The Optimal Targeting for Focused Ultrasound Thalamotomy Differs between Dystonic and Essential Tremor: A 12-Month Prospective Pilot Study

BACKGROUND

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is increasingly used to treat drug-resistant essential tremor (ET). Data on MRgFUS thalamotomy in dystonic tremor (DT) are anecdotal.

OBJECTIVES

To investigate efficacy, safety, and differences in target coordinates of MRgFUS thalamotomy in DT versus ET.

METHODS

Ten patients with DT and 35 with ET who consecutively underwent MRgFUS thalamotomy were followed for 12 months. Although in both groups the initial surgical planning coordinates corresponded to the ventralis intermediate (Vim), the final target could be modified intraoperatively based on clinical response.

RESULTS

Tremor significantly improved in both groups. The thalamic lesion was significantly more anterior in DT than ET. Considering both ET and DT groups, the more anterior the lesion, the lower the odds ratio for adverse events.

CONCLUSIONS

MRgFUS thalamotomy is safe and effective in DT and ET. Compared to classical Vim coordinates used for ET, more anterior targeting should be considered for DT.

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.

Continuous high-frequency deep brain stimulation of the anterior insula modulates autism-like behavior in a valproic acid-induced rat model

BACKGROUND

Until now, the treatment of patients with autism spectrum disorder (ASD) remain a difficult problem. The insula is involved in empathy and sensorimotor integration, which are often impaired in individuals with ASD. Deep brain stimulation, modulating neuronal activity in specific brain circuits, has recently been considered as a promising intervention for neuropsychiatric disorders. Valproic acid (VPA) is a potential teratogenic agent, and prenatal exposure can cause autism-like symptoms including repetitive behaviors and defective sociability. Herein, we investigated the effects of continuous high-frequency deep brain stimulation in the anterior insula of rats exposed to VPA and explored cognitive functions, behavior, and molecular proteins connected to autism spectrum disorder.

METHODS

VPA-exposed offspring were bilaterally implanted with electrodes in the anterior insula (Day 0) with a recovery period of 1 week. (Day 0-7). High-frequency deep brain stimulation was applied from days 11 to 29. Three behavioral tests, including three-chamber social interaction test, were performed on days 7, 13, 18, 25 and 36, and several rats were used for analysis of immediate early genes and proteomic after deep brain stimulation intervention. Meanwhile, animals were subjected to a 20 day spatial learning and cognitive rigidity test using IntelliCage on day 11.

RESULTS

Deep brain stimulation improved the sociability and social novelty preference at day 18 prior to those at day 13, and the improvement has reached the upper limit compared to day 25. As for repetitive/stereotypic-like behavior, self- grooming time were reduced at day 18 and reached the upper limit, and the numbers of burried marbles were reduced at day 13 prior to those at day 18 and day 25. The improvements of sociability and social novelty preference were persistent after the stimulation had ceased. Spatial learning ability and cognitive rigidity were unaffected. We identified 35 proteins in the anterior insula, some of which were intimately linked to autism, and their expression levels were reversed upon administration of deep brain stimulation.

CONCLUSIONS

Autism-like behavior was ameliorated and autism-related proteins were reversed in the insula by deep brain stimulation intervention, these findings reveal that the insula may be a potential target for DBS in the treatment of autism, which provide a theoretical basis for its clinical application., although future studies are still warranted.

Dual Pallidal and Thalamic Deep Brain Stimulation for Complex Ipsilateral Dystonia

PURPOSE

Globus pallidus pars interna (GPi) has become an established target for deep brain stimulation (DBS) in dystonia. Previous studies suggest that targeting the ventralis oralis (Vo) complex nucleus improves dystonic tremor or even focal dystonia. Research has also demonstrated that multi-target DBS shows some benefits over single target DBS. In this study, we reviewed patients who had undergone unilateral DBS targeting the GPi and Vo.

MATERIALS AND METHODS

Five patients diagnosed with medically refractory upper extremity dystonia (focal or segmental) underwent DBS. Two DBS electrodes each were inserted unilaterally targeting the ipsilateral GPi and Vo. Clinical outcomes were evaluated using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) and Disability Rating Scale.

