Altered striatal and pallidal connectivity in cervical dystonia

Botulinum Toxin: A Comprehensive Review of Its Molecular Architecture and Mechanistic Action

Botulinum toxin (BoNT), the most potent substance known to humans, likely evolved not to kill but to serve other biological purposes. While its use in cosmetic applications is well known, its medical utility has become increasingly significant due to the intricacies of its structure and function. The toxin's structural complexity enables it to target specific cellular processes with remarkable precision, making it an invaluable tool in both basic and applied biomedical research. BoNT's potency stems from its unique structural features, which include domains responsible for receptor recognition, membrane binding, internalization, and enzymatic cleavage. This division of labor within the toxin's structure allows it to specifically recognize and interact with synaptic proteins, leading to precise cleavage at targeted sites within neurons. The toxin's mechanism of action involves a multi-step process: recognition, binding, and catalysis, ultimately blocking neurotransmitter release by cleaving proteins like SNAP-25, VAMP, and syntaxin. This disruption in synaptic vesicle fusion causes paralysis, typically in peripheral neurons. However, emerging evidence suggests that BoNT also affects the central nervous system (CNS), influencing presynaptic functions and distant neuronal systems. The evolutionary history of BoNT reveals that its neurotoxic properties likely provided a selective advantage in certain ecological contexts. Interestingly, the very features that make BoNT a potent toxin also enable its therapeutic applications, offering precision in treating neurological disorders like dystonia, spasticity, and chronic pain. In this review, we highlight the toxin's structural, functional, and evolutionary aspects, explore its clinical uses, and identify key research gaps, such as BoNT's central effects and its long-term cellular impact. A clear understanding of these aspects could facilitate the representation of BoNT as a unique scientific paradigm for studying neuronal processes and developing targeted therapeutic strategies.

Moving on with (social) cognition in idiopathic cervical dystonia

OBJECTIVE

Cervical dystonia (CD) is a movement disorder characterized by involuntary muscle contractions causing sustained twisting movements and abnormal postures of the neck and head. Assumed affected neuronal regions are the cortico-striatal-thalamo-cortical circuits, which are also involved in cognitive functioning. Indeed, impairments in different cognitive domains have been found in CD patients. However, to date studies have only investigated a limited range of cognitive functions within the same sample. In particular, social cognition (SC) is often missing from study designs. Hence, we aimed to evaluate a broad range of cognitive functions including SC in CD patients.

METHOD

In the present study 20 idiopathic CD patients and 40 age-, gender-, and IQ-matched healthy controls (HCs) were assessed with tests for non-SC (verbal memory, psychomotor speed, and executive functions) as well as for SC (emotion recognition, Theory of Mind (ToM), and empathy).

RESULTS

CD patients scored on average significantly lower than HC on tests for non-SC, but did not show impairments on any of the tests for SC.

CONCLUSIONS

The current study showed impairments in non-SC in CD, but intact social cognitive functions. These results underline the importance of recognizing non-motor symptoms in idiopathic CD patients, but emphasize a focus on identifying strengths and weaknesses in cognitive functioning as these influence daily life activities.

Basis of movement control in dystonia and why botulinum toxin should influence it?

Dystonia is a network disorder involving multiple brain regions, such as the motor cortex, sensory cortex, basal ganglia, and cerebellum. Botulinum toxin (BoNT) is the first-line therapy for treating focal dystonia and is a potent molecule that blocks the release of acetylcholine at the peripheral neuromuscular junction. However, the clinical benefits of BoNT are not solely related to peripheral muscle relaxation or modulation of afferent input from the muscle spindle. An increasing body of evidence, albeit in smaller cohorts, has shown that BoNT leads to distant modulation of the pathological brain substrates implicated in dystonia. A single treatment session of BoNT has been observed to reduce excessive motor excitability and improve sensory processing. Furthermore, owing to plasticity effects that are induced by botulinum, neural reorganization of pathological networks occurs, presumably leading to defective motor programs of dystonia replaced with normal movement patterns. However, longitudinal studies investigating the effects of multiple treatment sessions in large, well-characterized homogenous cohorts of dystonia will provide further compelling evidence supporting central botulinum mechanisms.

Function and dysfunction of the dystonia network: an exploration of neural circuits that underlie the acquired and isolated dystonias

Dystonia is a highly prevalent movement disorder that can manifest at any time across the lifespan. An increasing number of investigations have tied this disorder to dysfunction of a broad "dystonia network" encompassing the cerebellum, thalamus, basal ganglia, and cortex. However, pinpointing how dysfunction of the various anatomic components of the network produces the wide variety of dystonia presentations across etiologies remains a difficult problem. In this review, a discussion of functional network findings in non-mendelian etiologies of dystonia is undertaken. Initially acquired etiologies of dystonia and how lesion location leads to alterations in network function are explored, first through an examination of cerebral palsy, in which early brain injury may lead to dystonic/dyskinetic forms of the movement disorder. The discussion of acquired etiologies then continues with an evaluation of the literature covering dystonia resulting from focal lesions followed by the isolated focal dystonias, both idiopathic and task dependent. Next, how the dystonia network responds to therapeutic interventions, from the "geste antagoniste" or "sensory trick" to botulinum toxin and deep brain stimulation, is covered with an eye towards finding similarities in network responses with effective treatment. Finally, an examination of how focal network disruptions in mouse models has informed our understanding of the circuits involved in dystonia is provided. Together, this article aims to offer a synthesis of the literature examining dystonia from the perspective of brain networks and it provides grounding for the perspective of dystonia as disorder of network function.

Social cognition deficits are associated with lower quality of life in cervical dystonia: A single centre study

Background and objectives

Patients with cervical dystonia (CD) demonstrate significant non-motor symptoms including sensory, psychiatric and cognitive features. It has been shown that the non-motor symptoms have a major influence on quality of life. Social cognition, particularly deficits in Theory of Mind (ToM), can affect the development of interpersonal relationships, understanding of social situations and can affect patient outcomes.We used the "Faux Pas" measure of social cognition to assess ToM in patients with CD and compared this with quality of life, disease severity and psychiatric symptoms.

