Post subthalamic area deep brain stimulation for tremors: a mini-review

Cognitive outcomes in patients with essential tremor treated with deep brain stimulation: a systematic review

Introduction

Essential tremor (ET) is a common neurological disease. Deep brain stimulation (DBS) to the thalamic ventral intermediate nucleus (VIM) or the adjacent structures, such as caudal zona incerta/ posterior subthalamic area (cZi/PSA), can be effective in treating medication refractory tremor. However, it is not clear whether DBS can cause cognitive changes, in which domain, and to what extent if so.

Methods

We systematically searched PubMed and the Web of Science for available publications reporting on cognitive outcomes in patients with ET who underwent DBS following the PICO (population, intervention, comparators, and outcomes) concept. The PRISMA guideline for systematic reviews was applied.

Results

Twenty relevant articles were finally identified and included for review, thirteen of which were prospective (one also randomized) studies and seven were retrospective. Cognitive outcomes included attention, memory, executive function, language, visuospatial function, and mood-related variables. VIM and cZi/PSA DBS were generally well tolerated, although verbal fluency and language production were affected in some patients. Additionally, left-sided VIM DBS was associated with negative effects on verbal abstraction, word recall, and verbal memory performance in some patients.

Conclusion

Significant cognitive decline after VIM or cZi/PSA DBS in ET patients appears to be rare. Future prospective randomized controlled trials are needed to meticulously study the effect of the location, laterality, and stimulation parameters of the active contacts on cognitive outcomes while considering possible medication change post-DBS, timing, standard neuropsychological battery, practice effects, the timing of assessment, and effect size as potential confounders.

Neuropsychological assessment protocol in an ongoing randomized controlled trial on posterior subthalamic area vs. ventral intermediate nucleus deep brain stimulation for essential tremor

Objective

Patients with essential tremor (ET) may experience cognitive-affective impairment. Deep brain stimulation (DBS) of different targets, such as the ventral intermediate nucleus (VIM) of the thalamus or the posterior subthalamic area (PSA), has been shown to be beneficial for refractory ET. However, there is little evidence regarding the possible neuropsychological effects of PSA-DBS on patients with ET, and there are few studies comparing it with VIM-DBS in this population.In this study, we aim to present the evaluation protocol and neuropsychological battery as used in an ongoing trial of DBS for ET comparing the already mentioned targets.

Methods

As part of a randomized, double-blind, crossover clinical trial comparing the effectiveness and safety of PSA-DBS vs. VIM-DBS, 11 patients with refractory ET will undergo a multi-domain neuropsychological battery assessment. This will include a pre-/post-implantation assessment (3 months after the stimulation of each target and 6 months after an open stage of DBS on the most optimal target).

Conclusion

Evidence on the neuropsychological effects of DBS in patients with refractory ET is very scarce, particularly in lesser-explored targets such as PSA. This study could contribute significantly in this field, particularly on pre-procedure safety analysis for tailored patient/technique selection, and to complete the safety analysis of the procedure. Moreover, if proven useful, this proposed neuropsychological assessment protocol could be extensible to other surgical therapies for ET.

Deep brain stimulation of the posterior subthalamic area as an alternative strategy for management of Holmes tremor: A case report and review of the literature

Background:

Holmes tremor is often refractory to medical treatment and deep brain stimulation of the ventralis intermedius nucleus of the thalamus (VIM-DBS) is the intervention of choice in controlling the tremor. Herein, we present a beneficial alternative strategy for the management of such situations, considering the posterior subthalamic area (PSA) as the target of stimulation.

Case Description:

We report a 57-year-old male with the right-sided tremor following a traumatic brain injury 20 years ago. He had been diagnosed with Holmes tremor that was not responsive to nonsurgical therapeutic options. When refractoriness confirmed, he became a candidate for VIM-DBS. During the operation, by performing macrostimulation with a maximum of 2 mA of amplitude, the tremor had no response to the stimulation of different tracts, and severe right hemi-body paresthesia occurred; therefore, we modified our approach and targeted the PSA, which resulted in satisfactory control of the tremor. The permanent lead was implanted into the left side PSA. At 1-year follow-up, the right side tremor was under complete control.

Conclusion:

Our case and other similar pieces of evidence are consistently indicating the potential regulatory effects of PSA-DBS in controlling the Holmes tremor as a feasible alternative strategy when VIM-DBS does not provide a satisfactory response. However, further studies with larger sample size are required to evaluate the long-term response and its possible long-term stimulation-related effects.

Targeting the vim by direct visualization of the cerebello-thalamo-cortical pathway in 3 T proton density MRI: correlation with focused ultrasound lesioning

Surgical targeting of the ventral intermediate nucleus of the thalamus (VIM) has been historically done using indirect strategies. Here we depict the cerebello-thalamo-cortical tract (CTCT) through 3 T proton density (PD) in a cohort of patients who underwent high-intensity focus ultrasound (HIFUS) thalamotomy. Forty-seven patients treated in our institution with MR-guided HIFUS VIM thalamotomy were included in this study. PD weighted 3 T MRI used for presurgical planning was compared with postoperative MRI obtained 1 month after surgery. Images were processed with ISTX software (Brain lab, Munich, Germany). The coordinates of the VIM lesion concerning the inter-commissural line (ICL) were annotated. Deterministic tractographies using three ROIs were used to verify the different tracts. The triangle seen in the 3 T PD sequence at the level of the mesencephalic-diencephalic junction was systematically recognized. The posterior angle of this triangle at the junction of the CTCT and the ZI was denominated as "point P." The area of this triangle corresponds to the posterior subthalamic area (PSA) harboring the Raprl fibers. The CTCT was visible from 1 to 2.5 mm below the ICL. The average center of the final HIFUS lesion (point F) was 11 mm from the medial thalamic border of the thalamus (14.9 mm from the midline), 6.4 mm anterior to PC, and 0.6 mm above the ICL. The FUS point was consistently 1-2 mm directly above point P. The anterior border of the external angle of this triangle (point P) can be used as an intraparenchymal point for targeting the ventral border of the VIM. Three ROIs placed in a single slice around this triangle are a fast way to originate tractography of the CTCT, lemniscus medialis, and pyramidal tract.

