Microelectrode-guided implantation of deep brain stimulators into the globus pallidus internus for dystonia: techniques, electrode locations, and outcomes

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.

Clinical outcomes following awake and asleep deep brain stimulation for Parkinson disease

OBJECTIVE

Recent studies have shown similar clinical outcomes between Parkinson disease (PD) patients treated with deep brain stimulation (DBS) under general anesthesia without microelectrode recording (MER), so-called “asleep” DBS, and historical cohorts undergoing “awake” DBS with MER guidance. However, few studies include internal controls. This study aims to compare clinical outcomes after globus pallidus internus (GPi) and subthalamic nucleus (STN) DBS using awake and asleep techniques at a single institution.

METHODS

PD patients undergoing awake or asleep bilateral GPi or STN DBS were prospectively monitored. The primary outcome measure was stimulation-induced change in motor function off medication 6 months postoperatively, measured using the Unified Parkinson’s Disease Rating Scale part III (UPDRS-III). Secondary outcomes included change in quality of life, measured by the 39-item Parkinson’s Disease Questionnaire (PDQ-39), change in levodopa equivalent daily dosage (LEDD), stereotactic accuracy, stimulation parameters, and adverse events.

RESULTS

Six-month outcome data were available for 133 patients treated over 45 months (78 GPi [16 awake, 62 asleep] and 55 STN [14 awake, 41 asleep]). UPDRS-III score improvement with stimulation did not differ between awake and asleep groups for GPi (awake, 20.8 points [38.5%]; asleep, 18.8 points [37.5%]; p = 0.45) or STN (awake, 21.6 points [40.3%]; asleep, 26.1 points [48.8%]; p = 0.20) targets. The percentage improvement in PDQ-39 and LEDD was similar for awake and asleep groups for both GPi (p = 0.80 and p = 0.54, respectively) and STN cohorts (p = 0.85 and p = 0.49, respectively).

CONCLUSIONS

In PD patients, bilateral GPi and STN DBS using the asleep method resulted in motor, quality-of-life, and medication reduction outcomes that were comparable to those of the awake method.

Single-unit activity of the anterior Globus pallidus internus in Tourette patients and posterior Globus pallidus internus in dystonic patients

OBJECTIVES

Our goal was to provide a detailed analysis of neurons' electrophysiological activity recorded in sub-territories of Globus pallidus internus (GPi) used as Deep Brain Stimulation (DBS) targets for these clinical conditions to potentially assist electrode targeting.

METHODS

We used intra-operative microelectrode recording during stereotactic neurosurgery to guide implantation of DBS lead.

RESULTS

Units in the medial anterior part of GPi of 7 Tourette's syndrome patients under general anesthesia were firing at mean and median rate of 32.1 and 21 Hz respectively (n = 101), with 45% of spikes fired during bursts and 21.3 bursts per minute. In the latero-posterior part of GPi of 7 dystonic patients under local anesthesia the mean and median activity were 46.1 and 30.6 Hz respectively (n = 27), and a mean of 21.7 bursts per minute was observed, with 30% of all spikes occurring during these bursts.

CONCLUSION

Units activity pattern - slow-regular, fast-irregular or fast-regular were present in different proportions between the two targets.

SIGNIFICANCE

The electrophysiological characteristics of the medial-anterior part of GPi and its latero-posterior portion can be used to assist DBS electrode targeting and also support the refinement of pathophysiological models of Tourette's syndrome and Dystonia.

Targeting Accuracy of the Subthalamic Nucleus in Deep Brain Stimulation Surgery: Comparison Between 3 T T2-Weighted Magnetic Resonance Imaging and Microelectrode Recording Results

BACKGROUND

Targeting accuracy in deep brain stimulation (DBS) surgery can be defined as the level of accordance between selected and anatomic real target reflected by characteristic electrophysiological results of microelectrode recording (MER).

OBJECTIVE

To determine the correspondence between the preoperative predicted target based on modern 3-T magnetic resonance imaging (MRI) and intraoperative MER results separately on the initial and consecutive second side of surgery.

METHODS

Retrospective cohort study of 86 trajectories of DBS electrodes implanted into the subthalamic nucleus (STN) of patients with Parkinson's disease. The entrance point of the electrode into the STN and the length of the electrode trajectory crossing the STN were determined by intraoperative MER findings and 3 T T2-weighted magnetic resonance images with 1-mm slice thickness.

RESULTS

Average difference between MRI- and MER-based trajectory lengths crossing the STN was 0.28 ± 1.02 mm (95% CI: −0.51 to −0.05 mm). There was a statistically significant difference between the MRI- and MER-based entry points on the initial and second side of surgery (P = .04). Forty-three percent of the patients had a difference of more than ±1 mm of the MRI-based-predicted and the MER-based-determined entry points into the STN with values ranging from −3.0 to + 4.5 mm.

CONCLUSION

STN MRI-based targeting is accurate in the majority of cases on the first and second side of surgery. In 43% of implanted electrodes, we found a relevant deviation of more than 1 mm, supporting the concept of MER as an important tool to guide and optimize targeting and electrode placement.

Intractable Blepharospasm Treated with Bilateral Pallidal Deep Brain Stimulation

BACKGROUND

Blepharospasm can be present as an isolated dystonia or in conjunction with other forms of cranial dystonia, causing significant disability.

CASE REPORT

We report a case of a 69-year-old male with craniocervical dystonia, manifesting primarily as incapacitating blepharospasm refractory to medical treatments. He underwent bilateral globus pallidus (GP) deep brain stimulation (DBS) with complete resolution of his blepharospasm and sustained benefit at 12 months postoperatively.

DISCUSSION

This case illustrates successful treatment of blepharospasm with pallidal stimulation. GP-DBS should be considered a reasonable therapeutic option for intractable blepharospasm.

Causes of failure of pallidal deep brain stimulation in cases with pre-operative diagnosis of isolated dystonia

INTRODUCTION

Pallidal deep brain stimulation (GPi-DBS) is an effective therapy for isolated dystonia, but 10-20% of patients show improvement below 25-30%. We here investigated causes of insufficient response to GPi-DBS in isolated dystonia in a cross-sectional study.

METHODS

Patients with isolated dystonia at time of surgery, and <30% improvement on the Burke-Fahn-Marsden dystonia-rating-scale (BFMDRS) after ≥6 months of continuous GPi-DBS were videotaped ON and OFF stimulation, and history, preoperative videos, brain MRI, medical records, stimulation settings, stimulation system integrity, lead location, and genetic information were obtained and reviewed by an expert panel.