Methods

Patients with adult-onset idiopathic isolated cervical dystonia were assessed using the "Faux Pas" questionnaire. Validated questionnaires were used to assess mood symptoms (BAI/BDI and HADS) and quality of life (CDIP-58). Disease-specific disability, motor severity and psychosocial symptoms were measured using TWSTRS2. Faux pas results were compared with published healthy control values.

Results

32 participants (19 female) were included with a mean age of 57.7 years. 20 participants met criteria for excess mood symptoms (anxiety and/or depression). Mean CDIP-58 was 31.9. There was no relationship between faux pas outcomes and motor severity. However, correlation analyses showed that participants who performed worse on the faux pas questionnaire had lower quality of life.

Conclusion

The non-motor symptoms, including social cognition, are often neglected. We have demonstrated that low quality of life in CD is associated with to abnormal social cognition. Clinicians should be mindful of these symptoms, particularly in patients reporting low treatment satisfaction.

Aberrant age-related alterations in spontaneous cortical activity in participants with cerebral palsy

Introduction

Cerebral Palsy (CP) is the most common neurodevelopmental motor disability, resulting in life-long sensory, perception and motor impairments. Moreover, these impairments appear to drastically worsen as the population with CP transitions from adolescents to adulthood, although the underlying neurophysiological mechanisms remain poorly understood.

Methods

We began to address this knowledge gap by utilizing magnetoencephalographic (MEG) brain imaging to study how the amplitude of spontaneous cortical activity (i.e., resting state) is altered during this transition period in a cohort of 38 individuals with spastic diplegic CP (Age range = 9.80-47.50 years, 20 females) and 67 neurotypical controls (NT) (Age range = 9.08-49.40 years, Females = 27). MEG data from a five-minute eyes closed resting-state paradigm were source imaged, and the power within the delta (2-4 Hz), theta (5-7 Hz), alpha (8-12 Hz), beta (15-29 Hz), and gamma (30-59 Hz) frequency bands were computed.

Results

For both groups, the delta and theta spontaneous power decreased in the bilateral temporoparietal and superior parietal regions with age, while alpha, beta, and gamma band spontaneous power increased in temporoparietal, frontoparietal and premotor regions with age. We also found a significant group x age interaction, such that participants with CP demonstrated significantly less age-related increases in the spontaneous beta activity in the bilateral sensorimotor cortices compared to NT controls.

Discussion

Overall, these results demonstrate that the spontaneous neural activity in individuals with CP has an altered trajectory when transitioning from adolescents to adulthood. We suggest that these differences in spontaneous cortical activity may play a critical role in the aberrant motor actions seen in this patient group, and may provide a neurophysiological marker for assessing the effectiveness of current treatment strategies that are directed at improving the mobility and sensorimotor impairments seen in individuals with CP.

Fixel-Based Analysis Reveals Whole-Brain White Matter Abnormalities in Cervical Dystonia

BACKGROUND

Cervical dystonia (CD) is a form of isolated focal dystonia typically associated to abnormal head, neck, and shoulder movements and postures. The complexity of the clinical presentation limits the investigation of its pathophysiological mechanisms, and the neural networks associated to specific motor manifestations are still the object of debate.

OBJECTIVES

We investigated the morphometric properties of white matter fibers in CD and explored the networks associated with motor symptoms, while regressing out nonmotor scores.

METHODS

Nineteen patients affected by CD and 21 healthy controls underwent diffusion-weighted magnetic resonance imaging. We performed fixel-based analysis, a novel method evaluating fiber orientation within specific fiber bundles, and compared fiber morphometric properties between groups. Moreover, we correlated fiber morphometry with the severity of motor symptoms in patients.

RESULTS

Compared to controls, patients exhibited decreased white matter fibers in the right striatum. Motor symptom severity negatively correlated with white matter fibers passing through inferior parietal areas and the head representation area of the motor cortex.

CONCLUSIONS

Abnormal white matter integrity at the basal ganglia level may affect several functional networks involved, for instance, in motor preparation and execution, visuomotor coordination, and multimodal integration. This may result in progressive maladaptive plasticity, culminating in overt symptoms of dystonia. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Interhemispheric parietal cortex connectivity reflects improvement in post-stroke spasticity due to treatment with botulinum toxin-A

In post-stroke spasticity (PSS), effective treatment with botulinum neurotoxin (BoNT) is associated with transient decrease in activation of the ipsilesional superior parietal lobule (SPL) and intraparietal sulcus (IPS). We hypothesized that this would be reflected in changes in resting-state functional connectivity (rsFC) of the SPL/IPS. Our aim was therefore to assess rsFC of the ipsilesional SPL/IPS in chronic stroke patients with hemiparesis both with and without PSS and to explore the relationship between SPL/IPS rsFC and PSS severity. To this end, fourteen chronic stroke patients with upper limb weakness and PSS (the PSS group) and 8 patients with comparable weakness but no PSS (the control group) underwent clinical evaluation and 3 fMRI examinations, at baseline (W0) and 4 and 11 weeks after BoNT (W4 and W11, respectively). Seed-based rsFC of the atlas-based SPL and IPS was evaluated using a group×time interaction analysis and a correlation analysis with PSS severity (modified Ashworth scale), integrity of the ipsilesional somatosensory afferent pathway (evoked potential N20 latency), and age. In the PSS group, transient improvement in PSS was associated with increase in rsFC between the ipsilesional IPS and the contralesional SPL at W4. The interhemispheric connectivity was negatively correlated with PSS severity at baseline and with PSS improvement at W4. We propose adaptation of the internal forward model as the putative underlying mechanism and discuss its possible association with increased limb use, diminished spastic dystonia, or improved motor performance, as well as its potential contribution to the clinical effects of BoNT.