Effect of Deep Brain Stimulation on Cerebellar Tremor Compared to Non-Cerebellar Tremor Using a Wearable Device in a Patient With Multiple Sclerosis: Case Report

Tremor of the upper extremity is a significant cause of disability in some patients with multiple sclerosis (MS). The MS tremor is complex because it contains an ataxic intentional tremor component due to the involvement of the cerebellum and cerebellar outflow pathways by MS plaques, which makes the MS tremor, in general, less responsive to medications or deep brain stimulation (DBS) than those associated with essential tremor or Parkinson's disease. The cerebellar component has been thought to be the main reason for making DBS less effective, although it is not clear whether it is due to the lack of suppression of the ataxic tremor by DBS or else. The goal of this study was to clarify the effect of DBS on cerebellar tremor compared to non-cerebellar tremor in a patient with MS. By wearing an accelerometer on the index finger of each hand, we were able to quantitatively characterize kinetic tremor by frequency and amplitude, with cerebellar ataxia component on one hand and that without cerebellar component on the other hand, at the beginning and end of the hand movement approaching a target at DBS Off and On status. We found that cerebellar tremor surprisingly had as good a response to DBS as the tremor without a cerebellar component, but the function control on cerebellar tremor was not as good due to its distal oscillation, which made the amplitude of tremor increasingly greater as it approached the target. This explains why cerebellar tremor or MS tremor with cerebellar component has a poor functional transformation even with a good percentage of tremor control. This case study provides a better understanding of the effect of DBS on cerebellar tremor and MS tremor by using a wearable device, which could help future studies improve patient selection and outcome prediction for DBS treatment of this disabling tremor.

Loss of long-term benefit from VIM-DBS in essential tremor: A secondary analysis of repeated measurements

AIMS

Deep brain stimulation (DBS) in the ventral intermediate nucleus (Vim-DBS) is the preferred surgical therapy for essential tremor (ET). Tolerance and disease progression are considered to be the two main reasons underlying the loss of long-term efficacy of Vim-DBS. This study aimed to explore whether Vim-DBS shows long-term loss of efficacy and to evaluate the reasons for this diminished efficacy from different aspects.

METHODS

In a repeated-measures meta-analysis of 533 patients from 18 studies, Vim-DBS efficacy was evaluated at ≤6 months, 7-12 months, 1-3 years, and ≥4 years. The primary outcomes were the score changes in different components of the Fahn-Tolosa-Marin Tremor Rating Scale (TRS; total score, motor score, hand-function score, and activities of daily living [ADL] score). Secondary outcomes were the long-term predictive factors.

RESULTS

The TRS total, motor, and ADL scores showed significant deterioration with disease progression (p = 0.002, p = 0.047, and p < 0.001, respectively), while the TRS total (p < 0.001), hand-function (p = 0.036), and ADL (p = 0.004) scores indicated a significant long-term reduction in DBS efficacy, although the motor subscore indicated no loss of efficacy. Hand-function (p < 0.001) and ADL (p = 0.028) scores indicated DBS tolerance, while the TRS total and motor scores did not. Stimulation frequency and preoperative score were predictive factors for long-term results.

CONCLUSION

This study provides level 3a evidence that long-term Vim-DBS is effective in controlling motor symptoms without waning benefits. The efficacy reduction for hand function was caused by DBS tolerance, while that for ADL was caused by DBS tolerance and disease progression. More attention should be given to actual functional recovery rather than changes in motor scores in patients with ET.

Speech Function Following Deep Brain Stimulation of the Caudal Zona Incerta: Effects of Habitual and High-Amplitude Stimulation

Purpose Deep brain stimulation (DBS) is often successful in alleviating motor symptoms of essential tremor (ET); however, DBS may also induce adverse speech effects. The caudal zona incerta (cZi) is a promising DBS target for tremor, but less is known about the consequences of cZi DBS for speech. This preliminary study examined how habitual cZi DBS and cZi stimulation at high amplitudes may affect speech function in persons with ET. Method Fourteen participants with ET were evaluated: off stimulation, on habitual cZi DBS, and with unilateral cZi stimulation at increasing stimulation amplitudes. At each stimulation condition, the participants read three 16-word sentences. Two speech-language pathologists made audio-perceptual consensus ratings of overall speech function, articulation, and voice using a visual sort and rate method. Rated functions when off stimulation, on habitual cZi DBS, and at maximal-amplitude stimulation were compared using Friedman nonparametric tests. For participants with bilateral habitual DBS (n = 5), the effects of bilateral and unilateral stimulation were described in qualitative terms. Results Habitual cZi DBS had no significant group-level effect on any of the investigated speech parameters. Maximal-amplitude stimulation had a small but significant negative effect on articulation. Participants with reduced articulatory precision (n = 9) had more medially placed electrodes than the nonaffected group (n = 5). Bilateral and unilateral left stimulation had comparable effects on speech. Conclusions Findings from this preliminary study of cZi DBS indicate that speech is generally not affected by stimulation at habitual levels. High-amplitude cZi stimulation may, however, induce adverse effects, particularly on articulation. Instances of decreased articulatory function were associated with stimulation of more medial electrode contacts, which could suggest cerebello-rubrospinal involvement.

Outcomes and Adverse Effects of Deep Brain Stimulation on the Ventral Intermediate Nucleus in Patients with Essential Tremor

Objective

This study was aimed at identifying the potential outcome predictors, comparing the efficacy in patients with different tremor characteristics, and summarizing the adverse effect rates (AERs) of deep brain stimulation on the ventral intermediate nucleus (VIM-DBS) for essential tremor (ET).

Methods

An extensive search of articles published to date in 2019 was conducted, and two main aspects were analyzed. Improvement was calculated as a percentage of change in any objective tremor rating scale (TRS) and analyzed by subgroup analyses of patients' tremor characteristics, laterality, and stimulation parameters. Furthermore, the AERs were analyzed as follows: the adverse effects (AEs) were classified as stimulation-related, surgical-related, or device-related effects. A simple regression analysis was used to identify the potential prognostic factors, and a two-sample mean-comparison test was used to verify the statistical significance of the subgroup analyses.

Results

Forty-six articles involving 1714 patients were included in the meta-analysis. The pooled improvement in any objective TRS score was 61.3% (95% CI: 0.564-0.660) at the mean follow-up visit (20.0 ± 17.3 months). The midline and extremity symptoms showed consistent improvement (P = 0.440), and the results of the comparison of postural and kinetic tremor were the same (P = 0.219). In addition, the improvement in rest tremor was similar to that in action tremor (OR = 2.759, P = 0.120). In the simple regression analysis, the preoperative Fahn-Tolosa-Marin Tremor Rating Scale (FTM-TRS) scores and follow-up time were negatively correlated with the percentage change in any objective TRS score (P < 0.05). The most common adverse event was dysarthria (10.5%), which is a stimulation-related AE (23.6%), while the rates of the surgical-related and device-related AEs were 6.4% and 11.5%, respectively.

Conclusion

VIM-DBS is an efficient and safe surgical method in ET, and the efficacy was not affected by the body distribution of tremor, age at surgery, and disease duration. Lower preoperative FTM-TRS scores likely indicate greater improvement, and the effect of VIM-DBS declines over time.

