Surgical targets for dystonic tremor: Considerations between the globus pallidus and ventral intermediate thalamic nucleus

Deep Brain Stimulation with Double Targeting of the VIM and PSA for the Treatment of Rare Tremor Syndromes

INTRODUCTION

In tremor syndromes, pharmacological therapy is the primary treatment, but deep brain stimulation (DBS) is used when it is insufficient. We explore the use of DBS, focusing on the globus pallidus internus for dystonia and the ventral intermediate nucleus (VIM) for tremor conditions. We introduce the posterior subthalamic area (PSA) as a potential target, suggesting its efficacy in tremor reduction, particularly in rare tremor syndromes. We aim to evaluate the efficacy and safety of double targeting the VIM and PSA in rare tremor conditions, highlighting the limited existing data on this.

METHODS

Between 2019 and 2023, 22 patients with rare tremor syndromes were treated with bilateral DBS of the VIM and PSA. This case series consisted of 7 isolated head tremor, 1 hepatic encephalopathic tremor due to Abernethy syndrome, 2 voice tremor, 4 dystonic tremor, and 8 Holmes tremor (2 multiple sclerosis, 2 cerebellar insult, and 4 posttraumatic) patients. Patients' preoperative and 12-month postoperative tremor scores were compared, and the optimum VIM and PSA stimulation areas were investigated.

RESULTS

There was a significant reduction in the mean TRS score from 3.70 (±0.57) to 0.45 (±0.68) after 12 months of surgery. Specific outcomes for different indications were observed: for head tremor, 6 of 7 patients showed a reduction in TRS scores to 0 points; the vocal tremor patients demonstrated improvement; this change was not statistically significant, which is likely to be due to the low number of patients in this subgroup; the dystonic tremor patients showed either complete tremor abolition or a reduction in TRS scores; the Holmes tremor patients showed an 80% reduction in TRS scores; and the hepatic encephalopathy tremor and Abernethy syndrome patients showed a 75% improvement in TRS scores. The stimulation parameters converged on the VIM and dorsal PSA. Complications included the need for electrode repositioning, infections requiring electrode removal and re-implantation, dysarthria, and stimulation-induced ataxia, which was resolved by adjusting the stimulation parameters.

DISCUSSION

The literature on DBS for rare tremors is limited. Double targeting of the VIM and PSA appears to produce promising improvements on the outcomes reported in the existing literature on VIM-only DBS. The proximity of the VIM and PSA allows for flexible electrode placement, contributing to the potential success of the dual-target approach. We also discuss the theoretical advantages of targeting the PSA based on the distribution of tremor circuits, emphasizing the need for further research and electrophysiological studies.

Hand Dystonia after Focused Ultrasound Thalamotomy in Essential Tremor

INTRODUCTION

Magnetic resonance guided focused ultrasound (MRgFUS) thalamotomy is an effective treatment for drug-resistant tremor. The most frequent side effects are ataxia, gait disturbance, paresthesias, dysgeusia, and hemiparesis. Here, we report the first case of thalamic hand dystonia rapidly occurring after MRgFUS thalamotomy of the ventral intermediate nucleus (V.im).

CASE PRESENTATION

MRgFUS thalamotomy was performed in a 60-year-old left-handed patient for his disabling medically refractory essential tremor. The intervention resulted in a marked reduction of his action tremor. However, the patient developed an unvoluntary abnormal posture in his left hand a few days after the procedure with difficulty holding a cigarette between his fingers. Brain MRI revealed the expected MRgFUS lesion within the right V.im as well as an extension of the lesion anteriorly to the V.im in the ventro-oralis nucleus. Tractography showed that the lesion disrupted the dentato-rubro-thalamic tract as expected with a lesion suppressing tremor. However, the lesion also was interrupted fibers connecting to the superior frontal and pre-central cortices (primary motor cortex, premotor cortex, and supplementary area). We hypothesized that the interventional MRgFUS thalamotomy was slightly off target, which induced a dysfunction within the cortico-striato-thalamo-cortical network and the cerebello-thalamo-cortical pathway reaching a sufficient threshold of basal ganglia/cerebellum circuitry interference to induce dystonia.

CONCLUSION

This rare side effect emphasizes the risk of imbalance within the dystonia network (i.e., basal ganglia-cerebello-thalamo-cortical circuit) secondary to V.im thalamotomy.

Effect of Thalamic versus Pallidal Deep Brain Stimulation on Head Tremor in Dystonic and Essential Tremor Patients-A Retrospective Video-Blinded Study

BACKGROUND

Head tremor is common in dystonia syndromes and difficult to treat. Deep brain stimulation (DBS) is a therapeutic option in medically-refractory cases. In most DBS-centers, the globus pallidus internus (GPi) is targeted in patients with predominant dystonia and the ventrointermediate nucleus of the thalamus (Vim) in predominant tremor. The aim of the study was to evaluate the effect of GPi- versus Vim-DBS in dystonic or essential head tremor.

METHODS

All patients with dystonia or essential tremor (ET) (n = 381) who underwent DBS surgery at our institution between 1999 and 2020 were screened for head tremor in our database according to predefined selection criteria. Of the 33 patients meeting inclusion criteria tremor and dystonia severity were assessed at baseline, short- (mean 10 months) and long-term follow-up (41 months) by two blinded video-raters.

RESULTS

Twenty-two patients with dystonic head tremor received either GPi- (n = 12) or Vim-stimulation (n = 10), according to the prevailing clinical phenotype. These two groups were compared with 11 patients with ET, treated with Vim-stimulation. The reduction in head tremor from baseline to short- and long-term follow-up was 60-70% and did not differ significantly between the three groups.

CONCLUSIONS

GPi-DBS effectively and sustainably reduced head tremor in idiopathic dystonia. The effect was comparable to the effect of Vim-DBS on head tremor in dystonia patients with predominant limb tremor and to the effect of Vim-DBS on head tremor in ET.

Outcomes of Focused Ultrasound Thalamotomy in Tremor Syndromes

BACKGROUND

The current literature comparing outcomes after a unilateral magnetic resonance image-guided focused ultrasound (MRgFUS) thalamotomy between tremor syndromes is limited and remains a possible preoperative factor that could help predict the long-term outcomes.

