Emerging concepts in the physiological basis of dystonia

The use of transcranial magnetic stimulation as a treatment for movement disorders: A critical review

BACKGROUND

Transcranial magnetic stimulation is a safe and painless non-invasive brain stimulation technique that has been largely used in the past 30 years to explore cortical function in healthy participants and, inter alia, the pathophysiology of movement disorders. During the years, its use has evolved from primarily research purposes to treatment of a large variety of neurological and psychiatric diseases. In this article, we illustrate the basic principles on which the therapeutic use of transcranial magnetic stimulation is based and review the clinical trials that have been performed in patients with movement disorders.

METHODS

A search of the PubMed database for research and review articles was performed on therapeutic applications of transcranial magnetic stimulation in movement disorders. The search included the following conditions: Parkinson's disease, dystonia, Tourette syndrome and other chronic tic disorders, Huntington's disease and choreas, and essential tremor. The results of the studies and possible mechanistic explanations for the relatively minor effects of transcranial magnetic stimulation are discussed. Possible ways to improve the methodology and achieve greater therapeutic efficacy are discussed.

CONCLUSION

Despite the promising and robust rationales for the use of transcranial magnetic stimulations as a treatment tool in movement disorders, the results taken as a whole are not as successful as were initially expected. There is encouraging evidence that transcranial magnetic stimulation may improve motor symptoms and depression in Parkinson's disease, but the efficacy in other movement disorders is unclear. Possible improvements in methodology are on the horizon but have yet to be implemented in large clinical studies. © 2019 International Parkinson and Movement Disorder Society © 2019 International Parkinson and Movement Disorder Society.

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.

Distinct roles of brain activity and somatotopic representation in pathophysiology of focal dystonia

Two main neural mechanisms including loss of cortical inhibition and maladaptive plasticity have been thought to be involved in the pathophysiology of focal task-specific dystonia. Such loss of inhibition and maladaptive plasticity likely correspond to cortical overactivity and disorganized somatotopy, respectively. However, the most plausible mechanism of focal task-specific dystonia remains unclear. To address this question, we assessed brain activity and somatotopic representations of motor-related brain areas using functional MRI and behavioral measurement in healthy instrumentalists and patients with embouchure dystonia as an example of focal task-specific dystonia. Dystonic symptoms were measured as variability of fundamental frequency during long tone playing. We found no significant differences in brain activity between the embouchure dystonia and healthy wind instrumentalists in the motor-related areas. Assessment of somatotopy, however, revealed significant differences in the somatotopic representations of the mouth area for the right somatosensory cortex between the two groups. Multiple-regression analysis revealed brain activity in the primary motor and somatosensory cortices, cerebellum, and putamen was significantly associated with variability of fundamental frequency signals representing dystonic symptoms. Conversely, somatotopic representations in motor-related brain areas were not associated with variability of fundamental frequency signals in embouchure dystonia. The present findings suggest that abnormal motor-related network activity and aberrant somatotopy correlate with different aspects of mechanisms underlying focal task-specific dystonia.

White Matter Changes in Cervical Dystonia Relate to Clinical Effectiveness of Botulinum Toxin Treatment

In a previous report showing white matter microstructural hemispheric asymmetries medial to the pallidum in focal dystonias, we showed preliminary evidence that this abnormality was reduced 4 weeks after botulinum toxin (BTX) injections. In the current study we report the completed treatment study in a full-size cohort of CD patients (n = 14). In addition to showing a shift toward normalization of the hemispheric asymmetry, we evaluated clinical relevance of these findings by relating white matter changes to degree of symptom improvement. We also evaluated whether the magnitude of the white matter asymmetry before treatment was related to severity, laterality, duration of dystonia, and/or number of previous BTX injections. Our results confirm the findings of our preliminary report: we observed significant fractional anisotropy (FA) changes medial to the pallidum 4 weeks after BTX in CD participants that were not observed in controls scanned at the same interval. There was a significant relationship between magnitude of hemispheric asymmetry and dystonia symptom improvement, as measured by percent reduction in dystonia scale scores. There was also a trend toward a relationship between magnitude of pre-injection white matter asymmetry and symptom severity, but not symptom laterality, disorder duration, or number of previous BTX injections. Post-hoc analyses suggested the FA changes at least partially reflected changes in pathophysiology, but a dissociation between patient perception of benefit from injections and FA changes suggested the changes did not reflect changes to the primary "driver" of the dystonia. In contrast, there were no changes or group differences in DTI diffusivity measures, suggesting the hemispheric asymmetry in CD does not reflect irreversible white matter tissue loss. These findings support the hypothesis that central nervous system white matter changes are involved in the mechanism by which BTX exerts clinical benefit.

Optogenetic augmentation of the hypercholinergic endophenotype in DYT1 knock-in mice induced erratic hyperactive movements but not dystonia

BACKGROUND

The most prevalent inherited form of generalized dystonia is caused by a mutation in torsinA (DYT1, ∆GAG) with incomplete penetrance. Rodent models with mutated torsinA do not develop dystonic symptoms, but previous ex vivo studies indicated abnormal excitation of cholinergic interneurons (ChI) and increased striatal acetylcholine.

METHODS

We used in vivo optogenetics to exacerbate this endophenotype in order to determine its capacity to trigger dystonic symptoms in freely behaving mice. Tor1a^+/Δgag DYT1 mice and wildtype littermates expressing channelrhodopsin2 under the Chat promotor were implanted bilaterally with optical LED cannulae and stimulated with blue light pulses of varied durations.

FINDINGS

Six months old DYT1 KI mice but not wildtype controls responded with hyperactivity to blue light specifically at 25 ms pulse duration, 10 Hz frequency. Neuronal activity (c-Fos) in cholinergic interneurons was increased immediately after light stimulation and persisted only in DYT1 KI over 15 min. Substance P was increased specifically in striosome compartments in naïve DYT1 KI mice compared to wildtype. Under optogenetic stimulation substance P increased in wildtype to match levels in Dyt1 KI, and acetylcholinesterase was elevated in the striatum of stimulated DYT1 KI. No signs of dystonic movements were observed under stimulation of up to one hour in both genotypes and age groups, and the sensorimotor deficit previously observed in 6 months old DYT1 KI mice persisted under stimulation.

INTERPRETATION

Overall this supports an endophenotype of dysregulated cholinergic activity in DYT1 dystonia, but depolarizing cholinergic interneurons was not sufficient to induce overt dystonia in DYT1 KI mice.