Effect of Deep Brain Stimulation on Swallowing Function: A Systematic Review

The effect of deep brain stimulation (DBS) on swallowing function in movement disorders is unclear. Here, we systematically reviewed this topic by searching keywords following PICOS strategy of problem (swallowing or swallow or dysphagia or aspiration) and intervention (deep brain stimulation, or DBS) in the PubMed and Web of Science in English in April 2020, with comparators [subthalamic nucleus (STN), globus pallidus interna (GPi), ventralis intermedius, (ViM), post-subthalamic area, or caudal zona incerta (PSA/cZi); ON/OFF DBS state/settings, ON/OFF medication state, Parkinson's disease (PD), dystonia, tremor], outcomes (swallowing function measures, subjective/objective) and study types (good quality original studies) in mind. We found that STN DBS at usual high-frequency stimulation could have beneficial effect (more so on subjective measures and/or OFF medication), no effect, or detrimental effect (more so on objective measures and/or ON medication) on swallowing function in patients with PD, while low-frequency stimulation (LFS) could have beneficial effect on swallowing function in patients with freezing of gait. GPi DBS could have a beneficial effect (regardless of medication state and outcome measures) or no effect, but no detrimental effect, on swallowing function in PD. GPi DBS also has beneficial effects on swallowing function in majority of the studies on Meige syndrome but not in other diseases with dystonia. PSA/cZi DBS rarely has detrimental effect on swallowing functions in patients with PD or tremor. There is limited information on ViM to assess. Information on swallowing function by DBS remains limited. Well-designed studies and direct comparison of targets are further needed.

Modulation of Nigrofugal and Pallidofugal Pathways in Deep Brain Stimulation for Parkinson Disease

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a well-established surgical therapy for patients with Parkinson disease (PD).

OBJECTIVE

To define the role of adjacent white matter stimulation in the effectiveness of STN-DBS.

METHODS

We retrospectively evaluated 43 patients with PD who received bilateral STN-DBS. The volumes of activated tissue were analyzed to obtain significant stimulation clusters predictive of 4 clinical outcomes: improvements in bradykinesia, rigidity, tremor, and reduction of dopaminergic medication. Tractography of the nigrofugal and pallidofugal pathways was performed. The significant clusters were used to calculate the involvement of the nigrofugal and pallidofugal pathways and the STN.

RESULTS

The clusters predictive of rigidity and tremor improvement were dorsal to the STN with most of the clusters outside of the STN. These clusters preferentially involved the pallidofugal pathways. The cluster predictive of bradykinesia improvement was located in the central part of the STN with an extension outside of the STN. The cluster predictive of dopaminergic medication reduction was located ventrolateral and caudal to the STN. These clusters preferentially involved the nigrofugal pathways.

CONCLUSION

Improvements in rigidity and tremor mainly involved the pallidofugal pathways dorsal to the STN. Improvement in bradykinesia mainly involved the central part of the STN and the nigrofugal pathways ventrolateral to the STN. Maximal reduction in dopaminergic medication following STN-DBS was associated with an exclusive involvement of the nigrofugal pathways.

Direct Comparison of Posterior Subthalamic Area Stimulation versus Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease

In this case report, we describe successful tremor capture via stimulation of the posterior subthalamic area (PSA) for a patient with tremor-predominant Parkinson's disease. In this scenario, the patient had a deep brain stimulation (DBS) lead placed in the PSA of the right hemisphere and a DBS lead placed in the subthalmic nucleus (STN) of the left hemisphere. Therefore, we were able to directly compare tremor capture in the same patient receiving stimulation in two different brain areas. We show that both placements are equally efficacious for tremor suppression, though the DBS lead placed in the PSA required slightly higher current intensity. This comparison in the same patient confirms that stimulation of the PSA can successfully suppress tremor in Parkinson's disease.

The Effects of Deep Brain Stimulation on Speech Intelligibility in Persons With Essential Tremor

Purpose The aim of this study was to investigate how deep brain stimulation (DBS) of the caudal zona incerta (cZi) affects speech intelligibility in persons with essential tremor. Method Thirty-five participants were evaluated: off stimulation, on chronic stimulation optimized to alleviate tremor, and during unilateral stimulation at increasing amplitude levels. At each stimulation condition, the participants read 10 unique nonsense sentences from the Swedish Test of Intelligibility. Two listeners, blinded to stimulation condition, transcribed all recorded sentences orthographically in a randomized procedure. A mean speech intelligibility score for each patient and stimulation condition was computed, and comparisons were made between scores off and on stimulation. Results Chronic cZi-DBS had no significant effect on speech intelligibility, and there was no difference in outcome between bilateral and unilateral treatments. During unilateral stimulation at increasing amplitudes, nine participants demonstrated deteriorating speech intelligibility. These nine participants were on average older and had more superior contacts activated during the evaluation compared with the participants without deterioration. Conclusions Chronic cZi-DBS, optimized for tremor suppression, does not generally affect speech intelligibility in persons with essential tremor. Furthermore, speech intelligibility may be preserved in many individuals, even when stimulated at high amplitudes. Adverse effects of high-amplitude unilateral stimulation observed in this study were associated with stimulation originating from a more superior location, as well as with the participants' age. These results, highlighting age and stimulation location as contributing to speech intelligibility outcomes, were, however, based on a limited number of individuals experiencing adverse effects with high-amplitude stimulation and should, therefore, be interpreted with caution.

Bilateral Posterior Subthalamic Area Deep Brain Stimulation for Essential Tremor: A Case Series

Background

Deep brain stimulation (DBS) of the posterior subthalamic area (PSA) provides a potentially effective treatment for medication-refractory essential tremor (ET).

Objective

To study the clinical benefits and adverse-event profile of bilateral PSA-DBS for refractory ET.

Methods

Seven patients with refractory ET underwent bilateral PSA-DBS surgery under general anesthesia between September 2017 and May 2018. Clinical outcome assessments, using the Essential Tremor Rating Scale, were performed at 1-, 6-, and 12-month follow-up, except for the last assessment of one patient who was followed up to 9 months. Analysis was focused on changes in patients’ motor symptoms and quality of life following surgery as well as documenting the adverse-event profile associated with the surgical PSA-DBS treatment.

Results

After surgery, patients’ motor symptoms, including upper limb tremor and head tremor, were improved by 84.2% and their quality of life by 81.25% at 1-month follow-up. The clinical benefits to patients were maintained at 6-month and last follow-up. Adverse side effects included dysarthria (n = 4), balance disorder (n = 2), and paresthesia of the right limb (n = 1). No habituation effects were observed throughout the follow-up.

Conclusion

Bilateral PSA-DBS seems to offer an effective and safe alternative treatment for medically intractable ET, warranting further research into its clinical utility, adverse-event profile, and comparative effectiveness.

