiating appropriate therapy.

A translational perspective on pathophysiological changes of oscillatory activity in dystonia and parkinsonism

Intracerebral recordings from movement disorders patients undergoing deep brain stimulation have allowed the identification of pathophysiological patterns in oscillatory activity that correlate with symptom severity. Changes in oscillatory synchrony occur within and across brain areas, matching the classification of movement disorders as network disorders. However, the underlying mechanisms of oscillatory changes are difficult to assess in patients, as experimental interventions are technically limited and ethically problematic. This is why animal models play an important role in neurophysiological research of movement disorders. In this review, we highlight the contributions of translational research to the mechanistic understanding of pathological changes in oscillatory activity, with a focus on parkinsonism and dystonia, while addressing the limitations of current findings and proposing possible future directions.

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.

Influence of Adverse Childhood Experiences and Perfectionism on Musician's Dystonia: a Case Control Study

Background

Musician's dystonia (MD) is a task-specific movement disorder characterized by muscle cramps and impaired voluntary motor-control whilst playing a musical instrument. Recent studies suggest an involvement of adverse childhood experiences (ACEs) in the development of MD.

Objectives

By investigating the prevalence of ACEs in MD patients with perfectionism as possible mediating factor this study aims to gain further insights into the etiology of MD.

Methods

The Adverse Childhood Experiences Scale (ACE-S), the Childhood Trauma Questionnaire (CTQ) and Frost's Multidimensional Perfectionism Scale (FMPS) were answered by 128 MD patients and 136 healthy musicians. Regression and mediator analyses were conducted to identify relevant predictors of MD and to investigate the role of perfectionism.

Results

The CTQ total score (OR: 1.04; 95% CI [1.01, 1.08]) and the sub-score "emotional neglect" (OR: 1.13; 95% CI [1.02, 1.25]) were identified as two predictors of MD. Patients scored significantly higher on the sub-score emotional neglect, but no significant differences were observed for other forms of ACEs. Perfectionism had no mediating function on the association between ACEs and MD.

Discussion

Though only slight differences between both groups were found, there is a trend towards higher rates of emotional neglect among dystonic musicians. A possible explanation for the association between musician's dystonia and emotional neglect could be a lower stress resilience in musicians with a history of ACEs, which increases vulnerability to acquire dysfunctional movement patterns.These tendencies should be further investigated in future studies in which the MD and HM groups are more evenly matched in sex and age.

Highlights

We investigated the role of Adverse Childhood Experiences in the development of musician's dystonia, comparing a large sample of healthy musicians and dystonia patients. Our findings suggest that experiencing emotional neglect might increase the probability to acquire musician's dystonia. The findings offer new implications for etiology and treatment of dystonia.

Oligodendrocyte and Extracellular Matrix Contributions to Central Nervous System Motor Function: Implications for Dystonia

The quest to elucidate nervous system function and dysfunction in disease has focused largely on neurons and neural circuits. However, fundamental aspects of nervous system development, function, and plasticity are regulated by nonneuronal elements, including glial cells and the extracellular matrix (ECM). The rapid rise of genomics and neuroimaging techniques in recent decades has highlighted neuronal-glial interactions and ECM as a key component of nervous system development, plasticity, and function. Abnormalities of neuronal-glial interactions have been understudied but are increasingly recognized to play a key role in many neurodevelopmental disorders. In this report, we consider the role of myelination and the ECM in the development and function of central nervous system motor circuits and the neurodevelopmental disease dystonia. © 2022 International Parkinson and Movement Disorder Society.