Cognitive outcome after unilateral pallidal stimulation in Parkinson's disease

Unilateral GPi-DBS Improves Ipsilateral and Axial Motor Symptoms in Parkinson’s Disease as Evidenced by a Brain Perfusion Single Photon Emission Computed Tomography Study

Introduction

Deep brain stimulation (DBS) is an effective treatment for advanced Parkinson’s disease (PD) with the targeting bilateral subthalamic nucleus or globus pallidus internus (STN or GPi-DBS). So far, detailed studies on the efficacy of unilateral STN-DBS for motor symptoms have been reported, but few studies have been conducted on unilateral GPi-DBS.

Materials and Methods

Seventeen patients with Parkinson’s disease (PwPD) who underwent unilateral GPi-DBS were selected. We conducted comparison analyses between scores obtained 6–42 months pre- and postoperatively using the following measurement tools: the Movement Disorder Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) part III, the Hoehn and Yahr stage, the presence/absence of dyskinesia, Mini-Mental State Examination (MMSE), Frontal Assessment Battery (FAB), Geriatric Depression Scale (GDS), levodopa equivalent dose (LED), and cerebral blood flow by single photon emission computed tomography (SPECT). Patient backgrounds were compared between four cohorts with favorable (good responders, ≥50% improvement) and unfavorable (poor responders, <50% improvement) postoperative outcome.

Results

Significant improvement was observed postoperatively in the following: total MDS-UPDRS Part III scores during the off period, contralateral scores, ipsilateral scores, and axial scores. Similarly, the Hoehn and Yahr stages during the off period, and GDS also showed significant decrease. In contrast, LED, MMSE, and FAB remained unchanged while the number of patients who scored positive for dyskinesia decreased by 40%. Abnormal cerebral blood flow preoperatively seen in the cerebral cortex had normalized in the total score-based good responder cohort. In the ipsilateral score-based good responder cohort, cerebral blood flow increased in the contralateral frontal lobe including in the premotor cortex, contralateral to the DBS. Compared to the poor responders, postoperative good responders demonstrated significantly higher preoperative MMSE scores.

Discussion

Unilateral GPi-DBS therapy was effective in improving contralateral, ipsilateral, and axial motor symptoms of patients with advanced PD; in particular, it was found to be especially beneficial in PwPD whose cognitive function was unimpaired; the treatment efficacy rivaled that of bilateral counterparts up till at least 6 months postoperatively. Finally, normalization of preoperative abnormalities in cerebral blood flow and increased cerebral blood flow in the contralateral frontal lobe indicated the beneficial potential of this therapy on ipsilateral motor symptoms.

Lateralized effects of deep brain stimulation in Parkinson's disease: evidence and controversies

The bilateral effects of deep brain stimulation (DBS) on motor and non-motor symptoms of Parkinson's disease (PD) have been extensively studied and reviewed. However, the unilateral effects-in particular, the potential lateralized effects of left- versus right-sided DBS-have not been adequately recognized or studied. Here we summarized the current evidence and controversies in the literature regarding the lateralized effects of DBS on motor and non-motor outcomes in PD patients. Publications in English language before February 2021 were obtained from the PubMed database and included if they directly compared the effects of unilateral versus contralateral side DBS on motor or non-motor outcomes in PD. The current literature is overall of low-quality and is biased by various confounders. Researchers have investigated mainly PD patients receiving subthalamic nucleus (STN) DBS while the potential lateralized effects of globus pallidus interna (GPi) DBS have not been adequately studied. Evidence suggests potential lateralized effects of STN DBS on axial motor symptoms and deleterious effects of left-sided DBS on language-related functions, in particular, the verbal fluency, in PD. The lateralized DBS effects on appendicular motor symptoms as well as other neurocognitive and neuropsychiatric domains remain inconclusive. Future studies should control for varying methodological approaches as well as clinical and DBS management heterogeneities, including symptom laterality, stimulation parameters, location of active contacts, and lead trajectories. This would contribute to improved treatment strategies such as personalized target selection, surgical planning, and postoperative management that ultimately benefit patients.

A Review of Cognitive Outcomes Across Movement Disorder Patients Undergoing Deep Brain Stimulation

Introduction: Although the benefit in motor symptoms for well-selected patients with deep brain stimulation (DBS) has been established, cognitive declines associated with DBS can produce suboptimal clinical responses. Small decrements in cognition can lead to profound effects on quality of life. The growth of indications, the expansion of surgical targets, the increasing complexity of devices, and recent changes in stimulation paradigms have all collectively drawn attention to the need for re-evaluation of DBS related cognitive outcomes.

Methods: To address the impact of cognitive changes following DBS, we performed a literature review using PubMed. We searched for articles focused on DBS and cognition. We extracted information about the disease, target, number of patients, assessment of time points, cognitive battery, and clinical outcomes. Diseases included were dystonia, Tourette syndrome (TS), essential tremor (ET), and Parkinson's disease (PD).

Results: DBS was associated with mild cognitive issues even when rigorous patient selection was employed. Dystonia studies reported stable or improved cognitive scores, however one study using reliable change indices indicated decrements in sustained attention. Additionally, DBS outcomes were convoluted with changes in medication dose, alleviation of motor symptoms, and learning effects. In the largest, prospective TS study, an improvement in attentional skills was noted, whereas smaller studies reported variable declines across several cognitive domains. Although, most studies reported stable cognitive outcomes. ET studies largely demonstrated deficits in verbal fluency, which had variable responses depending on stimulation setting. Recently, studies have focused beyond the ventral intermediate nucleus, including the post-subthalamic area and zona incerta. For PD, the cognitive results were heterogeneous, although deficits in verbal fluency were consistent and related to the micro-lesion effect.

Conclusion: Post-DBS cognitive issues can impact both motor and quality of life outcomes. The underlying pathophysiology of cognitive changes post-DBS and the identification of pathways underpinning declines will require further investigation. Future studies should employ careful methodological designs. Patient specific analyses will be helpful to differentiate the effects of medications, DBS and the underlying disease state, including disease progression. Disease progression is often an underappreciated factor that is important to post-DBS cognitive issues.

Neuropsychological performance changes following subthalamic versus pallidal deep brain stimulation in Parkinson's disease: a systematic review and metaanalysis

BACKGROUND

Studies comparing subthalamus (STN) and globus pallidus internus (GPi) deep brain stimulation (DBS) for the management of Parkinson's disease in terms of neuropsychological performance are scarce and heterogeneous. Therefore, we performed a systematic review and metaanalysis to compare neuropsychological outcomes following STN DBS versus GPi DBS.