OBJECTIVE

The aim was to report on the outcomes between different tremor syndromes after a unilateral MRgFUS thalamotomy.

METHODS

A total of 66 patients underwent a unilateral MRgFUS thalamotomy for tremor between November 2018 and May 2020 at St Vincent's Hospital Sydney. Each patient's tremor syndrome was classified prior to treatment. Clinical assessments, including the hand tremor score (HTS) and Quality of Life in Essential Tremor Questionnaire (QUEST), were performed at baseline and predefined intervals to 36 months.

RESULTS

A total of 63 patients, comprising 30 essential tremor (ET), 24 dystonic tremor (DT), and 9 Parkinson's disease tremor (PDT) patients, returned for at least one follow-up. In the ET patients, at 24 months there was a 61% improvement in HTS and 50% improvement in QUEST compared to baseline. This is in comparison to PDT patients, where an initial benefit in HTS and QUEST was observed, which waned at each follow-up, remaining significant only up until 12 months. In the DT patients, similar results were observed to the ET patients: at 24 months there was a 61% improvement in HTS and 43% improvement in QUEST compared to baseline.

CONCLUSION

These results support the use of unilateral MRgFUS thalamotomy for the treatment of DT, which appears to have a similar expected outcome to patients diagnosed with ET. Patients with PDT should be warned that there is a risk of treatment failure. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Challenge of Choosing the Right Stimulation Target for Dystonic Tremor-A Series of Instructive Cases

Background

Thalamic deep brain stimulation (DBS) is established for medically refractory tremor syndromes and globus pallidus stimulation (GPi-DBS) for medically refractory dystonia syndromes. For combined tremor and dystonia syndromes, the best target is unclear.

Objectives

We present four patients with two different profiles whose clinical course demonstrates that our current analysis of clinical symptomatology is not a sufficient predictor of surgical success.

Methods

Outcome parameters were assessed with observer-blinded video ratings and included the Fahn-Tolosa-Marin-Tremor Rating Scale (FTM-TRS) and the Unified Dystonia Rating Scale (UDRS).

Results

Two patients with "predominant lateralized action tremor" of the hands and mild cervical dystonia showed no relevant tremor improvement after GPi-DBS, but UDRS improved (mean, 45%). Rescue ventral intermediate nucleus of the thalamus (Vim)-DBS electrodes were implanted and both patients benefited significantly with a mean tremor reduction of 51%.Two other patients with "axial-predominant action tremor of the trunk and head" associated with cervical dystonia underwent bilateral Vim-DBS implantation with little effect on tremor (24% reduction in mean FTM-TRS total score) and no effect on dystonic symptoms. GPi rescue DBS was implanted and showed a significant effect on tremor (63% reduction in mean FTM-TRS) and dystonia (49% reduction in UDRS).

Conclusions

The diagnosis of dystonic tremor alone is not a sufficient predictor to establish the differential indication of GPi- or Vim-DBS. Further criteria (eg, proximal-distal distribution of tremor/dystonia) are needed to avoid rescue surgery in the future. On the other hand, the course of our patients encourages rescue surgery in such severely disabled patients if the first target fails.

DBS in tremor with dystonia: VIM, GPi or both? A review of the literature and considerations from a single-center experience

BACKGROUND

Deep brain stimulation (DBS) is an established treatment for dystonia and tremor. However, there is no consensus about the best surgical targeting strategy in patients with concomitant tremor and dystonia. Both the thalamic ventral intermediate nucleus (VIM) and the globus pallidus pars interna (GPi) have been proposed as targets. Few cases using them together in a double-target approach have also been reported.

METHODS

We reviewed the literature on this topic, summarizing results of different target choices. Additionally, we retrospectively report a case series of nine patients with sporadic dystonia and severe tremor treated with a double-target strategy at our center. Outcome measures were the Burke-Fahn-Marsden Dystonia Rating Scale (BFM) and Eq-5d scale.

RESULTS

In published studies of patients with dystonia and tremor, VIM-DBS is highly effective on tremor but raise some concerns about dystonia's control, while GPi-DBS is more effective on dystonia but does not always relieve tremor. GPi + VIM-DBS shows good efficacy but is rarely reported and reserved for selected patients. In our patients, the double-target strategy obtained a significant and durable improvement in tremor, dystonia, and quality of life. Additionally, compared with a cohort of patients with tremor treated with VIM-DBS only, significantly lower frequency and intensity of VIM stimulation were required to control tremor.

CONCLUSION

Our findings and published evidence seem to support the double-targeting approach as a safe and effective option in selected patients with tremor-dominant dystonia. This strategy appears to provide a more extensive control of either dystonia or tremor and may have a potential for limiting stimulation-related side effects.

Combined thalamic and pallidal deep brain stimulation for dystonic tremor

BACKGROUND

Deep brain stimulation (DBS) has been proposed to treat disabling dystonic tremor (DT), but there is debate about the optimal target. DBS of the globus pallidus interna (GPi) may be insufficient to control tremor, and DBS of the ventral intermediate thalamic nucleus (VIM) may inadequately control dystonic features, raising the question of combining both targets.

OBJECTIVES

To report the respective effects on DT symptoms of high-frequency stimulation of the VIM, the GPi and both targets simultaneously stimulated.

METHODS

Three patients with DT treated by bilateral high frequency DBS of 2 targets (VIM and GPi) were assessed 12 months after surgery in 4 conditions (VIM and GPi-DBS; GPi-DBS only; VIM-DBS only; DBS switched Off for both targets) by 3 independent movement disorders specialists blinded to the condition.

RESULTS

The Fahn-Tolosa-Marin-tremor-rating-scale (FTM-TRS) and Burke-Fahn-Marsden-dystonia-rating-scale (BFM-DRS) scores were more improved by combined DBS than VIM alone or GPi alone. Compared to Off/Off condition, mean total FTM-TRS score decrease was 34%, 42% and 63% respectively with VIM only, GPi only and combined VIM and GPi stimulation. Mean total BFM-DRS score decrease was 34%, 37% and 60% respectively with VIM only, GPi only and combined VIM and GPi stimulation, compared to Off/Off condition. Improvement concerned both motor, functional and activities of daily living sub-scores. No complications or adverse events were observed.

