Impaired eye blink classical conditioning distinguishes dystonic patients with and without tremor

Cerebellar Non-Invasive Brain Stimulation: A Frontier in Chronic Pain Therapy

Chronic pain poses a widespread and distressing challenge; it can be resistant to conventional therapies, often having significant side effects. Non-invasive brain stimulation (NIBS) techniques offer promising avenues for the safe and swift modulation of brain excitability. NIBS approaches for chronic pain management targeting the primary motor area have yielded variable outcomes. Recently, the cerebellum has emerged as a pivotal hub in human pain processing; however, the clinical application of cerebellar NIBS in chronic pain treatment remains limited. This review delineates the cerebellum's role in pain modulation, recent advancements in NIBS for cerebellar activity modulation, and novel biomarkers for assessing cerebellar function in humans. Despite notable progress in NIBS techniques and cerebellar activity assessment, studies targeting cerebellar NIBS for chronic pain treatment are limited in number. Nevertheless, positive outcomes in pain alleviation have been reported with cerebellar anodal transcranial direct current stimulation. Our review underscores the potential for further integration between cerebellar NIBS and non-invasive assessments of cerebellar function to advance chronic pain treatment strategies.

Neural control of blinking

Blinking is a motor act characterized by the sequential closing and opening of the eyelids, which is achieved through the reciprocal activation of the orbicularis oculi and levator palpebrae superioris muscles. This stereotyped movement can be triggered reflexively, occur spontaneously, or voluntarily initiated. During each type of blinking, the neural control of the antagonistic interaction between the orbicularis oculi and levator palpebrae superioris muscles is governed by partially overlapping circuits distributed across cortical, subcortical, and brainstem structures. This paper provides a comprehensive overview of the anatomical and physiological foundations underlying the neural control of blinking. We describe the infra-nuclear apparatus, as well as the supra-nuclear control mechanisms, i.e., how cortical, subcortical, and brainstem structures regulate and coordinate the different types of blinking.

The blink reflex and its modulation - Part 2: Pathophysiology and clinical utility

The blink reflex (BR) is integrated at the brainstem; however, it is modulated by inputs from various structures such as the striatum, globus pallidus, substantia nigra, and nucleus raphe magnus but also from afferent input from the peripheral nervous system. Therefore, it provides information about the pathophysiology of numerous peripheral and central nervous system disorders. The BR is a valuable tool for studying the integrity of the trigemino-facial system, the relevant brainstem nuclei, and circuits. At the same time, some neurophysiological techniques applying the BR may indicate abnormalities involving structures rostral to the brainstem that modulate or control the BR circuits. This is a state-of-the-art review of the clinical application of BR modulation; physiology is reviewed in part 1. In this review, we aim to present the role of the BR and techniques related to its modulation in understanding pathophysiological mechanisms of motor control and pain disorders, in which these techniques are diagnostically helpful. Furthermore, some BR techniques may have a predictive value or serve as a basis for follow-up evaluation. BR testing may benefit in the diagnosis of hemifacial spasm, dystonia, functional movement disorders, migraine, orofacial pain, and psychiatric disorders. Although the abnormalities in the integrity of the BR pathway itself may provide information about trigeminal or facial nerve disorders, alterations in BR excitability are found in several disease conditions. BR excitability studies are suitable for understanding the common pathophysiological mechanisms behind various clinical entities, elucidating alterations in top-down inhibitory systems, and allowing for follow-up and quantitation of many neurological syndromes.

An analysis of the efficacy of botulinum neurotoxin type a in treating cervical dystonia

BACKGROUND

The first-line treatment for cervical dystonia (CD) consists of repeated intramuscular injections of botulinum toxin (BoNT). However, the efficacy in some patients may be unsatisfactory and they may discontinue treatment.

OBJECTIVE

To examine the factors associated with the maximum rate of remission in patients with CD after initial botulinum neurotoxin type A (or botulinum toxin type A abbreviated as BTX-A or BoNT-A) treatment.

METHODS

Patients with CD who received BoNT-A injections were evaluated using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) and the Tsui scale, with follow-up endpoints lasting until the start of the second injection. Patients who did not receive a second injection of BoNT-A were followed up for at least 5 months. The maximum remission rates were determined using the lowest Tsui and TWSTRS total scores during the follow-up period. We obtained basic information about these patients such as age, gender, duration of disease, presence of additional disease, types of torticollis, presence of anxiety, depression, tremors, single-photon emission computed tomography (SPECT) findings, injected dose, and so on from their medical records.

RESULTS

A total of 70 patients with CD participated in this study, with males comprising 35.7% (25 individuals) with an average age of 45 ± 14 years old. The duration of disease was an independent risk factor for determining whether a complete remission has been attained using the Tsui scale (odds ratio [OR] = 0.978, 95% confidence interval [CI]: 0.959-0.997, P= 0.026). The optimal cut-off point for predicting patients who were unable to achieve complete remission based on duration of disease was 7.5 months (AUG = 0.711). Patients with CD with additional disease had greater difficulty achieving complete remission than those with CD alone based on TWSTRS assessments (P= 0.049). During the study, approximately 17% of all participants reported experiencing adverse reactions that lasted between 1 to 3 weeks before disappearing.

CONCLUSION

BoNT is an effective and safe method for treating CD. The maximum remission rates of patients after their first injections are influenced by the duration of their disease. Thus, treatment using BoNT injections must be administered as soon as possible.

Essential and dystonic head tremor: More similarities than differences

INTRODUCTION

Head tremor is a common symptom of essential tremor (ET) and cervical dystonia (CD). In clinical practice, it is often difficult to distinguish between these two conditions, especially in cases where head tremor predominates.

OBJECTIVES

To investigate which clinical and instrumental methods best differentiate ET and CD in patients with head tremor.