METHODS

A computer literature search of PubMed, the Web of Science, and Cochrane Central was conducted. Records were screened for eligible studies, and data were extracted and synthesized using Review Manager (v. 5.3 for Windows).

RESULTS

Seven studies were included in the qualitative synthesis. Of them, four randomized controlled trials (n=345 patients) were pooled in the metaanalysis models. The standardized mean difference (SMD) of change in the Stroop color-naming test favored the GPi DBS group (SMD=-0.31, p=0.009). However, other neuropsychological outcomes did not favor either of the two groups (Stroop word-reading: SMD=-0.21, p=0.08; the Wechsler Adult Intelligence Scale (WAIS) digits forward: SMD=0.08, p=0.47; Trail Making Test Part A: SMD=-0.05, p=0.65; WAIS-R digit symbol: SMD=-0.16, p=0.29; Trail Making Test Part B: SMD=-0.14, p=0.23; Stroop color-word interference: SMD=-0.16, p=0.18; phonemic verbal fluency: bilateral DBS SMD=-0.04, p=0.73, and unilateral DBS SMD=-0.05, p=0.83; semantic verbal fluency: bilateral DBS SMD=-0.09, p=0.37, and unilateral DBS SMD=-0.29, p=0.22; Boston Naming Test: SMD=-0.11, p=0.33; Beck Depression Inventory: bilateral DBS SMD=0.15, p=0.31, and unilateral DBS SMD=0.36, p=0.11).

CONCLUSIONS

There was no statistically significant difference in most of the neuropsychological outcomes. The present evidence does not favor any of the targets in terms of neuropsychological performance.

Cognitive Impact of Deep Brain Stimulation on Parkinson's Disease Patients

Subthalamic nucleus (STN) or globus pallidus interna (GPi) deep brain stimulation (DBS) is considered a robust therapeutic tool in the treatment of Parkinson's disease (PD) patients, although it has been reported to potentially cause cognitive decline in some cases. We here provide an in-depth and critical review of the current literature regarding cognition after DBS in PD, summarizing the available data on the impact of STN and GPi DBS as monotherapies and also comparative data across these two therapies on 7 cognitive domains. We provide evidence that, in appropriately screened PD patients, worsening of one or more cognitive functions is rare and subtle after DBS, without negative impact on quality of life, and that there is very little data supporting that STN DBS has a worse cognitive outcome than GPi DBS.

Improvement of Advanced Parkinson's Disease Manifestations with Deep Brain Stimulation of the Subthalamic Nucleus: A Single Institution Experience

We present our experience at the University of Illinois at Chicago (UIC) in deep brain stimulation (DBS) of the subthalamic nucleus (STN), describing our surgical technique, and reporting our clinical results, and morbidities. Twenty patients with advanced Parkinson’s disease (PD) who underwent bilateral STN-DBS were studied. Patients were assessed preoperatively and followed up for one year using the Unified Parkinson’s Disease Rating Scale (UPDRS) in “on” and “off” medication and “on” and “off” stimulation conditions. At one-year follow-up, we calculated significant improvement in all the motor aspects of PD (UPDRS III) and in activities of daily living (UPDRS II) in the “off” medication state. The “off” medication UPDRS improved by 49.3%, tremors improved by 81.6%, rigidity improved by 50.0%, and bradykinesia improved by 39.3%. The “off” medication UPDRS II scores improved by 73.8%. The Levodopa equivalent daily dose was reduced by 54.1%. The UPDRS IVa score (dyskinesia) was reduced by 65.1%. The UPDRS IVb score (motor fluctuation) was reduced by 48.6%. Deep brain stimulation of the STN improves the cardinal motor manifestations of the idiopathic PD. It also improves activities of daily living, and reduces medication-induced complications.

Major Cognitive Changes and Micrographia following Globus Pallidus Infarct

Importance. Globus pallidus (GP) lesions are well known to cause motor deficits but are less commonly—and perhaps not conclusively—associated with cognitive problems. Observations. We present a 45-year-old male with no significant neurological or psychological problems who after suffering a GP infarct was subsequently found to have substantial cognitive problems and micrographia. Formal neuropsychological testing was not possible due to lack of patient follow-up. Conclusions and Relevance. Despite the conflicting literature on the association of GP lesions and cognitive deficits, our patient demonstrated significant neuropsychological changes following his stroke. In addition, evidence of micrographia likely adds to the literature on the localization of this finding. Our case thus suggests that neuropsychological testing may be beneficial after GP strokes.

Criteria for deep-brain stimulation in Parkinson’s disease: review and analysis

Deep-brain stimulation is currently the most effective surgical treatment for advanced Parkinson's disease. The relevant targets to date are the subthalamic nucleus and the globus pallidus internus, although the thalamus (ventralis intermedius nucleus) is preferred in tremor-dominant, aged Parkinson's disease patients. Long-term benefit in cardinal parkinsonian signs, motor fluctuations and dyskinesia has been reported in 5-year follow-up studies of subthalamic nucleus deep-brain stimulation. However, some psychiatric consequences have raised important issues and emphasized the need for an experienced deep-brain stimulation surgical team. This team should be multidisciplinary and involve movement disorder neurologists, neurosurgeons, neuropsychologists and psychiatrists. The recent observation that deep-brain stimulation of the pedunculopontine nucleus improves axial signs, possibly even in those less responsive to levodopa, brings new hope to the management of advanced Parkinson's disease.

Deep brain stimulationfor movement disorders

Movement disorders remain the primary indication for the use of intracranial neurostimulation techniques. This review will discuss the history of this technology as well as the mechanisms of action, current clinical indications, and future prospects for the treatment of movement disorders.

