Different clinical course of pallidal deep brain stimulation for phasic- and tonic-type cervical dystonia

Intermuscular coherence during co-contraction eliciting tasks as a biomarker for dystonia and GPi-DBS efficacy

OBJECTIVE

Clinical rating scales often fail to capture the full spectrum of dystonic symptoms. Deep brain stimulation of the globus pallidus interna (GPi-DBS) effectively treats dystonia, but response variability necessitates a reliable biomarker. Intermuscular coherence (4-12 Hz) has been linked to abnormal activity in the cortico-basal ganglia-thalamo-cortical (CBGTC) loop and may serve as an objective measure of dystonia and GPi-DBS effectiveness.

METHODS

A retrospective cohort study included 12 dystonia patients undergoing GPi-DBS implantation. Clinical rating scales and a neurophysiological assessment were performed before and one year post-DBS. Coherence in the 4-12 Hz range was analyzed from electromyography (EMG) of antagonistic arm muscles. Comparisons were made between patients with and without arm dystonia, t-tests evaluated the differences between pre- and post-DBS, and correlations between coherence and clinical scales were performed.

RESULTS

Seven patients with arm dystonia appeared to have higher pre-operative intermuscular coherence compared to those without. Coherence was significantly decreased after GPi-DBS in the arm dystonia group. No strong correlations were found between coherence and clinical rating scales.

CONCLUSION

Intermuscular coherence is present in dystonic muscles and decreases following GPi-DBS. Correlations with motor scores were inconclusive due to patient heterogeneity and ill-fitting clinical scales.

SIGNIFICANCE

Intermuscular coherence has potential to aid GPi-DBS patient selection and optimization but larger studies are needed to validate its use.

PAllidal versus SubThalamic deep brain Stimulation for Cervical Dystonia (PASTS-CD): study protocol for a multicentre randomised controlled trial

INTRODUCTION

Deep brain stimulation (DBS) has been validated as a safe and effective treatment for refractory cervical dystonia (CD). Globus pallidus internus (GPi) and subthalamic nucleus (STN) are the two main stimulating targets. However, there has been no prospective study to clarify which target is the better DBS candidate for CD. The objective of this trial is to compare directly the efficacy and safety of GPi-DBS and STN-DBS, thereby instructing the selection of DBS target in clinical practice.

METHODS AND ANALYSIS

This multicentre, prospective, randomised, controlled study plans to enrol 98 refractory CD patients. Eligible CD patients will be randomly allocated to GPi-DBS group or STN-DBS group, with the DBS electrodes implanted into the posteroventral portion of GPi or the dorsolateral portion of STN, respectively. The primary outcome will be the improvement of symptomatic severity, measured by the changes in the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) severity subscale and the Tsui scale at 3 months, 6 months and 12 months after surgery. The secondary outcomes include the improvement of the TWSTRS-disability subscale, TWSTRS-pain subscale, quality of life, mental and cognitive condition, as well as the differences in stimulation parameters and adverse effects. In addition, this study intends to identify certain predictors of DBS efficacy for CD.

ETHICS AND DISSEMINATION

The trial has been approved by the Medical Ethics Committee of Chinese PLA General Hospital (S2022-613-01). The results of this study will be published in international peer-reviewed journals and shared in professional medical conferences.

TRIAL REGISTRATION NUMBER

NCT05715138.

Spastic dystonia: Still a valid term

Hypertonia in childhood may arise because of a variable combination of neuronal and non-neuronal factors. Involuntary muscle contraction may be due to spasticity or dystonia, which represent disorders of the spinal reflex arch and of central motor output respectively. Whilst consensus definitions for dystonia have been established, definitions of spasticity vary, highlighting the lack of a single unifying nomenclature in the field of clinical movement science. The term spastic dystonia refers to involuntary tonic muscle contraction in the context of an upper motor neuron (UMN) lesion. This review considers the utility of the term spastic dystonia, exploring our understanding of the pathophysiology of dystonia and the UMN syndrome. An argument is advanced that spastic dystonia is a valid construct that warrants further exploration. WHAT THIS PAPER ADDS: There is no single universally accepted definitions for terms commonly used to describe motor disorders. Spasticity and dystonia are phenomenologically and pathophysiologically distinct entities. Spastic dystonia represents a subset of dystonia, but with pathophysiological mechanisms more in common with spasticity.

