Unilateral pallidotomy versus bilateral subthalamic nucleus stimulation in PD

Research status and hotspots in the surgical treatment of tremor in Parkinson's disease from 2002 to 2022: a bibliometric and visualization analysis

Objective

This study aims to investigate the research status and hotspots of surgical treatment for tremor in Parkinson's disease (PD) from 2002 to 2022, utilizing bibliometric and visual analysis. Additionally, it aims to offer insights into future research trends in this field.

Methods

This study collected publications on the surgical treatment of tremor in PD from 2002 to 2022 using the Web of Science (WOS) database. CiteSpace, VOSviewer, and Scimago Graphica were employed to quantify the number of publications and analyze the bibliographic information networks, including the contributions of countries/cities, authors, keywords, and co-cited references.

Results

A total of 2,815 publications were included in the study, revealing that 541 scientific institutions experienced an increase in publications from 2002 to 2022. Michael Okun emerged as the most productive author, and the United States emerged as the leading hub for research. The study identified 772 keywords. Noteworthy citation bursts and long-term activity were observed in pallidotomy, bilateral stimulation, and focused ultrasound thalamotomy. The top 10 highly co-cited references comprised eight deep brain stimulation (DBS) studies (including two follow-up studies and six randomized controlled trials), one randomized controlled trial on focused ultrasound, and one consensus on tremor.

Conclusion

This study uses an in-depth and systematic bibliometric and visualization analysis to visualize the evolution of research and identify emerging hotspots. The identified hotspots are as follows: Firstly, DBS has received significant attention and widespread recognition as a surgical treatment for tremor in PD. Secondly, there are various key aspects to consider in DBS, such as operative indications, operative targets, and surgical protocols. Lastly, magnetic resonance-guided focused ultrasound (MRgFUS) has emerged as a promising treatment option in the surgical management of tremor in Parkinson's disease. This research also provides insights into the phenomenon of these hotspots, offering valuable prompts and reminders for further research.

Cognitive outcome following bilateral subthalamic nucleus deep brain stimulation for Parkinson's disease-a comparative observational study in Indian patients

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves motor symptoms and motor complications of Parkinson's disease (PD). The intervention is expected to result in some cognitive changes, the nature of which is not uniform across the studies which have reported them. PD itself is associated with progressive cognitive decline and hence longitudinal follow-up studies with medically managed control group of patients are needed to explore the cognitive deficits attributable to DBS.

METHODS

We conducted a prospective comparative observational study to assess the effects of bilateral STN DBS on cognition. Cognitive functions were assessed at baseline and after a minimum of two years after surgery, and compared with baseline and follow-up assessments in patients on medical management alone.

RESULTS

Thirty-four patients with PD who underwent bilateral STN DBS and thirty-four medically managed patients participated in the study. At a mean follow-up of around 33 months, we found a significant decline in verbal fluency scores in the DBS group compared to those on medical management alone (1.15 ± 1.23 vs 0.59 ± 0.93, p = 0.034) and a trend for decline was noted in digit span test. There was no difference in the performance in tests addressing other cognitive domains, or tests of global cognitive function. No patient developed dementia. Motor functions and activities of daily living (ADL) were significantly better in the surgical group.

CONCLUSION

STN DBS results in minor deficits in executive functions, particularly verbal fluency. These may be inconsequential, considering the marked improvement in motor functions and ADL.

Deep Brain Stimulation in Parkinson Disease: A Meta-analysis of the Long-term Neuropsychological Outcomes