Consensus Paper: Experimental Neurostimulation of the Cerebellum

The cerebellum is best known for its role in controlling motor behaviors. However, recent work supports the view that it also influences non-motor behaviors. The contribution of the cerebellum towards different brain functions is underscored by its involvement in a diverse and increasing number of neurological and neuropsychiatric conditions including ataxia, dystonia, essential tremor, Parkinson's disease (PD), epilepsy, stroke, multiple sclerosis, autism spectrum disorders, dyslexia, attention deficit hyperactivity disorder (ADHD), and schizophrenia. Although there are no cures for these conditions, cerebellar stimulation is quickly gaining attention for symptomatic alleviation, as cerebellar circuitry has arisen as a promising target for invasive and non-invasive neuromodulation. This consensus paper brings together experts from the fields of neurophysiology, neurology, and neurosurgery to discuss recent efforts in using the cerebellum as a therapeutic intervention. We report on the most advanced techniques for manipulating cerebellar circuits in humans and animal models and define key hurdles and questions for moving forward.

Comparison of posterior subthalamic area deep brain stimulation for tremor using conventional landmarks versus directly targeting the dentatorubrothalamic tract with tractography

OBJECTIVE

To compare posterior subthalamic area deep brain stimulation (PSA-DBS) performed in the conventional manner against diffusion tensor imaging and tractography (DTIT)-guided lead implantation into the dentatorubrothalamic tract (DRTT).

PATIENTS AND METHODS

Double-blind, randomised study involving 34 patients with either tremor-dominant Parkinson's disease or essential tremor. Patients were randomised to Group A (DBS leads inserted using conventional landmarks) or Group B (leads guided into the DRTT using DTIT). Tremor (Fahn-Tolosa-Marin) and quality-of-life (PDQ-39) scores were evaluated 0-, 6-, 12-, 36- and 60-months after surgery.

RESULTS

PSA-DBS resulted in marked tremor reduction in both groups. However, Group B patients had significantly better arm tremor control (especially control of intention tremor), increased mobility and activities of daily living, reduced social stigma and need for social support as well as lower stimulation amplitudes and pulse widths compared to Group A patients. The better outcomes were sustained for up to 60-months from surgery. The active contacts of Group B patients were consistently closer to the centre of the DRTT than in Group A. Speech problems were more common in Group A patients.

CONCLUSION

DTIT-guided lead placement results in better and more stable tremor control and fewer adverse effects compared to lead placement in the conventional manner. This is because DTIT-guidance allows closer and more consistent placement of leads to the centre of the DRTT than conventional methods.

A widespread visually-sensitive functional network relates to symptoms in essential tremor

Essential tremor is a neurological syndrome of heterogeneous pathology and aetiology that is characterized by tremor primarily in the upper extremities. This tremor is commonly hypothesized to be driven by a single or multiple neural oscillator(s) within the cerebello-thalamo-cortical pathway. Several studies have found an association of blood-oxygen level-dependent (BOLD) signal in the cerebello-thalamo-cortical pathway with essential tremor, but there is behavioural evidence that also points to the possibility that the severity of tremor could be influenced by visual feedback. Here, we directly manipulated visual feedback during a functional MRI grip force task in patients with essential tremor and control participants, and hypothesized that an increase in visual feedback would exacerbate tremor in the 4-12 Hz range in essential tremor patients. Further, we hypothesized that this exacerbation of tremor would be associated with dysfunctional changes in BOLD signal and entropy within, and beyond, the cerebello-thalamo-cortical pathway. We found that increases in visual feedback increased tremor in the 4-12 Hz range in essential tremor patients, and this increase in tremor was associated with abnormal changes in BOLD amplitude and entropy in regions within the cerebello-thalamo-motor cortical pathway, and extended to visual and parietal areas. To determine if the tremor severity was associated with single or multiple brain region(s), we conducted a birectional stepwise multiple regression analysis, and found that a widespread functional network extending beyond the cerebello-thalamo-motor cortical pathway was associated with changes in tremor severity measured during the imaging protocol. Further, this same network was associated with clinical tremor severity measured with the Fahn, Tolosa, Marin Tremor Rating Scale, suggesting this network is clinically relevant. Since increased visual feedback also reduced force error, this network was evaluated in relation to force error but the model was not significant, indicating it is associated with force tremor but not force error. This study therefore provides new evidence that a widespread functional network is associated with the severity of tremor in patients with essential tremor measured simultaneously at the hand during functional imaging, and is also associated with the clinical severity of tremor. These findings support the idea that the severity of tremor is exacerbated by increased visual feedback, suggesting that designers of new computing technologies should consider using lower visual feedback levels to reduce tremor in essential tremor.

Voice Tremor Response to Deep Brain Stimulation in Relation to Electrode Location in the Posterior Subthalamic Area

Background

Deep brain stimulation of the motor thalamus or the posterior subthalamic area (PSA) shows promising results for patients with voice tremor, although only for about 50% of patients. There are indications that voice tremor requires more focused stimulation within the target area compared with hand tremor. The objective of the present study was to determine the most efficient location for reducing voice tremor within the PSA.

Methods

Thirty-seven patients with essential tremor were evaluated off stimulation and in a set of experimental conditions with unilateral stimulation at increasing amplitude levels. Two listeners performed blinded assessments of voice tremor from recordings of sustained vowel productions.

Results

Twenty-five patients (68%) had voice tremor. Unilateral stimulation reduced voice tremor for the majority of patients, and only 6 patients had poor outcomes. Contacts yielding efficient voice tremor reduction were deeper relative to the midcommissural point (MCP) and more posterior relative to the posterior tip of the subthalamic nucleus (pSTN) (z^MCP = -3.1, y^pSTN = -0.2) compared with poor contacts (z^MCP = -0.7, y^pSTN = 1.0). High-amplitude stimulation worsened voice tremor for 7 patients and induced voice tremor in 2 patients. Hand tremor improved to a greater extent than voice tremor, and improvements could be seen throughout the target area.

Conclusions

Our results indicate that efficient voice tremor reduction can be achieved by stimulating contacts located in the inferior part of the PSA, close or slightly posterior to the pSTN. We observed cases in which voice tremor was induced by high-amplitude stimulation.

Deep Brain Stimulation of the Caudal Zona Incerta and Motor Thalamus for Postischemic Dystonic Tremor of the Left Upper Limb: Case Report and Review of the Literature

BACKGROUND

Dystonic tremor is defined as a tremor occurring in a body region affected by dystonia. The pathophysiologic mechanisms behind dystonic tremor supposedly involve anomalies affecting the pallidothalamic-receiving area (for the dystonic component) and the ventralis intermedius-cortical loop (for the tremor component). Interest in posterior subthalamic area stimulation for various types of involuntary abnormal movements has arisen owing to positive results in patients affected by tremor refractory to ventralis intermedius deep brain stimulation.