RESULTS

BFMDRS scores decreased by 55% at 1-month, 56% at 3-month, 59% at 6-month, and 64% at 12-month follow up. Disability Rating Scale scores decreased 41% at 1-month, 47% at 3-month, 50% at 6-month, and 60% at 12-month follow up. At 1 month after surgery, stimulating both targets improved clinical scores better than targeting GPi or Vo alone.

CONCLUSION

Unilateral thalamic and pallidal dual electrode DBS may be as effective or even superior to DBS of a single target for dystonia. Although the number of patients was small, our results reflected favorable clinical outcomes.

Brain oscillatory dysfunctions in dystonia

Dystonia is a hyperkinetic movement disorder associated with loss of inhibition, abnormal plasticity, dysfunctional sensorimotor integration, and brain oscillatory dysfunctions at cortical and subcortical levels of the central nervous system. Hence, dystonia is considered a network disorder that can, in many cases, be efficiently treated by pallidal deep brain stimulation (DBS). Abnormal oscillatory activity has been identified across the motor circuit of patients with dystonia. Increased low frequency (LF) synchronization in the internal pallidum is the most prominent abnormality. LF oscillations have been associated with the severity of dystonic motor symptoms; they are suppressed by DBS and localized to the clinically most effective stimulation site. Although the origin of these pathologic changes in brain activity needs further clarifications, their characterization will help in adjusting DBS parameters for successful clinical outcome.

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.

Advances and Future Directions of Neuromodulation in Neurologic Disorders

"Deep brain stimulation is a safe and effective therapy for the management of a variety of neurologic conditions with Food and Drug Administration or humanitarian exception approval for Parkinson disease, dystonia, tremor, and obsessive-compulsive disorder. Advances in neurophysiology, neuroimaging, and technology have driven increasing interest in the potential benefits of neurostimulation in other neuropsychiatric conditions including dementia, depression, pain, Tourette syndrome, and epilepsy, among others. New anatomic or combined targets are being investigated in these conditions to improve symptoms refractory to medications or standard stimulation."

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.

Deep brain stimulation: a review of the open neural engineering challenges

OBJECTIVE

Deep brain stimulation (DBS) is an established and valid therapy for a variety of pathological conditions ranging from motor to cognitive disorders. Still, much of the DBS-related mechanism of action is far from being understood, and there are several side effects of DBS whose origin is unclear. In the last years DBS limitations have been tackled by a variety of approaches, including adaptive deep brain stimulation (aDBS), a technique that relies on using chronically implanted electrodes on 'sensing mode' to detect the neural markers of specific motor symptoms and to deliver on-demand or modulate the stimulation parameters accordingly. Here we will review the state of the art of the several approaches to improve DBS and summarize the main challenges toward the development of an effective aDBS therapy.

APPROACH

We discuss models of basal ganglia disorders pathogenesis, hardware and software improvements for conventional DBS, and candidate neural and non-neural features and related control strategies for aDBS.

MAIN RESULTS

We identify then the main operative challenges toward optimal DBS such as (i) accurate target localization, (ii) increased spatial resolution of stimulation, (iii) development of in silico tests for DBS, (iv) identification of specific motor symptoms biomarkers, in particular (v) assessing how LFP oscillations relate to behavioral disfunctions, and (vi) clarify how stimulation affects the cortico-basal-ganglia-thalamic network to (vii) design optimal stimulation patterns.

SIGNIFICANCE

This roadmap will lead neural engineers novel to the field toward the most relevant open issues of DBS, while the in-depth readers might find a careful comparison of advantages and drawbacks of the most recent attempts to improve DBS-related neuromodulatory strategies.

Deep brain stimulation reduces pain in children with dystonia, including in dyskinetic cerebral palsy

AIM

To establish the prevalence of dystonic pain in children and their response to deep brain stimulation (DBS).

METHOD

Dystonic pain was assessed in a cohort of 140 children, 71 males and 69 females, median age 11 years 11 months (range 3y-19y 1mo), undergoing DBS in our centre over a period of 10 years. The cohort was divided into aetiological dystonia groups: 1a, inherited; 1b, heredodegenerative; 2, acquired; and 3, idiopathic. Motor responses were measured with the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS).