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or globus pallidum internus (GPi) improves motor functions in patients with Parkinson's disease (PD) but may cause a decline in specific cognitive domains. The aim of this systematic review and meta-analysis was to assess the long-term (1-3 years) effects of STN or GPi DBS on four cognitive functions: (i) memory (delayed recall, working memory, immediate recall), (ii) executive functions including inhibition control (Color-Word Stroop test) and flexibility (phonemic verbal fluency), (iii) language (semantic verbal fluency), and (iv) mood (anxiety and depression). Medline and Web of Science were searched, and studies published before July 2021 investigating long-term changes in PD patients following DBS were included. Random-effects model meta-analyses were performed using the R software to estimate the standardized mean difference (SMD) computed as Hedges' g with 95% CI. 2522 publications were identified, 48 of which satisfied the inclusion criteria. Fourteen meta-analyses were performed including 2039 adults with a clinical diagnosis of PD undergoing DBS surgery and 271 PD controls. Our findings add new information to the existing literature by demonstrating that, at a long follow-up interval (1-3 years), both positive effects, such as a mild improvement in anxiety and depression (STN, Hedges' g = 0,34, p = 0,02), and negative effects, such as a decrease of long-term memory (Hedges' g = -0,40, p = 0,02), verbal fluency such as phonemic fluency (Hedges' g = -0,56, p < 0,0001), and specific subdomains of executive functions such as Color-Word Stroop test (Hedges' g = -0,45, p = 0,003) were observed. The level of evidence as qualified with GRADE varied from low for the pre- verses post-analysis to medium when compared to a control group.

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.

Sleep Disturbance May Alter White Matter and Resting State Functional Connectivities in Parkinson's Disease

Study Objectives

To clarify whether sleep disturbance would alter the patterns of structural and functional networks underlying cognitive dysfunction in patients with Parkinson's disease (PD).

Methods

Among the 180 patients with nondemented PD in our cohort, 45 patients were classified as the group with sleep disturbance according to the 5-item scales for outcomes in Parkinson's disease nighttime scale. Based on propensity scores, another 45 PD patients without sleep disturbance were matched to this group. We performed a comparative analysis of cortical thickness, diffusion tensor imaging-based white matter integrity, resting-state functional connectivity, and cognitive performance between PD patients with and without sleep disturbance.

Results

PD patients with sleep disturbance showed poorer performance in attention and working memory and a tendency toward a lower score in frontal executive function relative to those without sleep disturbance. The PD with sleep disturbance group exhibited widespread white matter disintegration compared to the PD without sleep disturbance group, although there were no significant differences in cortical thickness between the PD subgroups. On functional network analysis, PD patients with sleep disturbance exhibited less severely decreased cortical functional connectivity within the default mode network, central executive network, and dorsal attention network when compared to those without sleep disturbance.

Conclusions

The present study suggests that sleep disturbance in PD patients could be associated with white matter and functional network alterations in conjunction with cognitive impairment.

Psychiatric and Cognitive Effects of Deep Brain Stimulation for Parkinson's Disease

Deep brain stimulation (DBS) is effective for Parkinson's disease (PD), dystonia, and essential tremor (ET). While motor benefits are well documented, cognitive and psychiatric side effects from the subthalamic nucleus (STN) and globus pallidus interna (GPi) DBS for PD are increasingly recognized. Underlying disease, medications, microlesions, and post-surgical stimulation likely all contribute to non-motor symptoms (NMS).

Neuroprotective and Therapeutic Strategies against Parkinson's Disease: Recent Perspectives

Parkinsonism is a progressive motor disease that affects 1.5 million Americans and is the second most common neurodegenerative disease after Alzheimer’s. Typical neuropathological features of Parkinson’s disease (PD) include degeneration of dopaminergic neurons located in the pars compacta of the substantia nigra that project to the striatum (nigro-striatal pathway) and depositions of cytoplasmic fibrillary inclusions (Lewy bodies) which contain ubiquitin and α-synuclein. The cardinal motor signs of PD are tremors, rigidity, slow movement (bradykinesia), poor balance, and difficulty in walking (Parkinsonian gait). In addition to motor symptoms, non-motor symptoms that include autonomic and psychiatric as well as cognitive impairments are pressing issues that need to be addressed. Several different mechanisms play an important role in generation of Lewy bodies; endoplasmic reticulum (ER) stress induced unfolded proteins, neuroinflammation and eventual loss of dopaminergic neurons in the substantia nigra of mid brain in PD. Moreover, these diverse processes that result in PD make modeling of the disease and evaluation of therapeutics against this devastating disease difficult. Here, we will discuss diverse mechanisms that are involved in PD, neuroprotective and therapeutic strategies currently in clinical trial or in preclinical stages, and impart views about strategies that are promising to mitigate PD pathology.