CONCLUSION

Combined VIM- and GPi-DBS, by modulating the cerebello-thalamo-cortical network and the basal ganglia-thalamo-cortical network, both involved in DT pathophysiology, may be more efficient than single DBS targeting only one of them.

Vim-Thalamic Deep Brain Stimulation for Cervical Dystonia and Upper-Limb Tremor: Quantification by Markerless-3D Kinematics and Accelerometry

Background:

Deep Brain Stimulation (DBS) for dystonia is usually targeted to the globus pallidus internus (GPi), though stimulation of the ventral-intermediate nucleus of the thalamus (Vim) can be an effective treatment for phasic components of dystonia including tremor. We report on a patient who developed a syndrome of bilateral upper limb postural and action tremor and progressive cervical dystonia with both phasic and tonic components which were responsive to Vim DBS. We characterize and quantify this effect using markerless-3D-kinematics combined with accelerometry.

Methods:

Stereo videography was used to record our subject in 3D. The DeepBehavior toolbox was applied to obtain timeseries of joint position for kinematic analysis [1]. Accelerometry was performed simultaneously for comparison with prior literature.

Results:

Bilateral Vim DBS improved both dystonic tremor magnitude and tonic posturing. DBS of the hemisphere contralateral to the direction of dystonic head rotation (left Vim) had greater efficacy. Assessment of tremor magnitude by 3D-kinematics was concordant with accelerometry and was able to quantify tonic dystonic posturing.

Discussion:

In this case, Vim DBS treated both cervical dystonic tremor and dystonic posturing. Markerless-3D-kinematics should be further studied as a method of quantifying and characterizing tremor and dystonia.

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.

Habituation After Deep Brain Stimulation in Tremor Syndromes: Prevalence, Risk Factors and Long-Term Outcomes

Deep brain stimulation (DBS) of the thalamus is an effective treatment for medically refractory essential, dystonic and Parkinson's tremor. It may also provide benefit in less common tremor syndromes including, post-traumatic, cerebellar, Holmes, neuropathic and orthostatic tremor. The long-term benefit of DBS in essential and dystonic tremor (ET/DT) often wanes over time, a phenomena referred to as stimulation "tolerance" or "habituation". While habituation is generally accepted to exist, it remains controversial. Attempts to quantify habituation have revealed conflicting reports. Placebo effects, loss of micro-lesional effect, disease related progression, suboptimal stimulation and stimulation related side-effects may all contribute to the loss of sustained long-term therapeutic effect. Habituation often presents as substantial loss of initial DBS benefit occurring as early as a few months after initial stimulation; a complex and feared issue when faced in the setting of optimal electrode placement. Simply increasing stimulation current tends only to propagate tremor severity and induce stimulation related side effects. The report by Paschen and colleagues of worsening tremor scores in the "On" vs. "Off" stimulation state over time, even after accounting for "rebound" tremor, supports the concept of habituation. However, these findings have not been consistent across all studies. Chronic high intensity stimulation has been hypothesized to induce detrimental plastic effects on tremor networks, with some lines of evidence that DT and ET may be more susceptible than Parkinson's tremor to habituation. However, Tsuboi and colleague's recent longitudinal follow-up in dystonic and "pure" essential tremor suggests otherwise. Alternatively, post-mortem findings support a biological adaption to stimulation. The prevalence and etiology of habituation is still not fully understood and management remains difficult. A recent study reported that alternating thalamic stimulation parameters at weekly intervals provided improved stability of tremor control consistent with reduced habituation. In this article the available evidence for habituation after DBS for tremor syndromes is reviewed; including its prevalence, time-course, possible mechanisms; along with expected long-term outcomes for tremor and factors that may assist in predicting, preventing and managing habituation.

Dystonia and Cerebellum: From Bench to Bedside

Dystonia pathogenesis remains unclear; however, findings from basic and clinical research suggest the importance of the interaction between the basal ganglia and cerebellum. After the discovery of disynaptic pathways between the two, much attention has been paid to the cerebellum. Basic research using various dystonia rodent models and clinical studies in dystonia patients continues to provide new pieces of knowledge regarding the role of the cerebellum in dystonia genesis. Herein, we review basic and clinical articles related to dystonia focusing on the cerebellum, and clarify the current understanding of the role of the cerebellum in dystonia pathogenesis. Given the recent evidence providing new hypotheses regarding dystonia pathogenesis, we discuss how the current evidence answers the unsolved clinical questions.

Comparative connectivity correlates of dystonic and essential tremor deep brain stimulation

The pathophysiology of dystonic tremor and essential tremor remains partially understood. In patients with medication-refractory dystonic tremor or essential tremor, deep brain stimulation (DBS) targeting the thalamus or posterior subthalamic area has evolved into a promising treatment option. However, the optimal DBS targets for these disorders remains unknown. This retrospective study explored the optimal targets for DBS in essential tremor and dystonic tremor using a combination of volumes of tissue activated estimation and functional and structural connectivity analyses. We included 20 patients with dystonic tremor who underwent unilateral thalamic DBS, along with a matched cohort of 20 patients with essential tremor DBS. Tremor severity was assessed preoperatively and approximately 6 months after DBS implantation using the Fahn-Tolosa-Marin Tremor Rating Scale. The tremor-suppressing effects of DBS were estimated using the percentage improvement in the unilateral tremor-rating scale score contralateral to the side of implantation. The optimal stimulation region, based on the cluster centre of gravity for peak contralateral motor score improvement, for essential tremor was located in the ventral intermediate nucleus region and for dystonic tremor in the ventralis oralis posterior nucleus region along the ventral intermediate nucleus/ventralis oralis posterior nucleus border (4 mm anterior and 3 mm superior to that for essential tremor). Both disorders showed similar functional connectivity patterns: a positive correlation between tremor improvement and involvement of the primary sensorimotor, secondary motor and associative prefrontal regions. Tremor improvement, however, was tightly correlated with the primary sensorimotor regions in essential tremor, whereas in dystonic tremor, the correlation was tighter with the premotor and prefrontal regions. The dentato-rubro-thalamic tract, comprising the decussating and non-decussating fibres, significantly correlated with tremor improvement in both dystonic and essential tremor. In contrast, the pallidothalamic tracts, which primarily project to the ventralis oralis posterior nucleus region, significantly correlated with tremor improvement only in dystonic tremor. Our findings support the hypothesis that the pathophysiology underpinning dystonic tremor involves both the cerebello-thalamo-cortical network and the basal ganglia-thalamo-cortical network. Further our data suggest that the pathophysiology of essential tremor is primarily attributable to the abnormalities within the cerebello-thalamo-cortical network. We conclude that the ventral intermediate nucleus/ventralis oralis posterior nucleus border and ventral intermediate nucleus region may be a reasonable DBS target for patients with medication-refractory dystonic tremor and essential tremor, respectively. Uncovering the pathophysiology of these disorders may in the future aid in further improving DBS outcomes.