RESULTS

22 patients from 11 centres were included (8 men, 14 women; 9 generalized, 9 segmental, 3 focal, 1 bibrachial dystonia; mean (range): age 48.7 (25-72) years, disease duration 22.0 (2-40) years, DBS duration 45.5 (6-131) months). Mean BFMDRS-score was 31.7 (4-93) preoperatively and 32.3 (5-101) postoperatively. Half of the patients (n = 11) had poor lead positioning alone or in combination with other problems (combined with: other disease n = 6, functional dystonia n = 1, other problems n = 2). Other problems were disease other than isolated inherited or idiopathic dystonia (n = 5), fixed deformities (n = 2), functional dystonia (n = 3), and other causes (n = 1). Excluding patients with poor lead location from further analysis, non-isolated dystonia accounted for 45.5%, functional dystonia for 27.3%, and fixed deformities for 18.2%. In patients with true isolated dystonia, lead location was the most frequent problem.

CONCLUSION

After exclusion of lead placement and stimulation programming issues, non-isolated dystonia, functional dystonia and fixed deformities account for the majority of GPi-DBS failures in dystonia.

An Analysis of the Use of Multichannel Microelectrode Recording During Deep Brain Stimulation Surgeries at a Single Center

BACKGROUND

Microelectrode recording (MER) can be used to map out the target nucleus and identify ideal lead placement.

OBJECTIVE

To assess the use of multichannel MER to increase the efficiency of lead placement without compromising patient safety.

METHODS

Analysis of a single center's technique for utilizing multichannel MER with 3 consistent anterior-to-posterior simultaneous passes that include an evaluation of the location of final lead placement, patient diagnosis, target nuclei, and additional work involved for refinement of targeting. Lead revision rates and rate of hemorrhage are also assessed.

RESULTS

There were a total of 237 lead placements in 123 patients over a 4-yr period. In 4.2% of lead placements, additional planning was required, while only 2.5% required additional MER. The lead placement matched 51.3% of the time in bilateral placements and was consistent regardless of target nuclei. In 84.8% of cases, the final lead placement was within the initial 3 MER passes. An additional 11.3% could be placed without the need for an additional pass. There were 2 lead revisions and no hemorrhage or stroke complications.

CONCLUSION

This series demonstrates that our technique of multichannel MER leads to accurate and efficient lead placement maintaining its safety profile.

"Asleep" Deep Brain Stimulation Surgery: A Critical Review of the Literature

OBJECTIVE

Although performing deep brain stimulation (DBS) with the patient under general anesthesia without microelectrode recording (MER) or intraoperative test stimulation (ITS) for movement disorders ("asleep" DBS) has become increasingly popular, its feasibility is based on the untested assumption that stereotactic accuracy correlates with positive clinical outcomes. To investigate outcomes after asleep DBS without MER or neurophysiological testing, we reviewed the medical literature on the topic.

METHODS

We searched PubMed to identify all studies reporting clinical outcomes for patients who underwent DBS without MER or ITS for Parkinson disease (PD) or essential tremor (ET).

RESULTS

We identified 9 studies with level 3b (n = 3) or level 4 evidence (n = 6). Eight PD studies (220 patients) reported asleep placement of 431 electrodes (341 subthalamic nucleus, 90 globus pallidus interna). Unified Parkinson Disease Rating Scale motor examination-III scores for 208 patients demonstrated significant improvement (40.2%-65%) at 6-12 months. The levodopa equivalent daily dose for 115 patients was significantly reduced (14%-49.3%) at 6-12 months in 103 patients. Two studies with a comparison cohort undergoing "awake" DBS with MER found no differences in postoperative Unified Parkinson Disease Rating Scale-III improvement or levodopa equivalent daily dose reduction. One study of asleep DBS for ET found no difference in functional outcomes between 17 patients undergoing asleep ventral intermediate nucleus DBS and 40 patients undergoing awake placement with ITS.

CONCLUSIONS

Initial evidence suggests that asleep DBS can be performed safely for PD and ET with good clinical outcomes. Long-term follow-up, larger cohorts, and double-armed studies are needed to validate these initial results.

Toward defining deep brain stimulation targets in MNI space: A subcortical atlas based on multimodal MRI, histology and structural connectivity

Three-dimensional atlases of subcortical brain structures are valuable tools to reference anatomy in neuroscience and neurology. For instance, they can be used to study the position and shape of the three most common deep brain stimulation (DBS) targets, the subthalamic nucleus (STN), internal part of the pallidum (GPi) and ventral intermediate nucleus of the thalamus (VIM) in spatial relationship to DBS electrodes. Here, we present a composite atlas based on manual segmentations of a multimodal high resolution brain template, histology and structural connectivity. In a first step, four key structures were defined on the template itself using a combination of multispectral image analysis and manual segmentation. Second, these structures were used as anchor points to coregister a detailed histological atlas into standard space. Results show that this approach significantly improved coregistration accuracy over previously published methods. Finally, a sub-segmentation of STN and GPi into functional zones was achieved based on structural connectivity. The result is a composite atlas that defines key nuclei on the template itself, fills the gaps between them using histology and further subdivides them using structural connectivity. We show that the atlas can be used to segment DBS targets in single subjects, yielding more accurate results compared to priorly published atlases. The atlas will be made publicly available and constitutes a resource to study DBS electrode localizations in combination with modern neuroimaging methods.

Improving the accuracy of microelectrode recording in deep brain stimulation surgery with intraoperative CT

Microelectrode recording (MER) is used to confirm electrophysiological signals within intended anatomic targets during deep brain stimulation (DBS) surgery. We describe a novel technique called intraoperative CT-guided extrapolation (iCTE) to predict the intended microelectrode trajectory and, if necessary, make corrections in real-time before dural opening. Prior to dural opening, a guide tube was inserted through the headstage and rested on dura. Intraoperative CT (iCT) was obtained, and a trajectory was extrapolated along the path of the guide tube to target depth using targeting software. The coordinates were recorded and compared to initial plan coordinates. If needed, adjustments were made using the headstage to correct for error. The guide tube was then inserted and MER ensued. At target, iCT was performed and microelectrode tip coordinates were compared with planned/adjusted track coordinates. Radial error between MER track and planned/adjusted track was calculated. For comparison, MER track error prior to the iCTE technique was assessed retrospectively in patients who underwent MER using iCT, whereby iCT was performed following completion of the first MER track. Forty-seven MER tracks were analyzed prior to iCTE (pre-iCTE), and 90 tracks were performed using the iCTE technique. There was no difference between radial error of pre-iCTE MER track and planned trajectory (2.1±0.12mm) compared to iCTE predicted trajectory and planned trajectory (1.76±0.13mm, p>0.05). iCTE was used to make trajectory adjustments which reduced radial error between the newly corrected and final microelectrode tip coordinates to 0.84±0.08mm (p<0.001). Inter-rater reliability was also tested using a second blinded measurement reviewer which showed no difference between predicted and planned MER track error (p=0.53). iCTE can predict and reduce trajectory error for microelectrode placement compared with the traditional use of iCT post MER.