Deep brain stimulation for Parkinson's disease - patient selection

Proper selection of patients who will reliably benefit from deep brain stimulation (DBS) is critical to its success. This requires careful evaluation that should be delivered by an expert multidisciplinary team involving a movement disorder neurologist, a neurosurgeon, a neuropsychologist, and a psychiatrist. The most suitable candidates for DBS suffer from Parkinson's disease with motor fluctuations and/or dyskinesias that are not adequately controlled with optimized medical therapy, or with medication-refractory tremor. During the best on-motor periods, gait difficulties, instability, and speech problems should be minimal, reflecting an excellent response to levodopa in the ideal candidate. The cognitive, psychiatric, and behavioral status must be normal or minimally affected, with the exception of dopamine agonist drug-induced impulse control disorders, which are usually improved after successful surgery and drug withdrawal. Moreover, the patients have no serious comorbidities. Most patients corresponding to this profile suffer from a relatively young onset of Parkinson's disease, and are aged less than 70 years at the time of surgery. Indeed, most patients fall outside this ideal description, and the medical art is to appreciate for each patient the extent to which the alterations of these features can be accepted. Eventually, patients make their own decision from detailed information of their individualized risks and benefits of DBS. Patient expectations, cooperation, and familial support are also important considerations.

Deep brain stimulation induces BOLD activation in motor and non-motor networks: an fMRI comparison study of STN and EN/GPi DBS in large animals

The combination of deep brain stimulation (DBS) and functional MRI (fMRI) is a powerful means of tracing brain circuitry and testing the modulatory effects of electrical stimulation on a neuronal network in vivo. The goal of this study was to trace DBS-induced global neuronal network activation in a large animal model by monitoring the blood oxygenation level-dependent (BOLD) response on fMRI. We conducted DBS in normal anesthetized pigs, targeting the subthalamic nucleus (STN) (n=7) and the entopeduncular nucleus (EN), the non-primate analog of the primate globus pallidus interna (n=4). Using a normalized functional activation map for group analysis and the application of general linear modeling across subjects, we found that both STN and EN/GPi DBS significantly increased BOLD activation in the ipsilateral sensorimotor network (FDR<0.001). In addition, we found differential, target-specific, non-motor network effects. In each group the activated brain areas showed a distinctive correlation pattern forming a group of network connections. Results suggest that the scope of DBS extends beyond an ablation-like effect and that it may have modulatory effects not only on circuits that facilitate motor function but also on those involved in higher cognitive and emotional processing. Taken together, our results show that the swine model for DBS fMRI, which conforms to human implanted DBS electrode configurations and human neuroanatomy, may be a useful platform for translational studies investigating the global neuromodulatory effects of DBS.

Cognitive assessment instruments in Parkinson's disease patients undergoing deep brain stimulation

Deep Brain Stimulation (DBS) is a widely used surgical technique in individuals with Parkinson's disease (PD) that can lead to significant reductions in motor symptoms.

Underlying neurobiology and clinical correlates of mania status after subthalamic nucleus deep brain stimulation in Parkinson's disease: a review of the literature

Deep brain stimulation (DBS) is a novel and effective surgical intervention for refractory Parkinson's disease (PD). The authors review the current literature to identify the clinical correlates associated with subthalamic nucleus (STN) DBS-induced hypomania/mania in PD patients. Ventromedial electrode placement has been most consistently implicated in the induction of STN DBS-induced mania. There is some evidence of symptom amelioration when electrode placement is switched to a more dorsolateral contact. Additional clinical correlates may include unipolar stimulation, higher voltage (&gt;3 V), male sex, and/or early-onset PD. STN DBS-induced psychiatric adverse events emphasize the need for comprehensive psychiatric presurgical evaluation and follow-up in PD patients. Animal studies and prospective clinical research, combined with advanced neuroimaging techniques, are needed to identify clinical correlates and underlying neurobiological mechanisms of STN DBS-induced mania. Such working models would serve to further our understanding of the neurobiological underpinnings of mania and contribute valuable new insight toward development of future DBS mood-stabilization therapies.

The cognitive effects of amygdalohippocampal deep brain stimulation in patients with temporal lobe epilepsy

The aim of this study was to examine the effects of amygdalohippocampal deep brain stimulation (AH-DBS) on cognitive functioning in patients with refractory temporal lobe epilepsy. The population consisted of 10 patients (7 men) who underwent ipsilateral (n=8) or bilateral (n=2) AH-DBS. Intellectual and neuropsychological evaluation was performed before and 6 months after initiation of AH-DBS. Group analyses revealed no overall pattern of change in cognitive measures, but improvement was seen in emotional well-being. Individual results varied over a broad spectrum ranging from no cognitive effects to negative effects on intelligence capacities, divided attention, and concept formation, to positive effects on speed of information processing and speed of finger movements. AH-DBS is a valuable treatment alternative for patients with refractory epilepsy that appears to have no major adverse neuropsychological consequences and enhances emotional well-being on the group level. Individual results are too diverse at this moment to allow viable interpretation. Additional studies are needed to confirm these preliminary results.

Relationship between neuropsychological outcome and DBS surgical trajectory and electrode location

BACKGROUND

The outcome literature of subthalamic nuclei (STN) deep brain stimulation (DBS) suggests that cognitive declines are commonly reported following surgery. We hypothesized that differences in electrode position and surgical trajectory may lead to a differential neuropsychological outcome.

METHODS

We conducted a standardized evaluation of the location of the DBS electrode tip and the active electrodes, the surgical trajectory through which they were placed, and their relation to neuropsychological change scores (mental status, verbal memory, verbal fluency, and psychological measures) in 17 bilateral STN DBS patients using 6 months post-surgical magnetic resonance imaging data.

RESULTS

Declines in mental status scores were related to electrodes that were more posterior-laterally placed within the frontal quadrant in either hemisphere or those located superiorally in the left hemisphere. Electrodes that were closer to the approximated STN and more superiorally located in the left hemisphere were associated with verbal learning declines at 6 months following surgery. In the right hemisphere, the electrodes that were located more in the lateral direction were related to verbal short-term memory declines; while for verbal long-term memory declines were found for electrodes located more posterior-laterally in the left hemisphere. Declines in verbal fluency scores were more variable with associations found between change scores and electrodes in the lateral and superior directions in the left hemisphere and those electrodes closer to the approximated STN and more superiorally and posteriorally located in the right hemisphere. In contrast, semantic fluency declines were only related to right hemisphere electrodes located more superiorally. Declines in mood were related to those electrodes located further away from the approximated STN, particularly those located more inferiorally and laterally in the left hemisphere. Anxiety change scores were not associated with the location of the electrodes.

CONCLUSIONS

The results provide preliminary evidence that 6 months following bilateral STN DBS cognitive and emotional changes may be related to the surgical trajectory and electrode placement.