Physiology of dystonia: Human studies

In this chapter, we discuss neurophysiological techniques that have been used in the study of dystonia. We examine traditional disease models such as inhibition and excessive plasticity and review the evidence that these play a causal role in pathophysiology. We then review the evidence for sensory and peripheral influences within pathophysiology and look at an emergent literature that tries to probe how oscillatory brain activity may be linked to dystonia pathophysiology.

Exploring clinical outcomes in patients with idiopathic/inherited isolated generalized dystonia and stimulation of the subthalamic region

BACKGROUND

 Deep Brain Stimulation (DBS) is an established treatment option for refractory dystonia, but the improvement among the patients is variable.

OBJECTIVE

 To describe the outcomes of DBS of the subthalamic region (STN) in dystonic patients and to determine whether the volume of tissue activated (VTA) inside the STN or the structural connectivity between the area stimulated and different regions of the brain are associated with dystonia improvement.

METHODS

 The response to DBS was measured by the Burke-Fahn-Marsden Dystonia Rating Scale (BFM) before and 7 months after surgery in patients with generalized isolated dystonia of inherited/idiopathic etiology. The sum of the two overlapping STN volumes from both hemispheres was correlated with the change in BFM scores to assess whether the area stimulated inside the STN affects the clinical outcome. Structural connectivity estimates between the VTA (of each patient) and different brain regions were computed using a normative connectome taken from healthy subjects.

RESULTS

 Five patients were included. The baseline BFM motor and disability subscores were 78.30 ± 13.55 (62.00-98.00) and 20.60 ± 7.80 (13.00-32.00), respectively. Patients improved dystonic symptoms, though differently. No relationships were found between the VTA inside the STN and the BFM improvement after surgery (p = 0.463). However, the connectivity between the VTA and the cerebellum structurally correlated with dystonia improvement (p = 0.003).

CONCLUSIONS

 These data suggest that the volume of the stimulated STN does not explain the variance in outcomes in dystonia. Still, the connectivity pattern between the region stimulated and the cerebellum is linked to outcomes of patients.

Double blind, nonrandomized crossover study of active recharge biphasic deep brain stimulation for primary dystonia

BACKGROUND

Deep brain stimulation (DBS) of the globus pallidus interna (GPi) is an effective therapy for select patients with primary dystonia. DBS programming for dystonia is often challenging due to variable time to symptomatic improvement or stimulation induced side effects (SISE) such as capsular or optic tract activation which can prolong device optimization.

OBJECTIVE

To characterize the safety and tolerability of active recharge biphasic DBS (bDBS) in primary dystonia and to compare it to conventional clinical DBS (clinDBS).

METHODS

Ten subjects with primary dystonia and GPi DBS underwent a single center, double blind, nonrandomized crossover study comparing clinDBS versus bDBS. The testing occurred over two-days. bDBS and clinDBS were administered on separate days and each was activated for 6 h. Rating scales were collected by video recording and scored by four blinded movement disorders trained neurologists.

RESULTS

The bDBS paradigm was safe and well-tolerated in all ten subjects. There were no persistent SISE reported. The mean change in the Unified Dystonia Rating Scale after 4 h of stimulation was greater in bDBS when compared to clinDBS (-6.5 vs 0.3, p < 0.04).

CONCLUSION

In this pilot study, we demonstrated that biphasic DBS is a novel stimulation paradigm which can be administered safely. The biphasic waveform revealed a greater immediate improvement. Further studies are needed to determine whether this immediate improvement persists with chronic stimulation or if clinDBS will eventually achieve similar levels of improvement to bDBS over time.

Deep brain stimulation in dystonia: factors contributing to variability in outcome in short and long term follow-up

PURPOSE OF REVIEW

Deep brain stimulation (DBS) is currently the most effective treatment for medically refractory dystonia with globus pallidus internus (GPi) usually the preferred target. Despite the overall success of DBS in dystonia, there remains variability in treatment outcome in both short and long-term follow-up, due to various factors. Factors contributing to variability in outcome comprise 'Dystonia Related' including dystonia classification, semiology, duration, body distribution, orthopaedic deformity, aetiology and genetic cause. The majority of these factors are identifiable from clinical assessment, brain MRI and genetic testing, and therefore merit careful preoperative consideration. 'DBS related' factors include brain target, accuracy of lead placement, stimulation parameters, time allowed for response, neurostimulation technology employed and DBS induced side-effects. In this review, factors contributing to variability in short and long-term dystonia DBS outcome are reviewed and discussed.