Botulinum Neurotoxin Therapy for Lingual Dystonia Using an Individualized Injection Method Based on Clinical Features

Lingual dystonia is a debilitating type of oromandibular dystonia characterized by involuntary, often task-specific, contractions of the tongue muscle activated by speaking or eating. Botulinum neurotoxin (BoNT) has been used to treat lingual dystonia; however, it is known to cause serious complications, such as dysphasia and aspiration. The purpose of this study was to evaluate the efficacy and adverse effects of individualized BoNT therapy for lingual dystonia. One-hundred-and-seventy-two patients (102 females and 70 males, mean age: 46.2 years) with lingual dystonia were classified into four subtypes based on symptoms of involuntary tongue movements: protrusion (68.6%), retraction (16.9%), curling (7.6%), and laterotrusion (7.0%). Patients were treated with BoNT injection into the genioglossus and/or intrinsic muscles via individualized submandibular and/or intraoral routes. Results were compared before and after BoNT therapy. Botulinum neurotoxin was injected in 136 patients (mean: 4.8 injections). Clinical sub-scores (mastication, speech, pain, and discomfort) in a disease-specific rating scale were reduced significantly (p < 0.001) after administration. Comprehensive improvement after BoNT injection, assessed using the rating scale, was 77.6%. The curling type (81.9%) showed the greatest improvement, while the retraction type showed the least improvement (67.9%). Mild and transient dysphasia occurred in 12.5% of patients (3.7% of total injections) but disappeared spontaneously within several days to two weeks. No serious side effects were observed. With careful diagnosis of subtypes and a detailed understanding of lingual muscle anatomy, individualized BoNT injection into dystonic lingual muscles can be effective and safe.

TorsinA dysfunction causes persistent neuronal nuclear pore defects

A critical challenge to deciphering the pathophysiology of neurodevelopmental disease is identifying which of the myriad abnormalities that emerge during CNS maturation persist to contribute to long-term brain dysfunction. Childhood-onset dystonia caused by a loss-of-function mutation in the AAA+ protein torsinA exemplifies this challenge. Neurons lacking torsinA develop transient nuclear envelope (NE) malformations during CNS maturation, but no NE defects are described in mature torsinA null neurons. We find that during postnatal CNS maturation torsinA null neurons develop mislocalized and dysfunctional nuclear pore complexes (NPC) that lack NUP358, normally added late in NPC biogenesis. SUN1, a torsinA-related molecule implicated in interphase NPC biogenesis, also exhibits localization abnormalities. Whereas SUN1 and associated nuclear membrane abnormalities resolve in juvenile mice, NPC defects persist into adulthood. These findings support a role for torsinA function in NPC biogenesis during neuronal maturation and implicate altered NPC function in dystonia pathophysiology.

The Use of Botulinum Toxin for Treatment of the Dystonias

Dystonias are characterized by involuntary muscle contractions, twisting movements, abnormal postures, and often tremor in various body regions. However, in the last decade several studies have demonstrated that dystonias are also characterized by sensory abnormalities. While botulinum toxin is the gold standard therapy for focal dystonia, exactly how it improves this disorder is not entirely understood. Neurophysiological studies in animals and humans have clearly demonstrated that botulinum toxin improves dystonic motor manifestations by inducing chemodenervation, therefore weakening the injected muscles. In addition, neurophysiological and neuroimaging evidence also suggests that botulinum toxin modulates the activity of various neural structures in the CNS distant from the injected site, particularly cortical motor and sensory areas. Concordantly, recent studies have shown that in patients with focal dystonias botulinum toxin ameliorates sensory disturbances, including reduced spatial discrimination acuity and pain. Overall, these observations suggest that in these patients botulinum toxin-induced effects encompass complex mechanisms beyond chemodenervation of the injected muscles.

Physiological effects of subthalamic nucleus deep brain stimulation surgery in cervical dystonia

BACKGROUND

Subthalamic nucleus deep brain stimulation (STN DBS) surgery is clinically effective for treatment of cervical dystonia; however, the underlying physiology has not been examined. We used transcranial magnetic stimulation (TMS) to examine the effects of STN DBS on sensorimotor integration, sensorimotor plasticity and motor cortex excitability, which are identified as the key pathophysiological features underlying dystonia.

METHODS

TMS paradigms of short latency afferent inhibition (SAI) and long latency afferent inhibition (LAI) were used to examine the sensorimotor integration. Sensorimotor plasticity was measured with paired associative stimulation paradigm, and motor cortex excitability was examined with short interval intracortical inhibition and intracortical facilitation. DBS was turned off and on to record these measures.

RESULTS

STN DBS modulated SAI and LAI, which correlated well with the acute clinical improvement. While there were no changes seen in the motor cortex excitability, DBS was found to normalise the sensorimotor plasticity; however, there was no clinical correlation.

CONCLUSION

Modulation of sensorimotor integration is a key contributor to clinical improvement with acute stimulation of STN. Since the motor cortex excitability did not change and the change in sensorimotor plasticity did not correlate with clinical improvement, STN DBS demonstrates restricted effects on the underlying physiology.

CLINICAL TRIAL REGISTRATION

NCT01671527.

Stereotactic Lesioning of the Thalamic Vo Nucleus for the Treatment of Writer's Cramp (Focal Hand Dystonia)

Writer's cramp (focal hand dystonia) is a sporadic focal dystonia that affects a specific part of the upper limb causing excessive co-contraction of antagonistic muscles. It usually presents as a task-specific dystonia, including, among others, writing of a character or playing a musical instrument. Although treatments for writer's cramp exist, medical therapy often results in unsatisfactory outcomes in patients with this type of dystonia. However, accumulating evidence suggests that long-term and complete remission of various types of focal hand dystonia can be achieved with stereotactic ablation or deep brain stimulation of the thalamic ventral-oralis complex (Vo) nucleus, which includes both the ventralis oralis posterior and anterior nuclei of the thalamus. Following the striking therapeutic success of Vo thalamotomy in patients with medically-refractory writer's cramp, we here introduce the use of stereotactic lesioning of the thalamic Vo nucleus for the treatment of this focal type of dystonia. Our findings identified patients with disabling writer's cramp (i.e., it prevents their success in their professional careers) to be good candidates for positive outcome with this surgical technique.