METHODS

65 patients were included, of which 23 were diagnosed with ET and head tremor (HT+), 21 with ET without head tremor (HT-) and 21 with CD and dystonic head tremor. 22 healthy volunteers served as controls. All patients were examined using the rating scales for ET (TETRAS), cervical dystonia (TWSTRS), and ataxia (SARA). The Somatosensory Temporal Discrimination Threshold (STDT) was defined as the shortest interval in which an individual recognizes two tactile stimuli as temporally separated.

RESULTS

TETRAS and SARA scores were higher in the HT+ group compared with HT- and CD, with no significant difference between mild head tremor subscores in HT+ and CD. In most HT+ and CD patients, head tremor disappeared supine. The STDT values were significantly higher in the HT+ group compared with controls.

CONCLUSION

While TWSTRS contributed to assess dystonia severity, the scales of tremor and ataxia were not helpful in differentiating head tremor syndromes. The cessation of head tremor in the supine position could be related to the overall mild head tremor scores in both groups. Increased SARA scores and STDT values in HT+ patients suggest a possible role of cerebellar involvement and altered somatosensory timing that merit further verification.

Dysfunctional Networks in Functional Dystonia

Functional dystonia, the second most common functional movement disorder, is characterized by acute or subacute onset of fixed limb, truncal, or facial posturing, incongruent with the action-induced, position-sensitive, and task-specific manifestations of dystonia. We review neurophysiological and neuroimaging data as the basis for a dysfunctional networks in functional dystonia. Reduced intracortical and spinal inhibition contributes to abnormal muscle activation, which may be perpetuated by abnormal sensorimotor processing, impaired selection of movements, and hypoactive sense of agency in the setting of normal movement preparation but abnormal connectivity between the limbic and motor networks. Phenotypic variability may be related to as-yet undefined interactions between abnormal top-down motor regulation and overactivation of areas implicated in self-awareness, self-monitoring, and active motor inhibition such as the cingulate and insular cortices. While there remain many gaps in knowledge, further combined neurophysiological and neuroimaging assessments stand to inform the neurobiological subtypes of functional dystonia and the potential therapeutic applications.

Cerebellar Dysfunction as a Source of Dystonic Phenotypes in Mice

There is now a substantial amount of compelling evidence demonstrating that the cerebellum may be a central locus in dystonia pathogenesis. Studies using spontaneous genetic mutations in rats and mice, engineered genetic alleles in mice, shRNA knockdown in mice, and conditional genetic silencing of fast neurotransmission in mice have all uncovered a common set of behavioral and electrophysiological defects that point to cerebellar cortical and cerebellar nuclei dysfunction as a source of dystonic phenotypes. Here, we revisit the Ptf1a^Cre/+;Vglut2^flox/flox mutant mouse to define fundamental phenotypes and measures that are valuable for testing the cellular, circuit, and behavioral mechanisms that drive dystonia. In this model, excitatory neurotransmission from climbing fibers is genetically eliminated and, as a consequence, Purkinje cell and cerebellar nuclei firing are altered in vivo, with a prominent and lasting irregular burst pattern of spike activity in cerebellar nuclei neurons. The resulting impact on behavior is that the mice have developmental abnormalities, including twisting of the limbs and torso. These behaviors continue into adulthood along with a tremor, which can be measured with a tremor monitor or EMG. Importantly, expression of dystonic behavior is reduced upon cerebellar-targeted deep brain stimulation. The presence of specific combinations of disease-like features and therapeutic responses could reveal the causative mechanisms of different types of dystonia and related conditions. Ultimately, an emerging theme places cerebellar dysfunction at the center of a broader dystonia brain network.

A Critical Investigation of Cerebellar Associative Learning in Isolated Dystonia

Background

Objective

Methods

Results

Conclusions

Bayesian Interpretation of Essential Tremor Plus

Essential tremor (ET) plus is a new tremor classification that was introduced in 2018 by a task force of the International Parkinson and Movement Disorder Society. Patients with ET plus meet the criteria for ET but have one or more additional systemic or neurologic signs of uncertain significance or relevance to tremor (“soft signs”). Soft signs are not sufficient to diagnose another tremor syndrome or movement disorder, and soft signs in ET plus are known to have poor interrater reliability and low diagnostic sensitivity and specificity. Therefore, the clinical significance of ET plus must be interpreted probabilistically when judging whether a patient is more likely to have ET or a combined tremor syndrome, such as dystonic tremor. Such a probabilistic interpretation is possible with Bayesian analysis. This review presents a Bayesian analysis of ET plus in patients suspected of having ET versus a dystonic tremor syndrome, which is the most common differential diagnosis in patients referred for ET. Bayesian analysis of soft signs provides an estimate of the probability that a patient with possible ET is more likely to have an alternative diagnosis. ET plus is a distinct tremor classification and should not be viewed as a subtype of ET. ET plus covers a more-comprehensive phenotyping of people with possible ET, and the clinical interpretation of ET plus is enhanced with Bayesian analysis of associated soft signs.