Probabilistic conversion of neurosurgical DBS electrode coordinates into MNI space

In neurosurgical literature, findings such as deep brain stimulation (DBS) electrode positions are conventionally reported in relation to the anterior and posterior commissures of the individual patient (AC/PC coordinates). However, the neuroimaging literature including neuroanatomical atlases, activation patterns, and brain connectivity maps has converged on a different population-based standard (MNI coordinates). Ideally, one could relate these two literatures by directly transforming MRIs from neurosurgical patients into MNI space. However obtaining these patient MRIs can prove difficult or impossible, especially for older studies or those with hundreds of patients. Here, we introduce a methodology for mapping an AC/PC coordinate (such as a DBS electrode position) to MNI space without the need for MRI scans from the patients themselves. We validate our approach using a cohort of DBS patients in which MRIs are available, and test whether several variations on our approach provide added benefit. We then use our approach to convert previously reported DBS electrode coordinates from eight different neurological and psychiatric diseases into MNI space. Finally, we demonstrate the value of such a conversion using the DBS target for essential tremor as an example, relating the site of the active DBS contact to different MNI atlases as well as anatomical and functional connectomes in MNI space.

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 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.

A comparative historical and demographic study of the neuromodulation management techniques of deep brain stimulation for dystonia and cochlear implantation for sensorineural deafness in children

Cochlear implants for sensorineural deafness in children is one of the most successful neuromodulation techniques known to relieve early chronic neurodisability, improving activity and participation. In 2012 there were 324,000 recipients of cochlear implants globally.

AIM

To compare cochlear implant (CI) neuromodulation with deep brain stimulation (DBS) for dystonia in childhood and explore relations between age and duration of symptoms at implantation and outcome.

METHODS

Comparison of published annual UK CI figures for 1985-2009 with a retrospective cohort of the first 9 years of DBS for dystonia in children at a single-site Functional Neurosurgery unit from 2006 to 14.

RESULTS

From 2006 to 14, DBS neuromodulation of childhood dystonia increased by a factor of 3.8 to a total of 126 cases over the first 9 years, similar to the growth in cochlear implants which increased by a factor of 4.1 over a similar period in the 1980s rising to 527 children in 2009. The CI saw a dramatic shift in practice from implantation at >5 years of age at the start of the programme towards earlier implantation by the mid-1990s. Best language results were seen for implantation <5 years of age and duration of cochlear neuromodulation >4 years, hence implantation <1 year of age, indicating that severely deaf, pre-lingual children could benefit from cochlear neuromodulation if implanted early. Similar to initial CI use, the majority of children receiving DBS for dystonia in the first 9 years were 5-15 years of age, when the proportion of life lived with dystonia exceeds 90% thus limiting benefits.

CONCLUSION

Early DBS neuromodulation for acquired motor disorders should be explored to maximise the benefits of dystonia reduction in a period of maximal developmental plasticity before the onset of disability. Learning from cochlear implantation, DBS can become an accepted management option in children under the age of 5 years who have a reduced proportion of life lived with dystonia, and not viewed as a last resort reserved for only the most severe cases where benefits may be at their most limited.

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.

The Symptomatic Treatment of Acquired Dystonia: A Systematic Review

Background

Acquired dystonia is caused by an acquired or exogenous event. Although the therapeutic armamentarium used in clinical practice is more or less similar to that used for inherited or idiopathic dystonia, formal proof of the efficacy of these interventions in acquired dystonia is lacking.

Methods

The authors attempt to provide a comprehensive and systematic review of the current evidence for medical and allied health care treatment strategies in acquired dystonias. The PubMed, Cochrane Library, MEDLINE, Web of Science, PiCarta, and PsycINFO databases were searched up to December 2015, including randomized controlled trials, patient-control studies, and case series or single case reports containing a report on clinical outcome.

Results

There are level 3 practice recommendations for botulinum toxin injections and globus pallidus pars interna deep brain stimulation for tardive dystonia and dystonic cerebral palsy as well as intrathecal baclofen for dystonic cerebral palsy. There are insufficient and conflicting data on the effect (vs. the hazard) of other pharmacological interventions, and limited work has been done on other forms of neurostimulation and allied health care. Because no class A1 or A2 studies were identified, level 1 or 2 practice recommendations could not be deducted for a specific treatment intervention.

Conclusions

To improve the current medical and allied health care treatment options for patients with acquired dystonia, high-quality trials that examine the efficacy of therapies need to be performed.

Modeling Laterality of the Globus Pallidus Internus in Patients With Parkinson's Disease

OBJECTIVE

Neurosurgical interventions such as deep brain stimulation surgery of the globus pallidus internus (GPi) play an important role in the treatment of medically refractory Parkinson's disease (PD), and require high targeting accuracy. Variability in the laterality of the GPi across patients with PD has not been well characterized. The aim of this report is to identify factors that may contribute to differences in position of the motor region of GPi.

MATERIALS AND METHODS

The charts and operative reports of 101 PD patients following deep brain stimulation surgery (70 males, aged 11-78 years) representing 201 GPi were retrospectively reviewed. Data extracted for each subject include age, gender, anterior and posterior commissures (AC-PC) distance, and third ventricular width. Multiple linear regression, stepwise regression, and relative importance of regressors analysis were performed to assess the predictive ability of these variables on GPi laterality.

RESULTS

Multiple linear regression for target vs. third ventricular width, gender, AC-PC distance, and age were significant for normalized linear regression coefficients of 0.333 (p < 0.0001), 0.206 (p = 0.00219), 0.168 (p = 0.0119), and 0.159 (p = 0.0136), respectively. Third ventricular width, gender, AC-PC distance, and age each account for 44.06% (21.38-65.69%, 95% CI), 20.82% (10.51-35.88%), 21.46% (8.28-37.05%), and 13.66% (2.62-28.64%) of the R² value, respectively. Effect size calculation was significant for a change in the GPi laterality of 0.19 mm per mm of ventricular width, 0.11 mm per mm of AC-PC distance, 0.017 mm per year in age, and 0.54 mm increase for male gender.

CONCLUSION

This variability highlights the limitations of indirect targeting alone, and argues for the continued use of MRI as well as intraoperative physiological testing to account for such factors that contribute to patient-specific variability in GPi localization.