A novel therapeutic agent, sodium oxybate, improves dystonic symptoms via reduced network-wide activity

Oral medications for the treatment of dystonia are not established. Currently, symptoms of focal dystonia are managed with botulinum toxin injections into the affected muscles. However, the injection effects are short-lived and not beneficial for all patients. We recently reported significant clinical improvement of symptoms with novel investigational oral drug, sodium oxybate, in patients with the alcohol-responsive form of laryngeal focal dystonia. Understanding the mechanism of action of this promising oral agent holds a strong potential for the development of a scientific rationale for its use in dystonia. Therefore, to determine the neural markers of sodium oxybate effects, which may underlie dystonic symptom improvement, we examined brain activity during symptomatic speech production before and after drug intake in patients with laryngeal dystonia and compared to healthy subjects. We found that sodium oxybate significantly attenuated hyperfunctional activity of cerebellar, thalamic and primary/secondary sensorimotor cortical regions. Drug-induced symptom improvement was correlated with decreased-to-normal levels of activity in the right cerebellum. These findings suggest that sodium oxybate shows direct modulatory effects on disorder pathophysiology by acting upon abnormal neural activity within the dystonic network.

Long-Lasting Electrophysiological After-Effects of High-Frequency Stimulation in the Globus Pallidus: Human and Rodent Slice Studies

Deep-brain stimulation (DBS) of the globus pallidus pars interna (GPi) is a highly effective therapy for movement disorders, yet its mechanism of action remains controversial. Inhibition of local neurons because of release of GABA from afferents to the GPi is a proposed mechanism in patients. Yet, high-frequency stimulation (HFS) produces prolonged membrane depolarization mediated by cholinergic neurotransmission in endopeduncular nucleus (EP, GPi equivalent in rodent) neurons. We applied HFS while recording neuronal firing from an adjacent electrode during microelectrode mapping of GPi in awake patients (both male and female) with Parkinson disease (PD) and dystonia. Aside from after-suppression and no change in neuronal firing, high-frequency microstimulation induced after-facilitation in 38% (26/69) of GPi neurons. In neurons displaying after-facilitation, 10 s HFS led to an immediate decrease of bursting in PD, but not dystonia patients. Moreover, the changes of bursting patterns in neurons with after-suppression or no change after HFS, were similar in both patient groups. To explore the mechanisms responsible, we applied HFS in EP brain slices from rats of either sex. As in humans, HFS in EP induced two subtypes of after-excitation: excitation or excitation with late inhibition. Pharmacological experiments determined that the excitation subtype, induced by lower charge density, was dependent on glutamatergic transmission. HFS with higher charge density induced excitation with late inhibition, which involved cholinergic modulation. Therefore HFS with different charge density may affect the local neurons through multiple synaptic mechanisms. The cholinergic system plays a role in mediating the after-facilitatory effects in GPi neurons, and because of their modulatory nature, may provide a basis for both the immediate and delayed effects of GPi-DBS. We propose a new model to explain the mechanisms of DBS in GPi.SIGNIFICANCE STATEMENT Deep-brain stimulation (DBS) in the globus pallidus pars interna (GPi) improves Parkinson disease (PD) and dystonia, yet its mechanisms in GPi remain controversial. Inhibition has been previously described and thought to indicate activation of GABAergic synaptic terminals, which dominate in GPi. Here we report that 10 s high-frequency microstimulation induced after-facilitation of neural firing in a substantial proportion of GPi neurons in humans. The neurons with after-facilitation, also immediately reduced their bursting activities after high-frequency stimulation in PD, but not dystonia patients. Based on these data and further animal experiments, a mechanistic hypothesis involving glutamatergic, GABAergic, and cholinergic synaptic transmission is proposed to explain both short- and longer-term therapeutic effects of DBS in GPi.

Neuroimaging Applications in Dystonia

Dystonia is a neurological disorder characterized by involuntary, repetitive movements. Although the precise mechanisms of dystonia development remain unknown, the diversity of its clinical phenotypes is thought to be associated with multifactorial pathophysiology, which is linked not only to alterations of brain organization, but also environmental stressors and gene mutations. This chapter will present an overview of the pathophysiology of isolated dystonia through the lens of applications of major neuroimaging methodologies, with links to genetics and environmental factors that play a prominent role in symptom manifestation.

Impaired white matter integrity between premotor cortex and basal ganglia in writer's cramp

INTRODUCTION

Writer's cramp (WC) as a focal hand dystonia is characterized by abnormal postures of the hand during writing. Impaired inhibition and maladaptive plasticity in circuits linking the basal ganglia and sensorimotor cortices have been described. In particular, a dysfunction of lateral premotor cortices has been associated with impaired motor control in WC. We applied diffusion tensor imaging to identify changes in white matter connectivity between premotor regions and important cortical and subcortical structures.

METHODS

Whole brain white matter tracts were reconstructed in 18 right-handed WC patients and 18 matched controls, using probabilistic fiber tracking. We restricted our analyses to left-hemispheric fibers between the middle frontal gyrus (MFG) and basal ganglia, thalamus, primary motor, and sensory cortex. Diffusion parameters (fractional anisotropy and linear anisotropy) were compared between both groups.

RESULTS

A significant reduction in fractional anisotropy values was shown for patients (mean ± SD: 0.37 ± 0.02) vs. controls (0.39 ± 0.03) regarding fibers between the left-sided MFG and the putamen (p < 0.05). The same applied for linear anisotropy values in this connection (p < 0.05).

CONCLUSIONS

Our results suggest an impaired structural connectivity between the left-hemispheric MFG and putamen with a loss of equally aligned fibers in WC patients. This could reflect a structural basis for functional findings interpreted as altered inhibition and plasticity, both within the premotor cortex and the basal ganglia, that at last lead to the clinical symptoms of WC.

Differential effects of propranolol on head and upper limb tremor in patients with essential tremor and dystonia

Propranolol is used as the first-line treatment in essential tremor and it has also been proposed as a treatment for tremor in dystonia. However, several issues remain uncertain. For example, it is still not clear whether propranolol exerts a beneficial effect on head tremor. Moreover, no studies have investigated whether the effect of propranolol on head and upper limb tremor in essential tremor differs from that in dystonia. We aimed to assess the effects of propranolol on tremor in different body parts in essential tremor and in patients with tremor and dystonia. Twenty-nine patients with head and upper limb tremor were enrolled in the study, 14 with essential tremor, and 15 with dystonia. Participants underwent a clinical and kinematic analysis of tremor in two sessions, i.e., without (baseline) and 'on therapy' with propranolol. We found that head tremor was more severe in patients with dystonia, while upper limb tremor was more evident in patients with essential tremor (P < 0.05). Propranolol had no effect on head tremor in either group (all Ps > 0.05), but it did reduce upper limb tremor in patients with essential tremor. The present study demonstrates differential effects of propranolol on head and upper limb tremor in patients with essential tremor. The lack of effect on head and upper limb tremor in patients with dystonia suggests that the pathophysiological mechanisms underlying tremor in these two conditions and in different body parts may be distinct.