Assessment of Botulinum Neurotoxin Injection for Dystonic Hand Tremor: A Randomized Clinical Trial

Importance

There is an unmet need for safe and efficacious treatments for upper-extremity dystonic tremor (DT). To date, only uncontrolled retrospective case series have reported the effect of botulinum neurotoxin (BoNT) injections on upper-extremity DT.

Objective

To assess the effect of BoNT injections on tremor in patients with upper-extremity DT.

Design, Setting, and Participants

In this placebo-controlled, parallel-group randomized clinical trial, 30 adult patients with upper-extremity DT treated at a movement disorder clinic in a tertiary care university hospital were randomized in a 1:1 ratio to BoNT or saline injection, 0.9%, using a computer-generated randomization sequence. Randomization was masked using opaque envelopes. The participant, injector, outcome assessor, and statistician were blinded to the randomization. Participants were recruited between November 20, 2018, and December 12, 2019, and the last follow-up was completed in March 2020.

Interventions

Participants received electromyographically guided intramuscular injections of BoNT or placebo into the tremulous muscles of the upper extremity. Injection patterns and doses were individualized according to tremor phenomenologic findings.

Main Outcomes and Measures

The primary outcome was the total score on the Fahn-Tolosa-Marin Tremor Rating Scale 6 weeks after the intervention. Outcomes were assessed at baseline, 6 weeks, and 12 weeks. All patients were offered open-label BoNT injections after 12 weeks and reassessed 6 weeks later.

Results

A total of 48 adult patients with a diagnosis of brachial dystonia with DT were screened. Fifteen were ineligible and 3 refused consent; therefore, 30 patients (mean [SD] age, 46.0 [18.6] years; 26 [86.7%] male) were recruited, with 15 randomized to receive BoNT and 15 to receive placebo. In the intention-to-treat group, the Fahn-Tolosa-Marin Tremor Rating Scale total score was significantly lower in the BoNT group at 6 weeks (adjusted mean difference, -10.9; 95% CI, -15.4 to -6.5; P < .001) and 12 weeks (adjusted mean difference, -5.7; 95% CI, -11.0 to -0.5; P = .03). More participants in the BoNT group reported global improvement on the Global Impression of Change (PGIC) assessment (PGIC 1, 2, and 3: BoNT: 4 [26.7%], 6 [40.0%], and 5 [33.3%]; placebo: 5 [33.3%], 10 [66.7%], and 0, respectively; P = .047). Subjective hand weakness (BoNT: 6 [40.0%]; placebo: 4 [28.6%], P = .52) and dynamometer-assessed grip strength (mean difference, -0.2 log10[kgf/m2]2/Hz-Hz; 95% CI, -0.9 to 0.4 log10[kgf/m2]2/Hz-Hz; P = .45) were similar in both groups.

Conclusions and Relevance

In this randomized clinical trial, botulinum neurotoxin injections were superior to placebo in reducing tremor severity in upper-extremity DT. An individualized approach to muscle selection and dosing was beneficial without unacceptable adverse effects.

Trial Registration

Clinical Trials Registry of India (http://ctri.nic.in) Identifier: CTRI/2018/02/011721.

Thalamic deep brain stimulation for acquired dystonia in children and young adults: a phase 1 clinical trial

OBJECTIVE

The aim of this study was to evaluate the feasibility and preliminary efficacy and safety of combined bilateral ventralis oralis posterior/ventralis intermedius (Vop/Vim) deep brain stimulation (DBS) for the treatment of acquired dystonia in children and young adults. Pallidal DBS is efficacious for severe, medication-refractory isolated dystonia, providing 50%-60% long-term improvement. Unfortunately, pallidal stimulation response rates in acquired dystonia are modest and unpredictable, with frequent nonresponders. Acquired dystonia, most commonly caused by cerebral palsy, is more common than isolated dystonia in pediatric populations and is more recalcitrant to standard treatments. Given the limitations of pallidal DBS in acquired dystonia, there is a need to explore alternative brain targets. Preliminary evidence has suggested that thalamic stimulation may be efficacious for acquired dystonia.

METHODS

Four participants, 3 with perinatal brain injuries and 1 with postencephalitic symptomatic dystonia, underwent bilateral Vop/Vim DBS and bimonthly evaluations for 12 months. The primary efficacy outcome was the change in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) and Barry-Albright Dystonia Scale (BADS) scores between the baseline and 12-month assessments. Video documentation was used for blinded ratings. Secondary outcomes included evaluation of spasticity (Modified Ashworth Scale score), quality of life (Pediatric Quality of Life Inventory [PedsQL] and modified Unified Parkinson's Disease Rating Scale Part II [UPDRS-II] scores), and neuropsychological assessments. Adverse events were monitored for safety.

RESULTS

All participants tolerated the procedure well, and there were no safety concerns or serious adverse events. There was an average improvement of 21.5% in the BFMDRS motor subscale score, but the improvement was only 1.6% according to the BADS score. Following blinded video review, dystonia severity ratings were even more modest. Secondary outcomes, however, were more encouraging, with the BFMDRS disability subscale score improving by 15.7%, the PedsQL total score by 27%, and the modified UPDRS-II score by 19.3%. Neuropsychological assessment findings were unchanged 1 year after surgery.