Cerebello-thalamic activity drives an abnormal motor network into dystonic tremor

Dystonic tremor syndromes are highly burdensome and treatment is often inadequate. This is partly due to poor understanding of the underlying pathophysiology. Several lines of research suggest involvement of the cerebello-thalamo-cortical circuit and the basal ganglia in dystonic tremor syndromes, but their role is unclear. Here we aimed to investigate the contribution of the cerebello-thalamo-cortical circuit and the basal ganglia to the pathophysiology of dystonic tremor syndrome, by directly linking tremor fluctuations to cerebral activity during scanning. In 27 patients with dystonic tremor syndrome (dystonic tremor: n = 23; tremor associated with dystonia: n = 4), we used concurrent accelerometery and functional MRI during a posture holding task that evoked tremor, alternated with rest. Using multiple regression analyses, we separated tremor-related activity from brain activity related to (voluntary) posture holding. Using dynamic causal modelling, we tested for altered effective connectivity between tremor-related brain regions as a function of tremor amplitude fluctuations. Finally, we compared grey matter volume between patients (n = 27) and matched controls (n = 27). We found tremor-related activity in sensorimotor regions of the bilateral cerebellum, contralateral posterior and anterior ventral lateral nuclei of the thalamus (VLp and VLa), contralateral primary motor cortex (hand area), contralateral pallidum, and the bilateral frontal cortex (laterality with respect to the tremor). Grey matter volume was increased in patients compared to controls in the portion of contralateral thalamus also showing tremor-related activity, as well as in bilateral medial and left lateral primary motor cortex, where no tremor-related activity was present. Effective connectivity analyses showed that inter-regional coupling in the cerebello-thalamic pathway, as well as the thalamic self-connection, were strengthened as a function of increasing tremor power. These findings indicate that the pathophysiology of dystonic tremor syndromes involves functional and structural changes in the cerebello-thalamo-cortical circuit and pallidum. Deficient input from the cerebellum towards the thalamo-cortical circuit, together with hypertrophy of the thalamus, may play a key role in the generation of dystonic tremor syndrome.

Head tremor and pain in cervical dystonia

BACKGROUND

Although head tremor (HT) and pain are prevalent in cervical dystonia (CD), their joint relationship to phenotypic features of focal dystonia remains unclear.

OBJECTIVES

We examined how severity of HT and pain are associated with age of CD onset and duration, and whether HT subtypes ("jerky" or "regular") exhibit distinct relationships between severity of HT and pain.

METHODS

The severity of HT and pain were assessed with the Toronto Western Spasmodic Torticollis Rating Scale in retrospective review of 188 CD patients recruited through the Dystonia Coalition.

RESULTS

HT severity was associated with longer CD duration (p < 0.0005), whereas pain severity was associated with younger age at onset (p = 0.043). HT severity and pain severity were not correlated for jerky HT (p = 0.996), but positively correlated for regular HT (p = 0.01).

CONCLUSIONS

The distinct associations of HT and pain with age at onset, disease duration, and HT subtype further characterize the heterogeneity of CD's clinical presentation and suggest similarly heterogeneous underlying mechanisms.

Brainstem Reflexes in Idiopathic Cervical Dystonia: Does Medullary Dysfunction Play a Role?

Background

Neurophysiological markers in dystonia have so far not been sistematically applied in clinical practice due to limited reproducibility of results and low correlations with clinical findings. Exceptions might be represented by the blink reflex (BR), including its recovery cycle (BRRC) and the trigemino‐cervical reflex (TCR) which, compared to other neurophysiological methods, have shown more consistent alterations in cervical dystonia (CD). However, a comparison between the two techniques, and their possible correlation with disease symptoms, have not been thoroughly investigated.

Objectives

To assess the role of BR, BRCC and TCR in the pathophysiology of idiopathic cervical dystonia.

Methods

Fourteen patients and 14 age‐matched healthy controls (HC) were recruited. Neurophysiological outcome measures included latency of R1 and R2 components of the BR, R2 amplitude, BRRC, latency and amplitude of P19/N31 complex of TCR. Clinical and demographic features of patients were also collected, including age at disease onset, disease duration, presence of tremor, sensory trick and pain. The Toronto Western Spasmodic Torticollis Rating Scale was used to characterize dystonia.

Results

Compared to HC, CD patients showed increased latency of the BR R2 and decreased suppression of the BRRC. They also showed increased latency of the P19 and decreased amplitude of P19/N31 complex of TCR. The latency of P19 component of TCR was positively correlated with disease duration.

Conclusions

We propose that the increased latency of R2 and P19 observed here might be reflective of brainstem dysfunction, mediated either by local interneuronal excitability changes or by subtle structural damage.

Motor learning deficits in cervical dystonia point to defective basal ganglia circuitry

Dystonia is conceptualized as a network disorder involving basal ganglia, thalamus, sensorimotor cortex and the cerebellum. The cerebellum has been implicated in dystonia pathophysiology, but studies testing cerebellar function in dystonia patients have provided equivocal results. This study aimed to further elucidate motor network deficits in cervical dystonia with special interest in the role of the cerebellum. To this end we investigated motor learning tasks, that differ in their dependence on cerebellar and basal ganglia functioning. In 18 cervical dystonia patients and 18 age matched healthy controls we measured implicit motor sequence learning using a 12-item serial reaction time task mostly targeting basal ganglia circuitry and motor adaptation and eyeblink conditioning as markers of cerebellar functioning. ANOVA showed that motor sequence learning was overall impaired in cervical dystonia (p = 0.01). Moreover, unlike healthy controls, patients did not show a learning effect in the first part of the experiment. Visuomotor adaptation and eyeblink conditioning were normal. In conclusion, these data lend support to the notion that motor learning deficits in cervical dystonia relate to basal ganglia-thalamo-cortical loops rather than being a result of defective cerebellar circuitry.

The Signature of Primary Writing Tremor Is Dystonic

BACKGROUND

It has been debated for decades whether primary writing tremor is a form of dystonic tremor, a variant of essential tremor, or a separate entity. We wished to test the hypothesis that primary writing tremor and dystonia share a common pathophysiology.

OBJECTIVES

The objective of the present study was to investigate the pathophysiological hallmarks of dystonia in patients affected by primary writing tremor.