Functional surgery for Parkinson's disease treatment: a structured analysis of a decade of published literature

The aim of this study was to analyse and compare published data during the last decade on the different approaches to Parkinson's disease surgery. Eighty-eight papers published between 1990 and 2001 fulfilled the inclusion criteria. Full-text and prospective papers on lesion and stimulation of GPi or STN were assessed. Descriptive analysis of surgery procedure and population under study was performed, as well as a meta-analysis of the most consistently reported variables. A total of 1702 patients underwent surgery with a mean age of 58.75 years (range 46.5 - 72.5), mean duration of illness 13.6 years (8.1 - 18.1) and a male:female ratio 1.5:1. Mean postoperative follow-up was 9 months (1 - 52). Single blind assessment was performed in two papers, while double blind evaluation was used in 6. In the GPi group, no difference was found between the pre- and postoperative levodopa equivalent daily dose (960.39 v. 943.13; p > 0.05), while the STN group showed a marked reduction (1104.8 v. 483.04; p < 0.05) of this dosage. Meta-analysis of the most consistently reported variables (UPDRS total score, UPDRS motor score, UPDRS ADL score and Schwab & England score showed that Nucleus, Bilaterality of Approach and Surgical Procedure were the best moderators for defining outcome. Bilateral DBS STN procedures proved to be associated with better outcome. Microelectrode recording was not found to be a moderator that influenced outcome. Although there was a significant improvement of dyskinesias among the different approaches described in the papers, the heterogeneity of data makes it impossible to perform a structured analysis on this item.

Deep brain stimulation for Parkinson's disease: prevalence of adverse events and need for standardized reporting

Deep brain stimulation (DBS) has assumed a prominent role in the treatment of Parkinson's disease (PD). In this manuscript, we attempt to estimate the prevalence and categorize adverse events (AEs) of DBS in PD, based on efficacy studies published over the last decade. We conclude that reliable categorization and quantification of AEs based on available data poses many challenges and argue that a standardized scheme for reporting AEs should be created. This would provide a foundation for a meaningful risk/benefit analysis, for comparison of results between centers and, ultimately, for a well informed decision by physicians and patients as to whether surgery should be pursued.

Surgical management of Parkinson's disease: update and review

SUMMARY

Although medical therapy is still the mainstay of treatment for Parkinson's disease, the development of surgical precision and decreased morbidity have made stereotatic lesioning and deep brain stimulation more popular. Neurosurgical ablations include pallidotomy, thalamotomy, and, more recently, subthalamotomy. Because of concern over the high risk of side-effects resulting from bilateral ablative procedure, alternative approaches have been explored.With improved deep brain stimulation (DBS) technology, DBS has been successfully applied in the internal globus pallidus, ventral intermediate nucleus and subthalamic nucleus for Parkinson's disease. In addition, recent surgical approaches including biological neurorestorative technologies - surgical therapies with transplantation, gene therapy, and growth factor are all being discussed in this review. Although a great deal of work remains to be done for researchers, advances in surgical therapies for the treatment of Parkinson's disease are moving forward at an unprecedented pace, and, not surprisingly, would give PD patients more choices and hope.

The treatment of movement disorders by deep brain stimulation

It has been understood, for some time, that modulation of deep brain nuclei within the basal ganglia and thalamus can have a therapeutic effect in patients with movement disorders. Because of its reversibility and adjustability, deep brain stimulation (DBS) has largely come to replace traditional ablation procedures. The clinical effects of DBS vary, depending both on the target being stimulated and on the parameters of stimulation. Both aspects are currently the subject of substantial research and discovery. The most common targets for DBS treatment include the subthalamic nucleus for the treatment of advanced Parkinson's disease, the ventral intermediate nucleus of the thalamus for the treatment of medically refractory essential tremor, and the globus pallidus interna for the treatment of both cervical and generalized dystonias and Parkinson's disease. We review the current indications, targets, outcomes, and general procedure of DBS for essential tremor, Parkinson's disease, and dystonia.

Limbic, associative, and motor territories within the targets for deep brain stimulation: Potential clinical implications

The use of deep brain stimulation (DBS) has recently been expanding for the treatment of many neurologic disorders such as Parkinson disease, dystonia, essential tremor, Tourette's syndrome, cluster headache, epilepsy, depression, and obsessive compulsive disorder. The target structures for DBS include specific segregated territories within limbic, associative, or motor regions of very small subnuclei. In this review, we summarize current clinical techniques for DBS, the cognitive/mood/motor outcomes, and the relevant neuroanatomy with respect to functional territories within specific brain targets. Future development of new techniques and technology that may include a more direct visualization of "motor" territories within target structures may prove useful for avoiding side effects that may result from stimulation of associative and limbic regions. Alternatively, newer procedures may choose and specifically target non-motor territories for chronic electrical stimulation.

Deep brain stimulation and the role of the neuropsychologist

Deep brain stimulation (DBS) now plays an important role in the treatment of Parkinson's disease, tremor, and dystonia. DBS may also have a role in the treatment of other disorders such as obsessive-compulsive disorder, Tourette's syndrome, and depression. The neuropsychologist plays a crucial role in patient selection, follow-up, and management of intra-operative and post-operative effects (Pillon, 2002; Saint-Cyr & Trepanier, 2000). There is now emerging evidence that DBS can induce mood, cognitive, and behavioral changes. These changes can have dramatic effects on patient outcome. There have been methodological problems with many of the studies of DBS on mood, cognition, and behavior. The neuropsychologist needs to be aware of these issues when following up patients, and constructing future studies. Additionally, this article will review all aspects of the DBS procedure that can result in mood, cognitive, and behavioral effects and what role(s) the neuropsychologist should play in screening and follow-up.

Neuropsychological performance following staged bilateral pallidal or subthalamic nucleus deep brain stimulation for Parkinson's disease

Deep brain stimulation (DBS) has the potential to significantly reduce motor symptoms in advanced Parkinson's disease (PD). Controversy remains about non-motor effects of DBS and the relative advantages of treatment at two brain targets, the globus pallidus internus (GPi) and the subthalamic nucleus (STN). We investigated effects of DBS on neuropsychological functioning in 42 patients with advanced PD randomly assigned to receive staged bilateral DBS surgery of either the GPi or STN. Patients underwent neuropsychological assessment prior to and 6 months after unilateral surgery. Twenty-nine subsequently underwent surgery to the contralateral side and completed a second follow-up neuropsychological evaluation 15 months later. Unilateral treatment resulted in small but statistically significant reductions in performance on several measures, including verbal fluency and working memory. A similar pattern was observed after bilateral treatment. Reductions in verbal associative fluency were significant only after left-sided treatment. There were few significant differences related to treatment at the two surgical targets. Supplementary analyses suggested that decrements in select neuropsychological domains following DBS are unrelated to age or post-surgical reduction in dopaminergic medication dose. Findings are discussed with reference to possible causes of neuropsychological decline and the need for further controlled studies of specific neuropsychological effects of DBS.