Actual and Illusory Perception in Parkinson's Disease and Dystonia: A Narrative Review

Sensory information is continuously processed so as to allow behavior to be adjusted according to environmental changes. Before sensory information reaches the cortex, a number of subcortical neural structures select the relevant information to send to be consciously processed. In recent decades, several studies have shown that the pathophysiological mechanisms underlying movement disorders such as Parkinson's disease (PD) and dystonia involve sensory processing abnormalities related to proprioceptive and tactile information. These abnormalities emerge from psychophysical testing, mainly temporal discrimination, as well as from experimental paradigms based on bodily illusions. Although the link between proprioception and movement may be unequivocal, how temporal tactile information abnormalities and bodily illusions relate to motor disturbances in PD and dystonia is still a matter of debate. This review considers the role of altered sensory processing in the pathophysiology of movement disorders, focusing on how sensory alteration patterns differ between PD and dystonia. We also discuss the evidence available and the potential for developing new therapeutic strategies based on the manipulation of multi-sensory information and bodily illusions in patients with these movement disorders.

Testing rTMS-Induced Neuroplasticity: A Single Case Study of Focal Hand Dystonia

Focal hand dystonia in musicians is a neurological motor disorder in which aberrant plasticity is caused by excessive repetitive use. This work's purposes were to induce plasticity changes in a dystonic musician through five daily thirty-minute sessions of 1 Hz repetitive transcranial magnetic stimulation (rTMS) applied to the left M1 by using neuronavigated stimulation and to reliably measure the effect of these changes. To this aim, the relationship between neuroplasticity changes and motor recovery was investigated using fine-grained kinematic analysis. Our results suggest a statistically significant improvement in motor coordination both in a task resembling the dystonic-inducing symptoms and in a reach-to-grasp task. This single case study supports the safe and effective use of noninvasive brain stimulation in neurologic patients and highlights the importance of evaluating outcomes in measurable ways. This issue is a key aspect to focus on to classify the clinical expression of dystonia. These preliminary results promote the adoption of kinematic analysis as a valuable diagnostic tool.

Aberrant cortical excitability reflects the loss of hand dexterity in musician's dystonia

KEY POINTS

Dystonia is a movement disorder characterized by abnormalities at multifaceted aspects of motor dexterity and neural functions. Evidence bridging between pathophysiology and movement abnormalities is limited. A novel finding was that in focal task-specific dystonia (FTSD), an aberrantly reduced inhibition at the motor cortex was related to the temporal imprecision of the dexterous finger movements, whereas an elevated facilitation was associated with an abnormally sluggish transition of finger movements from flexion to extension. We newly identified two sets of behavioural-physiological covariations as hallmarks of hand FTSD, which is clinically significant because these findings provide novel evidence connecting distinct types of malfunctions within the motor cortex at rest with distinct aspects of motor dexterity degradation in FTSD patients.

ABSTRACT

Focal task-specific dystonia (FTSD) compromises dexterous movements. A proposed pathophysiological mechanism of FTSD involves malfunction of the motor cortex (M1). However, no evidence is yet available regarding whether and how malfunctions of M1 are responsible for the loss of motor dexterity. Here, we addressed this issue by assessing both M1 excitability and detailed movement parameters, as well as their relationships. Transcranial magnetic stimulation was applied over M1 in 20 pianists with FTSD, 20 healthy pianists and 20 non-musicians. The patients demonstrated both reduced short-interval intracortical inhibition (SICI) and elevated intracortical facilitation (ICF) compared with the healthy controls. This indicates that the abnormal cortical excitability reflects pathophysiology but not current skills. Hand motor dexterity was evaluated by position sensors during piano playing at two tempi. The patients showed delayed transition from finger flexion to extension at the fastest tempo and greater timing variability of the finger movements. Furthermore, multivariate analyses identified distinct sets of covariation between cortical excitability and dexterity measures. Namely, the SICI measure and ICF measure were associated with the temporal variability of the movements and the quickness of the transition from flexion to extension, respectively. Specifically, the reduced inhibition and elevated facilitation at M1 in pianists was related to the temporal imprecision and impairment of quick transitions in the sequential finger movements. The present study provides novel evidence associating M1 malfunctions with dexterity loss.

GABAA Receptor Availability Changes Underlie Symptoms in Isolated Cervical Dystonia

GABA_A receptor availability changes within sensorimotor regions have been reported in some isolated forms of dystonia. Whether similar abnormalities underlie symptoms in cervical dystonia is not known. In the present study, a total of 15 cervical dystonia patients and 15 age- and sex-matched controls underwent ¹¹C-flumazenil PET/CT scanning. The density of available GABA_A receptors was estimated using a Simplified Reference Tissue Model 2. Group differences were evaluated using a two-sample T-test, and correlations with dystonia severity, as measured by the Toronto Western Spasmodic Torticollis Rating Scale, and disease duration were evaluated using a regression analysis. Voxel-based analyses revealed increased GABA_A availability within the right precentral gyrus in brain motor regions previously associated with head turning and the left parahippocampal gyrus. GABA_A availability within the bilateral cerebellum was negatively correlated with dystonia severity, and GABA_A availability within the right thalamus and a variety of cerebellar and cortical regions were negatively correlated with disease duration. While GABA_A availability changes within primary motor areas could represent a partial compensatory response to loss of inhibition within sensorimotor network, GABAergic signaling impairment within the cerebellum may be a key contributor to dystonia severity.

Systematic Review of Rehabilitation in Focal Dystonias: Classification and Recommendations

Background

Rehabilitation interventions are rarely utilized as an alternative or adjunct therapy for focal dystonias. Reasons for limited utilization are unknown, but lack of conclusive evidence of effectiveness is likely a crucial factor.

Methods and Findings

The purpose of this systematic review was to determine the level of evidence for rehabilitation interventions in focal dystonias. Rehabilitation interventions were classified based upon the underlying theoretical basis of different approaches, and the strength of evidence for each category was evaluated to identify gaps in the field. Prospective studies using rehabilitation methods in cervical, hand, and foot dystonia were reviewed. The key elements of treatments tested were identified and studies were grouped into six categories based on the theoretical basis of the intervention: (1) movement practice, (2) training with constraint, (3) sensory reorganization, (4) normalization of muscle activity with external techniques, (5) neuromodulation with training, and (6) compensatory strategies. Quality of the body of evidence ranged from very low‐to‐low according to the grades of recommendation, assessment, development, and evaluation (GRADE). Despite inconclusive evidence for these rehabilitation approaches, data suggest that intensive movement practice and neuromodulation combined with motor training should be further explored.