RECENT FINDINGS

The recognition of differential DBS benefit in monogenic dystonia, increasing experience with subthalamic nucleus (STN) DBS and in DBS for Meige syndrome, elucidation of DBS side effects and novel neurophysiological and imaging techniques to assist in predicting clinical outcome.

SUMMARY

Improved understanding of factors contributing to variability of DBS outcome in dystonia may assist in patient selection and predicting surgical outcomes.

Diving into the Subcortex: The Potential of Chronic Subcortical Sensing for Unravelling Basal Ganglia Function and Optimization of Deep Brain STIMULATION

Subcortical structures are a relative neurophysiological 'terra incognita' owing to their location within the skull. While perioperative subcortical sensing has been performed for more than 20 years, the neurophysiology of the basal ganglia in the home setting has remained almost unexplored. However, with the recent advent of implantable pulse generators (IPG) that are able to record neural activity, the opportunity to chronically record local field potentials (LFPs) directly from electrodes implanted for deep brain stimulation opens up. This allows for a breakthrough of chronic subcortical sensing into fundamental research and clinical practice. In this review an extensive overview of the current state of subcortical sensing is provided. The widespread potential of chronic subcortical sensing for investigational and clinical use is discussed. Finally, status and future perspectives of the most promising application of chronic subcortical sensing -i.e., adaptive deep brain stimulation (aDBS)- are discussed in the context of movement disorders. The development of aDBS based on both chronic subcortical and cortical sensing has the potential to dramatically change clinical practice and the life of patients with movement disorders. However, several barriers still stand in the way of clinical implementation. Advancements regarding IPG and lead technology, physiomarkers, and aDBS algorithms as well as harnessing artificial intelligence, multimodality and sensing in the naturalistic setting are needed to bring aDBS to clinical practice.

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.

Pallidal Deep Brain Stimulation for Monogenic Dystonia: The Effect of Gene on Outcome

Globus pallidus internus deep brain stimulation (GPi DBS) is the most effective intervention for medically refractory segmental and generalized dystonia in both children and adults. Predictive factors for the degree of improvement after GPi DBS include shorter disease duration and dystonia subtype with idiopathic isolated dystonia usually responding better than acquired combined dystonias. Other factors contributing to variability in outcome may include body distribution, pattern of dystonia and DBS related factors such as lead placement and stimulation parameters. The responsiveness to DBS appears to vary between different monogenic forms of dystonia, with some improving more than others. The first observation in this regard was reports of superior DBS outcomes in DYT-TOR1A (DYT1) dystonia, although other studies have found no difference. Recently a subgroup with young onset DYT-TOR1A, more rapid progression and secondary worsening after effective GPi DBS, has been described. Myoclonus dystonia due to DYT-SCGE (DYT11) usually responds well to GPi DBS. Good outcomes following GPi DBS have also been documented in X-linked dystonia Parkinsonism (DYT3). In contrast, poorer, more variable DBS outcomes have been reported in DYT-THAP1 (DYT6) including a recent larger series. The outcome of GPi DBS in other monogenic isolated and combined dystonias including DYT-GNAL (DYT25), DYT-KMT2B (DYT28), DYT-ATP1A3 (DYT12), and DYT-ANO3 (DYT24) have been reported with varying results in smaller numbers of patients. In this article the available evidence for long term GPi DBS outcome between different genetic dystonias is reviewed to reappraise popular perceptions of expected outcomes and revisit whether genetic diagnosis may assist in predicting DBS outcome.

Unilateral pallidotomy in the treatment of cervical dystonia: a retrospective observational study

OBJECTIVE

The objective of this study was to assess the efficacy of unilateral pallidotomy in patients with asymmetrical cervical dystonia.

METHODS

This study retrospectively included 25 consecutive patients with asymmetrical cervical dystonia refractory to botulinum toxin injections, who underwent unilateral pallidotomy between January 2015 and April 2017. Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) scores were evaluated preoperatively and 1 week, 3 months, and 6 months postoperatively. The clinical responses were defined as good responders, exhibiting > 50% improvement in the TWSTRS score at 6 months postsurgery, or poor responders, exhibiting < 50% improvement in TWSTRS scores at 6 months postsurgery.