The Collicular-Pulvinar-Amygdala Axis and Adult-Onset Idiopathic Focal Dystonias

Adult-onset idiopathic focal dystonias (AOIFD) are the most common type of dystonia. It has varied expression including multiple motor (depending on body part affected) and non-motor symptoms (psychiatric, cognitive and sensory). The motor symptoms are usually the main reason for presentation and are most often treated with botulinum toxin. However, non-motor symptoms are the main predictors of quality of life and should be addressed appropriately, as well as treating the motor disorder. Rather than considering AOIFD as a movement disorder, a syndromic approach should be taken, one that accommodates all the symptoms. Dysfunction of the collicular-pulvinar-amygdala axis, with the superior colliculus as a central node, can explain the diverse expression of this syndrome.

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.

Short- and Long-term Central Action of Botulinum Neurotoxin Treatment in Laryngeal Dystonia

BACKGROUND AND OBJECTIVES

Laryngeal dystonia (LD) is isolated task-specific focal dystonia selectively impairing speech production. The first choice of LD treatment is botulinum neurotoxin (BoNT) injections into the affected laryngeal muscles. However, whether BoNT has a lasting therapeutic effect on disorder pathophysiology is unknown. We investigated short-term and long-term effects of BoNT treatment on brain function in patients with LD.

METHODS

A total of 161 participants were included in the functional MRI study. Statistical analyses examined central BoNT effects in patients with LD who were stratified based on the effectiveness and duration of treatment.

RESULTS

Patients with LD who were treated and benefited from BoNT injections had reduced activity in the left precuneus compared with BoNT-naive and treatment nonbenefiting patients. In addition, BoNT-treated patients with adductor LD had decreased activity in the right thalamus, whereas BoNT-treated abductor patients with LD had reduced activity in the left inferior frontal cortex. No statistically significant differences in brain activity were found between patients with shorter (1-5 years) and longer (13-28 years) treatment durations. However, patients with intermediate treatment duration of 6-12 years showed reduced activity in the right cerebellum compared with patients with both shorter and longer treatment durations and reduced activity in the right prefrontal cortex compared with patients with shorter treatment duration.

DISCUSSION

Our findings suggest that the left precuneus is the site of short-term BoNT central action in patients with LD, whereas the prefrontal-cerebellar axis is engaged in the BoNT response in patients with intermediate treatment duration of 6-12 years. Involvement of these structures points to indirect action of BoNT treatment on the dystonic sensorimotor network through modulation of motor sequence planning and coordination.

Focal Dystonia: Functional Connectivity Changes in Cerebellar-Basal Ganglia-Cortical Circuit and Preserved Global Functional Architecture

BACKGROUND AND OBJECTIVES

Neuroimaging studies suggest that changes in the cerebellar-basal ganglia-thalamo-cortical sensorimotor circuit are a pathophysiologic feature of focal dystonia. However, it remains unclear whether structural and functional alterations vary in different forms of focal dystonia. Thus, in patients with cervical dystonia (CD) and blepharospasm (BSP), we aimed to investigate structural damage and resting-state functional alterations using whole-brain and seed-based approaches to test the hypothesis of possible functional connectivity (FC) alterations in specific circuits, including the cerebellum, basal ganglia, and cerebral cortex, in the context of preserved global FC.

METHODS

In this cross-sectional study, we applied a multimodal 3T MRI protocol, including 3-dimensional T1-weighted images to extract brain volumes and cortical thickness, and fMRI at rest to study FC of the dentate nucleus and globus pallidus with a seed-based approach and whole-brain FC with a graph theory approach.

RESULTS

This study included 33 patients (17 with CD [14 female] age 55.7 ± 10.1 years, 16 with BSP [11 female] age 62.9 ± 8.8 years) and 16 age- and sex-matched healthy controls (HC) (7 female) 54.3 ± 14.3 years if age. Patients with CD, patients with BSP, and HC did not differ in terms of cortical or subcortical volume. Compared to HC, both patients with CD and patients with BSP had a loss of dentate FC anticorrelation with the sensorimotor cortex. Patients with CD and those with BSP showed increased pallidal FC with the cerebellum, supplementary motor area, and prefrontal cortices with respect to HC. Increased dentate FC with the cerebellum and thalamus and increased pallidal FC with the bilateral thalamus, sensorimotor and temporo-occipital cortices, and right putamen were present in patients with CD but not patients with BSP compared to HC. Measures of global FC, that is, global efficiency and small-worldness, did not differ between patients and HC.

DISCUSSION

Both patients with CD and those with BSP showed altered dentate and pallidal FC with regions belonging to the integrated cerebellar-basal ganglia-thalamo-cortical sensorimotor circuit, supporting the concept that focal dystonia is a disorder of specific networks and not merely a result of basal ganglia alterations in the context of a preserved whole-brain functional architecture. Differences in functional interplay among specific brain structures may distinguish CD and BSP.

Changes in pallidal neural activity following long-term symptom improvement from botulinum toxin treatment in DYT6 dystonia: a case report

Background

The globus pallidus internus is the main target for the treatment of dystonia by deep brain stimulation. Unfortunately, for some genetic etiologies, the therapeutic outcome of dystonia is less predictable. In particular, therapeutic outcomes for deep brain stimulation in craniocervical and orolaryngeal dystonia in DYT6-positive patients are poor. Little is known about the neurophysiology of the globus pallidus internus in DYT6-positive dystonia, and how symptomatic treatment affects the neural activity of this region.

Case presentation

We present here the case of a 55-year-old Caucasian female DYT6-dystonic patient with blepharospasm, spasmodic dysphonia, and oromandibular dystonia where single-unit and local field potential activity was recorded from the globus pallidus internus during two deep brain stimulation revision surgeries 4 years apart with no symptomatic improvement. Botulinum toxin injections consistently improved dysphonia, while some of the other symptoms were only inconsistently or marginally improved. Neural activity in the globus pallidus internus during both revision surgeries were compared with previously published results from an idiopathic dystonic cohort. Single-cell firing characteristics and local field potential from the first revision surgery showed no differences with our control group. However, during the second revision surgery, the mean firing rate of single units and local field potential power in the gamma range were lower than those present during the first revision surgery or the control group.