Review of the therapeutic management of Parkinson's disease. Report of a joint task force of the European Federation of Neurological Societies (EFNS) and the Movement Disorder Society-European Section (MDS-ES). Part II: late (complicated) Parkinson's disease

To provide evidence-based recommendations for the management of late (complicated) Parkinson's disease (PD), based on a review of the literature. Complicated PD refers to patients suffering from the classical motor syndrome of PD along with other motor or non-motor complications, either disease-related (e.g. freezing) or treatment-related (e.g. dyskinesias or hallucinations). MEDLINE, Cochrane Library and INAHTA database literature searches were conducted. National guidelines were requested from all EFNS societies. Non-European guidelines were searched for using MEDLINE. Part II of the guidelines deals with treatment of motor and neuropsychiatric complications and autonomic disturbances. For each topic, a list of therapeutic interventions is provided, including classification of evidence. Following this, recommendations for management are given, alongside ratings of efficacy. Classifications of evidence and ratings of efficacy are made according to EFNS guidance. In cases where there is insufficient scientific evidence, a consensus statement ('good practice point') is made.

Deep brain stimulation: neuropsychological and neuropsychiatric issues

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor, cognitive, neuropsychiatric, autonomic, and other nonmotor symptoms. The efficacy of deep brain stimulation (DBS) for the motor symptoms of advanced PD is well established. However, the effects of DBS on the cognitive and neuropsychiatric symptoms are less clear. The neuropsychiatric aspects of DBS for PD have recently been of considerable clinical and pathophysiological interest. As a companion to the preoperative and postoperative sections of the DBS consensus articles, this article reviews the published literature on the cognitive and neuropsychiatric aspects of DBS for PD. The majority of the observed neuropsychiatric symptoms are transient, treatable, and potentially preventable. Outcome studies, methodological issues, pathophysiology, and preoperative and postoperative management of the cognitive and neuropsychiatric aspects and complications of DBS for PD are discussed.

Lessons learned in deep brain stimulation for movement and neuropsychiatric disorders

The introduction of deep brain stimulation (DBS) as a treatment for medication-refractory essential tremor in the late 1980s revealed, for the first time, that "chronically" implanted brain hardware had the potential to modulate neurologic function with surprisingly low morbidity. Over time, the therapeutic promise of DBS has become evident in Parkinson's disease and dystonia. In some experienced centers, complex tremor disorders, such as posttraumatic Holmes tremor and the tremor of multiple sclerosis, are being increasingly targeted. More recently, other indications, including obsessive-compulsive disorder, Tourette's syndrome, major depression, and chronic pain, have been proposed. As the field has expanded, our knowledge about potential cognitive side effects of DBS has also expanded. This article reviews the current knowledge regarding the impact of stimulation of the subthalamic nucleus, globus pallidus internus, and ventralis intermedius nucleus of the thalamus on symptoms in essential tremor, Parkinson's disease, and dystonia. Also discussed are the emerging targets, what is known about the cognitive sequelae of DBS, and what has been learned about the complications and therapeutic failures.

Behavioural changes after bilateral subthalamic stimulation in advanced Parkinson disease: a systematic review

INTRODUCTION

The long-lasting beneficial effects of subthalamic nucleus (STN) deep brain stimulation (DBS) on motor function have now largely been acknowledged. Whereas behavioural changes have been demonstrated in certain case reports and small case series, some authors have not observed behavioural changes at all. The extent to which these changes occur has not yet been established. The aim of the present study was to systematically analyse behavioural changes of bilateral STN DBS.

MATERIALS AND METHODS

A structured Medline search was conducted using previously described methods. Studies were selected according to specific in- and exclusion criteria. Data on patients, surgical technique, outcome and complications were collected and pooled.

RESULTS

In total 1,398 patients who underwent bilateral STN DBS were included. The total cumulative follow-up period was 1,480 patient-years. Cognitive problems were seen in 41%, depression in 8%, and (hypo)mania in 4% of the patients. Anxiety disorders were observed in less than 2%, and personality changes, hypersexuality, apathy, anxiety, and aggressiveness were observed in less than 0.5% of the group studied. About half of the patients did not experience behavioural changes.

CONCLUSION

Caregivers should be aware of the extent of these behavioural changes and a risk/benefit evaluation should be performed for individual patients.

Deep brain stimulation: Postoperative issues

Numerous factors need to be taken into account when managing a patient with Parkinson's disease (PD) after deep brain stimulation (DBS). Questions such as when to begin programming, how to conduct a programming screen, how to assess the effects of programming, and how to titrate stimulation and medication for each of the targeted sites need to be addressed. Follow-up care should be determined, including patient adjustments of stimulation, timing of follow-up visits and telephone contact with the patient, and stimulation and medication conditions during the follow-up assessments. A management plan for problems that can arise after DBS such as weight gain, dyskinesia, axial symptoms, speech dysfunction, muscle contractions, paresthesia, eyelid, ocular and visual disturbances, and behavioral and cognitive problems should be developed. Long-term complications such as infection or erosion, loss of effect, intermittent stimulation, tolerance, and pain or discomfort can develop and need to be managed. Other factors that need consideration are social and job-related factors, development of dementia, general medical issues, and lifestyle changes. This report from the Consensus on Deep Brain Stimulation for Parkinson's Disease, a project commissioned by the Congress of Neurological Surgeons and the Movement Disorder Society, outlines answers to a series of questions developed to address all aspects of DBS postoperative management and decision-making with a systematic overview of the literature (until mid-2004) and by the expert opinion of the authors. The report has been endorsed by the Scientific Issues Committee of the Movement Disorder Society and the American Society of Stereotactic and Functional Neurosurgery.