Patterns of Neuropsychological Profile and Cortical Thinning in Parkinson's Disease with Punding

BACKGROUND

Punding, one of dopamine replacement treatment related complications, refers to aimless and stereotyped behaviors. To identify possible neural correlates of punding behavior in patients with Parkinson's disease (PD), we investigated the patterns of cognitive profiles and cortical thinning.

METHODS

Of the 186 subjects with PD screened during the study period, we prospectively enrolled 10 PD patients with punding and 43 without punding on the basis of a structured interview. We performed comprehensive neuropsychological tests and voxel-based and regions-of-interest (ROIs)-based cortical thickness analysis between PD patients with and without punding.

RESULTS

The prevalence of punding in patients with PD was 5.4%. Punding behaviors were closely related to previous occupations or hobbies and showed a temporal relationship to changes of levodopa-equivalent dose (LED). Significant predisposing factors were a long duration of PD and intake of medications of PD, high total daily LED, dyskinesia, and impulse control disorder. Punding severity was correlated with LED (p = 0.029). The neurocognitive assessment revealed that PD patients with punding showed more severe cognitive deficits in the color Stroop task than did those without punding (p = 0.022). Voxel-based analysis showed that PD-punders had significant cortical thinning in the dorsolateral prefrontal area relative to controls. Additionally, ROI-based analysis revealed that cortical thinning in PD-punders relative to PD-nonpunders was localized in the prefrontal cortices, extending into orbitofrontal area.

CONCLUSIONS

We demonstrated that PD patients with punding performed poorly on cognitive tasks in frontal executive functions and showed severe cortical thinning in the dorsolateral prefrontal and orbitofrontal areas. These findings suggest that prefrontal modulation may be an essential component in the development of punding behavior in patients with PD.

The effect of deep brain stimulation on motor and cognitive symptoms of Parkinson's disease: A literature review

Deep brain stimulator (DBS) implant surgery is considered a breakthrough in the treatment of Parkinson's disease, especially in cases where motor symptoms cannot be controlled through conventional drug treatment. Its benefits have been studied extensively in the literature, particularly in relation to motor symptoms. However, the disease's cognitive aspects have been studied to a lesser extent.

Electrical engram: how deep brain stimulation affects memory

Deep brain stimulation (DBS) is a surgical procedure involving implantation of a pacemaker that sends electric impulses to specific brain regions. DBS has been applied in patients with Parkinson's disease, depression, and obsessive-compulsive disorder (among others), and more recently in patients with Alzheimer's disease to improve memory functions. Current DBS approaches are based on the concept that high-frequency stimulation inhibits or excites specific brain regions. However, because DBS entails the application of repetitive electrical stimuli, it primarily exerts an effect on extracellular field-potential oscillations similar to those recorded with electroencephalography. Here, we suggest a new perspective on how DBS may ameliorate memory dysfunction: it may enhance normal electrophysiological patterns underlying long-term memory processes within the medial temporal lobe.

Enhanced functional connectivity between putamen and supplementary motor area in Parkinson's disease patients

Parkinson's disease (PD) is a surprisingly heterogeneous disorder with symptoms including resting tremor, bradykinesia and rigidity. PD has been associated with abnormal task related brain activation in sensory and motor regions as well as reward related network. Although corticostriatal skeletomotor circuit dysfunction is implicated in the neurobiology of Parkinson's disease, the functional connectivity within this circuit at the resting state is still unclear for PD. Here we utilized resting state functional magnetic resonance imaging to measure the functional connectivity of striatum and motor cortex in 19 patients with PD and 20 healthy controls. We found that the putamen, but not the caudate, exhibited enhanced connectivity with supplementary motor area (SMA), using either the putamen or the SMA as the "seed region". Enhanced SMA-amygdala functional connectivity was also found in the PD group, compared with normal controls. Our findings highlight the key role of hyper-connected putamen-SMC circuit in the pathophysiology of PD.