Conclusions

Symptoms related to facial movements were greatly improved by botulinum toxin treatment between revision surgeries, which coincided with lower discharge rate and changes in gamma local field oscillations.

Abnormal Network Homogeneity in the Right Superior Medial Frontal Gyrus in Cervical Dystonia

Background: Increasing evidence from modern neuroimaging has confirmed that cervical dystonia (CD) is caused by network abnormalities. Specific brain networks are known to be crucial in patients suffering from CD. However, changes in network homogeneity (NH) in CD patients have not been characterized. Therefore, the purpose of this study was to investigate the NH of patients with CD.

Methods: An automated NH method was used to analyze resting-state functional magnetic resonance (fMRI) data from 19 patients with CD and 21 gender- and age-matched healthy controls (HC). Correlation analysis were conducted between NH, illness duration and symptom severity measured by the Tsui scale.

Results: Compared with the HC group, CD patients showed a lower NH in the right superior medial frontal gyrus. No significant correlations were found between abnormal NH values and illness duration or symptom severity.

Conclusion: Our findings suggest the existence of abnormal NH in the default mode network (DMN) of CD patients, and thereby highlight the importance of the DMN in the pathophysiology of CD.

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

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

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

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

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

Botulinum Neurotoxins in Central Nervous System: An Overview from Animal Models to Human Therapy

Botulinum neurotoxins (BoNTs) are potent inhibitors of synaptic vesicle fusion and transmitter release. The natural target of BoNTs is the peripheral neuromuscular junction (NMJ) where, by blocking the release of acetylcholine (ACh), they functionally denervate muscles and alter muscle tone. This leads them to be an excellent drug for the therapy of muscle hyperactivity disorders, such as dystonia, spasticity, and many other movement disorders. BoNTs are also effective in inhibiting both the release of ACh at sites other than NMJ and the release of neurotransmitters other than ACh. Furthermore, much evidence shows that BoNTs can act not only on the peripheral nervous system (PNS), but also on the central nervous system (CNS). Under this view, central changes may result either from sensory input from the PNS, from retrograde transport of BoNTs, or from direct injection of BoNTs into the CNS. The aim of this review is to give an update on available data, both from animal models or human studies, which suggest or confirm central alterations induced by peripheral or central BoNTs treatment. The data will be discussed with particular attention to the possible therapeutic applications to pathological conditions and degenerative diseases of the CNS.

Pallido-putaminal connectivity predicts outcomes of deep brain stimulation for cervical dystonia

Cervical dystonia is a non-degenerative movement disorder characterized by dysfunction of both motor and sensory cortico-basal ganglia networks. Deep brain stimulation targeted to the internal pallidum is an established treatment, but its specific mechanisms remain elusive, and response to therapy is highly variable. Modulation of key dysfunctional networks via axonal connections is likely important.

Fifteen patients underwent preoperative diffusion-MRI acquisitions and then progressed to bilateral deep brain stimulation targeting the posterior internal pallidum. Severity of disease was assessed preoperatively and later at follow-up. Scans were used to generate tractography-derived connectivity estimates between the bilateral regions of stimulation and relevant structures.

Connectivity to the putamen correlated with clinical improvement, and a series of cortical connectivity-based putaminal parcellations identified the primary motor putamen as the key node (r = 0.70, P = 0.004). A regression model with this connectivity and electrode coordinates explained 68% of the variance in outcomes (r = 0.83, P = 0.001), with both as significant explanatory variables.

We conclude that modulation of the primary motor putamen–posterior internal pallidum limb of the cortico-basal ganglia loop is characteristic of successful deep brain stimulation treatment of cervical dystonia. Preoperative diffusion imaging contains additional information that predicts outcomes, implying utility for patient selection and/or individualized targeting.

Hyper- and hypo-connectivity in sensorimotor network of drug-naïve patients with cervical dystonia

BACKGROUND

Cervical dystonia (CD) is the most common form of focal dystonia with involuntary movements and postures of the head. The pathogenesis and neural mechanisms underlying CD have not been fully elucidated.

METHODS

Twenty-seven newly drug-naïve patients with CD and 21 healthy controls (HCs) were recruited with clinical assessment and resting-state functional magnetic resonance imaging (rs-fMRI) scanning. Severity of CD was measured by Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) and Tsui scores. Whole-brain voxel-wise intrinsic connectivity (IC) and seed-based functional connectivity (FC) analyses were performed for detection of changes in the CD group relative to HCs, controlling for age, gender, and global time series correlation, followed by correlation analyses of IC, seed-based FC and clinically relevant features, respectively.

RESULTS

In comparison with HCs, CD patients showed significantly increased IC measurement in the anterior part of the left supramarginal gyrus and extended to the inferior left postcentral gyrus (AL-SMG/IL-PCG). With this cluster as a seed, decreased FC was found in the right precentral and postcentral gyrus. Moreover, the regional IC value in the AL-SMG/IL-PCG was significantly positively correlated with TWSTRS-1 (severity) score, and significantly negatively correlated with the associated seed-based FC strength.

CONCLUSIONS

Our results showed signs of both hyper- and hypo-connectivity in bilateral regions of the sensorimotor network related to CD. The imbalance of functional connectivity (both hyper- and hypo-) may hint both overloading and disrupted somatosensory or sensorimotor integration dysfunction within the sensorimotor network underlying the pathophysiology of CD, thus providing a network target for future therapies.

Correlates of deep brain stimulation consensus conference decision to treat primary dystonia

BACKGROUND

Deep brain stimulation (DBS) is an effective treatment for motor disturbance in people with primary dystonia (PWD). Numerous factors are considered by an interdisciplinary consensus conference before deciding candidacy for DBS surgery (e.g., demographic, medical, cognitive, and behavioral factors). However, little is known about which of these factors are associated with PWD DBS surgery consensus conference decisions.

OBJECTIVE

Our goal was to examine whether pre-operative demographic, medical, and cognitive/behavioral variables are associated DBS consensus conference decisions in patients with dystonia.