CONCLUSIONS

Bilateral thalamic neuromodulation by DBS for severe, medication-refractory acquired dystonia was well tolerated. Primary and secondary outcomes showed highly variable treatment effect sizes comparable to those of pallidal stimulation in this population. As previously described, improvements in quality of life and disability were not reflected in dystonia severity scales, suggesting a need for the development of scales specifically for acquired dystonia.Clinical trial registration no.: NCT03078816 (clinicaltrials.gov).

Long-Term Successful Outcome of Dystonic Head Tremor after Bilateral Deep Brain Stimulation of the Ventral Intermediate and Ventro-Oral Internus Nuclei: A Case Report and Literature Review of Dystonic Head Tremor

Head tremor in patients with dystonia is referred to as dystonic tremor. During surgical treatment, numerous targets may be selected, including the internal segment of the globus pallidus and the ventral intermediate (Vim) nucleus; however, there is no consensus concerning the most effective treatment target. We report herein a case of dystonic head tremor in which improvement persisted for 5 years after deep brain stimulation (DBS) of the bilateral thalamic Vim and ventro-oral internus (Voi) nuclei. The patient, a 67-year-old woman, has a horizontal head tremor associated with cervical dystonia that had been resistant to drug treatment over 3 years. Immediately following surgery, dystonia and tremor symptoms had completely improved. Voice volume declined and dysarthria occurred but improved upon adjusting the stimulation conditions. Over 5 years, both head tremor and cervical dystonia have been completely controlled, and no other obvious complications have been observed. As the Voi nucleus receives pallidothalamic projections involved in dystonia and the Vim nucleus receives cerebellothalamic projections involved in tremors, stimulating these 2 nuclei with the same electrode appears reasonable in the treatment of dystonic tremor. This case suggests that Vim-Voi DBS may be effective for treating dystonic head tremor.

Deep-Brain Stimulation for Essential Tremor and Other Tremor Syndromes: A Narrative Review of Current Targets and Clinical Outcomes

Tremor is a prevalent symptom associated with multiple conditions, including essential tremor (ET), Parkinson's disease (PD), multiple sclerosis (MS), stroke and trauma. The surgical management of tremor evolved from stereotactic lesions to deep-brain stimulation (DBS), which allowed safe and reversible interference with specific neural networks. This paper reviews the current literature on DBS for tremor, starting with a detailed discussion of current tremor targets (ventral intermediate nucleus of the thalamus (Vim), prelemniscal radiations (Raprl), caudal zona incerta (Zi), thalamus (Vo) and subthalamic nucleus (STN)) and continuing with a discussion of results obtained when performing DBS in the various aforementioned tremor syndromes. Future directions for DBS research are then briefly discussed.

Pallidal Deep Brain Stimulation in Patients with Prior Bilateral Pallidotomy and Selective Peripheral Denervation for Treatment of Dystonia

INTRODUCTION

Deep brain stimulation (DBS) of the globus pallidus internus has become an accepted treatment for severe isolated idiopathic and inherited dystonia. Patients who had other forms of surgery earlier, such as radiofrequency lesioning or selective peripheral denervation, however, usually are not considered candidates for DBS.

OBJECTIVE

The aim of this study was to evaluate the long-term outcome of pallidal DBS in a rare subgroup of patients who had undergone both pallidotomy and selective peripheral denervation previously with a waning effect over the years.

METHODS

Pallidal DBS was performed according to a prospective study protocol in 2 patients with isolated idiopathic dystonia, and patients were followed for a period of at least 6 years.

RESULTS

Both patients benefitted from long-lasting amelioration of dystonia after pallidal DBS, which was comparable to that of patients who did not have previous surgeries. In a 62-year-old female with cervical dystonia both the Burke-Fahn-Marsden (BFM) and the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) motor scores were improved at follow-up 8 years after surgery (50 and 39%). In a 32-year-old male with generalized dystonia, the BFM motor and disability scores showed marked improvement at 6.5 years of follow-up (82 and 66%).

CONCLUSIONS

Pallidal DBS can yield marked and long-lasting improvement in patients who underwent both pallidotomy and selective peripheral denervation earlier. Therefore, such patients, in general, should not be excluded from DBS.

Treatment of Dystonia: Medications, Neurotoxins, Neuromodulation, and Rehabilitation

Dystonia is a complex disorder with numerous presentations occurring in isolation or in combination with other neurologic symptoms. Its treatment has been significantly improved with the advent of botulinum toxin and deep brain stimulation in recent years, though additional investigation is needed to further refine these interventions. Medications are of critical importance in forms of dopa-responsive dystonia but can be beneficial in other forms of dystonia as well. Many different rehabilitative paradigms have been studied with variable benefit. There is growing interest in noninvasive stimulation as a potential treatment, but with limited long-term benefit shown to date, and additional research is needed. This article reviews existing evidence for treatments from each of these categories. To date, there are many examples of incomplete response to available treatments, and improved therapies are needed.

Deep Brain Stimulation and Thalamotomy for the Treatment of Dystonia Acquired by Moyamoya Disease with Stroke

Background:

Moyamoya disease (MMD) is a type of chronic cerebrovascular disease. Currently, revascularization surgery including direct/indirect procedure is recommended for symptomatic patients. However, some patients still respond poorly to the treatment or develop secondary symptoms.

Case report:

We report the first case of an MMD patient treated with deep brain stimulation (DBS) and thalamotomy. Symptoms of dystonia due to hemorrhage in the thalamus responded poorly to revascularization surgery, but were considerably alleviated by stereotactic neurosurgery.

Discussion:

Our case report provides a potential strategy for management of refractory symptomatic MMD patients with dystonia and also supports the combined efficacy of DBS with thalamotomies.

Highlights:

Approximately 30% of patients with Moyamoya disease (MMD) presenting movement symptoms do not respond well to revascularization surgery. We reported an MMD patient treated with deep brain stimulation (DBS) and thalamotomy with significant dystonia and dystonic tremor symptom amelioration. It indicates that DBS or stereotactic lesioning might be a potential treatment for the refractory movement symptoms of MMD.

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.

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.

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.