RESULTS

Dystonic pain was identified in 63 (45%) patients, 38% of whom had a diagnosis of cerebral palsy (CP). Dystonic pain improved in 90% of children and in all aetiological subgroups 1 year after DBS, while the BFMDRS motor score improved in 70%. Statistically significant improvement (p<0.01) was noted for the whole cohort on the Numerical Pain Rating Scale (n=27), Paediatric Pain Profile (n=17), and Caregivers Priorities and Child Health Index of Life with Disabilities questionnaire (n=48). There was reduction of pain severity, frequency, and analgesia requirement. Findings were similar for the whole cohort and aetiological subgroups other than the inherited heredodegenerative group where the improvement did not reach statistical significance.

INTERPRETATION

Dystonic pain is frequent in children with dystonia, including those with CP, who undergo DBS; this can be an important, realizable goal of surgery irrespective of aetiology. We encourage the use of multimodal approach in pain research to reduce the risk of bias.

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.

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.

Deep brain stimulation: current challenges and future directions

The clinical use of deep brain stimulation (DBS) is among the most important advances in the clinical neurosciences in the past two decades. As a surgical tool, DBS can directly measure pathological brain activity and can deliver adjustable stimulation for therapeutic effect in neurological and psychiatric disorders correlated with dysfunctional circuitry. The development of DBS has opened new opportunities to access and interrogate malfunctioning brain circuits and to test the therapeutic potential of regulating the output of these circuits in a broad range of disorders. Despite the success and rapid adoption of DBS, crucial questions remain, including which brain areas should be targeted and in which patients. This Review considers how DBS has facilitated advances in our understanding of how circuit malfunction can lead to brain disorders and outlines the key unmet challenges and future directions in the DBS field. Determining the next steps in DBS science will help to define the future role of this technology in the development of novel therapeutics for the most challenging disorders affecting the human brain.

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.

Long-term outcome of pallidal stimulation for Meige syndrome

OBJECTIVE Meige syndrome is characterized by blepharospasm and varied subphenotypes of craniocervical dystonia. Current literature on pallidal surgery for Meige syndrome is limited to case reports and a few small-scale studies. The authors investigated the clinical outcomes of deep brain stimulation (DBS) of the globus pallidus internus (GPi) in patients with Meige syndrome. METHODS Sixteen patients who underwent GPi DBS at the Tokyo Women's Medical University Hospital between 2002 and 2015 were included in this study. Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) movement subscale (BFMDRS-M) scores (range 0-120) obtained at the following 3 time points were included in this analysis: before surgery, 3 months after surgery, and at the most recent follow-up evaluation. RESULTS The patients' mean age (± SD) at symptom onset was 46.7 ± 10.1 years, and the mean disease duration at the time of the authors' initial evaluation was 5.9 ± 4.1 years. In 12 patients, the initial symptom was blepharospasm, and the other 4 patients presented with cervical dystonia. The mean postoperative follow-up period was 66.6 ± 40.7 months (range 13-150 months). The mean total BFMDRS-M scores at the 3 time points were 16.3 ± 5.5, 5.5 ± 5.6 (66.3% improvement, p < 0.001), and 6.7 ± 7.3 (58.9% improvement, p < 0.001). CONCLUSIONS The results indicate long-term efficacy for GPi DBS for the majority of patients with Meige syndrome.

Fatigue Is Associated With Global and Regional Thalamic Morphometry in Veterans With a History of Mild Traumatic Brain Injury

OBJECTIVE

Fatigue is a complex, multidimensional phenomenon that commonly occurs following traumatic brain injury (TBI). The thalamus-a structure vulnerable to both primary and secondary injuries in TBI-is thought to play a pivotal role in the manifestation of fatigue. We explored how neuroimaging markers of local and global thalamic morphometry relate to the subjective experience of fatigue post-TBI.

METHODS

Sixty-three Veterans with a history of mild TBI underwent structural magnetic resonance imaging and completed questionnaires related to fatigue and psychiatric symptoms. FMRIB's Software (FSL) was utilized to obtain whole brain and thalamic volume estimates, as well as to perform regional thalamic morphometry analyses.

RESULTS

Independent of age, sex, intracranial volume, posttraumatic stress disorder, and depressive symptoms, greater levels of self-reported fatigue were significantly associated with decreased right (P = .026) and left (P = .046) thalamic volumes. Regional morphometry analyses revealed that fatigue was significantly associated with reductions in the anterior and dorsomedial aspects of the right thalamic body (P < .05). Similar trends were observed for the left thalamic body (P < .10).