METHODS

Ten patients with idiopathic dystonic tremor syndrome, 7 with primary writing tremor, 10 with essential tremor, and 10 healthy subjects were recruited. They underwent eyeblink classic conditioning, blink recovery cycle, and transcranial magnetic stimulation assessment, including motor-evoked potentials and short- and long-interval intracortical inhibition at baseline. Transcranial magnetic stimulation measures were also recorded after paired-associative plasticity protocol.

RESULTS

Primary writing tremor and dystonic tremor syndrome had a similar pattern of electrophysiological abnormalities, consisting of reduced eyeblink classic conditioning learning, reduced blink recovery cycle inhibition, and a lack of effect of paired-associative plasticity on long-interval intracortical inhibition. The latter 2 differ from those obtained in essential tremor and healthy subjects. Although not significant, slightly reduced short-interval intracortical inhibition and a larger effect of paired-associative plasticity in primary writing tremor and dystonic tremor syndrome, compared with essential tremor and healthy subjects, was observed.

CONCLUSIONS

Our initial hypothesis of a common pathophysiology between dystonia and primary writing tremor has been confirmed. Primary writing tremor might be considered a form of dystonic tremor. © 2021 International Parkinson and Movement Disorder Society.

Defective Somatosensory Inhibition and Plasticity Are Not Required to Develop Dystonia

BACKGROUND

Dystonia may have different neuroanatomical substrates and pathophysiology. This is supported by studies on the motor system showing, for instance, that plasticity is abnormal in idiopathic dystonia, but not in dystonia secondary to basal ganglia lesions.

OBJECTIVE

The aim of this study was to test whether somatosensory inhibition and plasticity abnormalities reported in patients with idiopathic dystonia also occur in patients with dystonia caused by basal ganglia damage.

METHODS

Ten patients with acquired dystonia as a result of basal ganglia lesions and 12 healthy control subjects were recruited. They underwent electrophysiological testing at baseline and after a single 45-minute session of high-frequency repetitive somatosensory stimulation. Electrophysiological testing consisted of somatosensory temporal discrimination, somatosensory-evoked potentials (including measurement of early and late high-frequency oscillations and the spatial inhibition ratio of N20/25 and P14 components), the recovery cycle of paired-pulse somatosensory-evoked potentials, and primary motor cortex short-interval intracortical inhibition.

RESULTS

Unlike previous reports of patients with idiopathic dystonia, patients with acquired dystonia did not differ from healthy control subjects in any of the electrophysiological measures either before or after high-frequency repetitive somatosensory stimulation, except for short-interval intracortical inhibition, which was reduced at baseline in patients compared to control subjects.

CONCLUSIONS

The data show that reduced somatosensory inhibition and enhanced cortical plasticity are not required for the clinical expression of dystonia, and that the abnormalities reported in idiopathic dystonia are not necessarily linked to basal ganglia damage. © 2020 International Parkinson and Movement Disorder Society.

The Pathophysiology of Dystonic Tremors and Comparison With Essential Tremor

There are two types of dystonic tremor syndromes (DTS), dystonic tremor (DT) and tremor associated with dystonia (TAWD), and neither is understood. DTS likely share some mechanisms with nontremulous dystonia, and there may also be overlaps with essential tremor (ET). We studied 21 ET (8 females, 13 males) and 22 DTS human patients (10 females, 12 males), including 13 human patients with DT (writer's cramp with writing tremor) and 9 human patients with tremor associated with dystonia (TAWD; cervical dystonia with hand tremor). Tremors were analyzed using accelerometry and surface EMG of the antagonist pairs of arm muscles during posture, simple kinetic movement, and writing. Cerebellar inhibition was performed to assess cerebello-thalamo-cortical involvement. DT exhibited higher variability of peak frequency and greater instability of tremor burst intervals over time (higher tremor stability index) than ET or TAWD regardless of tasks. Intermuscular coherence magnitude between the antagonist pairs increased during the writing task in DT, but not ET or TAWD. ET and TAWD exhibited different phase relationships of the temporal fluctuations of voluntary movement and tremor in the kinetic condition. A linear discriminant classifier based on these tremor parameters was able to distinguish the three groups with a classification accuracy of 95.1%. Cerebellar inhibition was significantly reduced in DT, but not in TAWD, compared with ET and healthy controls. Our study shows that the two DTS are distinct entities with DT closer to nontremorous dystonia and TAWD closer to ET.SIGNIFICANCE STATEMENT This study provides novel findings about characteristics and pathophysiology of the two different types of dystonic tremor syndromes compared with essential tremor. Patients with DTS are classified into DT who have dystonia and tremor in the same area, and tremor associated with dystonia (TAWD) who have dystonia and tremor elsewhere. Our results showed that DT exhibits increased tremor variability, instability, and intermuscular coherence, and decreased cerebello-thalamo-cortical inhibition compared with TAWD. Our study shows that DT and TAWD are distinct phenotypes, and that the physiological characteristics of DT are more similar to nontremorous dystonia, and TAWD is closer to ET.

Motor and Sensory Features of Cervical Dystonia Subtypes: Data From the Italian Dystonia Registry

Introduction: Cervical dystonia (CD) is one of the most common forms of adult-onset isolated dystonia. Recently, CD has been classified according to the site of onset and spread, in different clinical subgroups, that may represent different clinical entities or pathophysiologic subtypes. In order to support this hypothesis, in this study we have evaluated whether different subgroups of CD, that clinically differ for site of onset and spread, also imply different sensorimotor features.

Methods: Clinical and demographic data from 842 patients with CD from the Italian Dystonia Registry were examined. Motor features (head tremor and tremor elsewhere) and sensory features (sensory trick and neck pain) were investigated. We analyzed possible associations between motor and sensory features in CD subgroups [focal neck onset, no spread (FNO-NS); focal neck onset, segmental spread (FNO-SS); focal onset elsewhere with segmental spread to neck (FOE-SS); segmental neck involvement without spread (SNI)].