State of the Art for Deep Brain Stimulation Therapy in Movement Disorders: A Clinical and Technological Perspective

Deep brain stimulation (DBS) therapy is a widely used brain surgery that can be applied for many neurological and psychiatric disorders. DBS is American Food and Drug Administration approved for medication refractory Parkinson's disease, essential tremor and dystonia. Although DBS has shown consistent success in many clinical trials, the therapy has limitations and there are well-recognized complications. Thus, only carefully selected patients are ideal candidates for this surgery. Over the last two decades, there have been significant advances in clinical knowledge on DBS. In addition, the surgical techniques and technology related to DBS has been rapidly evolving. The goal of this review is to describe the current status of DBS in the context of movement disorders, outline the mechanisms of action for DBS in brief, discuss the standard surgical and imaging techniques, discuss the patient selection and clinical outcomes in each of the movement disorders, and finally, introduce the recent advancements from a clinical and technological perspective.

Parkinson’s disease outcomes after intraoperative CT-guided “asleep” deep brain stimulation in the globus pallidus internus

OBJECT

Recent studies show that deep brain stimulation can be performed safely and accurately without microelectrode recording ortest stimulation but with the patient under general anesthesia. The procedure couples techniques for direct anatomical targeting on MRI with intraoperative imaging to verify stereotactic accuracy. However, few authors have examined the clinical outcomes of Parkinson’s disease (PD) patients after this procedure. The purpose of this study was to evaluate PD outcomes following “asleep” deep brain stimulation in the globus pallidus internus (GPi).

METHODS

The authors prospectively examined all consecutive patients with advanced PD who underwent bilateral GPi electrode placement while under general anesthesia. Intraoperative CT was used to assess lead placement accuracy. The primary outcome measure was the change in the off-medication Unified Parkinson’s Disease Rating Scale motor score 6 months after surgery. Secondary outcomes included effects on the 39-Item Parkinson’s Disease Questionnaire (PDQ-39) scores, on-medication motor scores, and levodopa equivalent daily dose. Lead locations, active contact sites, stimulation parameters, and adverse events were documented.

RESULTS

Thirty-five patients (24 males, 11 females) had a mean age of 61 years at lead implantation. The mean radial error off plan was 0.8 mm. Mean coordinates for the active contact were 21.4 mm lateral, 4.7 mm anterior, and 0.4 mm superior to the midcommissural point. The mean off-medication motor score improved from 48.4 at baseline to 28.9 (40.3% improvement) at 6 months (p < 0.001). The PDQ-39 scores improved (50.3 vs 42.0; p = 0.03), and the levodopa equivalent daily dose was reduced (1207 vs 1035 mg; p = 0.004). There were no significant adverse events.

CONCLUSIONS

Globus pallidus internus leads placed with the patient under general anesthesia by using direct anatomical targeting resulted in significantly improved outcomes as measured by the improvement in the off-medication motor score at 6 months after surgery.

Deep brain stimulation for intractable tardive dystonia: Literature overview

BACKGROUND

Tardive dystonia (TD) represents a side effect of prolonged intake of dopamine receptor blocking compounds. TD can be a disabling movement disorder persisting despite available medical treatment. Deep brain stimulation (DBS) has been reported successful in this condition although the number of treated patients with TD is still limited to small clinical studies or case reports. The aim of this study was to present the systematical overview of the existing literature regarding DBS for intractable TD.

METHODS AND RESULTS

A literature search was carried out in PudMed. Clinical case series or case reports describing the patients with TD after DBS treatment were included in the present overview. Literature search revealed 19 articles reporting 59 individuals operated for TD. GPi was the target in 55 patients, while subthalamic nucleus (STN) was the target in the remaining 4. In most studies the motor part of Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) was improved by more than 80% when compared to preoperative BFMDRS scores.

CONCLUSIONS

The performed literature analysis indicates that bilateral GPi DBS is an effective treatment for disabling TD. The response of TD to bilateral GPi DBS may be very rapid and occurs within days/weeks after the procedure. The efficacy of bilateral GPi DBS in TD patients is comparable to results achieved in patients with primary generalized dystonia.

Long-Term Clinical Outcome of Internal Globus Pallidus Deep Brain Stimulation for Dystonia

Background

GPi (Internal globus pallidus) DBS (deep brain stimulation) is recognized as a safe, reliable, reversible and adjustable treatment in patients with medically refractory dystonia.

Objectives

This report describes the long-term clinical outcome of 36 patients implanted with GPi DBS at the Neurosurgery Department of Seoul National University Hospital.

Methods

Nine patients with a known genetic cause, 12 patients with acquired dystonia, and 15 patients with isolated dystonia without a known genetic cause were included. When categorized by phenomenology, 29 patients had generalized, 5 patients had segmental, and 2 patients had multifocal dystonia. Patients were assessed preoperatively and at defined follow-up examinations postoperatively, using the Burke-Fahn-Marsden dystonia rating scale (BFMDRS) for movement and functional disability assessment. The mean follow-up duration was 47 months (range, 12–84)

Results

The mean movement scores significantly decreased from 44.88 points preoperatively to 26.45 points at 60-month follow up (N = 19, P = 0.006). The mean disability score was also decreased over time, from 11.54 points preoperatively to 8.26 points at 60-month follow up, despite no statistical significance (N = 19, P = 0.073). When analyzed the movement and disability improvement rates at 12-month follow up point, no significant difference was noted according to etiology, disease duration, age at surgery, age of onset, and phenomenology. However, the patients with DYT-1 dystonia and isolated dystonia without a known genetic cause showed marked improvement.

Conclusions

GPi DBS is a safe and efficient therapeutic method for treatment of dystonia patients to improve both movement and disability. However, this study has some limitations caused by the retrospective design with small sample size in a single-center.

Therapeutic Perspective on Tardive Syndrome with Special Reference to Deep Brain Stimulation

Tardive syndrome (TDS) is a potentially permanent and irreversible hyperkinetic movement disorder caused by exposure to dopamine receptor blocking agents. Guidelines published by the American Academy of Neurology recommend pharmacological first-line treatment for TDS with clonazepam (level B), ginkgo biloba (level B), amantadine (level C), and tetrabenazine (level C). Recently, a class II study provided level C evidence for use of deep brain stimulation (DBS) of the globus pallidus internus (GPi) in patients with TDS. Although the precise pathogenesis of TDS remains to be elucidated, the beneficial effects of GPi-DBS in patients with TDS suggest that the disease may be a basal ganglia disorder. In addition to recent advances in understanding the pathophysiology of TDS, this article introduces the current use of DBS in the treatment of medically intractable TDS.