METHODS

Thirty-two PWD completed comprehensive presurgery workup included neurological and neuropsychological exams, and neuroimaging in consideration for DBS surgery. An interdisciplinary conference committee either recommended or did not recommend DBS surgery based upon these data. Demographic and medical data (e.g., dystonia disease characteristics, medical comorbidities, medications) were also collected. We also examined impact from cardiovascular disease factors, using a Revised Cardiac Risk Index. PWD were grouped based on DBS conference decision (eligible: n = 21, ineligible: n = 11) and compared across demographic, medical, and cognitive/behavioral variables.

RESULTS

Across clinical variables, PWD who were deemed ineligible for DBS surgery had a higher Revised Cardiac Risk Index. PWD who were classified as ineligible displayed lower global cognitive functioning, working memory, phonemic fluency, memory retrieval, and cognitive flexibility.

CONCLUSIONS

Consensus decision making regarding DBS surgery eligibility involves a multifactorial process. We found that deficits in executive functioning were associated with the DBS consensus committee decision. We also observed elevated cardiac risk among these individuals, likely reflecting the relation between vascular health and cognition. Implications, and clinical and scientific applications of these findings are discussed.

Botulinum toxin injection changes resting state cerebellar connectivity in cervical dystonia

In cervical dystonia, functional MRI (fMRI) evidence indicates changes in several resting state networks, which revert in part following the botulinum neurotoxin A (BoNT) therapy. Recently, the involvement of the cerebellum in dystonia has gained attention. The aim of our study was to compare connectivity between cerebellar subdivisions and the rest of the brain before and after BoNT treatment. Seventeen patients with cervical dystonia indicated for treatment with BoNT were enrolled (14 female, aged 50.2 ± 8.5 years, range 38-63 years). Clinical and fMRI examinations were carried out before and 4 weeks after BoNT injection. Clinical severity was evaluated using TWSTRS. Functional MRI data were acquired on a 1.5 T scanner during 8 min rest. Seed-based functional connectivity analysis was performed using data extracted from atlas-defined cerebellar areas in both datasets. Clinical scores demonstrated satisfactory BoNT effect. After treatment, connectivity decreased between the vermis lobule VIIIa and the left dorsal mesial frontal cortex. Positive correlations between the connectivity differences and the clinical improvement were detected for the right lobule VI, right crus II, vermis VIIIb and the right lobule IX. Our data provide evidence for modulation of cerebello-cortical connectivity resulting from successful treatment by botulinum neurotoxin.

The Central Effects of Botulinum Toxin in Dystonia and Spasticity

In dystonic and spastic movement disorders, however different in their pathophysiological mechanisms, a similar impairment of sensorimotor control with special emphasis on afferentation is assumed. Peripheral intervention on afferent inputs evokes plastic changes within the central sensorimotor system. Intramuscular application of botulinum toxin type A (BoNT-A) is a standard evidence-based treatment for both conditions. Apart from its peripheral action on muscle spindles, a growing body of evidence suggests that BoNT-A effects could also be mediated by changes at the central level including cerebral cortex. We review recent studies employing electrophysiology and neuroimaging to investigate how intramuscular application of BoNT-A influences cortical reorganization. Based on such data, BoNT-A becomes gradually accepted as a promising tool to correct the maladaptive plastic changes within the sensorimotor cortex. In summary, electrophysiology and especially neuroimaging studies with BoNT-A further our understanding of pathophysiology underlying dystonic and spastic movement disorders and may consequently help develop novel treatment strategies based on neural plasticity.

Contemporary clinical neurophysiology applications in dystonia

The complex phenomenological understanding of dystonia has transcended from the clinics to genetics, imaging and neurophysiology. One way in which electrophysiology will impact into the clinics are cases wherein a dystonic clinical presentation may not be typical or a "forme fruste" of the disorder. Indeed, the physiological imprints of dystonia are present regardless of its clinical manifestation. Underpinnings in the understanding of dystonia span from the peripheral, segmental and suprasegmental levels to the cortex, and various electrophysiological tests have been applied in the course of time to elucidate the origin of dystonia pathophysiology. While loss of inhibition remains to be the key finding in this regard, intricacies and variabilities exist, thus leading to a notion that perhaps dystonia should best be gleaned as network disorder. Interestingly, the complex process has now spanned towards the understanding in terms of networks related to the cerebellar circuitry and the neuroplasticity. What is evolving towards a better and cohesive view will be neurophysiology attributes combined with structural dynamic imaging. Such a sound approach will significantly lead to better therapeutic modalities in the future.

Functional connectivity of the motor system in dystonia due to PKAN

Purpose

To demonstrate deviations of functional connectivity within the motor system in dystonic patients suffering from Pantothenate Kinase Associated Neurodegeneration, a genetic and metabolic disease, which is characterized by a primary lesion in the globus pallidus.

Material and methods

Functional Magnetic Resonance Imaging data were measured during resting state in 12 patients suffering from a confirmed mutation of the PANK2 gene. In this region-of-interest based analysis, data were evaluated in respect to correlation of signal time course between basal ganglia, motor-related cortical regions and cerebellum, were related to clinical data and were compared to a control group of 20 healthy volunteers.

Results

During resting state, correlation coefficients within the motor system were significantly lower in patients than in controls (0.025 vs. 0.133, p < 0.05). Network analysis by Network Based Statistics showed that these differences mainly affected the connectivity between a sub-network consisting of the basal ganglia and another one, the motor system-related cortical areas (p < 0.05). 6 out of 12 connections, which correlated significantly to duration of disease, were connections between both sub-networks.

Conclusion

The finding of a reduced functional connectivity within the motor network, between the basal ganglia and cortical motor-related areas, fits well into the concept of a general functional disturbance of the motor system in PKAN.

•

For the first time, connectivity of fMRI signal during resting state of motor-related areas was measured in PKAN dystonia.

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NBS analysis of networks showed two sub-networks, one between basal ganglia and another one between cortical areas.

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Connectivity between both sub-networks was reduced in patients and correlated significantly to duration of disease.

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Findings support the view of widespread network abnormalities in PKAN dystonia, not just confined to the globus pallidus.