Toward adaptive deep brain stimulation for dystonia

The presence of abnormal neural oscillations within the cortico-basal ganglia-thalamo-cortical (CBGTC) network has emerged as one of the current principal theories to explain the pathophysiology of movement disorders. In theory, these oscillations can be used as biomarkers and thereby serve as a feedback signal to control the delivery of deep brain stimulation (DBS). This new form of DBS, dependent on different characteristics of pathological oscillations, is called adaptive DBS (aDBS), and it has already been applied in patients with Parkinson's disease. In this review, the authors summarize the scientific research to date on pathological oscillations in dystonia and address potential biomarkers that might be used as a feedback signal for controlling aDBS in patients with dystonia.

Botulinum toxin and occupational therapy for Writer's cramp

BACKGROUND

Writer's cramp (WC) is a form of focal hand dystonia, for which focal botulinum neurotoxin (BoNT) injections are the current best therapy. Past studies have shown that some types of rehabilitative therapy can be useful. We hypothesized that BoNT together with a specific type of occupational therapy would be better than BoNT alone for treating WC patients comparing the effects with a patient-rated subjective scale.

METHODS

Twelve WC patients were randomized to two groups. Six received only BoNT therapy and 6 received BoNT & occupational therapy. The occupational therapy involved specific exercises of finger movements in the direction opposite to the dystonic movements during writing. BoNT was injected by movement disorders neurologists in the affected muscles under electromyography-guidance. The primary outcome was the patient-rated subjective scale at 20 weeks. Secondary exploratory outcomes included the writer's cramp rating scale (WCRS), writer's cramp impairment scale (WCIS), the writer's cramp disability scale (WCDS), handgrip strength and kinetic parameters.

RESULTS

The patient-rated subjective scale scores at 20 weeks were not significantly different between the two groups. Significant objective improvement was noted in the BoNT & occupational therapy group, as noted by the decrease (28%) in WCIS scores.

CONCLUSIONS

Improvement of the primary outcome measure, the patient-rated subjective scale, was not achieved. However, significant improvement was found in the BoNT & occupational therapy group in a secondary measure of impairment. Our hypothesis-driven study results are likely limited by small sample size, and further large-scale studies of occupational therapy methods to improve the efficacy of BoNT seems worthwhile.

[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.

Importance of the initial response to GPi deep brain stimulation in dystonia: A nine year quality of life study

BACKGROUND

Long-term efficacy of deep brain stimulation (DBS) on health-related quality-of-life (HRQoL) for isolated dystonia is not well established. This study aims to determine the long-term impact of DBS on HRQoL outcomes and identify clinical predictors.

METHODS

We retrospectively investigated 16 inherited or idiopathic isolated dystonia patients treated with bilateral globus pallidus internus DBS who were followed beyond 9 years at our center. The cohort consisted of 9 males, 7 females; 10 generalized, 6 segmental; mean (range) age at implantation, 37.0 (8-67) years; mean follow-up duration after implantation, 10.9 (9-13) years. We employed the Unified Dystonia Rating Scale for motor and Short Form Health Survey for HRQoL assessments to monitor the change longitudinally. We analyzed the changes in motor and HRQoL at 1-2 years (short-term) and ≥9 years (long-term) follow-up as compared to baseline with a Wilcoxon signed-rank test. We assessed the factors that predicted motor and HRQoL improvement with univariate regression analyses.

RESULTS

Motor (41.6%; p = 0.004) and HRQoL (total score, p = 0.039) improvements remained significant at long-term follow-up and, in the regression analysis, change in HRQoL outcomes correlated significantly with change in motor outcomes (R² = 0.384, p = 0.010). Additionally, short-term motor and HRQoL improvements predicted the long-term motor (R² = 0.384, p = 0.010) and HRQoL (total score, R² = 0.594, p < 0.001) outcomes, respectively.

CONCLUSION

Motor and HRQoL improvements with DBS in isolated dystonia remain sustained for nearly a decade and may largely be predictable by the short-term response to DBS.

Thalamus Stimulation for Myoclonus Dystonia Syndrome: Five Cases and Long-Term Follow-up

BACKGROUND

Myoclonic dystonia syndrome (MDS) is a rare inherited movement disorder characterized by the coexistence of myoclonic jerks and dystonia. Deep brain stimulation (DBS) is a promising treatment for patients with MDS that targets the globus pallidus internus or ventral intermediate nucleus (Vim) of the thalamus. However, there are few studies regarding the long-term effects of Vim DBS in patients with MDS and even fewer in those without gene mutations.

METHODS

Two positive and three negative SGCE mutation patients presenting with predominant myoclonus underwent Vim DBS. The Unified Myoclonus Rating Scale and the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) were assessed pre- and postoperation.

RESULTS

Over an average follow-up period of 50 months, the myoclonus improvement rate was 92.7%. The average improvement in the BFMDRS motor score was 71.4% and the average improvement in the BFMDRS disabling score was 75.8%.

CONCLUSIONS

This study suggests that Vim DBS can be a safe and effective treatment option for patients with MDS. Vim DBS alone may be preferable for patients with myoclonus-dominated MDS regardless of the identification of an SGCE mutation. Additional globus pallidus internus DBS may be used for progressive dystonia after Vim DBS.

Surgical treatments for tremors

Stereotactic surgery is an increasingly popular option for disabling tremors whenever it is insufficiently improved by drug treatment. Surgical approaches are expanding. Thalamic deep brain stimulation is one of the most efficacious treatments. Its recent technological advances with adaptive stimulation and new electrodes configuration will allow a more physiological stimulation. However, a reappraisal of less invasive, new lesioning procedures is underway. Gamma Knife thalamotomy and magnetic resonance-guided focused ultrasounds encounter very few contraindications. Recent studies reported their efficacy on tremor control and safety profile. Besides the ventralis intermedius nucleus of the thalamus, alternative targets are also emerging. The effectiveness of surgical therapies on essential tremor and Parkinson's disease tremor is well established. For more uncommon tremors, preliminary studies are encouraging. All these surgical therapies can be proposed as treatment option for medically refractory tremors.

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.