Bilateral deep brain stimulation of the fornix for Alzheimer's disease: surgical safety in the ADvance trial

OBJECT This report describes the stereotactic technique, hospitalization, and 90-day perioperative safety of bilateral deep brain stimulation (DBS) of the fornix in patients who underwent DBS for the treatment of mild, probable Alzheimer's disease (AD). METHODS The ADvance Trial is a multicenter, 12-month, double-blind, randomized, controlled feasibility study being conducted to evaluate the safety, efficacy, and tolerability of DBS of the fornix in patients with mild, probable AD. Intraoperative and perioperative data were collected prospectively. All patients underwent postoperative MRI. Stereotactic analyses were performed in a blinded fashion by a single surgeon. Adverse events (AEs) were reported to an independent clinical events committee and adjudicated to determine the relationship between the AE and the study procedure. RESULTS Between June 6, 2012, and April 28, 2014, a total of 42 patients with mild, probable AD were treated with bilateral fornix DBS (mean age 68.2 ± 7.8 years; range 48.0-79.7 years; 23 men and 19 women). The mean planned target coordinates were x = 5.2 ± 1.0 mm (range 3.0-7.9 mm), y = 9.6 ± 0.9 mm (range 8.0-11.6 mm), z = -7.5 ± 1.2 mm (range -5.4 to -10.0 mm), and the mean postoperative stereotactic radial error on MRI was 1.5 ± 1.0 mm (range 0.2-4.0 mm). The mean length of hospitalization was 1.4 ± 0.8 days. Twenty-six (61.9%) patients experienced 64 AEs related to the study procedure, of which 7 were serious AEs experienced by 5 patients (11.9%). Four (9.5%) patients required return to surgery: 2 patients for explantation due to infection, 1 patient for lead repositioning, and 1 patient for chronic subdural hematoma. No patients experienced neurological deficits as a result of the study, and no deaths were reported. CONCLUSIONS Accurate targeting of DBS to the fornix without direct injury to it is feasible across surgeons and treatment centers. At 90 days after surgery, bilateral fornix DBS was well tolerated by patients with mild, probable AD. Clinical trial registration no.: NCT01608061 ( clinicaltrials.gov ).

Motor System Interactions in the Beta Band Decrease during Loss of Consciousness

Communication between brain areas and how they are influenced by changes in consciousness are not fully understood. One hypothesis is that brain areas communicate via oscillatory processes, utilizing network-specific frequency bands, that can be measured with metrics that reflect between-region interactions, such as coherence and phase amplitude coupling (PAC). To evaluate this hypothesis and understand how these interactions are modulated by state changes, we analyzed electrophysiological recordings in humans at different nodes of one well-studied brain network: the basal ganglia-thalamocortical loops of the motor system during loss of consciousness induced by anesthesia. We recorded simultaneous electrocorticography over primary motor cortex (M1) with local field potentials from subcortical motor regions (either basal ganglia or thalamus) in 15 movement disorder patients during anesthesia (propofol) induction as a part of their surgery for deep brain stimulation. We observed reduced coherence and PAC between M1 and the subcortical nuclei, which was specific to the beta band (∼18-24 Hz). The fact that this pattern occurs selectively in beta underscores the importance of this frequency band in the motor system and supports the idea that oscillatory interactions at specific frequencies are related to the capacity for normal brain function and behavior.

Postoperative MRI localisation of electrodes and clinical efficacy of pallidal deep brain stimulation in cervical dystonia

INTRODUCTION

Pallidal deep brain stimulation (DBS) has been shown to be effective in cervical dystonia (CD) with an improvement of about 50-60% in the Toronto Western Spasmodic Torticollis Rating (TWSTR) Scale. However, predictive factors for the efficacy of DBS in CD are missing with the anatomical location of the electrodes being one of the most important potential predictive factors.

METHODS

In the present blinded observational study we correlated the anatomical localisation of DBS contacts with the relative clinical improvement (CI %) in the TWSTR as achieved by DBS at different pallidal contacts in 20 patients with CD. Localisations of DBS contacts were derived from postoperative MRI-data following anatomical normalisation into the standard Montreal Neurological Institute stereotactic space. The CIs following 76 bilateral test stimulations of 24 h were mapped to stereotactic coordinates of the corresponding bilateral 152 active contacts and were allocated to low CI (<30%; n=74), intermediate CI (≥30%; <60%; n=52) or high CI (≥60%; n=26).

RESULTS

Euclidean distances between contacts and the centroid differed between the three clusters (p<0.001) indicating different anatomical variances between clusters. The Euclidean distances between contacts and the centroid of the cluster with high CIs correlated with the individual level of CIs (r=-0.61; p<0.0001). This relationship was best fitted with an exponential regression curve (r(2)=0.41).

DISCUSSION

Our data show that the clinical effect of pallidal DBS on CD displays an exponential decay over anatomical distance from an optimised target localisation within a subregion of the internal pallidum. The results will allow a comparison of future DBS studies with postoperative MRI by verifying optimised (for instance pallidal) targeting in DBS-treated patients.

Pallidal stimulation for Holmes tremor: clinical outcomes and single-unit recordings in 4 cases

OBJECT

Holmes tremor (HT) is characterized by irregular, low-frequency (< 4.5 Hz) tremor occurring at rest, with posture, and with certain actions, often affecting proximal muscles. Previous reports have tended to highlight the use of thalamic deep brain stimulation (DBS) in cases of medication-refractory HT. In this study, the authors report the clinical outcome and analysis of single-unit recordings in patients with medication-refractory HT treated with globus pallidus internus (GPi) DBS.

METHODS

The authors retrospectively reviewed the medical charts of 4 patients treated with pallidal DBS for medication-refractory HT at the University of California, San Francisco, and San Francisco Veterans Affairs Medical Center. Clinical outcomes were measured at baseline and after surgery using an abbreviated motor-severity Fahn-Tolosa-Marin (FTM) tremor rating scale. Intraoperative microelectrode recordings were performed with patients in the awake state. The neurophysiological characteristics identified in HT were then also compared with characteristics previously described in Parkinson's disease (PD) studied at the authors' institution.

RESULTS

The mean percentage improvement in tremor motor severity was 78.87% (range 59.9%–94.4%) as measured using the FTM tremor rating scale, with an average length of follow-up of 33.75 months (range 18–52 months). Twenty-eight GPi neurons were recorded intraoperatively in the resting state and 13 of these were also recorded during contralateral voluntary arm movement. The mean firing rate at rest in HT was 56.2 ± 28.5 Hz, and 63.5 ± 19.4 Hz with action, much lower than the GPi recordings in PD. GPi unit oscillations of 2–8 Hz were prominent in both patients with HT and those with PD, but in HT, unlike PD, these oscillations were not suppressed by voluntary movement.