CASE DESCRIPTION

A 23-year-old man, with a 15-year history of left upper limb dystonic tremor due to a stroke in the right thalamus, underwent deep brain stimulation with a single electrode passing through the right ventralis oralis anterior/ventralis oralis posterior nuclei and caudal zona incerta. Objective movement outcomes were assessed through the Unified Dystonia Rating Scale and Fahn-Tolosa-Marin Clinical Rating Scale for Tremor. The impact of tremor on activities of daily living was assessed with the ADL-T24 questionnaire, and quality of life was assessed with the Quality of Life Scale. All questionnaires were administered before deep brain stimulation and at 5-year follow-up. Unified Dystonia Rating Scale and Fahn-Tolosa-Marin Clinical Rating Scale for Tremor scores decreased from 14.5 to 4.5 and from 46 to 7, respectively. ADL-T24 score decreased from 19 to 3, whereas Quality of Life Scale score increased from 49 to 82.

CONCLUSIONS

Stimulation of motor thalamus and caudal zona incerta could be a viable treatment for patients affected by tremor of various origins, including dystonic tremor, refractory to medical therapy.

Effect of deep brain simulation on arm, leg, and chin tremor in Parkinson disease

OBJECTIVE

The efficacy of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in the treatment of Parkinson disease (PD)-related tremor has been well established. However, the relative impact on arm, leg, and chin tremor has been less clearly elucidated. The authors evaluated the distribution of tremors in a PD cohort undergoing STN DBS and sought to evaluate the differential impact of DBS as a function of tremor location.

METHODS

A retrospective study of patients with PD with tremor who underwent DBS surgery between 2012 and 2016 was performed to evaluate the impact of STN stimulation on overall and regional tremor scores.

RESULTS

Across 66 patients the authors found an average of 78% overall reduction in tremor after 6 months. In this cohort, the authors found that tremor reduction was somewhat better for arm than for leg tremors, especially in instances of higher preoperative tremor (84% vs 71% reduction, respectively, for initial tremor scores ≥ 2). No significant difference in response was found between patients with medication-responsive versus medication-nonresponsive tremors.

CONCLUSIONS

The authors found that although DBS improved tremor in all regions, the improvement was not uniform between chin, arm, and leg-even within the same patient. The reasons behind these differing responses are speculative but suggest that STN DBS may more reliably reduce arm tremors than leg tremors.

DBS of the PSA and the VIM in essential tremor

Objective

To evaluate deep brain stimulation (DBS) of the posterior subthalamic area (PSA) in essential tremor (ET) and compare it to the ventral intermediate nucleus of the thalamus (VIM) in terms of stimulation efficacy, efficiency, and side effects.

Methods

DBS leads were implanted such that contacts were placed in the VIM, on the intercommissural line, and in the PSA. Thirteen patients with ET entered a randomized, double-blind crossover phase and completed a 1-year follow-up.

Results

PSA-DBS significantly reduced tremor severity and improved quality of life. There were no relevant differences in quality and frequency of stimulation side effects between VIM and PSA, with a tendency toward greater tremor improvement with PSA stimulation. Clinical benefit was achieved at significantly lower stimulation amplitudes in the PSA. The majority of patients remained with PSA-DBS after 1 year.

Conclusion

In accordance with previous retrospective investigations, our prospective data suggest that PSA-DBS is at least equally effective as but possibly more efficient than VIM-DBS.

Classification of evidence

This study provides Class I evidence that for patients with essential tremor, PSA-DBS is not significantly different from VIM-DBS in suppressing tremor, but clinical benefit from PSA-DBS is attained at lower stimulation amplitudes.

Deep brain stimulation in the caudal zona incerta versus best medical treatment in patients with Parkinson's disease: a randomised blinded evaluation

BACKGROUND

Several open-label studies have shown good effect of deep brain stimulation (DBS) in the caudal zona incerta (cZi) on tremor, including parkinsonian tremor, and in some cases also a benefit on akinesia and axial symptoms. The aim of this study was to evaluate objectively the effect of cZi DBS in patients with Parkinson's disease (PD).

METHOD

25 patients with PD were randomised to either cZi DBS or best medical treatment. The primary outcomes were differences between the groups in the motor scores of the Unified Parkinson's Disease Rating Scale (UPDRS-III) rated single-blindly at 6 months and differences in the Parkinson's Disease Questionnaire 39 items (PDQ-39). 19 patients, 10 in the medical arm and 9 in the DBS arm, fulfilled the study.

RESULTS

The DBS group had 41% better UPDRS-III scores off-medication on-stimulation compared with baseline, whereas the scores of the non-surgical patients off-medication were unchanged. In the on-medication condition, there were no differences between the groups, neither at baseline nor at 6 months. Subitems of the UPDRS-III showed a robust effect of cZi DBS on tremor. The PDQ-39 domains 'stigma' and 'ADL' improved only in the DBS group. The PDQ-39 summary index improved in both groups.

CONCLUSION

This is the first randomised blinded evaluation of cZi DBS showing its efficacy on PD symptoms. The most striking effect was on tremor; however, the doses of dopaminergic medications could not be decreased. cZi DBS in PD may be an addition to existing established targets, enabling tailoring the surgery to the needs of the individual patient.

Subthalamotomy for Parkinson's disease: clinical outcome and topography of lesions

OBJECTIVE

Subthalamotomy is an effective alternative for the treatment of Parkinson's disease (PD). However, uncertainty about the optimal target location and the possibility of inducing haemichorea-ballism have limited its application. We assessed the correlation between the topography of radiofrequency-based lesions of the subthalamic nucleus (STN) with motor improvement and the emergence of haemichorea-ballism.

METHODS

Sixty-four patients with PD treated with subthalamotomy were evaluated preoperatively and postoperatively using the Unified Parkinson's Disease Rating Scale motor score (UPDRSm), MRI and tractography. Patients were classified according to the degree of clinical motor improvement and dyskinesia scale. Lesions were segmented on MRI and averaged in a standard space. We examined the relationship between the extent of lesion-induced disruption of fibres surrounding the STN and the development of haemichorea-ballism.

RESULTS

Maximum antiparkinsonian effect was obtained with lesions located within the dorsolateral motor region of the STN as compared with those centre-placed in the dorsal border of the STN and the zona incerta (71.3%, 53.5% and 20.8% UPDRSm reduction, respectively). However, lesions that extended dorsally beyond the STN showed lower probability of causing haemichorea-ballism than those placed entirely within the nucleus. Tractography findings indicate that interruption of pallidothalamic fibres probably determines a low probability of haemichorea-ballism postoperatively.