Differential effects of subthalamic nucleus stimulation in advanced Parkinson disease on reaction time performance

The aim of the present study was to assess the effect of bilateral subthalamic nucleus (STN) stimulation and dopaminergic medication on speed of mental processing and motor function. Thirty-nine patients suffering from advanced Parkinson disease (PD) were operated on. Motor function and reaction time (RT) performance [simple RT (SRT) and complex RT (CRT)] were evaluated under four experimental conditions with stimulation (stim) and medication (med) on and off: stim-on/med-on, stim-on/med-off, stim-off/med-off and stim-off/med-on. In the last condition, the patients received either low medication (usual dose) or high medication (suprathreshold dose). STN stimulation improved the motor performance in the SRT and CRT tasks. Furthermore, STN deep brain stimulation (DBS) also improved response preparation as shown by the significant improvement of the RT performance in the SRT task. This effect of STN DBS on the RT performance in the SRT task was greater as compared with the CRT task. This is due to the more complex information processing that is required in the CRT task as compared to the SRT task. These data suggest that treatment of STN hyperactivity by DBS improves motor function, confirming earlier reports, but has a differential effect on cognitive functions. The STN seems to be an important modulator of cognitive processing and STN DBS can differentially affect motor and associative circuits.

Surgical treatment for Parkinson's disease

Since the early 1930s, physicians have developed and refined various surgical therapies for the treatment of Parkinson's disease. In this review we examine some of the problems associated with early surgical therapies, the development of new techniques and targets, and the results of clinical trials examining the safety and efficacy of these techniques. Ablative techniques include pallidotomy, thalamotomy, and, more recently, subthalamotomy. Because of concern over the high incidence of side-effects associated with bilateral ablative procedures, alternative approaches were explored. Deep brain stimulation (DBS) was subsequently developed and successfully applied in the internal globus pallidus, subthalamic nucleus, and thalamus for the treatment of Parkinson's disease. Recent approaches include biological neurorestorative techniques--surgical therapies with transplantation, gene therapy, and growth factors are all being studied. Although a great deal of work remains to be done, advances in surgical therapies for the treatment of Parkinson's disease are moving forward at an unprecedented pace.

Neuropsychiatric complications of medical and surgical therapies for Parkinson's disease

This review deals with the range of neuropsychiatric problems that may arise from the use of medical and surgical therapies in the treatment of Parkinson's disease. As new approaches emerge, these problems are diversifying. Well-recognized drug-related complications include hallucinations and psychosis and the so-called dopamine-dysregulation syndrome. The etiology of these problems has not been fully established and is not clearly dose related, while the management can be difficult and needs to be tailored to the individual patient. Cholinergic and dopaminergic drugs may both influence cognitive function. The development of pharmacogenetics could improve the therapeutic ratio of medical approaches to PD in the future. The literature relating to the neuropsychiatric issues complicating the surgical treatment of Parkinson's disease is more recent and frequently suffers from methodological problems, lack of a systematic approach, and adequate patient follow-up. The emergence of neuropsychiatric problems in association with surgery has shed new light upon the pathophysiological mechanisms underpinning these symptoms. Depression, hypomania, euphoria, mirth, and hypersexuality have all been described following deep brain stimulation procedures, although most studies have concentrated upon the depressive features. Anxiety has been described only rarely to date. Fortunately, permanent cognitive complications appear to be rare. The optimal management approach for surgically related neuropsychiatric problems is unknown at present. Prospective multicenter studies would contribute significantly to resolving this therapeutic uncertainty.

Long-term motor effect of unilateral pallidal stimulation in 26 patients with advanced Parkinson disease

OBJECT

The aim of this study was to evaluate the long-term effects of unilateral pallidal stimulation on motor function in selected patients with advanced Parkinson disease (PD).

METHODS

The authors enrolled 26 patients with idiopathic PD in whom there was an asymmetric distribution of symptoms and, despite optimal pharmocological treatment, severe response fluctuations and/or dyskinesias. After the patient had received a local anesthetic agent, a quadripolar electrode (Medtronic model 3387) was implanted at the side opposite the side affected or, if both sides were affected, the side contralateral to the more affected side. No serious complications occurred. After 3 months, the total Unified PD Rating Scale (UPDRS) Part III score decreased by 50.7% while patients were in the off-medication state (from 26.5 +/- 9.2 to 13.1 +/- 6.1) and by 55.4% while they were in the on-medication state (from 10.6 +/- 6.3 to 4.7 +/- 4.4). Only during the on state was the contralateral effect clearly more pronounced. The UPDRS Part IVa score decreased by 75% (from 3.7 +/- 2.5 to 0.9 +/- 1.1) and the UPDRS Part IVb score by 54.7% (from 3.3 +/- 1.3 to 1.5 +/- 1.3). At long-term follow-up review (32.7 +/- 10.7 months), there was an 8.3% increase in the UPDRS Part III score while patients were in the off state (from 26.5 +/- 9.2 to 28.7 +/- 7.6) and a 40.2% increase in this score while patients were in the on state (from 10.6 +/- 6.3 to 14.9 +/- 5.1). The UPDRS Part IVa score decreased by 28.1% (from 3.7 +/- 2.5 to 2.7 +/- 2.3) and the UPDRS Part IVb score increased by 3.5% (from 3.3 +/- 1.3 to 3.4 +/- 1.6).

CONCLUSIONS

Based on these unsatisfactory results at long-term review, the authors conclude that unilateral pallidal stimulation is not an effective treatment option for patients with advanced PD.

Analysis of probabilistic classification learning in patients with Parkinson's disease before and after pallidotomy surgery

This study examined the characteristics of probabilistic classification learning, a form of implicit learning previously shown to be impaired in patients with basal ganglia dysfunction (e.g., Parkinson's disease). In this task, subjects learn to predict the weather using associations that are formed gradually across many trials, because of the probabilistic nature of the cue-outcome relationships. Patients with Parkinson's disease, both before and after pallidotomy, and age-matched control subjects, exhibited evidence of probabilistic classification learning across 100 training trials. However, pallidotomy appears to hinder the learning of associations most implicit in nature (i.e., weakly associated cues). Although subjects were most sensitive to single-cue associations when learning the task, there is evidence that cue combinations contribute significantly to probability learning. The utility of multiple dependent measures is discussed.

Neuropsychology for movement disorders neurosurgery

The neuropsychologist plays a crucial role in three phases of the neurosurgical treatment of movement disorder patients, namely screening, outcome evaluation and research. In screening patients, the differential diagnosis of dementia, impact of depression or other psychiatric conditions, and the influence of disease and medication-induced symptoms on cognitive performance must be determined. Postoperatively, systematic evaluations elucidate the cognitive costs or benefits of the procedure. The neuropsychologist is then able to provide feedback and counselling to the professional staff, patient and family to inform management strategies. Neuropsychologists also study alteration of cognitive processing due to lesions or stimulation, which, in tandem with functional imaging, shed light on plasticity in cortical and subcortical processing.