CONCLUSIONS

The efficacy of GPi DBS exceeded that reported in prior studies of ventrolateral thalamus DBS and suggest GPi may be a better target for treating HT. These clinical and neurophysiological findings help illuminate evolving models of HT and highlight the importance of cerebellar–basal ganglia interactions.

Wavelet methodology to improve single unit isolation in primary motor cortex cells

The proper isolation of action potentials recorded extracellularly from neural tissue is an active area of research in the fields of neuroscience and biomedical signal processing. This paper presents an isolation methodology for neural recordings using the wavelet transform (WT), a statistical thresholding scheme, and the principal component analysis (PCA) algorithm. The effectiveness of five different mother wavelets was investigated: biorthogonal, Daubachies, discrete Meyer, symmetric, and Coifman; along with three different wavelet coefficient thresholding schemes: fixed form threshold, Stein's unbiased estimate of risk, and minimax; and two different thresholding rules: soft and hard thresholding. The signal quality was evaluated using three different statistical measures: mean-squared error, root-mean squared, and signal to noise ratio. The clustering quality was evaluated using two different statistical measures: isolation distance, and L-ratio. This research shows that the selection of the mother wavelet has a strong influence on the clustering and isolation of single unit neural activity, with the Daubachies 4 wavelet and minimax thresholding scheme performing the best.

Uncommon applications of deep brain stimulation in hyperkinetic movement disorders

Background

In addition to the established indications of tremor and dystonia, deep brain stimulation (DBS) has been utilized less commonly for several hyperkinetic movement disorders, including medication-refractory myoclonus, ballism, chorea, and Gilles de la Tourette (GTS) and tardive syndromes. Given the lack of adequate controlled trials, it is difficult to translate published reports into clinical use. We summarize the literature, draw conclusions regarding efficacy when possible, and highlight concerns and areas for future study.

Methods

A Pubmed search was performed for English-language articles between January 1980 and June 2014. Studies were selected if they focused primarily on DBS to treat the conditions of focus.

Results

We identified 49 cases of DBS for myoclonus-dystonia, 21 for Huntington's disease, 15 for choreacanthocytosis, 129 for GTS, and 73 for tardive syndromes. Bilateral globus pallidus interna (GPi) DBS was the most frequently utilized procedure for all conditions except GTS, in which medial thalamic DBS was more common. While the majority of cases demonstrate some improvement, there are also reports of no improvement or even worsening of symptoms in each condition. The few studies including functional or quality of life outcomes suggest benefit. A limited number of studies included blinded on/off testing. There have been two double-blind controlled trials performed in GTS and a single prospective double-blind, uncontrolled trial in tardive syndromes. Patient characteristics, surgical target, stimulation parameters, and duration of follow-up varied among studies.

Discussion

Despite these extensive limitations, the literature overall supports the efficacy of DBS in these conditions, in particular GTS and tardive syndromes. For other conditions, the preliminary evidence from small studies is promising and encourages further study.

The optimal pallidal target in deep brain stimulation for dystonia: a study using a functional atlas based on nonlinear image registration

BACKGROUND

Deep brain stimulation (DBS) of the globus pallidus internus is established as efficacious for dystonia, yet the optimal target within this structure is not well defined. Published evidence suggests that spatial normalization provides a better estimate of DBS lead location than traditional methods based on standard stereotactic coordinates.

METHODS

We retrospectively reviewed our pallidal implanted dystonia population. Patient imaging scans were morphed into an MRI atlas using a nonlinear image registration algorithm. Active contact locations were projected onto the atlas and clusters analyzed for the degree of variance in two groups: (1) good and poor responders and (2) cervical (CD) and generalized dystonia (GD).

RESULTS

The average active contact location between CD and GD good responders was distinct but not significantly different. The mean active contact for CD poor responders was significantly different from CD responders and GD poor responders in the dorsoventral direction.

CONCLUSIONS

A normalized imaging space is arguably more accurate in visualizing postoperative leads. Despite some separation between groups, this data suggests there was not an optimal pallidal target for common dystonia patients. Degrees of variance overlapped due to a large degree of individual target variation. Patient selection may ultimately be the key to maximizing patient outcomes.

Correlation of diffusion tensor tractography and intraoperative macrostimulation during deep brain stimulation for Parkinson disease

Object

The purpose of this study was to investigate whether diffusion tensor imaging (DTI) of the corticospinal tract (CST) is a reliable surrogate for intraoperative macrostimulation through the deep brain stimulation (DBS) leads. The authors hypothesized that the distance on MRI from the DBS lead to the CST as determined by DTI would correlate with intraoperative motor thresholds from macrostimulations through the same DBS lead.

Methods

The authors retrospectively reviewed pre- and postoperative MRI studies and intraoperative macrostimulation recordings in 17 patients with Parkinson disease (PD) treated by DBS stimulation. Preoperative DTI tractography of the CST was coregistered with postoperative MRI studies showing the position of the DBS leads. The shortest distance and the angle from each contact of each DBS lead to the CST was automatically calculated using software-based analysis. The distance measurements calculated for each contact were evaluated with respect to the intraoperative voltage thresholds that elicited a motor response at each contact.

Results

There was a nonsignificant trend for voltage thresholds to increase when the distances between the DBS leads and the CST increased. There was a significant correlation between the angle and the voltage, but the correlation was weak (coefficient of correlation [R] = 0.36).

Conclusions

Caution needs to be exercised when using DTI tractography information to guide DBS lead placement in patients with PD. Further studies are needed to compare DTI tractography measurements with other approaches such as microelectrode recordings and conventional intraoperative MRI–guided placement of DBS leads.

Interventional MRI-guided deep brain stimulation in pediatric dystonia: first experience with the ClearPoint system

OBJECT

The placement of deep brain stimulation (DBS) leads in adults is traditionally performed using physiological confirmation of lead location in the awake patient. Most children are unable to tolerate awake surgery, which poses a challenge for intraoperative confirmation of lead location. The authors have developed an interventional MRI (iMRI)-guided procedure to allow for real-time anatomical imaging, with the goal of achieving very accurate lead placement in patients who are under general anesthesia.

METHODS

Six pediatric patients with primary dystonia were prospectively enrolled. Patients were candidates for surgery if they had marked disability and medical therapy had been ineffective. Five patients had the DYT1 mutation, and mean age at surgery was 11.0 ± 2.8 years. Patients underwent bilateral globus pallidus internus (GPi, n = 5) or sub-thalamic nucleus (STN, n = 1) DBS. The leads were implanted using a novel skull-mounted aiming device in conjunction with dedicated software (ClearPoint system), used within a 1.5-T diagnostic MRI unit in a radiology suite, without physiological testing. The Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) was used at baseline, 6 months, and 12 months postoperatively. Further measures included lead placement accuracy, quality of life, adverse events, and stimulation settings.