CONCLUSIONS

The topography of the lesion is a major factor in the antiparkinsonian effect of subthalamotomy in patients with PD. Lesions involving the motor STN and pallidothalamic fibres induced significant motor improvement and were associated with a low incidence of haemichorea-ballism.

Surgical treatments for essential tremor

INTRODUCTION

Essential tremor is the most common form of pathologic tremor. Surgical therapies disrupt tremorogenic oscillation in the cerebellothalamocortical pathway and are capable of abolishing severe tremor that is refractory to available pharmacotherapies. Surgical methods are raspidly improving and are the subject of this review. Areas covered: A PubMed search on 18 January 2018 using the query essential tremor AND surgery produced 839 abstracts. 379 papers were selected for review of the methods, efficacy, safety and expense of stereotactic deep brain stimulation (DBS), stereotactic radiosurgery (SRS), focused ultrasound (FUS) ablation, and radiofrequency ablation of the cerebellothalamocortical pathway. Expert commentary: DBS and SRS, FUS and radiofrequency ablations are capable of reducing upper extremity tremor by more than 80% and are far more effective than any available drug. The main research questions at this time are: 1) the relative safety, efficacy, and expense of DBS, SRS, and FUS performed unilaterally and bilaterally; 2) the relative safety and efficacy of thalamic versus subthalamic targeting; 3) the relative safety and efficacy of atlas-based versus direct imaging tractography-based anatomical targeting; and 4) the need for intraoperative microelectrode recordings and macroelectrode stimulation in awake patients to identify the optimum anatomical target. Randomized controlled trials are needed.

Current concepts in multiple sclerosis therapy

Over the past 20 years, the available therapies for multiple sclerosis have expanded exponentially. With several more agents likely to be approved for public funding in Australia in the next 12 months on top of the existing multitude of Australian Pharmaceutical Benefits Scheme-subsidized therapies, the choice is becoming even more complex. This review summarizes the current state of available therapies and anticipates likely future directions, including an important focus on contemporary symptom management. For each agent, the major trials, side effects, and clinical utility are summarized, with a particular focus on the Australian experience of these therapies. It is hoped this review provides an up-to-date reference of the exciting current state of multiple sclerosis therapy.

Efficacy of Fiber Tractography in the Stereotactic Surgery of the Thalamus for Patients with Essential Tremor

Several targets and targeting methods are utilized in stereotactic surgery to achieve tremor suppression for patients with intractable tremor. Recent developments in magnetic resonance imaging, including diffusion tensor imaging, have enabled the setting of appropriate targets in stereotactic surgery. In this retrospective study, the optimal target to suppress tremors in stereotactic surgery was explored using diffusion tensor image-based fiber tractography. Four tracts were focused on in this study, namely: the cerebello-thalamo-premotor cortical fiber tract, cerebello-thalamo-primary motor cortical fiber tract, spino-thalamo-somatosensory cortical fiber tract, and pyramidal tract. In 10 patients with essential tremor, we evaluated the thalamotomy lesions and active contacts of the lead in thalamic stimulation by diffusion tensor image-based fiber tractography to reveal which part of the cerebral cortex is most affected by stereotactic surgery. Tremor suppression and adverse events were also evaluated in the patients involved in this study. Consequently, the good tremor suppression was achieved in all patients. There had been no permanent adverse events 3 months after surgery. Twelve lesions in thalamotomy patients or active contacts of the lead in thalamic stimulation patients were on the cerebello-thalamo-premotor cortical fiber tract (12/14 lesions or active contacts: 86%). In conclusion, the cerebello-thalamo-premotor cortical fiber tract may be an optimal target for tremor suppression. Diffusion tensor image-based fiber tractography may enable us to both determine the optimal target to achieve strong tremor suppression and to reduce the number of adverse events by keeping lesions or electrodes away from important fiber tracts, such as the pyramidal tract and spinothalamic fibers.

Emerging strategies in the management of essential tremor

Currently available therapies for essential tremor (ET) provide sufficient control only for less than a half of patients and many unmet needs exist. This is in part due to the empiric nature of existing treatment options and persisting uncertainties about the pathogenesis of ET. The emerging concept of ET as a possible neurodegenerative disorder, better understanding of associated biochemical changes, including alterations in the γ-aminobutyric acid (GABA)-ergic system and gap junctions, and the identification of the role of the leucine-rich repeat and immunoglobulin-like domain-containing 1 (LINGO-1) gene in ET pathogenesis suggest new avenues for more targeted therapies. Here we review the most promising new approaches to treating ET, including allosteric modulation of GABA receptors and modifications of the LINGO-1 pathway. Medically refractory tremor can be successfully treated by high-frequency deep brain stimulation (DBS) of the ventral intermediate nucleus, but surgical therapies are also fraught with limitations due to adverse effects of stimulation and the loss of therapeutic response. The selection of additional thalamic and extrathalamic targets for electrode placements and the development of a closed-loop DBS system enabling automatic adjustment of stimulation parameters in response to changes in electrophysiologic brain activity are also reviewed. Tremor cancellation methods using exoskeleton and external hand-held devices are also briefly discussed.

Probabilistic mapping of deep brain stimulation effects in essential tremor

Objective

To create probabilistic stimulation maps (PSMs) of deep brain stimulation (DBS) effects on tremor suppression and stimulation-induced side-effects in patients with essential tremor (ET).

Method

Monopolar reviews from 16 ET-patients which consisted of over 600 stimulation settings were used to create PSMs. A spherical model of the volume of neural activation was used to estimate the spatial extent of DBS for each setting. All data was pooled and voxel-wise statistical analysis as well as nonparametric permutation testing was used to confirm the validity of the PSMs.

Results

PSMs showed tremor suppression to be more pronounced by stimulation in the zona incerta (ZI) than in the ventral intermediate nucleus (VIM). Paresthesias and dizziness were most commonly associated with stimulation in the ZI and surrounding thalamic nuclei.

Discussion

Our results support the assumption, that the ZI might be a very effective target for tremor suppression. However stimulation inside the ZI and in its close vicinity was also related to the occurrence of stimulation-induced side-effects, so it remains unclear whether the VIM or the ZI is the overall better target. The study demonstrates the use of PSMs for target selection and evaluation. While their accuracy has to be carefully discussed, they can improve the understanding of DBS effects and can be of use for other DBS targets in the therapy of neurological or psychiatric disorders as well. Furthermore they provide a priori information about expected DBS effects in a certain region and might be helpful to clinicians in programming DBS devices in the future.

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A revised method to create probabilistic stimulation maps for large DBS datasets

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Data for DBS in essential tremor targeting the ventral intermediate nucleus (VIM).

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Zona incerta shows higher tremor suppression but also more side effects than VIM.