RESULTS

Twelve and 9 patients showed right- and left-side rotation, respectively; 1 and 3 patients had right- and left-side laterocollis, respectively. The mean age of onset and duration of the disease were 40.2 ± 13.9 and 8.9 ± 10.9 years, respectively. Mean TWSTRS scores were 38.4 ± 12.6 (p < 0.001), 17.3 ± 12.4 (p < 0.001), 19.5 ± 13.4 (p < 0.001), and 20.0 ± 14.7 (p < 0.001), preoperatively and 1 week, 3 months, and 6 months postoperatively, respectively. Fourteen patients (56%) demonstrated > 50% improvement in their TWSTRS total score (mean improvement of TWSTRS total score = 70.5%) 6 months postsurgically. Furthermore, preoperative TWSTRS severity score was a prognostic factor (odds ratio 1.37, 95% confidence interval 1.06-1.78, p = 0.003).

CONCLUSIONS

These results suggest that unilateral pallidotomy is an acceptable treatment option for asymmetrical cervical dystonia. Further investigations with a larger number of cases and longer follow-up period are required to confirm these data.

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.

Neurophysiological insights in dystonia and its response to deep brain stimulation treatment

Dystonia is a movement disorder characterised by involuntary muscle contractions resulting in abnormal movements, postures and tremor. The pathophysiology of dystonia is not fully understood but loss of neuronal inhibition, excessive sensorimotor plasticity and defective sensory processing are thought to contribute to network dysfunction underlying the disorder. Neurophysiology studies have been important in furthering our understanding of dystonia and have provided insights into the mechanism of effective dystonia treatment with pallidal deep brain stimulation. In this article we review neurophysiology studies in dystonia and its treatment with Deep Brain Stimulation, including Transcranial magnetic stimulation studies, studies of reflexes and sensory processing, and oscillatory activity recordings including local field potentials, micro-recordings, EEG and evoked potentials.

Treatment of dystonia and tics

Treatment of dystonia and tics continues to evolve. In dystonia, while oral agents such as benzodiazepines, baclofen and anticholinergics remain in use, botulinum toxin (BoNT) continues to be regarded as the treatment of choice for focal and segmental dystonia, but new preparations are being studied. While deep brain stimulation (DBS) has typically focused on targeting the globus pallidus internus (GPi) when treating dystonia, more recent research has expanded the targets to include subthalamic nucleus (STN) and other targets. In addition to DBS, thalamotomies continue to show therapeutic benefit in focal hand dystonias. Treatment of tics includes a growing armamentarium of options besides the three FDA-approved drugs, all dopamine receptor blockers (haloperidol, pimozide and aripiprazole). Because of lower risk of adverse effects, dopamine depleters (e.g. tetrabebazine, deutetrabenazine, and valbenazine), along with novel D1 receptor antagonists, are currently studied as treatment alternatives in patients with tics. Practice guidelines for the treatment of tics and Tourette syndrome have been recently updated. Data regarding the use of DBS in treatment of tics remains relatively sparse, but international registries have expanded our understanding of the effect of stimulation at several targets.

Range of voluntary neck motility predicts outcome of pallidal DBS for cervical dystonia

BACKGROUND

The effectiveness of pallidal deep brain stimulation (GPi DBS) for cervical dystonia has been extensively described, but controversies exist about which prognostic factor is clinically useful. We previously reported that classification of tonic- or phasic-type cervical dystonia is useful for predicting clinical prognosis; however, the approach used by physicians to distinguish between the two types remains subjective.

OBJECTIVE

The aim of this study was to develop a prognostic factor of GPi DBS for cervical dystonia.

METHODS

By identifying distributions of range of motion scores between phasic- and tonic-type cervical dystonia, a new prognostic factor group was developed based on whether the patients could voluntarily move their head to the opposite side against dystonic motions. The prognosis for GPi DBS in the two groups was analyzed according to the time sequence.

RESULTS

Patients who were able to move their head past the midline had a better long-term prognosis after GPi DBS than did those who could not. In the early post-operative phase, there were no significant differences in the clinical outcomes between the two groups.

CONCLUSION

A range of voluntary neck motility with respect to the midline is an objective factor that is useful in predicting the prognosis of patients with cervical dystonia. This result renders needs for future study addressing neuroplastic changes in the brain network caused by GPi DBS.

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.