RESULTS

A single brain penetration was used for placement of all 12 leads. The mean difference (± SD) between the intended target location and the actual lead location, in the axial plane passing through the intended target, was 0.6 ± 0.5 mm, and the mean surgical time (leads only) was 190 ± 26 minutes. The mean percent improvement in the BFMDRS movement scores was 86.1% ± 12.5% at 6 months (n = 6, p = 0.028) and 87.6% ± 19.2% at 12 months (p = 0.028). The mean stimulation settings at 12 months were 3.0 V, 83 μsec, 135 Hz for GPi DBS, and 2.1 V, 60 μsec, 145 Hz for STN DBS). There were no serious adverse events.

CONCLUSIONS

Interventional MRI-guided DBS using the ClearPoint system was extremely accurate, provided real-time confirmation of DBS placement, and could be used in any diagnostic MRI suite. Clinical outcomes for pediatric dystonia are comparable with the best reported results using traditional frame-based stereotaxy. Clinical trial registration no.: NCT00792532 ( ClinicalTrials.gov ).

Defining a therapeutic target for pallidal deep brain stimulation for dystonia

OBJECTIVE

To create a data-driven computational model that identifies brain regions most frequently influenced by successful deep brain stimulation (DBS) of the globus pallidus (GP) for advanced, medication-resistant, generalized dystonia.

METHODS

We studied a retrospective cohort of 21 DYT1 primary dystonia patients treated for at least 1 year with bilateral pallidal DBS. We first created individual volume of tissue activation (VTA) models utilizing neuroimaging and postoperative stimulation and clinical data. These models were then combined into a standardized probabilistic dystonia stimulation atlas (DSA). Finally, we constructed a candidate target volume from electrodes demonstrating at least 75% improvement in contralateral symptoms, utilizing voxels stimulated by least 75% of these electrodes.

RESULTS

Pallidal DBS resulted in a median contralateral hemibody improvement of 90% (mean = 83%, standard deviation [SD] = 20) after 1 year of treatment. Individual VTA models of the 42 active electrodes included in the study demonstrated a mean stimulation volume of 501mm ([SD] = 284). The resulting DSA showed that areas most frequently stimulated were located squarely in the middle of the posterior GP, with a common target volume measuring 153mm(3) .

INTERPRETATION

Our results provide a map of the region of influence of therapeutic DBS for dystonia and represent a potential target to refine current methods of surgical planning and stimulation parameters selection. Based on their role in alleviating symptoms, these regions may also provide anatomical and physiological information relevant to disease models of dystonia. Further experimental and clinical studies will be needed to validate their importance.

Coordinate-based lead location does not predict Parkinson's disease deep brain stimulation outcome

Background

Effective target regions for deep brain stimulation (DBS) in Parkinson's disease (PD) have been well characterized. We sought to study whether the measured Cartesian coordinates of an implanted DBS lead are predictive of motor outcome(s). We tested the hypothesis that the position and trajectory of the DBS lead relative to the mid-commissural point (MCP) are significant predictors of clinical outcomes. We expected that due to neuroanatomical variation among individuals, a simple measure of the position of the DBS lead relative to MCP (commonly used in clinical practice) may not be a reliable predictor of clinical outcomes when utilized alone.

Methods

55 PD subjects implanted with subthalamic nucleus (STN) DBS and 41 subjects implanted with globus pallidus internus (GPi) DBS were included. Lead locations in AC-PC space (x, y, z coordinates of the active contact and sagittal and coronal entry angles) measured on high-resolution CT-MRI fused images, and motor outcomes (Unified Parkinson's Disease Rating Scale) were analyzed to confirm or refute a correlation between coordinate-based lead locations and DBS motor outcomes.

Results

Coordinate-based lead locations were not a significant predictor of change in UPDRS III motor scores when comparing pre- versus post-operative values. The only potentially significant individual predictor of change in UPDRS motor scores was the antero-posterior coordinate of the GPi lead (more anterior lead locations resulted in a worse outcome), but this was only a statistical trend (p<.082).

Conclusion

The results of the study showed that a simple measure of the position of the DBS lead relative to the MCP is not significantly correlated with PD motor outcomes, presumably because this method fails to account for individual neuroanatomical variability. However, there is broad agreement that motor outcomes depend strongly on lead location. The results suggest the need for more detailed identification of stimulation location relative to anatomical targets.

Deep brain stimulation in DYT1 dystonia: a 10-year experience

BACKGROUND

Globus Pallidus Interna (GPi) deep brain stimulation (DBS) is an effective treatment for DYT1-associated dystonia, but long-term results are lacking.

OBJECTIVE

To evaluate the long-term effects of GPi DBS in patients with DYT1 dystonia.

METHODS

A retrospective chart review (cohort study) of 47 consecutive DYT1+ patients treated by a single surgical team over a 10-year period and followed for up to 96 months (mean, 46 months) was performed. Symptom severity was quantified with the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) motor (M) and disability (D) sub-scores.

RESULTS

As measured with the BFMDRS (M), symptom severity was reduced to less than 20% of baseline after 2 years of DBS therapy (P = .001). The disability scores were reduced to <30% of baseline (P = .001). Symptomatic improvement was durable throughout available follow-up. Sixty-one percent of patients had discontinued all dystonia-related medications at their last follow-up. Ninety-one percent had discontinued at least 1 class of medication. Infections requiring removal and later reimplantation of hardware occurred in 4 of 47 patients (8.5%). Hardware malfunction including lead fractures occurred in 4 of 47 cases (8.5%). Lead revision to address poor clinical response was performed in 2 of 92 implanted leads (2.2%).

CONCLUSION

GPi DBS is an effective therapy for DYT1-associated torsion dystonia. Statistically significant efficacy is maintained for up to 7 years. Neurologic complications are rare, but long-term hardware-related complications can be significant.

Deep brain stimulation for dystonia

Deep brain stimulation (DBS) is an effective surgical treatment for medication-refractory movement disorders, and has been approved by the United States Food and Drug Administration for treatment of dystonia. The success of DBS in the treatment of dystonia depends on our understanding of the anatomy and physiology of this disorder and close collaboration between neurosurgeons, neurologists, clinical neurophysiologists, neuroradiologists and neuropsychologists. Currently, pallidal DBS is an established treatment option for medically refractive dystonia. This review is intended to provide a comprehensive review of the use of DBS for dystonia, focusing mainly on the surgical aspects, clinical outcome, MRI findings and side effects of DBS.