Cognitive and behavioural effects of chronic stimulation of the subthalamic nucleus in patients with Parkinson's disease

OBJECTIVE

To investigate cognitive and behavioural effects of bilateral lead implants for high frequency stimulation (HFS) of the subthalamic nucleus in patients with Parkinson's disease; and to discriminate between HFS and the effects of surgical intervention on cognitive function by carrying out postoperative cognitive assessments with the stimulators turned on or off.

METHODS

Motor, cognitive, behavioural, and functional assessments were undertaken in 20 patients with Parkinson's disease before implantation and then at three, six, and 12 months afterwards. Nine patients were also examined 18 months after surgery. Postoperative cognitive assessments were carried out with stimulators turned off at three and 18 months, and turned on at six and 12 months.

RESULTS

Cognitive assessment showed a significant postoperative decline in performance on tasks of letter verbal fluency (across all postoperative assessments, but more pronounced at three months) and episodic verbal memory (only at three months, with stimulators off). At three, six, and 12 months after surgery, there was a significant improvement in the mini-mental state examination and in a task of executive function (modified Wisconsin card sorting test). On all postoperative assessments, there was an improvement in parkinsonian motor symptoms, quality of life, and activities of daily living while off antiparkinsonian drugs. A significant postoperative decrease in depressive and anxiety symptoms was observed across all assessments. Similar results were seen in the subgroup of nine patients with an 18 month follow up. Following implantation, three patients developed transient manic symptoms and one showed persistent psychic akinesia.

CONCLUSIONS

Bilateral HFS of the subthalamic nucleus is a relatively safe procedure with respect to long term cognitive and behavioural morbidity, although individual variability in postoperative cognitive and behavioural outcome invites caution. Stimulation of the subthalamic nucleus does not per se appear to impair cognitive performance in patients with Parkinson's disease and may alleviate the postoperative decline in verbal fluency.

Pallidal stimulation for parkinsonism: improved brain activation during sequence learning

We used (15)O-labeled water and positron emission tomography to assess the effect of deep brain stimulation of the internal globus pallidus on motor sequence learning in Parkinson's disease. Seven right-handed patients were scanned on and off stimulation while they were performing a motor sequence learning task and a kinematically matched motor execution reference task. The scans were performed after a 12-hour medication washout. Stimulation parameters were adjusted for maximal motor improvement; experimental task parameters were held constant across stimulation conditions. Internal globus pallidus stimulation improved motor ratings by 37% (p < 0.01). During the sequence learning task, stimulation improved performance as measured by several correct anticipatory movements (p < 0.01) and by verbal report (p < 0.001). Concurrent positron emission tomography imaging during learning demonstrated significant (p < 0.01) increases in brain activation with stimulation in the left dorsolateral prefrontal cortex, bilaterally in premotor cortex, and in posterior parietal and occipital association areas. Stimulation did not affect the activity of these regions during the performance of the motor execution reference task. These findings suggest that internal globus pallidus deep brain stimulation can enhance the activity of prefrontal cortico-striato-pallidothalamic loops and related transcortical pathways. Improved sequence learning with stimulation may be directly related to these functional changes.

Neuropsychological sequelae of subthalamic nucleus deep brain stimulation in Parkinson's disease: a critical review

Neuropsychologists are increasingly involved in surgical candidacy evaluations and postoperative neurobehavioral assessments of patients with movement disorders, most notably those with Parkinson's disease (PD). We review here the initial studies regarding neuropsychological outcomes of deep brain stimulation (DBS) within the subthalamic nucleus (STN) for treatment of PD. Overall, these initial investigations provide preliminary support for the cognitive and neurobehavioral safety of STN DBS. Improvements in self-reported symptoms of depression and diminished verbal fluency were the most common findings, whereas changes in global cognitive abilities, memory, attention, and frontal/executive functions were inconsistent and most often described as nominal and/or transient. The generalizability of this literature is hindered by several methodological limitations, including small samples and the absence of appropriate control participants. The clinical and theoretical implications of these initial studies are highlighted and recommendations are offered to guide future research.

Neuropsychological assessment for management of patients with deep brain stimulation

The inclusion of cognitive and behavioural criteria has been recommended for the management of patients with deep brain stimulation. A neuropsychological assessment may contribute to different issues: (1) selection of the best candidates for surgery, (2) evaluation of the consequences of surgery, (3) research of the best electrode implantation. Recent neuropsychological studies indicate that (1) with appropriate inclusion criteria, the effects of surgery on cognitive functions are limited; (2) an aggravation of behavioural disorders might be related to subthalamic nucleus (STN) stimulation and depend on electrode location; (3) subthalamic nucleus stimulation, but not the internal globus pallidus stimulation, improves psychomotor efficiency and working memory. These results would suggest that the implanted electrodes are not solely targeting the motor circuit and that the cognitive and motor circuits are not completely segregated.

Treatment results: Parkinson's disease

Deep brain stimulation (DBS) is a neurosurgical treatment of Parkinson's disease that is applied to three targets: the ventral intermediate nucleus of the thalamus (Vim), the globus pallidus internas (GPi) and the subthalamic nucleus (STN). Vim DBS mainly improves contralateral tremor and, therefore, is being supplanted by DBS of the two other targets, even in patients with tremor dominant disease. STN and GPi DBS improve off-motor phases and dyskinesias. There is little comparative data between these procedures. The magnitude of the motor improvement seems more constant with STN than GPi DBS. STN DBS allows a decrease in antiparkinsonian drug doses and consumes moderate current. These advantages of STN over GPi DBS are offset by the need for more intensive postoperative management. The DBS procedure has the unique advantage of reversibility and adjustability over time. Patients with young-onset Parkinson's disease suffering from levodopa-induced motor complications but still responding well to levodopa and who exhibit no behavioral, mood, or cognitive impairment benefit the most from STN DBS. Adverse effects more specific of the DBS procedure are infection, cutaneous erosion, and lead breaking or disconnection. Intracranial electrode implantation can induce a hematoma or contusion. Most authors agree that the benefit to risk ratio of DBS is favorable.