Conclusions

This systematic review presents a novel approach to classify studies of rehabilitation in focal dystonias based on the theoretical basis of intervention. The proposed classification system will move toward a unified theoretical understanding of rehabilitation interventions in dystonia. Moreover, it will help provide recommendations for clinical applications and future investigations.

Early structural and functional plasticity alterations in a susceptibility period of DYT1 dystonia mouse striatum

The onset of abnormal movements in DYT1 dystonia is between childhood and adolescence, although it is unclear why clinical manifestations appear during this developmental period. Plasticity at corticostriatal synapses is critically involved in motor memory. In the Tor1a^+/Δgag DYT1 dystonia mouse model, long-term potentiation (LTP) appeared prematurely in a critical developmental window in striatal spiny neurons (SPNs), while long-term depression (LTD) was never recorded. Analysis of dendritic spines showed an increase of both spine width and mature mushroom spines in Tor1a^+/Δgag neurons, paralleled by an enhanced AMPA receptor (AMPAR) accumulation. BDNF regulates AMPAR expression during development. Accordingly, both proBDNF and BDNF levels were significantly higher in Tor1a^+/Δgag mice. Consistently, antagonism of BDNF rescued synaptic plasticity deficits and AMPA currents. Our findings demonstrate that early loss of functional and structural synaptic homeostasis represents a unique endophenotypic trait during striatal maturation, promoting the appearance of clinical manifestations in mutation carriers.

Deep brain stimulation for dystonia due to cerebral palsy: A review

Cerebral palsy (CP) is a heterogeneous group of syndromes that cause a non-progressive disorder of early onset, with abnormal control of movement and posture. Various aetiologies can cause the CP clinical spectrum, but all have a disruption of motor control in common. CP can be divided into four major types based on the motor disability: predominant spastic, dyskinetic, ataxic and mixed form. Dyskinetic CP (DCP) is the most common cause of acquired dystonia in children. The treatment of DCP is challenging because most individuals have mixed degrees of chorea, athetosis and dystonia. Pharmacological treatment is often unsatisfactory. Functional neurosurgery, in particular deep brain stimulation targeting the basal ganglia or the cerebellum, is emerging as a promising therapeutic approach in selected patients with DCP. We evaluated herein the effects of DBS on patients with DCP in a review of published patient data in the largest available studies.

Basal ganglia mechanisms in action selection, plasticity, and dystonia

Basal ganglia circuits are organized to selected desired actions and to inhibit potentially competing unwanted actions. This is accomplished through a complex circuitry that is modified through development and learning. Mechanisms of neural plasticity underlying these modifications are increasingly understood, but new mechanisms continue to be discovered. Dystonia, a movement disorder characterized by involuntary muscle contractions that cause abnormal postures and movements. Emerging evidence points to important links between mechanisms of plasticity and the manifestations of dystonia. Investigation of these mechanisms has improved understanding of the action of currently used medication and is informing the development of new treatments.

Relationships between Serotonin Transporter Binding in the Raphe Nuclei, Basal Ganglia, and Hippocampus with Clinical Symptoms in Cervical Dystonia: A [11C]DASB Positron Emission Tomography Study

Purpose

Alterations of the central serotonergic system have been implicated in the pathophysiology of dystonia. In this molecular imaging study, we assessed whether altered presynaptic serotonin transporter (SERT) binding contributes to the pathophysiology of cervical dystonia (CD), concerning both motor and non-motor symptoms (NMS).

Methods

We assessed the non-displaceable binding potential (BP_ND) using the selective SERT tracer [¹¹C]DASB and positron emission tomography (PET) in 14 CD patients and 12 age- and gender-matched controls. Severity of motor symptoms was scored using the Toronto Western Spasmodic Torticollis Rating Scale and Clinical Global Impression jerks/tremor scale. NMS for depressive symptoms, anxiety, fatigue, and sleep disturbances were assessed with quantitative rating scales. The relationship between SERT binding and clinical patient characteristics was analyzed with the Spearman’s rho test and multiple regression.

Results

When comparing the CD patients with controls, no significant differences in BP_ND were found. Higher BP_ND in the dorsal raphe nucleus was statistically significantly correlated (p < 0.001) with motor symptom severity (r_s = 0.65), pain (r_s = 0.73), and sleep disturbances (r_s = 0.73), with motor symptom severity being the most important predictor of SERT binding. Furthermore, fatigue was negatively associated with the BP_ND in the medial raphe nucleus (r_s = −0.61, p = 0.045), and sleep disorders were positively associated with the BP_ND in the caudate nucleus (r_s = 0.58, p = 0.03) and the hippocampus (r_s = 0.56, p = 0.02).

Conclusion

Motor symptoms, as well as pain, sleep disturbances, and fatigue in CD showed a significant relationship with SERT binding in the raphe nuclei. Moreover, fatigue showed a significant relationship with the medial raphe nucleus and sleep disorders with the caudate nucleus and hippocampus. These findings suggest that an altered serotonergic signaling in different brain areas in CD is related to different motor as well as NMS, which will further stimulate research on the role of serotonin in the pathogenesis of dystonia.

Basic and Translational Neuroscience of Childhood-Onset Dystonia: A Control-Theory Perspective

Dystonia is a collection of symptoms with involuntary muscle activation causing hypertonia, hyperkinetic movements, and overflow. In children, dystonia can have numerous etiologies with varying neuroanatomic distribution. The semiology of dystonia can be explained by gain-of-function failure of a feedback controller that is responsible for stabilizing posture and movement. Because postural control is maintained by a widely distributed network, many different anatomic regions may be responsible for symptoms of dystonia, although all features of dystonia can be explained by uncontrolled activation or hypersensitivity of motor cortical regions that can cause increased reflex gain, inserted postures, or sensitivity to irrelevant sensory variables. Effective treatment of dystonia in children requires an understanding of the relationship between etiology, anatomy, and the specific mechanism of failure of postural stabilization.

Isolated Focal Dystonia as a Disorder of Large-Scale Functional Networks

Isolated focal dystonias are a group of disorders with diverse symptomatology but unknown pathophysiology. Although recent neuroimaging studies demonstrated regional changes in brain connectivity, it remains unclear whether focal dystonia may be considered a disorder of abnormal networks. We examined topology as well as the global and local features of large-scale functional brain networks across different forms of isolated focal dystonia, including patients with task-specific (TSD) and nontask-specific (NTSD) dystonias. Compared with healthy participants, all patients showed altered network architecture characterized by abnormal expansion or shrinkage of neural communities, such as breakdown of basal ganglia-cerebellar community, loss of a pivotal region of information transfer (hub) in the premotor cortex, and pronounced connectivity reduction within the sensorimotor and frontoparietal regions. TSD were further characterized by significant connectivity changes in the primary sensorimotor and inferior parietal cortices and abnormal hub formation in insula and superior temporal cortex, whereas NTSD exhibited abnormal strength and number of regional connections. We suggest that isolated focal dystonias likely represent a disorder of large-scale functional networks, where abnormal regional interactions contribute to network-wide functional alterations and may underline the pathophysiology of isolated focal dystonia. Distinct symptomatology in TSD and NTSD may be linked to disorder-specific network aberrations.