Abnormal regional homogeneity and its relationship with symptom severity in cervical dystonia: a rest state fMRI study

BACKGROUND

Although several brain networks play important roles in cervical dystonia (CD) patients, regional homogeneity (ReHo) changes in CD patients have not been clarified. We investigated to explore ReHo in CD patients at rest and analyzed its correlations with symptom severity as measured by Tsui scale.

METHODS

A total of 19 CD patients and 21 gender-, age-, and education-matched healthy controls underwent fMRI scans at rest state. Data were analyzed by ReHo method.

RESULTS

Patients showed increased ReHo in the right cerebellum crus I and decreased ReHo in the right superior medial prefrontal cortex (MPFC). Moreover, the right precentral gyrus, right insula, and bilateral middle cingulate gyrus also showed increased ReHo values. A significantly positive correlation was observed between ReHo value in the right cerebellum crus I and symptom severity (p < 0.05).

CONCLUSIONS

Our investigation suggested abnormal ReHo existed in brain regions of the "pain matrix" and salience network (the right insula and bilateral middle cingulate gyrus), the motor network (the right precentral gyrus), the cerebellum and MPFC and further highlighted the significance of these networks in the pathology of CD.

Brain connectivity abnormalities and treatment-induced restorations in patients with cervical dystonia

BACKGROUND

The relationship between brain abnormalities and phenotypic characteristics in cervical dystonia (CD) patients has not been fully established, and little is known about the neuroplastic changes induced by botulinum toxin type A (BoNT-A) treatment.

METHODS

Ninety-two CD patients presenting with rotational torticollis and 45 healthy controls from our database were retrospectively screened. After clinical assessment, the 92 patients underwent baseline magnetic resonance imaging (MRI) followed by a single-dose injection of BoNT-A. Four weeks later, 76 out of the 92 patients were re-evaluated with the Tsui scale for dystonia severity, and 33 out of 76 patients completed post-treatment MRI scanning. Data-driven global brain connectivity and regional homogeneity in tandem with seed-based connectivity analyses were used to examine the functional abnormalities in CD and longitudinal circuit alterations that scaled with clinical response to BoNT-A. Multiple regression models were employed for the prediction analysis of treatment efficacy.

RESULTS

Cervical dystonia patients exhibited elevated baseline connectivity of the right postcentral gyrus with the left dorsomedial prefrontal cortex and right caudate nucleus, which was associated with their symptom severity. BoNT-A reduced excessive functional connectivity between the sensorimotor cortex and right superior frontal gyrus, which was significantly correlated with changes in Tsui score. Moreover, pre-treatment regional homogeneity of the left middle frontal gyrus was linearly related to varied response to treatment.

CONCLUSIONS

Our findings unravel dissociable connectivity of the sensorimotor cortex underlying the pathology of CD and central effects of BoNT-A therapy. Furthermore, baseline regional homogeneity with the left middle frontal gyrus may represent a potential evidence-based marker of patient stratification for BoNT-A therapy in CD.

Regional, not global, functional connectivity contributes to isolated focal dystonia

OBJECTIVE

To test the hypothesis that there is shared regional or global functional connectivity dysfunction in a large cohort of patients with isolated focal dystonia affecting different body regions compared to control participants. In this case-control study, we obtained resting-state MRI scans (three or four 7.3-minute runs) with eyes closed in participants with focal dystonia (cranial [17], cervical [13], laryngeal [18], or limb [10]) and age- and sex-matched controls.

METHODS

Rigorous preprocessing for all analyses was performed to minimize effect of head motion during scan acquisition (dystonia n = 58, control n = 47 analyzed). We assessed regional functional connectivity by computing a seed-correlation map between putamen, pallidum, and sensorimotor cortex and all brain voxels. We assessed significant group differences on a cluster-wise basis. In a separate analysis, we applied 300 seed regions across the cortex, cerebellum, basal ganglia, and thalamus to comprehensively sample the whole brain. We obtained participant whole-brain correlation matrices by computing the correlation between seed average time courses for each seed pair. Weighted object-oriented data analysis assessed group-level whole-brain differences.

RESULTS

Participants with focal dystonia had decreased functional connectivity at the regional level, within the striatum and between lateral primary sensorimotor cortex and ventral intraparietal area, whereas whole-brain correlation matrices did not differ between focal dystonia and control groups. Rigorous quality control measures eliminated spurious large-scale functional connectivity differences between groups.

CONCLUSION

Regional functional connectivity differences, not global network level dysfunction, contributes to common pathophysiologic mechanisms in isolated focal dystonia. Rigorous quality control eliminated spurious large-scale network differences between patients with focal dystonia and control participants.

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

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

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.

Neural Correlates of Abnormal Temporal Discrimination in Unaffected Relatives of Cervical Dystonia Patients

Background: An abnormal temporal discrimination threshold in cervical dystonia (CD) is considered to be a mediational endophenotype; in unaffected relatives it is hypothesized to indicate non-manifesting gene carriage. The pathogenesis underlying this condition remains unknown. Investigation of the neural networks involved in disordered temporal discrimination may highlight its pathomechanisms.

Objective: To examine resting state brain function in unaffected relatives of CD patients with normal and abnormal temporal discrimination. We hypothesized that the endophenotype, an abnormal temporal discrimination, would manifest as altered connectivity in relatives in regions associated with CD, thereby illuminating the neural substrates of the link between temporal discrimination and CD.

Methods: Rs-fMRI data was analyzed from two sex- and age-matched cohorts: 16 unaffected relatives of CD patients with normal temporal discrimination and 16 with abnormal temporal discrimination. Regional and whole brain functional connectivity measures were extracted via Independent Component Analysis (ICA), Regional Homogeneity (ReHo), and Amplitude of Low Frequency (ALFF) analyses.

Results: Our ICA analysis revealed increased connectivity within both the executive control and cerebellar networks and decreased connectivity within the sensorimotor network in relatives with abnormal temporal discrimination when compared to relatives with normal temporal discrimination. The ReHo and ALFF analyses complimented these results and demonstrated connectivity differences in areas corresponding to motor planning, movement coordination, visual information processing, and eye movements in unaffected relatives with abnormal temporal discrimination.