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Insights into the possible neuroanatomical origins of different DBS side effects

Deep brain stimulation of the posterior subthalamic area and the thalamus in patients with essential tremor: study protocol for a randomized controlled pilot trial

BACKGROUND

Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) of the thalamus is effective in medication refractory essential tremor (ET). In recent years, evidence has accumulated that the region ventral to the VIM, the posterior subthalamic area (PSA), might be an equally or even more effective target for electrode implantation. However, this evidence is primarily based on case series, cross-sectional observations, and retrospective data.

METHODS/DESIGN

A prospective crossover pilot study investigating the effects of PSA stimulation in medication refractory ET patients was designed. In this study, bilateral electrodes are implanted such that at least one of the electrode contacts is located in the PSA and VIM, respectively. This implantation approach allows (1) a prospective double-blind investigation of the effects of PSA stimulation compared to baseline, as well as (2) a crossover comparison between VIM and PSA stimulation with respect to tremor suppression and side effect profiles.

DISCUSSION

The results of this double-blinded, prospective study will allow a better understanding of the effects and side effects of PSA compared to VIM-DBS in patients with ET.

TRIAL REGISTRATION

German Clinical Trials Register: DRKS00004235 . Registered on 4 July 2012.

STN-DBS Reduces Saccadic Hypometria but Not Visuospatial Bias in Parkinson's Disease Patients

In contrast to its well-established role in alleviating skeleto-motor symptoms in Parkinson's disease, little is known about the impact of deep brain stimulation (DBS) of the subthalamic nucleus (STN) on oculomotor control and attention. Eye-tracking data of 17 patients with left-hemibody symptom onset was compared with 17 age-matched control subjects. Free-viewing of natural images was assessed without stimulation as baseline and during bilateral DBS. To examine the involvement of ventral STN territories in oculomotion and spatial attention, we employed unilateral stimulation via the left and right ventralmost contacts respectively. When DBS was off, patients showed shorter saccades and a rightward viewing bias compared with controls. Bilateral stimulation in therapeutic settings improved saccadic hypometria but not the visuospatial bias. At a group level, unilateral ventral stimulation yielded no consistent effects. However, the evaluation of electrode position within normalized MNI coordinate space revealed that the extent of early exploration bias correlated with the precise stimulation site within the left subthalamic area. These results suggest that oculomotor impairments "but not higher-level exploration patterns" are effectively ameliorable by DBS in therapeutic settings. Our findings highlight the relevance of the STN topography in selecting contacts for chronic stimulation especially upon appearance of visuospatial attention deficits.

Deep Brain Stimulation Target Selection for Parkinson’s Disease

During the “DBS Canada Day” symposium held in Toronto July 4-5, 2014, the scientific committee invited experts to discuss three main questions on target selection for deep brain stimulation (DBS) of patients with Parkinson’s disease (PD). First, is the subthalamic nucleus (STN) or the globus pallidus internus (GPi) the ideal target? In summary, both targets are equally effective in improving the motor symptoms of PD. STN allows a greater medications reduction, while GPi exerts a direct antidyskinetic effect. Second, are there further potential targets? Ventral intermediate nucleus DBS has significant long-term benefit for tremor control but insufficiently addresses other motor features of PD. DBS in the posterior subthalamic area also reduces tremor. The pedunculopontine nucleus remains an investigational target. Third, should DBS for PD be performed unilaterally, bilaterally or staged? Unilateral STN DBS can be proposed to asymmetric patients. There is no evidence that a staged bilateral approach reduces the incidence of DBS-related adverse events.

Speech intelligibility in Parkinson's disease patients with zona incerta deep brain stimulation

OBJECTIVES

To investigate the effects of l-dopa (Levodopa) and cZi-DBS (deep brain stimulation in caudal zona incerta) on spontaneous speech intelligibility in patients with PD (Parkinson's disease).

MATERIALS AND METHODS

Spontaneous utterances were extracted from anechoic recordings from 11 patients with PD preoperatively (off and on l-dopa medication) and 6 and 12 months post bilateral cZi-DBS operation (off and on stimulation, with simultaneous l-dopa medication). Background noise with an amplitude corresponding to a clinical setting was added to the recordings. Intelligibility was assessed through a transcription task performed by 41 listeners in a randomized and blinded procedure.

RESULTS

A group-level worsening in spontaneous speech intelligibility was observed on cZi stimulation compared to off 6 months postoperatively (8 adverse, 1 positive, 2 no change). Twelve months postoperatively, adverse effects of cZi-DBS were not frequently observed (2 positive, 3 adverse, 6 no change). l-dopa administered preoperatively as part of the evaluation for DBS operation provided the overall best treatment outcome (1 adverse, 4 positive, 6 no change).

CONCLUSIONS

cZi-DBS was shown to have smaller negative effects when evaluated from spontaneous speech compared to speech effects reported previously. The previously reported reduction in word-level intelligibility 12 months postoperatively was not transferred to spontaneous speech for most patients. Reduced intelligibility due to cZi stimulation was much more prominent 6 months postoperatively than at 12 months.

The Feasibility of Using Acoustic Markers of Speech for Optimizing Patient Outcomes during Randomized Amplitude Variation in Deep Brain Stimulation: A Proof of Principle Methods Study

Background

Deep brain stimulation (DBS) is an effective treatment for reducing symptoms of tremor. A common and typically subjectively determined adverse effect of DBS is dysarthria. Current assessment protocols are driven by the qualitative judgments of treating clinicians and lack the sensitivity and objectivity required to optimize patient outcomes where multiple stimulation parameters are trialed.

Objective

To examine the effect of DBS on speech in patients receiving stimulation to the posterior sub-thalamic area (PSA) via randomized manipulation of amplitude parameters.

Methods

Six patients diagnosed with tremor receiving treatment via DBS of the PSA were assessed in a double-blinded, within-subjects experimental protocol. Amplitude (i.e., voltage or current) was randomly adjusted across 10 settings, while speech samples (e.g., sustained vowel, counting to 10) were recorded to identify the patient-specific settings required for optimal therapeutic benefit (reduced tremor) with minimal adverse effects (altered speech). Speech production between stimulation parameters was quantified using acoustic analysis.

Results

Speech changed as a response to DBS but those changes were not uniform across patients nor were they generally in line with changes in amplitude with the exception of reduced vocal control and increased mean silence length in two patients. Speech outcomes did not correlate with changes in tremor.

Conclusion

Intra-individual changes in speech were detected as a response to modified amplitude; however, no clear pattern was observed across patients as a group. The use of objective acoustic measures allows for quantification of speech changes during DBS optimization protocols, even when those changes are subtle and potentially difficult to detect perceptually.