How Many Types of Dystonia? Pathophysiological Considerations

Dystonia can be seen in a number of different phenotypes that may arise from different etiologies. The pathophysiological substrate of dystonia is related to three lines of research. The first postulate a loss of inhibition which may account for the excess of movement and for the overflow phenomena. A second abnormality is sensory dysfunction which is related to the mild sensory complaints in patients with focal dystonias and may be responsible for some of the motor dysfunction. Finally, there are strong pieces of evidence from animal and human studies suggesting that alterations of synaptic plasticity characterized by a disruption of homeostatic plasticity, with a prevailing facilitation of synaptic potentiation may play a pivotal role in primary dystonia. These working hypotheses have been generalized in all form of dystonia. On the other hand, several pieces of evidence now suggest that the pathophysiology may be slightly different in the different types of dystonia. Therefore, in the present review, we would like to discuss the neural mechanisms underlying the different forms of dystonia to disentangle the different weight and role of environmental and predisposing factors.

A unifying motor control framework for task-specific dystonia

Task-specific dystonia is a movement disorder characterized by a painless loss of dexterity specific to a particular motor skill. This disorder is prevalent among writers, musicians, dancers and athletes. No current treatment is predictably effective, and the disorder generally ends the careers of affected individuals. Traditional disease models of dystonia have a number of limitations with regard to task-specific dystonia. We therefore discuss emerging evidence that the disorder has its origins within normal compensatory mechanisms of a healthy motor system in which the representation and reproduction of motor skill are disrupted. We describe how risk factors for task-specific dystonia can be stratified and translated into mechanisms of dysfunctional motor control. The proposed model aims to define new directions for experimental research and stimulate therapeutic advances for this highly disabling disorder.

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.

The cerebellum and dystonia

Dystonia is a heterogeneous disorder characterized by involuntary muscle contractions, twisting movements, and abnormal postures in various body regions. It is widely accepted that the basal ganglia are involved in the pathogenesis of dystonia. A growing body of evidence, however, is challenging the traditional view and suggest that the cerebellum may also play a role in dystonia. Studies on animals indicate that experimental manipulations of the cerebellum lead to dystonic-like movements. Several clinical observations, including those from secondary dystonia cases as well as neurophysiologic and neuroimaging studies in human patients, provide further evidence in humans of a possible relationship between cerebellar abnormalities and dystonia. Claryfing the role of the cerebellum in dystonia is an important step towards providing alternative treatments based on noninvasive brain stimulation techniques.

Biased Visuospatial Attention in Cervical Dystonia

OBJECTIVES

There is increasing evidence of non-motor, sensory symptoms, mainly involving the spatial domain, in cervical dystonia (CD). These manifestations are likely driven by dysfunctional overactivity of the parietal cortex during the execution of a sensory task. Few studies also suggest the possibility that visuospatial attention might be specifically affected in patients with CD. Therefore, we asked whether non-motor manifestations in CD might also comprise impairment of higher level visuospatial processing.

METHODS

To this end, we investigated visuospatial attention in 23 CD patients and 12 matched healthy controls (for age, gender, education, and ocular dominance). The patients were identified according to the dystonia pattern type (laterocollis vs. torticollis). Overall, participants were right-handers, and the majority of them was right-eye dominant. Visuospatial attention was assessed using a line bisection task. Participants were asked to bisect horizontal lines, using their right or left hand.

RESULTS

Participants bisected more to the left of true center when using their left hand to perform the task than when using their right hand. However, overall, torticollis patients produced a significantly greater leftward deviation than controls.

CONCLUSIONS

These data are consistent with preliminary findings suggesting the presence of biased spatial attention in patients with idiopathic cervical dystonia. The presence of an attentional bias in patients with torticollis seem to indicate that alterations of attentional circuits might be implicated in the pathophysiology of this type of CD. (JINS, 2018, 24, 23-32).

Evolving concepts in the pathogenesis of dystonia

INTRODUCTION

The dystonias are a group of disorders defined by over-contraction of muscles leading to abnormal movements and postures. In recent years, enormous advances have been made in elucidating the neurobiological mechanisms responsible for many types of dystonia.

METHODS

A literature review was conducted focusing on evolving concepts in dystonia genetics, anatomy and physiology.

RESULTS

The list of genes related to dystonia has grown from a relatively small number to more than 100. Concepts regarding the neuroanatomical basis for dystonia have evolved from a relatively narrow focus on dysfunction of the basal ganglia to a broader motor network model in which the basal ganglia, cerebellum, cerebral cortex, and other brain regions play a key role. Physiologically, our understanding of the core abnormalities has matured; and numerous changes in neural signaling have been revealed in the basal ganglia, cerebellum and cortex.

CONCLUSION

Although the dystonias share certain clinical aspects such as over-contraction of muscles leading to abnormal movements and postures, they actually comprise a very clinically and etiologically heterogeneous group of disorders. Understanding their neurobiological basis is important for devising rational therapies appropriately targeted for specific subgroups of patients.

Altered functional connectivity in blepharospasm/orofacial dystonia

INTRODUCTION

Blepharospasm is characterized by involuntary eyelid spasms. It can be associated with perioral dystonia (Meige's syndrome or orofacial dystonia). We aimed at studying resting-state functional brain connectivity in these patients and its potential modulation by therapeutic botulinum toxin injections.

METHODS

We performed resting-state functional MRI and a region of interest-based analysis of functional connectivity in 13 patients with blepharospasm/Meige's syndrome in comparison to 13 healthy controls. Patients were studied before and 4 weeks after botulinum toxin treatment. Simultaneous facial electromyography was applied to control for involuntary facial movements.

RESULTS

Before botulinum toxin treatment, patients showed reduced functional connectivity between caudate and primary sensorimotor, somatosensory association and visual cortices as well as between putamen and parietal association cortex. Cerebellar areas displayed decreased functional connectivity to somatosensory and visual association cortices. On the cortical level, connectivity was reduced between the cingulate cortex and the primary sensorimotor/premotor and parietal association cortex, between premotor areas and the primary somatosensory cortices, and between the postcentral gyrus and temporoparietal, secondary somatosensory, cingular, and cerebellar regions. Botulinum toxin treatment modulated functional connectivity, especially between cerebellum and visual cortices.