Results: In FNO-NS, FOE-SS, and SNI subgroups, head tremor was associated with the presence of tremor elsewhere. Sensory trick was associated with pain in patients with FNO-NS and with head tremor in patients with FNO-SS.

Conclusion: The frequent association between head tremor and tremor elsewhere may suggest a common pathophysiological mechanism. Two mechanisms may be hypothesized for sensory trick: a gating mechanism attempting to reduce pain and a sensorimotor mechanism attempting to control tremor.

Delineating the electrophysiological signature of dystonia

Over the last 30 years, the concept of dystonia has dramatically changed, from being considered a motor neurosis, to a pure basal ganglia disorder, to finally reach the definition of a network disorder involving the basal ganglia, cerebellum, thalamus and sensorimotor cortex. This progress has been possible due to the collaboration between clinicians and scientists, and the development of increasingly sophisticated electrophysiological techniques able to non-invasively investigate pathophysiological mechanisms in humans. This review is a chronological excursus of the electrophysiological studies that laid the foundation for the understanding of the pathophysiology of dystonia and delineated its electrophysiological signatures. Evidence for neurophysiological abnormalities is grouped according to the neural system involved, and a unifying theory, bringing together all the hypothesis and evidence provided to date, is proposed at the end.

Motor outcomes and adverse effects of deep brain stimulation for dystonic tremor: A systematic review

Dystonic tremor (DT) is defined as the tremor in body parts affected by dystonia. Although deep brain stimulation (DBS) has been used to manage medically-refractory DT patients, its efficacy has not been well established. The objective of this study is to provide an up-to-date systematic review of DBS outcomes for DT patients. We conducted a literature search using Medline, Embase, and Cochrane Library databases in February 2020 according to the PRISMA guidelines. From 858 publications, we identified 30 articles involving 89 DT patients who received DBS of different targets. Thalamic DBS was the most common (n = 39) and improved tremor by 40-50% potentially in the long-term over five years with variable effects on dystonic symptoms. Globus pallidus internus (GPi), subthalamic, and subthalamic nucleus (STN) DBS improved both tremor and dystonic symptoms; however, data were limited. A few studies have reported better tremor and dystonia outcomes with combinations of different targets. Concerning adverse effects, gait/balance disorders, and ataxia seemed to be more common among patients treated with thalamic or subthalamic DBS, whereas parkinsonian adverse effects were observed only in patients treated with subthalamic or GPi DBS. Comparative benefits and limitations of these targets remain unclear because of the lack of randomized controlled trials. In conclusion, DBS of these targets may improve tremor with a variable effect on dystonia with different adverse effect profiles. The shortcomings in the literature include long-term motor outcomes, quality of life outcomes, optimal DBS targeting, and DBS programming strategy.

Rest tremor in dystonia: epidemiology, differential diagnosis, and pathophysiology

BACKGROUND

The most common type of tremor reported in dystonia patients is postural and kinetic. There is uncertainty regarding the prevalence of rest tremor in dystonia.

OBJECTIVE

This review focuses on the clinical and neurophysiological features of rest tremor in dystonia, its differential diagnosis, and methods to distinguish it from other rest tremor syndromes.

METHODS

A PubMed search was done, and the available literature identified. Bibliography of the available literature was reviewed for relevant references.

RESULTS

Rest tremor in dystonia has been reported with a variable frequency of 1.81-12.05%. The most common body distribution is arm, and it tends to be asymmetric. Most of the affected patients have multifocal and segmental dystonia. Rest tremor is a late-onset phenomenon associated with severe and spreading dystonia. Clinically, it is difficult to distinguish rest tremor in dystonia from other rest tremor syndromes based on tremor characteristics; however, other neurological signs can provide clues to differentiate these syndromes. Surface electromyography and other neurophysiological tests can help differentiate the various rest tremor syndromes.

CONCLUSION

Rest tremor in dystonia can be differentiated from other rest tremor syndromes based on neurophysiological techniques. There is some evidence to suggest that SWEDDs could be a form of dystonic tremor, but further studies are required to clarify this diagnostic dilemma. Data regarding the treatment of rest tremor in dystonia are virtually nonexistent, and there is an urgent need for prospective studies focusing its medical management and to know the surgical targets.

Evidence for normal intracortical inhibitory recruitment properties in cervical dystonia

OBJECTIVE

Dystonia is associated with reduced intracortical inhibition as measured by the cortical silent period (cSP); however, this may be due to abnormal cSP threshold or input-output properties. This study evaluated cSP recruitment properties in people with cervical dystonia (CD).

METHODS

Bilateral electromyographic recordings were collected in the upper trapezius muscle in response to transcranial magnetic stimulation of the left and right primary motor cortex in a group with CD (n = 19) and controls (n = 21). cSP threshold, cSP input-output properties at stimulation intensities from 1 to 1.4x the cSP threshold, ipsilateral silent period duration (iSP) and timing and magnitude of the contralateral and ipsilateral motor evoked potential (MEP) were assessed.

RESULTS

The cSP threshold, input-output properties, and contralateral MEP magnitude were not significantly different between groups (all p > 0.07). Hemispheric symmetry was present in the control group while the CD group had reduced iSP (p < 0.01) and a trend for reduced ipsilateral MEP response (p = 0.053) in the left hemisphere.

CONCLUSIONS

Recruitment properties of intracortical inhibition are similar between control and CD groups. Transcallosal inhibition is asymmetric between hemispheres in people with CD.

SIGNIFICANCE

Evidence of normal intracortical inhibition recruitment properties challenge the commonly held view that cortical inhibition is reduced in dystonia.