Current management of relapsing-remitting multiple sclerosis

Multiple sclerosis was without effective disease-modifying therapy for many years. The introduction of the injectable therapies (interferon and glatiramer acetate) some 20 years ago was considered a major advance. Recent years have heralded a revolution in treatment options with the introduction of intravenous natalizumab and, even more recently, three oral agents. We are currently in a period of determining the best use of these therapies to ensure prevention of disease progression while maintaining patient safety. Despite these new treatments, there are still many patients living with disability as a result of multiple sclerosis and significant attention must be given to symptomatic management.

Rat subthalamic nucleus and zona incerta share extensively overlapped representations of cortical functional territories

The subthalamic nucleus (STN) and the zona incerta (ZI) are two major structures of the subthalamus. The STN has strong connections between the basal ganglia and related nuclei. The ZI has strong connections between brainstem reticular nuclei, sensory nuclei, and nonspecific thalamic nuclei. Both the STN and ZI receive heavy projections from a subgroup of layer V neurons in the cerebral cortex. The major goal of this study was to investigate the following two questions about the cortico-subthalamic projections using the lentivirus anterograde tracing method in the rat: 1) whether cortical projections to the STN and ZI have independent functional organizations or a global organization encompassing the entire subthalamus as a whole; and 2) how the cortical functional zones are represented in the subthalamus. This study revealed that the subthalamus receives heavy projections from the motor and sensory cortices, that the cortico-subthalamic projections have a large-scale functional organization that encompasses both the STN and two subdivisions of the ZI, and that the group of cortical axons that originate from a particular area of the cortex sequentially innervate and form separate terminal fields in the STN and ZI. The terminal zones formed by different cortical functional areas have highly overlapped and fuzzy borders, as do the somatotopic representations of the sensorimotor cortex in the subthalamus. The present study suggests that the layer V neurons in the wide areas of the sensorimotor cortex simultaneously control STN and ZI neurons. Together with other known afferent and efferent connections, possible new functionality of the STN and ZI is discussed.

STN vs. GPi Deep Brain Stimulation: Translating the Rematch into Clinical Practice

When formulating a deep brain stimulation (DBS) treatment plan for a patient with Parkinson's disease (PD), two critical questions should be addressed: 1- Which brain target should be chosen to optimize this patient's outcome? and 2- Should this patient's DBS operation be unilateral or bilateral? Over the past two decades, two targets have emerged as leading contenders for PD DBS; the subthalamic nucleus (STN) and the globus pallidus internus (GPi). While the GPi target does have a following, most centers have uniformly employed bilateral STN DBS for all Parkinson's disease cases (Figure 1). This bilateral STN "one-size-fits-all" approach was challenged by an editorial entitled "STN vs. GPi: The Rematch," which appeared in the Archives of Neurology in 2005. Since 2005, a series of well designed clinical trials and follow-up studies have addressed the question as to whether a more tailored approach to DBS therapy might improve overall outcomes. Such a tailored approach would include the options of targeting the GPi, or choosing a unilateral operation. The results of the STN vs. GPi 'rematch' studies support the conclusion that bilateral STN DBS may not be the best option for every Parkinson's disease surgical patient. Off period motor symptoms and tremor improve in both targets, and with either unilateral or bilateral stimulation. Advantages of the STN target include more medication reduction, less frequent battery changes, and a more favorable economic profile. Advantages of GPi include more robust dyskinesia suppression, easier programming, and greater flexibility in adjusting medications. In cases where unilateral stimulation is anticipated, the data favor GPi DBS. This review summarizes the accumulated evidence regarding the use of bilateral vs. unilateral DBS and the selection of STN vs. GPi DBS, including definite and possible advantages of different targets and approaches. Based on this evidence, a more patient-tailored, symptom specific approach will be proposed to optimize outcomes of PD DBS therapy. Finally, the importance of an interdisciplinary care team for screening and effective management of DBS patients will be reaffirmed. Interdisciplinary teams can facilitate the proposed patient-specific DBS treatment planning and provide a more thorough analysis of the risk-benefit ratio for each patient.

Surgical treatment of Parkinson's disease: patients, targets, devices, and approaches

Surgical treatment for Parkinson's disease (PD) has evolved from ablative procedures, within a variety of brain regions, to implantation of electrodes into specific targets of the basal ganglia. Electrode implantation surgery, referred to as deep brain stimulation (DBS), is preferred to ablative procedures by many experts owing to its reversibility, programmability, and the ability to be safely performed bilaterally. Several randomized clinical studies have demonstrated the effectiveness of DBS surgery for control of PD symptoms. Many brain targets, including the subthalamic nucleus and the globus pallidus internus, have emerged as potentially effective, with each target being closely associated with important pros and cons. Selection of appropriate PD candidates through a methodical interdisciplinary screening is considered a prerequisite for a successful surgical outcome. Despite recent growth in DBS knowledge, there is currently no consensus on the ideal surgical technique, the best surgical approach, and the most appropriate surgical target. DBS is now targeted towards treating specific PD-related symptoms in a given individual, and not simply addressing the disease with one pre-defined approach. In this review we will discuss the historical aspects of surgical treatments, the selection of an appropriate DBS candidate, the current surgical techniques, and recently introduced DBS-related technologies. We will address important pre- and postoperative issues related to DBS. We will also discuss the lessons learned from the randomized clinical studies for DBS and the shifting paradigm to tailor to a more patient-centered and symptom-specific approach.

Current clinical application of deep-brain stimulation for essential tremor

BACKGROUND

Deep-brain stimulation (DBS) is an established treatment for medically refractory essential tremor (ET). This article reviews the current evidence supporting the efficacy and safety of DBS targets, including the ventral intermediate (VIM) nucleus and posterior subthalamic area (PSA) in treatment of ET.

METHODS

A structured PubMed search was performed through December 2012 with keywords "deep brain stimulation (DBS)," "essential tremor (ET)," "ventral intermediate (VIM) nucleus," "posterior subthalamic area (PSA)," "safety," and "efficacy."

RESULTS

Based on level IV evidence, both VIM and PSA DBS targets appear to be safe and efficacious in ET patients in tremor reduction and improving activities of daily living, though the literature on PSA DBS is limited in terms of bilateral stimulation and long-term follow-up. DBS-related adverse effects are typically mild and stimulation-related. Hardware-related complications after DBS may not be uncommon, and often require additional surgical procedures. Few studies assessed quality-of-life and cognition outcomes in ET patients undergoing DBS stimulation.

CONCLUSION

DBS appears to be a safe and effective treatment for medically refractory ET. More systematic studies comparing VIM and PSA targets are needed to ascertain the most safe and effective DBS treatment for medically refractory ET. More research is warranted to assess quality-of-life and cognition outcomes in ET patients undergoing DBS.