Conclusion: Disordered connectivity in unaffected relatives with abnormal temporal discrimination illuminates neural substrates underlying endophenotype expression and supports the hypothesis that genetically determined aberrant connectivity, when later coupled with unknown environmental triggers, may lead to disease penetrance.

Central Effects of Botulinum Neurotoxin-Evidence from Human Studies

For more than three decades, Botulinum neurotoxin (BoNT) has been used to treat a variety of clinical conditions such as spastic or dystonic disorders by inducing a temporary paralysis of the injected muscle as the desired clinical effect. BoNT is known to primarily act at the neuromuscular junction resulting in a biochemical denervation of the treated muscle. However, recent evidence suggests that BoNT’s pharmacological properties may not only be limited to local muscular denervation at the injection site but may also include additional central effects. In this review, we report and discuss the current evidence for BoNT’s central effects based on clinical observations, neurophysiological investigations and neuroimaging studies in humans. Collectively, these data strongly point to indirect mechanisms via changes to sensory afferents that may be primarily responsible for the marked plastic effects of BoNT on the central nervous system. Importantly, BoNT-related central effects and consecutive modulation and/or reorganization of the brain may not solely be considered “side-effects” but rather an additional therapeutic impact responsible for a number of clinical observations that cannot be explained by merely peripheral actions.

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.

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.

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.

Alterations of resting-state fMRI measurements in individuals with cervical dystonia

Cervical dystonia (CD) is a neurological disorder with typical symptoms of involuntary and abnormal movements and postures of the head. CD-associated alterations of functional brain networks have not been well characterized. Previous studies of CD using resting-state functional MRI (rfMRI) are limited in two aspects: (i) the analyses were not directly focused on the functional brain network related to head movement and (ii) rfMRI measurements other than functional connectivity (FC) were not investigated. The present study examined alterations of FC in CD by capitalizing on newly identified brain regions supporting isometric head rotation (Prudente et al.: J Neurosci 35 (2015) 9163-9172). In addition to FC, which only reflects inter-regional signal synchronization, local, or intraregional alterations were also examined using rfMRI measurements of the fractional amplitude of low-frequency fluctuations and regional homogeneity (ReHo). Finally, with alterations of different rfMRI measures identified, a support vector machine (SVM) learning algorithm was implemented for group classification. The results revealed both inter- (FC) and intra-regional (ReHo) alterations extensively distributed in both cortical and subcortical structures; and common alterations of these measures were identified bilaterally in the postcentral gyrus as well as in the basal ganglia and thalamus. Of the rfMRI features examined, seven of them (four FC and three ReHo measures) survived the SVM procedure of recursive feature elimination and together provided the highest group classification accuracy of 90.6%. The present findings extend previous studies of rfMRI in CD and offer insight into the underlying pathophysiology of the disorder in relation to network dysfunction and somatosensory disturbances. Hum Brain Mapp 38:4098-4108, 2017. © 2017 Wiley Periodicals, Inc.

A Functional Magnetic Resonance Imaging Study of Head Movements in Cervical Dystonia

Cervical dystonia (CD) is a neurological disorder characterized by abnormal movements and postures of the head. The brain regions responsible for these abnormal movements are not well understood, because most imaging techniques for assessing regional brain activity cannot be used when the head is moving. Recently, we mapped brain activation in healthy individuals using functional magnetic resonance imaging during isometric head rotation, when muscle contractions occur without actual head movements. In the current study, we used the same methods to explore the neural substrates for head movements in subjects with CD who had predominantly rotational abnormalities (torticollis). Isometric wrist extension was examined for comparison. Electromyography of neck and hand muscles ensured compliance with tasks during scanning, and any head motion was measured and corrected. Data were analyzed in three steps. First, we conducted within-group analyses to examine task-related activation patterns separately in subjects with CD and in healthy controls. Next, we directly compared task-related activation patterns between participants with CD and controls. Finally, considering that the abnormal head movements in CD occur in a consistently patterned direction for each individual, we conducted exploratory analyses that involved normalizing data according to the direction of rotational CD. The between-group comparisons failed to reveal any significant differences, but the normalization procedure in subjects with CD revealed that isometric head rotation in the direction of dystonic head rotation was associated with more activation in the ipsilateral anterior cerebellum, whereas isometric head rotation in the opposite direction was associated with more activity in sensorimotor cortex. These findings suggest that the cerebellum contributes to abnormal head rotation in CD, whereas regions in the cerebral cortex are involved in opposing the involuntary movements.

Brain Activity in Patients With Adductor Spasmodic Dysphonia Detected by Functional Magnetic Resonance Imaging

OBJECTIVES

Spasmodic dysphonia (SD) is considered a focal dystonia. However, the detailed pathophysiology of SD remains unclear, despite the detection of abnormal activity in several brain regions. The aim of this study was to clarify the pathophysiological background of SD.

STUDY DESIGN

This is a case-control study.

METHODS

Both task-related brain activity measured by functional magnetic resonance imaging by reading the five-digit numbers and resting-state functional connectivity (FC) measured by 150 T2-weighted echo planar images acquired without any task were investigated in 12 patients with adductor SD and in 16 healthy controls.

RESULTS

The patients with SD showed significantly higher task-related brain activation in the left middle temporal gyrus, left thalamus, bilateral primary motor area, bilateral premotor area, bilateral cerebellum, bilateral somatosensory area, right insula, and right putamen compared with the controls. Region of interest voxel FC analysis revealed many FC changes within the cerebellum-basal ganglia-thalamus-cortex loop in the patients with SD. Of the significant connectivity changes between the patients with SD and the controls, the FC between the left thalamus and the left caudate nucleus was significantly correlated with clinical parameters in SD.

CONCLUSION

The higher task-related brain activity in the insula and cerebellum was consistent with previous neuroimaging studies, suggesting that these areas are one of the unique characteristics of phonation-induced brain activity in SD. Based on FC analysis and their significant correlations with clinical parameters, the basal ganglia network plays an important role in the pathogenesis of SD.