Longitudinal follow-up with VIM thalamic deep brain stimulation for dystonic or essential tremor

OBJECTIVE

To assess longitudinal tremor outcomes with ventral intermediate nucleus deep brain stimulation (VIM DBS) in patients with dystonic tremor (DT) and to compare with DBS outcomes in essential tremor (ET).

METHODS

We retrospectively investigated VIM DBS outcomes for 163 patients followed at our center diagnosed with either DT or ET. The Fahn-Tolosa-Marin tremor rating scale (TRS) was used to assess change in tremor and activities of daily living (ADL) at 6 months, 1 year, 2-3 years, 4-5 years, and ≥6 years after surgery.

RESULTS

Twenty-six patients with DT and 97 patients with ET were analyzed. Compared to preoperative baseline, there were significant improvements in TRS motor up to 4-5 years (52.2%; p = 0.032) but this did not reach statistical significance at ≥6 years (46.0%, p = 0.063) in DT, which was comparable to the outcomes in ET. While the improvements in the upper extremity tremor, head tremor, and axial tremor were also comparable between DT and ET throughout the follow-up, the ADL improvements in DT were lost at 2-3 years follow-up.

CONCLUSION

Overall, tremor control with VIM DBS in DT and ET was comparable and remained sustained at long term likely related to intervention at the final common node in the pathologic tremor network. However, the long-term ADL improvements in DT were not sustained, possibly due to inadequate control of concomitant dystonia symptoms. These findings from a large cohort of DT indicate that VIM targeting is reasonable if the tremor is considerably more disabling than the dystonic features.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that VIM DBS improves tremor in patients with DT or ET.

Advances in the pathophysiology of adult-onset focal dystonias: recent neurophysiological and neuroimaging evidence

Focal dystonia is a movement disorder characterized by involuntary muscle contractions that determine abnormal postures. The traditional hypothesis that the pathophysiology of focal dystonia entails a single structural dysfunction (i.e. basal ganglia) has recently come under scrutiny. The proposed network disorder model implies that focal dystonias arise from aberrant communication between various brain areas. Based on findings from animal studies, the role of the cerebellum has attracted increased interest in the last few years. Moreover, it has been increasingly reported that focal dystonias also include nonmotor disturbances, including sensory processing abnormalities, which have begun to attract attention. Current evidence from neurophysiological and neuroimaging investigations suggests that cerebellar involvement in the network and mechanisms underlying sensory abnormalities may have a role in determining the clinical heterogeneity of focal dystonias.

Spontaneous, Voluntary, and Reflex Blinking in Clinical Practice

Blinking is one of the motor acts performed more frequently by healthy human subjects. It involves the reciprocal action of at least two muscles: the orbicularis oculi shows a brief phasic activation while the levator palpebrae shows transient inhibition. In clinical practice, noninvasive recording of the orbicularis oculi activity is sufficient to obtain useful information for electrodiagnostic testing. Blinking can be spontaneous, voluntary, or reflex. Although the analysis of spontaneous blinks can already furnish interesting data, most studies are based on reflex blinking. This article is a review of some of the alterations that can be observed in blinking, focusing in four patterns of abnormality that can be distinguished in the blink reflex: (1) afferent versus efferent, which allows characterization of trigeminal or facial lesions; (2) peripheral versus central, which distinguishes alterations in nerve conduction from those involving synaptic delay; (3) upper versus lower brainstem lesions, which indicates the lesions involving specific circuits for trigeminal and somatosensory blink reflexes; and (4) asymmetric abnormal excitability pattern, which shows a unilateral alteration in the descending control of excitability in brainstem circuits. The blink reflex excitability recovery curve to paired stimuli may provide information about other modulatory inputs to trigemino-facial circuits, such as those proposed for the connection between basal ganglia and trigeminal neurons. Finally, prepulse inhibition of blink reflex reflects the motor surrogate of subcortical gating on sensory volleys, which is still another window by which electrodiagnosis can document motor control mechanisms and their abnormalities in neurologic diseases.

Postural Directionality and Head Tremor in Cervical Dystonia

Background

Although abnormal head and neck postures are defining features of cervical dystonia (CD), head tremor (HT) is also common. However, little is known about the relationship between abnormal postures and HT in CD.

Methods

We analyzed clinical data and video recordings from 185 patients enrolled by the Dystonia Coalition. We calculated the likelihood of their HT and HT type ("regular" vs. "jerky") given directionality of abnormal head postures, disease duration, sex, and age.

Results

Patients with retrocollis were more likely to have HT than patients with anterocollis (X2 (1, N = 121) = 7.98, p = 0.005). There was no difference in HT likelihood given left or right turning in laterocollis and rotation. Patients with HT had longer disease duration (t(183) = 2.27, p = 0.024). There was no difference in age between patients with and without HT. In a logistic regression model, anterocollis/retrocollis direction (X2 (1, N = 121) = 6.04, p = 0.014), disease duration (X2 (1, N = 121) = 7.28, p = 0.007), and the interaction term between age and disease duration (X2 (1, N = 121) = 7.77, p = 0.005) collectively contributed to HT likelihood. None of the postural directionality or demographic variables were associated with differential likelihood of having regular versus jerky HT.

Discussion

We found that HT is more likely for CD patients with a specific directionality in their predominant posture. Our finding that CD patients with longer disease duration have a higher likelihood of HT also raises the question of whether HT becomes more likely over time in individual patients.

Temporal discrimination threshold and blink reflex recovery cycle in cervical dystonia - two sides of the same coin?

INTRODUCTION

Elevated temporal discrimination thresholds (TDT) have been found in cervical dystonia (CD) and unaffected first-degree relatives, indicating autosomal dominant inheritance with reduced penetrance, serving as an endophenotype and being indicative of abnormal inhibitory processing within the brainstem-basal ganglia circuits. The blink reflex R2 recovery cycle (BRRC) is also a measure of excitability of brainstem-basal ganglia circuits, and inconsistent findings are reported in CD. The aim was to investigate TDT and BRRC in CD and evaluate its reliability as an endophenotype.