CONCLUSIONS

Both global and regional thalamic morphometric changes are associated with the subjective experience of fatigue in Veterans with a history of mild TBI. These findings support a theory in which disruption of thalamocorticostriatal circuitry may result in the manifestation of fatigue in individuals with a history of neurotrauma.

Deep brain stimulation of the ventroanterior and ventrolateral thalamus improves motor function in a rat model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease with affected individuals exhibiting motor symptoms of bradykinesia, muscle rigidity, tremor, postural instability and gait dysfunction. The current gold standard treatment is pharmacotherapy with levodopa, but long-term use is associated with motor response fluctuations and can cause abnormal movements called dyskinesias. An alternative treatment option is deep brain stimulation (DBS) with the two FDA-approved brain targets for PD situated in the basal ganglia; specifically, in the subthalamic nucleus (STN) and globus pallidus pars interna (GPi). Both improve quality of life and motor scores by ~50-70% in well-selected patients but can also elicit adverse effects on cognition and other non-motor symptoms. Therefore, identifying a novel DBS target that is efficacious for patients not optimally responsive to current DBS targets with fewer side-effects has clear clinical merit. Here, we investigate whether the ventroanterior (VA) and ventrolateral (VL) motor nuclei of the thalamus can serve as novel and effective DBS targets for PD. In the limb-use asymmetry test (LAT), hemiparkinsonian rats showcased left forelimb akinesia and touched only 6.5 ± 1.3% with that paw. However, these animals touched equally with both forepaws with DBS at 10 Hz, 100 μsec pulse width and 100 uA cathodic stimulation in the VA (n = 7), VL (n = 8) or at the interface between the two thalamic nuclei which we refer to as the VA|VL (n = 12). With whole-cell patch-clamp recordings, we noted that VA|VL stimulation in vitro increased the number of induced action potentials in proximal neurons in both areas albeit VL neurons transitioned from bursting to non-bursting action potentials (APs) with large excitatory postsynaptic potentials time-locked to stimulation. In contrast, VA neurons were excited with VA|VL electrical stimulation but with little change in spiking phenotype. Overall, our findings show that DBS in the VA, VL or VA|VL improved motor function in a rat model of PD; plausibly via increased excitation of residing neurons.

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

Tremor is a phenomenon observed in a broad spectrum of diseases with different pathophysiologies. While patients with tremor may not complain in the clinic of symptoms of imbalance, gait difficulties, or falls, laboratory research studies using quantitative analysis of gait and posture and neurophysiologic techniques have demonstrated impaired gait and balance across a variety of tremor etiologies. These findings have been supported by careful epidemiologic studies assessing symptoms of imbalance. Imaging and neurophysiologic studies have identified cerebellar networks as important mediators of tremor, and therefore a likely common site of dysfunction to explain the phenomenologic overlap between impaired postural and gait control with tremor. Further understanding of these mechanisms and networks is of crucial importance in the development of new treatments, particularly surgical or minimally invasive lesional therapies.

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.

Surgery for Dystonia and Tremor

Surgical procedures for dystonia and tremor have evolved over the past few decades, and our understanding of risk, benefit, and predictive factors has increased substantially in that time. Deep brain stimulation (DBS) is the most utilized surgical treatment for dystonia and tremor, though lesioning remains an effective option in appropriate patients. Dystonic syndromes that have shown a substantial reduction in severity secondary to DBS are isolated dystonia, including generalized, cervical, and segmental, as well as acquired dystonia such as tardive dystonia. Essential tremor is quite amenable to DBS, though the response of other forms of postural and kinetic tremor is not nearly as robust or consistent based on available evidence. Regarding targeting, DBS lead placement in the globus pallidus internus has shown marked efficacy in dystonia reduction. The subthalamic nucleus is an emerging target, and increasing evidence suggests that this may be a viable target in dystonia as well. The ventralis intermedius nucleus of the thalamus is the preferred target for essential tremor, though targeting the subthalamic zone/caudal zona incerta has shown promise and may emerge as another option in essential tremor and possibly other tremor disorders. In the carefully selected patient, DBS and lesioning procedures are relatively safe and effective for the management of dystonia and tremor.