Drug-induced dyskinesia in Parkinson's disease. Should success in clinical management be a function of improvement of motor repertoire rather than amplitude of dyskinesia?

BACKGROUND

Dyskinesia, a major complication in the treatment of Parkinson's disease (PD), can require prolonged monitoring and complex medical management.

DISCUSSION

The current paper proposes a new way to view the management of dyskinesia in an integrated fashion. We suggest that dyskinesia be considered as a factor in a signal-to-noise ratio (SNR) equation where the signal is the voluntary movement and the noise is PD symptomatology, including dyskinesia. The goal of clinicians should be to ensure a high SNR in order to maintain or enhance the motor repertoire of patients. To understand why such an approach would be beneficial, we first review mechanisms of dyskinesia, as well as their impact on the quality of life of patients and on the health-care system. Theoretical and practical bases for the SNR approach are then discussed.

SUMMARY

Clinicians should not only consider the level of motor symptomatology when assessing the efficacy of their treatment strategy, but also breadth of the motor repertoire available to patients.

Selecting deep brain stimulation or infusion therapies in advanced Parkinson's disease: an evidence-based review

Motor complications in Parkinson's disease (PD) result from the short half-life and irregular plasma fluctuations of oral levodopa. When strategies of providing more continuous dopaminergic stimulation by adjusting oral medication fail, patients may be candidates for one of three device-aided therapies: deep brain stimulation (DBS), continuous subcutaneous apomorphine infusion, or continuous duodenal/jejunal levodopa/carbidopa pump infusion (DLI). These therapies differ in their invasiveness, side-effect profile, and the need for nursing care. So far, very few comparative studies have evaluated the efficacy of the three device-aided therapies for specific motor problems in advanced PD. As a result, neurologists currently lack guidance as to which therapy could be most appropriate for a particular PD patient. A group of experts knowledgeable in all three therapies reviewed the currently available literature for each treatment and identified variables of clinical relevance for choosing one of the three options such as type of motor problems, age, and cognitive and psychiatric status. For each scenario, pragmatic and (if available) evidence-based recommendations are provided as to which patients could be candidates for either DBS, DLI, or subcutaneous apomorphine.

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.

Parkinson's disease therapeutics: new developments and challenges since the introduction of levodopa

The demonstration that dopamine loss is the key pathological feature of Parkinson's disease (PD), and the subsequent introduction of levodopa have revolutionalized the field of PD therapeutics. This review will discuss the significant progress that has been made in the development of new pharmacological and surgical tools to treat PD motor symptoms since this major breakthrough in the 1960s. However, we will also highlight some of the challenges the field of PD therapeutics has been struggling with during the past decades. The lack of neuroprotective therapies and the limited treatment strategies for the nonmotor symptoms of the disease (ie, cognitive impairments, autonomic dysfunctions, psychiatric disorders, etc.) are among the most pressing issues to be addressed in the years to come. It appears that the combination of early PD nonmotor symptoms with imaging of the nigrostriatal dopaminergic system offers a promising path toward the identification of PD biomarkers, which, once characterized, will set the stage for efficient use of neuroprotective agents that could slow down and alter the course of the disease.

BILATERAL EFFECTS OF UNILATERAL SUBTHALAMIC DEEP BRAIN STIMULATION ON PARKINSON's DISEASE AT 1 YEAR

OBJECTIVE

To quantify the benefit of unilateral subthalamic nucleus (STN) deep brain stimulation (DBS) on contralateral, ipsilateral, and axial symptoms of advanced Parkinson's disease.

METHODS

Thirty-seven patients received unilateral STN DBS and were rated on the Unified Parkinson's Disease Rating Scale (UPDRS) and timed tests of motor function in the “practically defined off” state at baseline and at 3, 6, and 12 months postoperatively.