Deep-brain stimulation for dystonia: current indications and future orientations

ABSTRACT: Deep-brain stimulation of the internal globus pallidus is a therapeutic option for dystonia. However, the available data are heterogeneous, ranging from single case reports to a few controlled studies. The outcomes are also largely heterogeneous, depending mostly on the etiology of the dystonia. Except for some well-established good indications, such as primary generalized dystonia and tardive dyskinesia, the efficacy of globus pallidus stimulation remains debated for several forms of dystonia. In addition, many issues are still unsolved, such as the best target of stimulation and the interest of simultaneously combining multiple targets of stimulation or not. Finally the efficacy of new strategies of treatment, such as cortical stimulation, remains to be determined. The aim of this review is to cover these different aspects and give an overview of the current indications and future orientations.

Tolerance of early pallidal stimulation in pediatric generalized dystonia

The authors report on 2 cases of pediatric generalized dystonia with a DYT1 mutation; the patients, an 11-year-old girl and a 9-year-old boy, underwent chronic, pallidal deep brain stimulation (DBS) of the globus pallidus internus (GPi). The dystonic postures in both cases showed dramatic improvements with pallidal DBS, but each patient's symptoms gradually recurred within a year, irrespective of exhaustive readjustments of the stimulation settings. After the recurrence of the dystonic symptoms, the DBS leads were replaced within the GPi in one patient (Case 1) and additional DBS leads were implanted into the bilateral subthalamic nuclei in the other patient (Case 2). Neither measure produced any further clinical benefit, and the patient in Case 2 died of status dystonicus 2 days after reoperation. These findings suggest that early pallidal DBS for pediatric dystonia is indeed effective, although there are some cases in which its therapeutic effect is lost. One possible reason may be the ability of the preadolescent brain to tolerate chronic electrical stimuli during the active maturation process.

Deep brain stimulation in children and young adults with secondary dystonia: the Children's Hospital Los Angeles experience

Background

Dystonia is a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. It can be classified as primary or secondary. There is no cure for dystonia and the goal of treatment is to provide a better quality of life for the patient.

Surgical intervention is considered for patients in whom an adequate trial of medical treatment has failed. Deep brain stimulation (DBS), specifically of the globus pallidus interna (GPi), has been shown to be extremely effective in primary generalized dystonia. There is much less evidence for the use of DBS in patients with secondary dystonia. However, given the large number of patients with secondary dystonia, the significant burden on the patients and their families, and the potential for DBS to improve their functional status and comfort level, it is important to continue to investigate the use of DBS in the realm of secondary dystonia.

Object

The objective of this study is to review a series of cases involving patients with secondary dystonia who have been treated with pallidal DBS.

Methods

A retrospective review of 9 patients with secondary dystonia who received treatment with DBS between February 2011 and February 2013 was performed. Preoperative and postoperative videos were scored using the Barry-Albright Dystonia Scale (BADS) and Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) by a neurologist specializing in movement disorders. In addition, the patients' families completed a subjective questionnaire to assess the perceived benefit of DBS.

Results

The average age at DBS unit implantation was 15.1 years (range 6–20 years). The average time to follow-up for the BADS evaluation from battery implantation was 3.8 months (median 3 months). The average time to follow-up for the subjective benefit evaluation was 10.6 months (median 9.5 months). The mean BADS scores improved by 9% from 26.5 to 24 (p = 0.04), and the mean BFMDRS scores improved by 9.3% (p = 0.055). Of note, even in patients with minimal functional improvement, there seemed to be decreased contractures and spasms leading to improved comfort. There were no complications such as infections or hematoma in this case series. In the subjective benefit evaluation, 3 patients' families reported “good” benefit, 4 reported “minimal” benefit, and 1 reported no benefit.

Conclusions

These early results of GPi stimulation in a series of 9 patients suggest that DBS is useful in the treatment of secondary generalized dystonia in children and young adults. Objective improvements in BADS and BFMDRS scores are demonstrated in some patients with generalized secondary dystonia but not in others. Larger follow-up studies of DBS for secondary dystonia, focusing on patient age, history, etiology, and patterns of dystonia, are needed to learn which patients will respond best to DBS.

Neuromodulation for dystonia: target and patient selection

Treatment of dystonia refractory to oral medications or botulinum toxin injections includes the use of deep brain stimulation (DBS). Expectations should be established based on patient-related factors, including type of dystonia, genetic cause, target symptoms, age at the time of surgery, disease duration, or the presence of fixed skeletal deformities. Premorbid conditions such as psychiatric illness and cognitive impairment should be considered. Target selection is an emerging issue in DBS for dystonia. Although efficacy has been established for targeting the globus pallidus internus for dystonia, other brain targets such as the subthalamic nucleus, thalamus, or cortex may be promising alternatives.

Connectivity patterns of pallidal DBS electrodes in focal dystonia: a diffusion tensor tractography study

Deep brain stimulation (DBS) of the internal pallidal segment (GPi: globus pallidus internus) is gold standard treatment for medically intractable dystonia, but detailed knowledge of mechanisms of action is still not available. There is evidence that stimulation of ventral and dorsal GPi produces opposite motor effects. The aim of this study was to analyse connectivity profiles of ventral and dorsal GPi. Probabilistic tractography was initiated from DBS electrode contacts in 8 patients with focal dystonia and connectivity patterns compared. We found a considerable difference in anterior-posterior distribution of fibres along the mesial cortical sensorimotor areas between the ventral and dorsal GPi connectivity. This finding of distinct GPi connectivity profiles further confirms the clinical evidence that the ventral and dorsal GPi belong to different functional and anatomic motor subsystems. Their involvement could play an important role in promoting clinical DBS effects in dystonia.

Deep brain stimulation for dystonia

The few controlled studies that have been carried out have shown that bilateral internal globus pallidum stimulation is a safe and long-term effective treatment for hyperkinetic disorders. However, most recent published data on deep brain stimulation (DBS) for dystonia, applied to different targets and patients, are still mainly from uncontrolled case reports (especially for secondary dystonia). This precludes clear determination of the efficacy of this procedure and the choice of the 'good' target for the 'good' patient. We performed a literature analysis on DBS for dystonia according to the expected outcome. We separated those with good evidence of favourable outcome from those with less predictable outcome. In the former group, we review the main results for primary dystonia (generalised/focal) and highlight recent data on myoclonus-dystonia and tardive dystonia (as they share, with primary dystonia, a marked beneficial effect from pallidal stimulation with good risk/benefit ratio). In the latter group, poor or variable results have been obtained for secondary dystonia (with a focus on heredodegenerative and metabolic disorders). From this overview, the main results and limits for each subgroup of patients that may help in the selection of dystonic patients who will benefit from DBS are discussed.