METHODS

29 patients with isolated cervical dystonia (mean age: 56.1 ± 14.3, female n = 18) and 29 age- and gender-matched healthy controls (mean age: 56.0 ± 14.2, female n = 18) were evaluated using a TDT-paradigm, performed as previously described by testing visual, tactile and visual-tactile temporal discrimination thresholds, and the BRRC, investigated with electrical and air puff stimulation.

RESULTS

Mean visual-tactile (p = 0.001) and visual TDTs (p = 0.015) differed between CD and controls; tactile TDTs revealed no group differences (p = 0.232). No between group differences were found for BRRC using either electrical or air puff stimulation (p = 0.117). There was no correlation between the elevation of TDTs and the degree of BRRC-inhibition in CD.

CONCLUSION

Our findings support the hypothesis that the TDT is an endophenotype in CD. BRRC testing did not demonstrate disinhibition of brainstem-basal ganglia circuits in CD. In contrast to TDT, the BRRC seems not to represent an endophenotype in cervical dystonia.

Network localization of cervical dystonia based on causal brain lesions

Cervical dystonia is a neurological disorder characterized by sustained, involuntary movements of the head and neck. Most cases of cervical dystonia are idiopathic, with no obvious cause, yet some cases are acquired, secondary to focal brain lesions. These latter cases are valuable as they establish a causal link between neuroanatomy and resultant symptoms, lending insight into the brain regions causing cervical dystonia and possible treatment targets. However, lesions causing cervical dystonia can occur in multiple different brain locations, leaving localization unclear. Here, we use a technique termed 'lesion network mapping', which uses connectome data from a large cohort of healthy subjects (resting state functional MRI, n = 1000) to test whether lesion locations causing cervical dystonia map to a common brain network. We then test whether this network, derived from brain lesions, is abnormal in patients with idiopathic cervical dystonia (n = 39) versus matched controls (n = 37). A systematic literature search identified 25 cases of lesion-induced cervical dystonia. Lesion locations were heterogeneous, with lesions scattered throughout the cerebellum, brainstem, and basal ganglia. However, these heterogeneous lesion locations were all part of a single functionally connected brain network. Positive connectivity to the cerebellum and negative connectivity to the somatosensory cortex were specific markers for cervical dystonia compared to lesions causing other neurological symptoms. Connectivity with these two regions defined a single brain network that encompassed the heterogeneous lesion locations causing cervical dystonia. These cerebellar and somatosensory regions also showed abnormal connectivity in patients with idiopathic cervical dystonia. Finally, the most effective deep brain stimulation sites for treating dystonia were connected to these same cerebellar and somatosensory regions identified using lesion network mapping. These results lend insight into the causal neuroanatomical substrate of cervical dystonia, demonstrate convergence across idiopathic and acquired dystonia, and identify a network target for dystonia treatment.

[The new tremor classification of the International Parkinson and Movement Disorder Society : Update on frequent tremors]

Tremor is one of the most frequent movement disorders. The recently published new classification of the Movement Disorder Society separates the clinical description of tremor syndromes as so-called axis 1 symptom constellations from the etiologies of tremor (axis 2). The same tremor syndromes can therefore be combined with different causes and vice versa. The terminology used in this classification is precisely defined and thereby also the necessary language for medical communication. Frequent tremor syndromes, such as enhanced physiologic tremor, dystonic and parkinsonian tremor as well as focal tremors and task and position-specific tremors are discussed with respect to the phenomenology, and current therapy.

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.

Cerebellar Theta-Burst Stimulation Impairs Memory Consolidation in Eyeblink Classical Conditioning

Associative learning of sensorimotor contingences, as it occurs in eyeblink classical conditioning (EBCC), is known to involve the cerebellum, but its mechanism remains controversial. EBCC involves a sequence of learning processes which are thought to occur in the cerebellar cortex and deep cerebellar nuclei. Recently, the extinction phase of EBCC has been shown to be modulated after one week by cerebellar continuous theta-burst stimulation (cTBS). Here, we asked whether cerebellar cTBS could affect retention and reacquisition of conditioned responses (CRs) tested immediately after conditioning. We also investigated a possible lateralized cerebellar control of EBCC by applying cTBS on both the right and left cerebellar hemispheres. Both right and left cerebellar cTBSs induced a statistically significant impairment in retention and new acquisition of conditioned responses (CRs), the disruption effect being marginally more effective when the left cerebellar hemisphere was stimulated. These data support a model in which cTBS impairs retention and reacquisition of CR in the cerebellum, possibly by interfering with the transfer of memory to the deep cerebellar nuclei.

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.

Tremor in motor neuron disease may be central rather than peripheral in origin

BACKGROUND AND PURPOSE

Motor neuron disease (MND) refers to a spectrum of degenerative diseases affecting motor neurons. Recent clinical and post-mortem observations have revealed considerable variability in the phenotype. Rhythmic involuntary oscillations of the hands during action, resembling tremor, can occur in MND, but their pathophysiology has not yet been investigated.

METHODS

A total of 120 consecutive patients with MND were screened for tremor. Twelve patients with action tremor and no other movement disorders were found. Ten took part in the study. Tremor was recorded bilaterally using surface electromyography (EMG) and triaxial accelerometer, with and without a variable weight load. Power spectra of rectified EMG and accelerometric signal were calculated. To investigate a possible cerebellar involvement, eyeblink classic conditioning was performed in five patients.