Deep brain stimulation of the thalamic ventral intermediate nucleus for Benedikt's syndrome mainly present as tremor: a long-term case observation

Benedikt's syndrome (BS) is caused by the lesion in the midbrain and specifically manifests a series of symptoms, including ipsilateral third nerve palsy, contralateral tremor, hemiataxia, and hyperactive tendon reflexes. Deep brain stimulation (DBS) for BS emerges as a new approach and achieves successfully results. We report a successful case report of thalamic ventral intermediate (VIM) nucleus DBS for a patient with BS. During follow-up of 3 years, DBS successfully control the tremor and greatly improve his living and working quality. We consider that VIM DBS may have sustained benefit for refractory BS that mainly presents as tremor.

Deep Brain Stimulation Management of Essential Tremor with Dystonic Features

Clinical Vignette

A 64-year-old female with essential tremor (ET) presents for evaluation of deep brain stimulation (DBS) candidacy. Examination revealed subtle dystonic features as well as a disabling postural-action tremor.

Clinical Dilemma

Can dystonia occur in the setting of the diagnosis of ET and can its presence alter DBS target selection?

Clinical Solution

Unilateral DBS implantation of the ventralis intermedius (Vim) led to improvement in both tremor and dystonic posturing.

Gap in Knowledge

Case reports of DBS in dystonic tremor suggest Vim, globus pallidus internus (GPi), and subthalamic targets may all be effective, to varying degrees, in improving both tremor and dystonia. More rigorous studies are needed to identify the optimal target(s).

Expert Commentary

This case underscores the limited evidence available to guide a clinician’s choice of DBS targets in patients with ET and dystonia. The severity of the dystonia and the presence of more generalized dystonia may alter the thinking about optimal targeting. Vim, GPi, and subthalamic targets appear potentially acceptable options, though Vim is usually the first target attempted when postural-action tremor is the chief complaint. Occasionally, a second rescue DBS lead may be necessary.

Surgical treatment of dystonia

INTRODUCTION

Treatment of dystonia should be individualized and tailored to the specific needs of patients. Surgical treatment is an important option in medically refractory cases. Several issues regarding type of the surgical intervention, targets, and predict factors of benefit are still under debate. Areas covered: To date, several clinical trials have proven the benefit and safety of deep brain stimulation (DBS) for inherited and idiopathic isolated dystonia, whereas there is still insufficient evidence in combined and acquired dystonia. The globus pallidus internus (GPi) is the target with the best evidence, but data on the subthalamic nucleus seems also to be promising. Evidence suggests that younger patients with shorter disease duration experience greater benefit following DBS. Pallidotomy and thalamotomy are currently used in subset of carefully selected patients. The development of MRI-guided focused ultrasound might bring new options to ablation approach in dystonia. Expert commentary: GPi-DBS is effective and safe in isolated dystonia and should not be delayed when symptoms compromise quality of life and functionality. Identifying the best candidates to surgery on acquired and combined dystonias is still necessary. New insights about pathophysiology of dystonia and new technological advances will undoubtedly help to tailor surgery and optimize clinical effects.

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.

Thalamic deep brain stimulation for tremor in Parkinson disease, essential tremor, and dystonia

OBJECTIVE

To report on the long-term outcomes of deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) in Parkinson disease (PD), essential tremor (ET), and dystonic tremor.

METHODS

One hundred fifty-nine patients with PD, ET, and dystonia underwent VIM DBS due to refractory tremor at the Grenoble University Hospital. The primary outcome was a change in the tremor scores at 1 year after surgery and at the latest follow-up (21 years). Secondary outcomes included the relationship between tremor score reduction over time and the active contact position. Tremor scores (Unified Parkinson's Disease Rating Scale-III, items 20 and 21; Fahn, Tolosa, Marin Tremor Rating Scale) and the coordinates of the active contacts were recorded.

RESULTS

Ninety-eight patients were included. Patients with PD and ET had sustained improvement in tremor with VIM stimulation (mean improvement, 70% and 66% at 1 year; 63% and 48% beyond 10 years, respectively; p < 0.05). There was no significant loss of stimulation benefit over time (p > 0.05). Patients with dystonia exhibited a moderate response at 1-year follow-up (41% tremor improvement, p = 0.027), which was not sustained after 5 years (30% improvement, p = 0.109). The more dorsal active contacts' coordinates in the right lead were related to a better outcome 1 year after surgery (p = 0.029). During the whole follow-up, forty-eight patients (49%) experienced minor side effects, whereas 2 (2.0%) had serious events (brain hemorrhage and infection).

CONCLUSIONS

VIM DBS is an effective long-term (beyond 10 years) treatment for tremor in PD and ET. Effects on dystonic tremor were modest and transient.

CLASSIFICATION OF EVIDENCE

This provides Class IV evidence. It is an observational study.

Deep brain stimulation for dystonia: a novel perspective on the value of genetic testing

The dystonias are a group of disorders characterized by excessive muscle contractions leading to abnormal movements and postures. There are many different clinical manifestations and underlying causes. Deep brain stimulation (DBS) provides an effect treatment, but outcomes can vary considerably among the different subtypes of dystonia. Several variables are thought to contribute to this variation including age of onset and duration of dystonia, specific characteristics of the dystonic movements, location of stimulation and stimulator settings, and others. The potential contributions of genetic factors have received little attention. In this review, we summarize evidence that some of the variation in DBS outcomes for dystonia is due to genetic factors. The evidence suggests that more methodical genetic testing may provide useful information in the assessment of potential surgical candidates, and in advancing our understanding of the biological mechanisms that influence DBS outcomes.

Deep brain stimulation for myoclonus-dystonia syndrome with double mutations in DYT1 and DYT11

Myoclonus-dystonia syndrome (MDS) is a rare autosomal dominant inherited disorder characterized by the presentation of both myoclonic jerks and dystonia. Evidence is emerging that deep brain stimulation (DBS) may be a promising treatment for MDS. However, there are no studies reporting the effects of DBS on MDS with double mutations in DYT1 and DYT11. Two refractory MDS patients with double mutations were treated between 2011 and 2015 in our center. Genetic testing for DYT1 and DYT11 was performed through polymerase chain reaction amplification and direct sequencing of the specific exons of genes. For the first patient, initial bilateral ventral intermediate thalamus nucleus (Vim) DBS was performed. Because of worsening dystonia after initial improvement in symptoms, subsequent bilateral globus pallidus internus (GPi) DBS was offered at 43 months after initial surgery, which reversed the deterioration and restored the motor function. For the second patient, initial improvement in motor symptoms and quality of life was sustained at the follow-up 6 months after bilateral Vim DBS treatment. Thus, DBS may be an effective therapeutic option for MDS, even in patients with double mutations. Moreover, GPi DBS may be used as a supplementary treatment when initial Vim DBS fails to control MDS symptoms.