CONCLUSIONS

Patients with blepharospasm/Meige's syndrome show altered functional connectivity at rest in widespread brain regions including basal ganglia, cerebellar, primary/secondary sensorimotor, and visual areas. Functionally, this may reflect a predisposition for defective movement inhibition and sensorimotor integration. Botulinum toxin treatment could modulate brain connectivity in blepharospasm by altering visual and sensory input.

Clinical and Phenomenological Characteristics of Patients with Task-Specific Lingual Dystonia: Possible Association with Occupation

BACKGROUND

Lingual dystonia is a subtype of oromandibular dystonia, which is a movement disorder characterized by involuntary sustained or intermittent contraction of the masticatory and/or tongue muscles. Lingual dystonia interferes with important daily activities, such as speaking, chewing, and swallowing, resulting in vocational and social disability.

OBJECTIVE

The aim of this study was to investigate a possible relationship between occupation and the development of lingual dystonia.

METHODS

Phenomenological and clinical characteristics of 95 patients [53 females (55.8%) and 42 males (44.2%), mean age 48.0 years] with task-specific, speech-induced lingual dystonia were analyzed. Structured interviews were carried out to obtain information regarding primary occupation, including overtime work and stress during work. The factors that might have influenced the development of lingual dystonia were estimated using multivariate logistic regression analysis of the 95 patients with lingual dystonia and 95 controls [68 females (71.6%) and 27 males (28.4%), mean age 47.2 years] with temporomandibular disorders.

RESULTS

Overall, 84.2% of the patients had regular occupations; 73.8% of the patients with regular occupations reported working overtime more than twice a week, and 63.8% of them experienced stress at the workplace. Furthermore, 82.1% of the patients had engaged in occupations that required them to talk to customers or other people under stressful situations over prolonged periods of time for many years (mean: 15.6 years). The most common occupation was sales representative (17.9%), followed by telephone operator (13.7%), customer service representative (10.5%), health care worker (9.5%), waiter or waitress (5.3%), receptionist (5.3%), and cashier (5.3%). Twenty-nine patients (30.5%) had tardive lingual dystonia. Logistic regression analyses revealed that frequent requirements for professional speaking (p = 0.011, odds ratio: 5.66), high stress during work (p = 0.043, odds ratio: 5.4), and neuroleptic use (p = 0.032, odds ratio: 2.52) were significant contributors to the manifestation of lingual dystonia.

CONCLUSION

Professions in which conversations in stressful situations are unavoidable may trigger lingual dystonia. Therefore, speech-induced lingual dystonia can be regarded as occupational dystonia in certain cases.

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.

Temporal Discrimination: Mechanisms and Relevance to Adult-Onset Dystonia

Temporal discrimination is the ability to determine that two sequential sensory stimuli are separated in time. For any individual, the temporal discrimination threshold (TDT) is the minimum interval at which paired sequential stimuli are perceived as being asynchronous; this can be assessed, with high test–retest and inter-rater reliability, using a simple psychophysical test. Temporal discrimination is disordered in a number of basal ganglia diseases including adult-onset dystonia, of which the two most common phenotypes are cervical dystonia and blepharospasm. The causes of adult-onset focal dystonia are unknown; genetic, epigenetic, and environmental factors are relevant. Abnormal TDTs in adult-onset dystonia are associated with structural and neurophysiological changes considered to reflect defective inhibitory interneuronal processing within a network which includes the superior colliculus, basal ganglia, and primary somatosensory cortex. It is hypothesized that abnormal temporal discrimination is a mediational endophenotype and, when present in unaffected relatives of patients with adult-onset dystonia, indicates non-manifesting gene carriage. Using the mediational endophenotype concept, etiological factors in adult-onset dystonia may be examined including (i) the role of environmental exposures in disease penetrance and expression; (ii) sexual dimorphism in sex ratios at age of onset; (iii) the pathogenesis of non-motor symptoms of adult-onset dystonia; and (iv) subcortical mechanisms in disease pathogenesis.

The influence of occlusal stabilization appliances on cervical dystonia symptoms

Objectives

The aim of this study was to assess the therapeutic efficiency of the occlusal stabilization appliance (OSA) in patients with cervical dystonia (CD).

Methods

The study included 11 patients aged between 29 and 80 years, 7 women and 4 men, diagnosed with primary CD. The patients underwent an extra- and intra-oral clinical examination, followed by para-clinical examinations, necessary for the specifications of the OSA. The following data were recorded: demographic parameters, CD duration, management of the disease, dental impression, recording of the centric relationship, recording of the position of the upper jaw with the facial bow. A standardized OSA was manufactured in a private dental laboratory. Patients received instructions for wearing the OSA for 24 hours. Patients filled a questionnaire designed by us, which evaluated the effects of wearing the OSA over a 24-hours period on the symptoms of CD: muscles contraction, pain, discomfort while walking, sleep quality, tremor. The patients kept the dental appliances, and after three months they completed the questionnaire one more time.

Results

The OSA was applied on the lower arch in 3 (27.3%) patients and on the upper arch in 8 (72.7%) patients. The OSA wearing time for the first 24 h was on average 19.2±6 hours. Total relaxation of dystonic muscles was reported by 9 (81.8%) patients, while 2 (18.2%) patients related partial muscle relaxation. Seven (63.6%) patients reported a pain decrease. Increased comfort while walking was observed by 8 (72.7%) patients. Two (18.2%) patients described an increase of sleep quality. In two (18.2%) patients the tremor disappeared. All patients reported difficulties while eating and removed the OSA during meals. Patients who wore the OSA for more hours, experienced a pain decrease (p=0.08), an increase in sleep quality (p=0.1), the disappearance of the tremor (p=0.1). After three months, only seven patients continued to use the OSA. More patients described a pain decrease after three months (5 (71.4%) vs. 4 (57.1%); p=0.5), relaxation of dystonic muscles (7 (100%) vs. 6 (85.7%); p=0.3).

Conclusions

The use of OSA might be beneficial in CD patients, as it reduced the dystonic symptoms, pain severity and improved the quality of sleep.