Resting-state functional connectivity by independent component analysis-based markers corresponds to areas of initial seizure propagation established by prior modalities from the hypothalamus

OBJECTIVE

The aims of this study were to evaluate a clinically practical functional connectivity protocol designed to blindly identify the corresponding areas of initial seizure propagation and also to differentiate these areas from remote secondary areas affected by seizure. The patients in this cohort had intractable epilepsy caused by intrahypothalamic hamartoma, which is the location of the ictal focus. The ictal propagation pathway is homogeneous and established, thus creating the optimum situation for the proposed method validation study.

METHODS

Twelve patients with seizures from hypothalamic hamartoma and 6 normal control patients underwent resting state functional MRI, using independent component analysis to identify network differences in patients. This was followed by seed-based connectivity measures to determine the extent of functional connectivity derangement between hypothalamus and these areas. The areas with significant change in connectivity were compared with the results of prior studies' modalities used to evaluate seizure propagation.

RESULTS

The left amygdala-parahippocampal gyrus area, cingulate gyrus, and occipito-temporal gyrus demonstrated the highest derangement in connectivity with the hypothalamus, p < 0.01, corresponding to the initial seizure propagation areas established by prior modalities. Areas of secondary ictal propagation were differentiated from these initial locations by first being identified as an abnormal neuronal signal source via independent component analysis, but did not show significant connectivity directly with the known ictal focus.

CONCLUSION

Non-invasive connectivity measures correspond to areas of initial ictal propagation and differentiate such areas from secondary ictal propagation, which may aid in ictal focus surgical disconnection planning and support the use of this newer modality for adjunctive information in epilepsy surgery evaluation.

Cortical sensorimotor alterations classify clinical phenotype and putative genotype of spasmodic dysphonia

BACKGROUND AND PURPOSE

Spasmodic dysphonia (SD), or laryngeal dystonia, is a task-specific isolated focal dystonia of unknown causes and pathophysiology. Although functional and structural abnormalities have been described in this disorder, the influence of its different clinical phenotypes and genotypes remains scant, making it difficult to explain SD pathophysiology and to identify potential biomarkers.

METHODS

We used a combination of independent component analysis and linear discriminant analysis of resting-state functional magnetic resonance imaging data to investigate brain organization in different SD phenotypes (abductor versus adductor type) and putative genotypes (familial versus sporadic cases) and to characterize neural markers for genotype/phenotype categorization.

RESULTS

We found abnormal functional connectivity within sensorimotor and frontoparietal networks in patients with SD compared with healthy individuals as well as phenotype- and genotype-distinct alterations of these networks, involving primary somatosensory, premotor and parietal cortices. The linear discriminant analysis achieved 71% accuracy classifying SD and healthy individuals using connectivity measures in the left inferior parietal and sensorimotor cortices. When categorizing between different forms of SD, the combination of measures from the left inferior parietal, premotor and right sensorimotor cortices achieved 81% discriminatory power between familial and sporadic SD cases, whereas the combination of measures from the right superior parietal, primary somatosensory and premotor cortices led to 71% accuracy in the classification of adductor and abductor SD forms.

CONCLUSIONS

Our findings present the first effort to identify and categorize isolated focal dystonia based on its brain functional connectivity profile, which may have a potential impact on the future development of biomarkers for this rare disorder.

Quantitative assessment of brain iron by R2* relaxometry in patients with cervical dystonia

BACKGROUND

The pathophysiology of cervical dystonia is poorly understood. Increased brain iron deposition has been described in different movement disorders. Our aim was to investigate brain iron content in patients with cervical dystonia, using R2* relaxation rate, a validated MRI marker of brain iron level.

METHODS

Twelve female patients with primary focal cervical dystonia (mean age: 45.4 ± 8.0 years) and 12 age-matched healthy female subjects (mean age: 45.0 ± 8.0 years) underwent 3T MRI to obtain regional R2* relaxation rates of the thalamus, caudate nucleus, putamen, and globus pallidus (GP). Regions of interest were delineated automatically on T1-weighted MRIs.

RESULTS

R2* values in the putamen were positively correlated with age. Patients with cervical dystonia showed elevated R2* values in the GP.

CONCLUSIONS

This pilot study provides the first quantitative support for increased brain iron deposition in cervical dystonia. Further studies are needed to explore the implications of this finding.

The role of dopamine and dopaminergic pathways in dystonia: insights from neuroimaging

Background

Dystonia constitutes a heterogeneous group of movement abnormalities, characterized by sustained or intermittent muscle contractions causing abnormal postures. Overwhelming data suggest involvement of basal ganglia and dopaminergic pathways in dystonia. In this review, we critically evaluate recent neuroimaging studies that investigate dopamine receptors, endogenous dopamine release, morphology of striatum, and structural or functional connectivity in cortico-basal ganglia-thalamo-cortical and related cerebellar circuits in dystonia.

Method

A PubMed search was conducted in August 2014.

Results

Positron emission tomography (PET) imaging offers strong evidence for altered D2/D3 receptor binding and dopaminergic release in many forms of idiopathic dystonia. Functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) data reveal likely involvement of related cerebello-thalamo-cortical and sensory-motor networks in addition to basal ganglia.

Discussion

PET imaging of dopamine receptors or transmitter release remains an effective means to investigate dopaminergic pathways, yet may miss factors affecting dopamine homeostasis and related subcellular signaling cascades that could alter the function of these pathways. fMRI and DTI methods may reveal functional or anatomical changes associated with dysfunction of dopamine-mediated pathways. Each of these methods can be used to monitor target engagement for potential new treatments. PET imaging of striatal phosphodiesterase and development of new selective PET radiotracers for dopamine D3-specific receptors and Mechanistic target of rampamycin (mTOR) are crucial to further investigate dopaminergic pathways. A multimodal approach may have the greatest potential, using PET to identify the sites of molecular pathology and magnetic resonance methods to determine their downstream effects.