RESULTS

Action tremor was present in about 10% of our population. All patients showed distal postural tremor of low amplitude and constant frequency, bilateral with a small degree of asymmetry. Two also showed simple kinetic tremor. A peak at the EMG and accelerometric recordings ranging from 4 to 12 Hz was found in all patients. Loading did not change peak frequency in either the electromyographic or accelerometric power spectra. Compared with healthy volunteers, patients had a smaller number of conditioned responses during eyeblink classic conditioning.

CONCLUSIONS

Our data suggest that patients with MND can present with action tremor of a central origin, possibly due to a cerebellar dysfunction. This evidence supports the novel idea of MND as a multisystem neurodegenerative disease and that action tremor can be part of this condition.

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.

The Anatomical Basis for Dystonia: The Motor Network Model

Background

The dystonias include a clinically and etiologically very diverse group of disorders. There are both degenerative and non-degenerative subtypes resulting from genetic or acquired causes. Traditionally, all dystonias have been viewed as disorders of the basal ganglia. However, there has been increasing appreciation for involvement of other brain regions including the cerebellum, thalamus, midbrain, and cortex. Much of the early evidence for these other brain regions has come from studies of animals, but multiple recent studies have been done with humans, in an effort to confirm or refute involvement of these other regions. The purpose of this article is to review the new evidence from animals and humans regarding the motor network model, and to address the issues important to translational neuroscience.

Methods

The English literature was reviewed for articles relating to the neuroanatomical basis for various types of dystonia in both animals and humans.

Results

There is evidence from both animals and humans that multiple brain regions play an important role in various types of dystonia. The most direct evidence for specific brain regions comes from animal studies using pharmacological, lesion, or genetic methods. In these studies, experimental manipulations of specific brain regions provide direct evidence for involvement of the basal ganglia, cerebellum, thalamus and other regions. Additional evidence also comes from human studies using neuropathological, neuroimaging, non-invasive brain stimulation, and surgical interventions. In these studies, the evidence is less conclusive, because discriminating the regions that cause dystonia from those that reflect secondary responses to abnormal movements is more challenging.

Discussion

Overall, the evidence from both animals and humans suggests that different regions may play important roles in different subtypes of dystonia. The evidence so far provides strong support for the motor network model. There are obvious challenges, but also advantages, of attempting to translate knowledge gained from animals into a more complete understanding of human dystonia and novel therapeutic strategies.

Alcohol improves cerebellar learning deficit in myoclonus-dystonia: A clinical and electrophysiological investigation

OBJECTIVE

To characterize neurophysiological subcortical abnormalities in myoclonus-dystonia and their modulation by alcohol administration.

METHODS

Cerebellar associative learning and basal ganglia-brainstem interaction were investigated in 17 myoclonus-dystonia patients with epsilon-sarcoglycan (SGCE) gene mutation and 21 age- and sex-matched healthy controls by means of classical eyeblink conditioning and blink reflex recovery cycle before and after alcohol intake resulting in a breath alcohol concentration of 0.08% (0.8g/l). The alcohol responsiveness of clinical symptoms was evaluated by 3 blinded raters with a standardized video protocol and clinical rating scales including the Unified Myoclonus Rating Scale and the Burke-Fahn-Marsden Dystonia Rating Scale.

RESULTS

Patients showed a significantly reduced number of conditioned eyeblink responses before alcohol administration compared to controls. Whereas the conditioning response rate decreased under alcohol intake in controls, it increased in patients (analysis of variance: alcohol state × group, p = 0.004). Blink reflex recovery cycle before and after alcohol intake did not differ between groups. Myoclonus improved significantly after alcohol intake (p = 0.016). The severity of action myoclonus at baseline correlated negatively with the conditioning response in classical eyeblink conditioning in patients.

INTERPRETATION

The combination of findings of reduced baseline acquisition of conditioned eyeblink responses and normal blink reflex recovery cycle in patients who improved significantly with alcohol intake suggests a crucial role of cerebellar networks in the generation of symptoms in these patients. Ann Neurol 2017;82:543-553.

Adaptation of feedforward movement control is abnormal in patients with cervical dystonia and tremor

OBJECTIVE

It is under debate whether the cerebellum plays a role in dystonia pathophysiology and in the expression of clinical phenotypes. We investigated a typical cerebellar function (anticipatory movement control) in patients with cervical dystonia (CD) with and without tremor.

METHODS

Twenty patients with CD, with and without tremor, and 17 healthy controls were required to catch balls of different load: 15 trials with a light ball, 25 trials with a heavy ball (adaptation) and 15 trials with a light ball (post-adaptation). Arm movements were recorded using a motion capture system. We evaluated: (i) the anticipatory adjustment (just before the impact); (ii) the extent and rate of the adaptation (at the impact) and (iii) the aftereffect in the post-adaptation phase.

RESULTS

The anticipatory adjustment was reduced during adaptation in CD patients with tremor respect to CD patients without tremor and controls. The extent and rate of adaptation and the aftereffect in the post-adaptation phase were smaller in CD with tremor than in controls and CD without tremor.

CONCLUSION

Patients with cervical dystonia and tremor display an abnormal predictive movement control.

SIGNIFICANCE

Our findings point to a possible role of cerebellum in the expression of a clinical phenotype in dystonia.

Cerebellum: An explanation for dystonia?

Dystonia is a movement disorder that is characterized by involuntary muscle contractions, abnormal movements and postures, as well as by non-motor symptoms, and is due to abnormalities in different brain areas. In this article, we focus on the growing number of experimental studies aimed at explaining the pathophysiological role of the cerebellum in dystonia. Lastly, we highlight gaps in current knowledge and issues that future research studies should focus on as well as some of the potential applications of this research avenue. Clarifying the pathophysiological role of cerebellum in dystonia is an important concern given the increasing availability of invasive and non-invasive stimulation techniques and their potential therapeutic role in this condition.