Intermuscular coherence as biomarker for pallidal deep brain stimulation efficacy in dystonia

OBJECTIVE

Finding a non-invasive biomarker for Globus Pallidus interna Deep Brain Stimulation (GPi-DBS) efficacy. Dystonia heterogeneity leads to a wide variety of clinical response to GPi-DBS, making it hard to predict GPi-DBS efficacy for individual patients.

METHODS

EEG-EMG recordings of twelve dystonia patients who received bilateral GPi-DBS took place pre- and 1 year post-surgery ON and OFF stimulation, during a rest, pinch, and flexion task. Dystonia severity was assessed using the BFMDRS and TWSTRS (pre- and post-surgery ON stimulation). Intermuscular coherence (IMC) and motorcortex corticomuscular coherence (CMC) were calculated. Low frequency (4-12 Hz) and beta band (13-30 Hz) peak coherences were studied.

RESULTS

Dystonia severity improved after 1 year GPi-DBS therapy (BFMDRS: 30%, median 7.8 (IQR 3-10), TWSTRS: 22%, median 6.8 (IQR 4-9)). 86% of IMC were above the 95% confidence limit. The highest IMC peak decreased significantly with GPi-DBS in the low frequency and beta band. Low frequency and beta band IMC correlated partly with dystonia severity and severity improvement. CMC generally were below the 95% confidence limit.

CONCLUSIONS

Peak low frequency IMC functioned as biomarker for GPi-DBS efficacy, and partly correlated with dystonia severity.

SIGNIFICANCE

IMC can function as biomarker. Confirmation in a larger study is needed for use in clinical practice.

Toward Electrophysiology-Based Intelligent Adaptive Deep Brain Stimulation for Movement Disorders

Deep brain stimulation (DBS) represents one of the major clinical breakthroughs in the age of translational neuroscience. In 1987, Benabid and colleagues demonstrated that high-frequency stimulation can mimic the effects of ablative neurosurgery in Parkinson's disease (PD), while offering two key advantages to previous procedures: adjustability and reversibility. Deep brain stimulation is now an established therapeutic approach that robustly alleviates symptoms in patients with movement disorders, such as Parkinson's disease, essential tremor, and dystonia, who present with inadequate or adverse responses to medication. Currently, stimulation electrodes are implanted in specific target regions of the basal ganglia-thalamic circuit and stimulation pulses are delivered chronically. To achieve optimal therapeutic effect, stimulation frequency, amplitude, and pulse width must be adjusted on a patient-specific basis by a movement disorders specialist. The finding that pathological neural activity can be sampled directly from the target region using the DBS electrode has inspired a novel DBS paradigm: closed-loop adaptive DBS (aDBS). The goal of this strategy is to identify pathological and physiologically normal patterns of neuronal activity that can be used to adapt stimulation parameters to the concurrent therapeutic demand. This review will give detailed insight into potential biomarkers and discuss next-generation strategies, implementing advances in artificial intelligence, to further elevate the therapeutic potential of DBS by capitalizing on its modifiable nature. Development of intelligent aDBS, with an ability to deliver highly personalized treatment regimens and to create symptom-specific therapeutic strategies in real-time, could allow for significant further improvements in the quality of life for movement disorders patients with DBS that ultimately could outperform traditional drug treatment.

Benefits of pallidal stimulation in dystonia are linked to cerebellar volume and cortical inhibition

Clinical benefits of pallidal deep brain stimulation (GPi DBS) in dystonia increase relatively slowly suggesting slow plastic processes in the motor network. Twenty-two patients with dystonia of various distribution and etiology treated by chronic GPi DBS and 22 healthy subjects were examined for short-latency intracortical inhibition of the motor cortex elicited by paired transcranial magnetic stimulation. The relationships between grey matter volume and intracortical inhibition considering the long-term clinical outcome and states of the GPi DBS were analysed. The acute effects of GPi DBS were associated with a shortening of the motor response whereas the grey matter of chronically treated patients with a better clinical outcome showed hypertrophy of the supplementary motor area and cerebellar vermis. In addition, the volume of the cerebellar hemispheres of patients correlated with the improvement of intracortical inhibition which was generally less effective in patients than in controls regardless of the DBS states. Importantly, good responders to GPi DBS showed a similar level of short-latency intracortical inhibition in the motor cortex as healthy controls whereas non-responders were unable to increase it. All these results support the multilevel impact of effective DBS on the motor networks in dystonia and suggest potential biomarkers of responsiveness to this treatment.