The essential tremor syndromes

PURPOSE OF REVIEW

Essential tremor has not been defined or used consistently in clinical diagnosis and research. Other monosymptomatic disorders are often referred to as essential tremor variants.

RECENT FINDINGS

There is now solid evidence that essential tremor, however defined, is a syndrome with multiple causes.

SUMMARY

A new tremor classification scheme is being developed by the International Parkinson and Movement Disorder Society Task Force on Tremor. In this scheme, tremor in the absence of other neurological signs is called isolated tremor, and tremor in combination with other signs is called combined tremor. Many isolated and combined tremor syndromes can be defined on the basis of commonly recurring or unique clinical symptoms and signs, including historical features (age at onset, family history, and temporal evolution) and tremor characteristics (body distribution, activation condition, associated features). Essential tremor, however defined, is simply a syndrome and not a specific disease. Essential tremor should be defined and used consistently, or this term should be abandoned. As essential tremor is an arbitrarily defined syndrome, it makes no sense to refer to other tremors as variants of essential tremor or essential tremor syndromes.

Deep brain stimulation for childhood dystonia: Is 'where' as important as in 'whom'?

Deep brain stimulation (DBS) has become a mainstay of dystonia management in adulthood. Typically targeting electrode placement in the GPi, sustained improvement in dystonic symptoms are anticipated in adults with isolated genetic dystonias. Dystonia in childhood is more commonly a symptomatic condition, with dystonia frequently expressed on the background of a structurally abnormal brain. Outcomes following DBS in this setting are much more variable, the reasons for which have yet to be elucidated. Much of the focus on improving outcomes following DBS in dystonia management has been on the importance of patient selection, with, until recently, little discussion of the choice of target. In this review, we advance the argument that patient selection for DBS in childhood cannot be made separate from the choice of target nuclei. The anatomy of common DBS targets is considered, and factors influencing their choice for electrode insertion are discussed. We propose an "ABC" for DBS in childhood dystonia is proposed: Appropriate Child selected; Best nuclei chosen for electrode insertion; Correct position within that nucleus.

Stimulating at the right time: phase-specific deep brain stimulation

SEE MOLL AND ENGEL DOI101093/AWW308 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: Brain regions dynamically engage and disengage with one another to execute everyday actions from movement to decision making. Pathologies such as Parkinson's disease and tremor emerge when brain regions controlling movement cannot readily decouple, compromising motor function. Here, we propose a novel stimulation strategy that selectively regulates neural synchrony through phase-specific stimulation. We demonstrate for the first time the therapeutic potential of such a stimulation strategy for the treatment of patients with pathological tremor. Symptom suppression is achieved by delivering stimulation to the ventrolateral thalamus, timed according to the patient's tremor rhythm. Sustained locking of deep brain stimulation to a particular phase of tremor afforded clinically significant tremor relief (up to 87% tremor suppression) in selected patients with essential tremor despite delivering less than half the energy of conventional high frequency stimulation. Phase-specific stimulation efficacy depended on the resonant characteristics of the underlying tremor network. Selective regulation of neural synchrony through phase-locked stimulation has the potential to both increase the efficiency of therapy and to minimize stimulation-induced side effects.

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

INTRODUCTION

Tremor is frequently associated with dystonia, but its pathophysiology is still unclear. Dysfunctions of cerebellar circuits are known to play a role in the pathophysiology of action-induced tremors, and cerebellar impairment has frequently been associated to dystonia. However, a link between dystonic tremor and cerebellar abnormalities has not been demonstrated so far.

METHODS

Twenty-five patients with idiopathic isolated cervical dystonia, with and without tremor, were enrolled. We studied the excitability of inhibitory circuits in the brainstem by measuring the R2 blink reflex recovery cycle (BRC) and implicit learning mediated by the cerebellum by means of eyeblink classical conditioning (EBCC). Results were compared with those obtained in a group of age-matched healthy subjects (HS).

RESULTS

Statistical analysis did not disclose any significant clinical differences among dystonic patients with and without tremor. Patients with dystonia (regardless of the presence of tremor) showed decreased inhibition of R2 blink reflex by conditioning pulses compared with HS. Patients with dystonic tremor showed a decreased number of conditioned responses in the EBCC paradigm compared to HS and dystonic patients without tremor.

CONCLUSION

The present data show that cerebellar impairment segregates with the presence of tremor in patients with dystonia, suggesting that the cerebellum might have a role in the occurrence of dystonic tremor.

Deep brain stimulation for the treatment of uncommon tremor syndromes

Introduction: Deep brain stimulation (DBS) has become a standard therapy for the treatment of select cases of medication refractory essential tremor and Parkinson’s disease however the effectiveness and long-term outcomes of DBS in other uncommon and complex tremor syndromes has not been well established. Traditionally, the ventralis intermedius nucleus (VIM) of the thalamus has been considered the main target for medically intractable tremors; however alternative brain regions and improvements in stereotactic techniques and hardware may soon change the horizon for treatment of complex tremors.

Areas covered: In this article, we conducted a PubMed search using different combinations between the terms ‘Uncommon tremors’, ‘Dystonic tremor’, ‘Holmes tremor’ ‘Midbrain tremor’, ‘Rubral tremor’, ‘Cerebellar tremor’, ‘outflow tremor’, ‘Multiple Sclerosis tremor’, ‘Post-traumatic tremor’, ‘Neuropathic tremor’, and ‘Deep Brain Stimulation/DBS’. Additionally, we examined and summarized the current state of evolving interventions for treatment of complex tremor syndromes.

Expertcommentary: Recently reported interventions for rare tremors include stimulation of the posterior subthalamic area, globus pallidus internus, ventralis oralis anterior/posterior thalamic subnuclei, and the use of dual lead stimulation in one or more of these targets. Treatment should be individualized and dictated by tremor phenomenology and associated clinical features.