RESULTS

UPDRS motor scores improved significantly at 3, 6, and 12 months relative to the preoperative baseline (P &lt; 0.001, 37.1% at 1 year). There was improvement in the contralateral UPDRS subscores (P &lt; 0.001, 54.6% at 1 year), and although contralateral benefit was larger on all outcome measures, ipsilateral benefit was present at 3 and 6 months on the UPDRS subscore (P = 0.013 and 23.5%, P = 0.005 and 27.7%, respectively). A trend toward ipsilateral benefit was present on the UPDRS subscore at 12 months; however, the effect was not statistically significant. Two timed tests of motor function in the upper extremities showed significant ipsilateral benefit in bradykinesia at 12 months (P &lt; 0.001 and P = 0.014, respectively). Significant benefit was also observed in the UPDRS part 2 “off” medications and the UPDRS part 4 after unilateral STN DBS at 12 months (both P &lt; 0.001).

CONCLUSION

Considering the bilateral effects and tolerability of unilateral STN DBS, unilateral stimulation followed by a contralateral procedure later, if necessary, is a reasonable option for patients with advanced Parkinson's disease, especially with prominent asymmetry.

GDNF therapy for Parkinson's disease

With an increase in the aging population, the incidence of Parkinson's disease (PD), a disabling neurodegenerative disorder mainly affecting motor function, will inevitably present a challenge to an already overburdened healthcare system. Current medical and surgical therapies offer symptomatic relief but do not provide a cure. Experimental studies suggest that GDNF has the ability to protect degenerating dopamine neurons in PD as well as promote regeneration of the nigrostriatal dopamine system. However, clinical trials of GDNF infusion to date remain inconclusive. This review will examine the experimental and clinical evidence of GDNF use in PD with particular focus on its potential as an effective therapy in the treatment of PD.

Five-year follow-up of unilateral posteroventral pallidotomy in Parkinson's disease

BACKGROUND

Neurocognitive outcome research of individuals with Parkinson's disease after unilateral pallidotomy is inconsistent. Although some studies reported few cognitive changes, other investigations have more consistently shown both transient and long-term cognitive decline postoperatively.

METHODS

We report the long-term motor and neurocognitive outcome 5 years post surgery for 18 patients with Parkinson's disease (12 men and 6 woman; all right-handed) who underwent right or left unilateral posteroventral pallidotomy.

RESULTS

Pallidotomy patients revealed long-term motor benefits from the surgery in their "off" state and control of dopa-induced dyskinesias in their "on" state, which is consistent with previous research. We found mild declines in oral and visuomotor information processing speed, verbal recognition memory, and mental status 5 years after surgery, which differs from previous literature regarding the long-term neurocognitive outcome after pallidotomy. Differences between the right and left pallidotomy patients for both motor and cognitive skills were not found.

CONCLUSION

Although deep brain stimulation is presently the treatment of choice, pallidotomy continues to be performed around the world. Consequently, although unilateral pallidotomy should be considered a treatment option for patients with Parkinson's disease who suffer from severe unilateral disabling motor symptoms or dyskinesias, the long-term neurocognitive outcome should also be considered in treatment decisions.

[Letter fluency: psychometric properties and Dutch normative data]

Normative data were collected for a Dutch version of the Controlled Oral Word Association Test (COWAT) in 200 healthy subjects between 17 and 89 years of age. The COWAT is a letterfluency task that is widely used in clinical neuropsychology. Fluency is an important aspect of executive functioning. The psychometric properties of the Dutch version of the test were largely comparable to those of the original COWAT. Its reliability is 0.80, and its scores are significantly related to level of education and/or vocabulary, but not to age or gender. A regression formula is provided by which the raw scores can be corrected for level of education.