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.

Update on Deep Brain Stimulation for Dyskinesia and Dystonia: A Literature Review

Deep brain stimulation (DBS) has been an established surgical treatment option for dyskinesia from Parkinson disease and for dystonia. The present article deals with the timing of surgical intervention, selecting an appropriate target, and minimizing adverse effects. We provide an overview of current evidences and issues for dyskinesia and dystonia as well as emerging DBS technology.

Tremor in dystonia

Tremor has been recognized as an important clinical feature in dystonia. Tremor in dystonia may occur in the body part affected by dystonia known as dystonic tremor or unaffected body regions known as tremor associated with dystonia. The most common type of tremor seen in dystonia patients is postural and kinetic which may be mistaken for familial essential tremor. Similarly familial essential tremor patients may have associated dystonia leading to diagnostic uncertainties. The pathogenesis of tremor in dystonia remains speculative, but its neurophysiological features are similar to dystonia which helps in differentiating it from essential tremor patients. Treatment of tremor in dystonia depends upon the site of involvement. Dystonic hand tremor is treated with oral pharmacological therapy and dystonic head, jaw and voice tremor is treated with injection botulinum toxin. Neurosurgical interventions such as deep brain stimulation and lesion surgery should be an option in patients not responding to the pharmacological treatment.

Deep brain stimulation for movement disorders: update on recent discoveries and outlook on future developments

Modern deep brain stimulation (DBS) has become a routine therapy for patients with movement disorders such as Parkinson's disease, generalized or segmental dystonia and for multiple forms of tremor. Growing numbers of publications also report beneficial effects in other movement disorders such as Tourette's syndrome, various forms of chorea and DBS is even being studied for Parkinson's-related dementia. While exerting remarkable effects on many motor symptoms, DBS does not restore normal neurophysiology and therefore may also have undesirable side effects including speech and gait deterioration. Furthermore, its efficacy might be compromised in the long term, due to progression of the underlying disease. Various programming strategies have been studied to try and address these issues, e.g., the use of low-frequency rather than high-frequency stimulation or the targeting of alternative brain structures such as the pedunculopontine nucleus. In addition, further technical developments will soon provide clinicians with an expanded choice of hardware such as segmented electrodes allowing for a steering of the current to optimize beneficial effects and reduce side effects as well as the possibility of adaptive stimulation systems based on closed-loop concepts with or without accompanying advances in programming and imaging software. In the present article, we will provide an update on the most recent achievements and discoveries relevant to the application of DBS in the treatment of movement disorder patients and give an outlook on future clinical and technical developments.

Effect of subthalamic nucleus deep brain stimulation on dual-task cognitive and motor performance in isolated dystonia

OBJECTIVE

Subthalamic nucleus (STN) deep brain stimulation (DBS) can improve motor complications of Parkinson's disease (PD) but may worsen specific cognitive functions. The effect of STN DBS on cognitive function in dystonia patients is less clear. Previous reports indicate that bilateral STN stimulation in patients with PD amplifies the decrement in cognitive-motor dual-task performance seen when moving from a single-task to dual-task paradigm. We aimed to determine if the effect of bilateral STN DBS on dual-task performance in isolated patients with dystonia, who have less cognitive impairment and no dementia, is similar to that seen in PD.

METHODS

Eight isolated predominantly cervical patients with dystonia treated with bilateral STN DBS, with average dystonia duration of 10.5 years and Montreal Cognitive Assessment score of 26.5, completed working memory (n-back) and motor (forced-maintenance) tests under single-task and dual-task conditions while on and off DBS.

RESULTS

A multivariate, repeated-measures analysis of variance showed no effect of stimulation status (On vs Off) on working memory (F=0.75, p=0.39) or motor function (F=0.22, p=0.69) when performed under single-task conditions, though as working memory task difficulty increased, stimulation disrupted the accuracy of force-tracking. There was a very small worsening in working memory performance (F=9.14, p=0.019) when moving from single-task to dual-tasks when using the 'dual-task loss' analysis.

CONCLUSIONS

This study suggests the effect of STN DBS on working memory and attention may be much less consequential in patients with dystonia than has been reported in PD.