Rethinking status dystonicus

Status dystonicus is a movement disorder emergency that has been a source of controversy in terms of terminology, phenomenology, and management since it was first described in 1982. Here we argue that the current use of the term status dystonicus falls well short of the precision needed for either clinical or academic use. We performed a critical review on this topic, describing possible pathophysiological mechanisms and areas of uncertainties. This review also addresses the problems derived by the extreme clinical heterogeneity of this condition, as the lack of an objective criterion useful for the definition, or the fact that status dystonicus may present not only in the context of a known dystonic syndrome. We propose a new possible definition that includes not only dystonia but also other hyperkinetic movements in the wide range of movement disorders that can be seen during an episode. The new definition keeps the term status dystonicus and highlights the fact that this is a medical emergency based on the impairment of bulbar and/or respiratory function requiring hospital admission as the principal feature. Furthermore, the new definition should not consider as necessary unspecific features as patient's condition at baseline, the distribution of dystonia, occurrence of systemic symptoms such as fever or laboratory findings. We hope that this proposal will stimulate the debate on this subject among our peers, further developing a clinical and pathophysiological understanding of status dystonicus. © 2017 International Parkinson and Movement Disorder Society.

Does the Somatosensory Temporal Discrimination Threshold Change over Time in Focal Dystonia?

Background

The somatosensory temporal discrimination threshold (STDT) is defined as the shortest interval at which an individual recognizes two stimuli as asynchronous. Some evidence suggests that STDT depends on cortical inhibitory interneurons in the basal ganglia and in primary somatosensory cortex. Several studies have reported that the STDT in patients with dystonia is abnormal. No longitudinal studies have yet investigated whether STDT values in different forms of focal dystonia change during the course of the disease.

Methods

We designed a follow-up study on 25 patients with dystonia (15 with blepharospasm and 10 with cervical dystonia) who were tested twice: upon enrolment and 8 years later. STDT values from dystonic patients at the baseline were also compared with those from a group of 30 age-matched healthy subjects.

Results

Our findings show that the abnormally high STDT values observed in patients with focal dystonia remained unchanged at the 8-year follow-up assessment whereas disease severity worsened.

Conclusions

Our observation that STDT abnormalities in dystonia remain unmodified during the course of the disease suggests that the altered activity of inhibitory interneurons—either at cortical or at subcortical level—responsible for the increased STDT does not deteriorate as the disease progresses.

Sensory Alterations in Patients with Isolated Idiopathic Dystonia: An Exploratory Quantitative Sensory Testing Analysis

Abnormalities in the somatosensory system are increasingly being recognized in patients with dystonia. The aim of this study was to investigate whether sensory abnormalities are confined to the dystonic body segments or whether there is a wider involvement in patients with idiopathic dystonia. For this purpose, we recruited 20 patients, 8 had generalized, 5 had segmental dystonia with upper extremity involvement, and 7 had cervical dystonia. In total, there were 13 patients with upper extremity involvement. We used Quantitative Sensory Testing (QST) at the back of the hand in all patients and at the shoulder in patients with cervical dystonia. The main finding on the hand QST was impaired cold detection threshold (CDT), dynamic mechanical allodynia (DMA), and thermal sensory limen (TSL). The alterations were present on both hands, but more pronounced on the side more affected with dystonia. Patients with cervical dystonia showed a reduced CDT and hot detection threshold (HDT), enhanced TSL and DMA at the back of the hand, whereas the shoulder QST only revealed increased cold pain threshold and DMA. In summary, QST clearly shows distinct sensory abnormalities in patients with idiopathic dystonia, which may also manifest in body regions without evident dystonia. Further studies with larger groups of dystonia patients are needed to prove the consistency of these findings.

Network-specific resting-state connectivity changes in the premotor-parietal axis in writer's cramp

Background

Writer's cramp is a task-specific dystonia impairing writing and sometimes other fine motor tasks. Neuroimaging studies using manifold designs have shown varying results regarding the nature of changes in the disease.

Objective

To clarify and extend the knowledge of underlying changes by investigating functional connectivity (FC) in intrinsic connectivity networks with putative sensorimotor function at rest in an increased number of study subjects.

Methods

Resting-state functional magnetic resonance imaging with independent component analysis was performed in 26/27 writer's cramp patients/healthy controls, and FC within and between resting state networks with putative sensorimotor function was compared. Additionally, voxel-based morphometry was carried out on the subjects' structural images.

Results

Patients displayed increased left- and reduced right-hemispheric primary sensorimotor FC in the premotor-parietal network. Mostly bilaterally altered dorsal/ventral premotor FC, as well as altered parietal FC were observed within multiple sensorimotor networks and showed differing network-dependent directionality. Beyond within-network FC changes and reduced right cerebellar grey matter volume in the structural analysis, the positive between-network FC of the cerebellar network and the basal ganglia network was reduced.

Conclusions

Abnormal resting-state FC in multiple networks with putative sensorimotor function may act as basis of preexisting observations made during task-related neuroimaging. Further, altered connectivity between the cerebellar and basal ganglia network underlines the important role of these structures in the disease.

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Investigation of FC changes in various sensorimotor ICNs at rest in writer's cramp.

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We saw multiple, network-specific FC changes in primary/higher sensorimotor cortices.

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This may act as basis of the varying nature of sensorimotor changes during task-fMRI.

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Further, findings supporting disrupted cerebellar-basal ganglia interaction were made.

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An additional morphometric analysis demonstrated structural cerebellar abnormality.

Microstructural white matter abnormalities in patients with COL6A3 mutations (DYT27 dystonia)

INTRODUCTION

Recently, mutations in the collagen gene COL6A3 have been reported in patients with autosomal-recessive, isolated dystonia (DYT27). Zebrafish models of COL6A3 mutations showed deficits in axonal targeting mechanisms. Therefore, COL6A3 mutations have been considered to contribute to irregular sensorimotor circuit formation. To test this hypothesis, we examined structural abnormalities in cerebral fiber tracts of dystonia patients with COL6A3 mutations using diffusion tensor imaging.

METHODS

We performed a voxel-wise statistical analysis to compare fractional anisotropy within whole-brain white matter in four of the previously reported dystonia patients with COL6A3 mutations and 12 healthy controls. Region of interests-based probabilistic tractography was performed as a post-hoc-analysis.

RESULTS

Dystonia patients with COL6A3 mutations showed significantly decreased fractional anisotropy bilaterally in midbrain, pons, cerebellar peduncles, thalamus, internal capsule and in frontal and parietal subcortical regions compared to healthy controls. Tractography revealed a decreased fractional anisotropy in patients with COL6A3-associated dystonia between bilateral dentate nucleus and thalamus.

CONCLUSION

Diffusion tensor imaging demonstrates an altered white matter structure especially in various parts of the cerebello-thalamo-cortical network in dystonia patients with COL6A3 mutations. This suggests that COL6A3 mutations could contribute to abnormal circuit formation as potential basis of dystonia.