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.

Motor Cortical Plasticity Relates to Symptom Severity and Clinical Benefit From Deep Brain Stimulation in Cervical Dystonia

OBJECTIVE

To investigate the relationship between motor cortical plasticity, intracortical inhibition, and clinical response to pallidal deep brain stimulation (DBS) in patients with cervical dystonia (CD).

MATERIALS AND METHODS

Response to paired associative stimulation (PAS) and short interval intracortical inhibition (SICI) were assessed in patients with CD before and after three months of DBS and correlated with severity of dystonic symptoms as assessed by Toronto-Western-Spasmodic Torticollis Rating Scale (TWSTRS) severity score. Relations of electrophysiological parameters with clinical improvement were explored with correlation analysis.

RESULTS

Patients with higher levels of plasticity before surgery showed higher symptom severity (R = 0.83, p = 0.008) but had also the larger clinical benefit following DBS (R = 0.88, p = 0.003). This correlation was independent from preoperative (preOP) TWSTRS motor score as revealed by partial correlation analysis. Intracortical inhibition was not altered in CD and not related to clinical outcome after DBS.

CONCLUSIONS

Our findings indicate that a high degree of preOP plasticity is associated with higher symptom severity, underlining the role of abnormal plasticity in the pathophysiology of dystonia. At the same time individual degree of plasticity may drive reestablishment of normal motor programs, leading to better clinical outcome with DBS. The latter suggests that individual PAS-response may indicate the susceptibility for neuromodulatory processes as an important factor for clinical DBS effects. It might therefore serve as a neurophysiological marker to predict outcome and guide patient selection.

Electrophysiological interpretations of the clinical response to stimulation parameters of pallidal deep brain stimulation for cervical dystonia

OBJECTIVE

Deep brain stimulation (DBS) at the posterolateral ventral portion of the globus pallidus internus (GPi) has been regarded as a good therapeutic modality. Because the theoretical principle behind the stimulation parameters is yet to be determined, this study aimed to interpret analyses of the stimulation parameters used in our department based on an electrophysiological review.

METHODS

Nineteen patients with medically refractory idiopathic cervical dystonia who underwent GPi DBS were enrolled. The baseline and follow-up parameters were analyzed according to their dependence on time after DBS. The pattern of changes in the stimulation parameters over time, the differences across the four active contacts, and the relationship between the stimulation parameters and clinical benefits were evaluated.

RESULTS

Mean age and disease duration were 50.9 years and 54.7 months, respectively. Mean follow-up duration was 22.6 months. The amplitude and frequency exhibited significant increasing temporal patterns, i.e., a mean amplitude and frequency of 3.1 V and 132.2 Hz at the initial setting and 4.0 V and 142.6 Hz at the last follow-up, respectively. The better clinical response group (clinical improvement rate of 65-100 %) used a narrower pulse width (mean value of 78.4 μs) than the worse clinical response group (clinical improvement rate of 5-60 %, mean of value of 88.6 μs). Active contact at the GPe was used more often in the worse clinical response group than in the better response group.

CONCLUSIONS

Based on electrophysiological considerations, these patterns of stimulation parameters could be interpreted. This interpretation was based on a theoretical understanding of the mechanisms of action of DBS, i.e., that the abnormal neural signal is substituted by an induced neural signal, which is generated by therapeutic DBS.

Advances in surgery for movement disorders

Movement disorder surgery has evolved throughout history as our knowledge of motor circuits and ways in which to manipulate them have expanded. Today, the positive impact on patient quality of life for a growing number of movement disorders such as Parkinson's disease is now well accepted and confirmed through several decades of randomized, controlled trials. Nevertheless, residual motor symptoms after movement disorder surgery such as deep brain stimulation and lack of a definitive cure for these conditions demand that advances continue to push the boundaries of the field and maximize its therapeutic potential. Similarly, advances in related fields - wireless technology, artificial intelligence, stem cell and gene therapy, neuroimaging, nanoscience, and minimally invasive surgery - mean that movement disorder surgery stands at a crossroads to benefit from unique combinations of all these developments. In this minireview, we outline some of these developments as well as evidence supporting topics of recent discussion and controversy in our field. Moving forward, expectations remain high that these improvements will come to encompass an even broader range of patients who might benefit from this therapy and decrease the burden of disease associated with these conditions. © 2016 International Parkinson and Movement Disorder Society.