Lexical-semantic inhibitory mechanisms in Parkinson's disease as a function of subthalamic stimulation

Inhibitory control may be affected by Parkinson's disease (PD) due to impairment within the non-motor basal ganglia-thalamocortical circuits. The present study aimed to identify the effects of chronic stimulation of the subthalamic nucleus (STN) on lexical-semantic inhibitory control. Eighteen participants with PD who had undergone surgery for deep brain stimulation (DBS) of the STN, completed a picture-word interference (PWI) task and the Hayling test in on and off stimulation conditions. The results of PD participants were compared with 21 non-neurologically impaired control participants. PD participants performed no differently from controls on the PWI task, and no significant differences between on and off stimulation conditions were revealed, therefore suggesting that PD participants are not impaired in lexical-semantic interference control. In contrast, in the off stimulation condition, PD participants had significantly delayed reaction times and increased errors on the inhibition section of the Hayling test compared with the STN stimulation condition and control participants. These results suggest that PD patients are impaired in aspects of inhibitory control that are dependent on behavioural inhibition (such as the suppression of prepotent responses) and selection from competing alternatives without the presence of external cues. Furthermore, STN stimulation acts to restore these behavioural inhibitory processes.

Surgical considerations in movement disorders: deep brain stimulation, ablation and transplantation

Surgical therapy for movement disorders has been practiced since the early 20th century, mostly for Parkinson's disease. At its onset, large destructive procedures like open resection of cortex, parts of the basal ganglia or its fibre connections produced variable, ill-documented results. With the introduction of the stereotactic operating technique in the second half of the century, ablative surgery became more refined, and more selective interventions became possible to alleviate the suffering of those patients for whom no other treatment modalities were yet available. However, the introduction of levodopa-based pharmacological therapy pushed surgical therapy almost completely to the background. In the past two decades, there has been a resurgence of interest in surgery for movement disorders, due to both limitations of long-term pharmacological therapy and the advent of the treatment modality of deep brain stimulation. The subject has now grown into a large field of clinical and scientific interest. Parkinson's disease is the most widespread surgical indication, but in other movement disorders considerable improvement can be achieved by surgery as well, most notably in dystonia. A short review of the surgical therapy for these disorders is presented.

Cognitive sequelae of subthalamic nucleus deep brain stimulation in Parkinson's disease: a meta-analysis

BACKGROUND

Deep brain stimulation of the subthalamic nucleus (STN DBS) is an increasingly common treatment for Parkinson's disease. Qualitative reviews have concluded that diminished verbal fluency is common after STN DBS, but that changes in global cognitive abilities, attention, executive functions, and memory are only inconsistently observed and, when present, often nominal or transient. We did a quantitative meta-analysis to improve understanding of the variability and clinical significance of cognitive dysfunction after STN DBS.

METHODS

We searched MedLine, PsycLIT, and ISI Web of Science electronic databases for articles published between 1990 and 2006, and extracted information about number of patients, exclusion criteria, confirmation of target by microelectrode recording, verification of electrode placement via radiographic means, stimulation parameters, assessment time points, assessment measures, whether patients were on levodopa or dopaminomimetics, and summary statistics needed for computation of effect sizes. We used the random-effects meta-analytical model to assess continuous outcomes before and after STN DBS.

FINDINGS

Of 40 neuropsychological studies identified, 28 cohort studies (including 612 patients) were eligible for inclusion in the meta-analysis. After adjusting for heterogeneity of variance in study effect sizes, the random effects meta-analysis revealed significant, albeit small, declines in executive functions and verbal learning and memory. Moderate declines were only reported in semantic (Cohen's d 0.73) and phonemic verbal fluency (0.51). Changes in verbal fluency were not related to patient age, disease duration, stimulation parameters, or change in dopaminomimetic dose after surgery.

INTERPRETATION

STN DBS, in selected patients, seems relatively safe from a cognitive standpoint. However, difficulty in identification of factors underlying changes in verbal fluency draws attention to the need for uniform and detailed reporting of patient selection, demographic, disease, treatment, surgical, stimulation, and clinical outcome parameters.