Results of chronic subthalamic nucleus stimulation for Parkinson's disease: a 1-year follow-up study

BACKGROUND

Deep brain stimulation (DBS) has been established as an alternative approach for the treatment of advanced Parkinson's disease (PD). Recently, the subthalamic nucleus (STN) has been identified as the optimal target for DBS.

METHODS

Thirty-eight patients have undergone surgery for advanced PD since 1996. They include 12 females and 26 males with a mean age of 55.6 years. The mean stage on the Hoehn and Yahr Scale was 3.5 (off condition). Electrodes (Medtronic DBS 31389) were stereotactically implanted into the STN bilaterally. Targeting was performed using computerized tomography (CT) scans and ventriculography (VG). After 4 days of external stimulation, permanent neurostimulators were implanted. Patients were evaluated preoperatively and 1, 6, and 12 months postoperatively. Evaluations were performed in defined on and off states using the Unified Parkinson's Disease Rating Scale (UPDRS) as well as the Hoehn and Yahr Scale, the dyskinesia scale, and the Activities of Daily Living (ADL) Scale.

RESULTS

Significant improvement of all motor symptoms was found in all patients (UPDRS motor score 32/48 preoperatively versus 15/30 at 12-month follow-up, p < 0.001). Daily off-times were reduced by 35%. Dyskinesias also improved markedly (UPDRS IV: 3.2/3.1 [on/off] vs. 0.9/1.3 at 12 months follow-up). Postoperative L-dopa medication was adjusted (mean reduction: 53%). Complications occurred in two patients (5%) who developed infections, leading to system removal. Systems were replaced after 6 months. Two patients (5%) had a permanent worsening of a previously known depressive state and developed progressive dementia.

CONCLUSIONS

TN stimulation is a relatively safe procedure for treating advanced PD. The possibility of readjusting the stimulation parameters postoperatively improves the therapeutic outcome and reduces side effects in comparison to ablative methods.

Long-term pallidal deep brain stimulation in patients with advanced Parkinson disease: 1-year follow-up study

OBJECT

The goal of this study was to investigate the efficacy of long-term deep brain stimulation (DBS) of the posteroventral lateral globus pallidus internus (GPi) accomplished using a single-contact monopolar electrode in patients with advanced Parkinson disease (PD).

METHODS

Sixteen patients suffering from severe PD and levodopa-induced side effects such as dyskinesias and on-off fluctuations were enrolled in a prospective study protocol. There were six women and 10 men and their mean age at surgery was 65 years. All patients underwent implantation of a monopolar electrode in the posteroventral lateral GPi. Initially, nine patients received unilateral stimulation. Three of these patients underwent contralateral surgery at a later time. Ten patients received bilateral stimulation (contemporaneous bilateral surgery was performed in seven patients and staged bilateral surgery in the three patients who had received unilateral stimulation initially). Formal assessments were performed during both off-medication and on-medication (levodopa) periods preoperatively, and at 3 and 12 months postoperatively. There were no serious complications related to surgery or to DBS. Two transient adverse events occurred: in one patient a small pallidal hematoma developed, resulting in a prolonged micropallidotomy effect, and in another patient a subcutaneous hemorrhage occurred at the site of the pacemaker. In patients who received unilateral DBS, the Unified Parkinson's Disease Rating Scale activities of daily living (ADL) score during the off-levodopa period decreased from 30.8 at baseline to 20.4 at 3 months (34% improvement) and 20.6 at 12 months (33% improvement) postoperatively. The motor score during the off period improved from 57.2 at baseline to 35.2 at 3 months (38% improvement) and 35.3 at 12 months (38% improvement) postoperatively. Bilateral DBS resulted in a reduction in the ADL score during the off period from 34.9 at baseline to 22.3 at 3 months (36% improvement) and 22.9 at 12 months (34% improvement). The motor score for the off period changed from 63.4 at baseline to 40.3 at 3 months (36% improvement) and 37.5 at 12 months (41% improvement). In addition, there were significant improvements in patients' symptoms during the on period and in on-off motor fluctuations.

CONCLUSIONS

Pallidal DBS accomplished using a monopolar electrode is a safe and effective procedure for treatment of advanced PD. Compared with pallidotomy, the advantages of pallidal DBS lie in its reversibility and the option to perform bilateral surgery in one session. Comparative studies in which DBS is applied to other targets are needed.

Deep brain stimulation in neuropsychiatric disorders

Deep brain stimulation (DBS) of the ventral intermediate nucleus of the thalamus, subthalamic nucleus, and internal globus pallidus has been put forth as an alternative to surgical ablation for the treatment of movement disorders. In this paper, the authors discuss the history and putative physiologic mechanisms underlying DBS of these target regions. The authors then review empirical findings pertaining to the effects of DBS on neurological symptoms, cognitive functioning, and psychiatric symptoms in Parkinson's disease and essential tremor, the disorders for which the procedure has been most extensively applied. Finally, emerging and potential novel areas of application of DBS for the treatment of neuropsychiatric disorders and symptoms are discussed.

Updated guidelines for the management of Parkinson's disease

New data on diagnosis, drug therapy, surgery and psychosocial concerns have emerged since the publication of the 1998 Guidelines for the Management of Parkinson's Disease. This article reviews new data and addresses issues left unanswered in the previous guidelines.

Treatment of Parkinson's disease

The aim of current treatment of Parkinson's disease is to ameliorate the symptoms while seeking to lessen the potential development of late levodopa complications. To this end, there is ample evidence that the early use of dopamine agonists is beneficial in younger Parkinsonian patients but monotherapy with dopamine agonists is for only a select few. Nonergot dopamine agonists offer the potential for fewer side effects. Lower dose levodopa therapy delays the onset and reduces severity of dyskinesia and end of dose failure. However levodopa remains the treatment of choice in Parkinson's disease and should not be restricted unnecessarily in patients with disability. There is no evidence that levodopa is toxic to dopaminergic neurons in people with Parkinson's disease. As yet, no drugs are of proven neuroprotective value. Dopamine agonists, catechol-o-methyltransferase inhibitors, amantadine and apomorphine have differing but beneficial roles in the management of levodopa side effects. Ablative surgery and deep brain stimulation of thalamus, globus pallidus and subthalamic nucleus are increasingly available but choice of procedure depends not just on patient symptomatology, but also on local experience and results. Ideally, deep brain stimulation is the treatment of choice as it offers less morbidity than bilateral ablative surgery, the possibility of postoperative adjustments and the potential for reversibility if better treatments become available.