Cognitive declines one year after unilateral deep brain stimulation surgery in Parkinson's disease: a controlled study using reliable change

Differential Cognitive Effects of Unilateral Subthalamic Nucleus Deep Brain Stimulation for Parkinson's Disease

OBJECTIVE

The aim of this study was to investigate the cognitive effects of unilateral directional versus ring subthalamic nucleus deep brain stimulation (STN DBS) in patients with advanced Parkinson's disease.

METHODS

We examined 31 participants who underwent unilateral STN DBS (left n = 17; right n = 14) as part of an National Institutes of Health (NIH)-sponsored randomized, double-blind, crossover study contrasting directional versus ring stimulation. All participants received unilateral DBS implants in the hemisphere more severely affected by motor parkinsonism. Measures of cognition included verbal fluency, auditory-verbal memory, and response inhibition. We used mixed linear models to contrast the effects of directional versus ring stimulation and implant hemisphere on longitudinal cognitive function.

RESULTS

Crossover analyses showed no evidence for group-level changes in cognitive performance related to directional versus ring stimulation. Implant hemisphere, however, impacted cognition in several ways. Left STN participants had lower baseline verbal fluency than patients with right implants (t [20.66 = -2.50, p = 0.02]). Verbal fluency declined after left (p = 0.013) but increased after right STN DBS (p < 0.001), and response inhibition was faster following right STN DBS (p = 0.031). Regardless of hemisphere, delayed recall declined modestly over time versus baseline (p = 0.001), and immediate recall was unchanged.

INTERPRETATION

Directional versus ring STN DBS did not differentially affect cognition. Similar to prior bilateral DBS studies, unilateral left stimulation worsened verbal fluency performance. In contrast, unilateral right STN surgery increased performance on verbal fluency and response inhibition tasks. Our findings raise the hypothesis that unilateral right STN DBS in selected patients with predominant right brain motor parkinsonism could mitigate declines in verbal fluency associated with the bilateral intervention. ANN NEUROL 2024;95:1205-1219.

Can the Montreal Cognitive Assessment and Mini-Mental State Examination detect cognitive decline in elderly patients with essential tremor?

Objective Given the association between essential tremor (ET) and higher rates of cognitive decline, assessing this decline is an important element of research and clinical care. The Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA) are two broad, brief measures that are widely used to monitor cognitive impairment in various neurological disorders. We sought to determine the relative ability of the MoCA and the MMSE to detect cognitive decline in elderly patients with ET. Methods We administered a neuropsychological battery to an ET cohort every 18 months over 4.5 years. We defined the gold standard for change in cognition as the change in neuropsychological test scores over consecutive evaluations and applied the Reliable Change Method to detect meaningful increases/decreases in test scores. We performed receiver operating characteristics (ROC) analysis to quantify the area under the curve (AUC) and compare the ability of the MoCA and the MMSE to detect cognitive decline. Results The AUCs for the MoCA and the MMSE did not differ significantly at any interval or when all intervals were pooled for analysis. Across all intervals, the ability of the MoCA and the MMSE to detect cognitive decline was consistently fair or poor. Conclusions We found that the ability of the MoCA and the MMSE to detect cognitive decline in ET patients over 18-month intervals is inadequate. Unchanged scores on the MoCA and the MMSE in ET over time should be approached with caution. We propose that these screening tools should be supplemented with additional neuropsychological tests.

Differential cognitive effects of unilateral left and right subthalamic nucleus deep brain stimulation for Parkinson disease

Objective

To investigate hemispheric effects of directional versus ring subthalamic nucleus (STN) deep brain stimulation (DBS) surgery on cognitive function in patients with advanced Parkinson's disease (PD).

Methods

We examined 31 PD patients (Left STN n = 17; Right STN n = 14) who underwent unilateral subthalamic nucleus (STN) DBS as part of a NIH-sponsored randomized, cross-over, double-blind (ring vs directional) clinical trial. Outcome measures were tests of verbal fluency, auditory-verbal memory, and response inhibition. First, all participants were pooled together to study the effects of directional versus ring stimulation. Then, we stratified the groups by surgery hemisphere and studied the longitudinal changes in cognition post-unilateral STN DBS.

Results

Relative to pre-DBS cognitive baseline performances, there were no group changes in cognition following unilateral DBS for either directional or ring stimulation. However, assessment of unilateral DBS by hemisphere revealed a different pattern. The left STN DBS group had lower verbal fluency than the right STN group (t(20.66 = -2.50, p = 0.02). Over a period of eight months post-DBS, verbal fluency declined in the left STN DBS group (p = 0.013) and improved in the right STN DBS group over time (p < .001). Similarly, response inhibition improved following right STN DBS (p = 0.031). Immediate recall did not significantly differ over time, nor was it affected by implant hemisphere, but delayed recall equivalently declined over time for both left and right STN DBS groups (left STN DBS p = 0.001, right STN DBS differ from left STN DBS p = 0.794).

Conclusions

Directional and ring DBS did not differentially or adversely affect cognition over time. Regarding hemisphere effects, verbal fluency decline was observed in those who received left STN DBS, along with the left and right STN DBS declines in delayed memory. The left STN DBS verbal fluency decrement is consistent with prior bilateral DBS research, likely reflecting disruption of the basal-ganglia-thalamocortical network connecting STN and inferior frontal gyrus. Interestingly, we found an improvement in verbal fluency and response inhibition following right STN DBS. It is possible that unilateral STN DBS, particularly in the right hemisphere, may mitigate cognitive decline.

Cognitive Impact of Deep Brain Stimulation in Parkinson’s Disease Patients: A Systematic Review

Introduction

Parkinson’s disease (PD) patients have a significantly higher risk of developing dementia in later disease stages, leading to severe impairments in quality of life and self-functioning. Questions remain on how deep brain stimulation (DBS) affects cognition, and whether we can individualize therapy and reduce the risk for adverse cognitive effects. Our aim in this systematic review is to assess the current knowledge in the field and determine if the findings could influence clinical practice.

Methods

We have conducted a systematic review according to PRISMA guidelines through MEDLINE and Embase databases, with studies being selected for inclusion via a set inclusion and exclusion criteria.

Results

Sixty-seven studies were included in this systematic review according to the selected criteria. This includes 6 meta-analyses, 18 randomized controlled trials, 17 controlled clinical trials, and 26 observational studies with no control arms. The total number of PD patients encompassed in the studies cited in this review is 3677, not including the meta-analyses.

Conclusion

Cognitive function in PD patients can deteriorate, in most cases mildly, but still impactful to the quality of life. The strongest evidence is present for deterioration in verbal fluency, while inconclusive evidence is still present for executive function, memory, attention and processing speed. Global cognition does not appear to be significantly impacted by DBS, especially if cognitive screening is performed prior to the procedure, as lower baseline cognitive function is connected to poor outcomes. Further randomized controlled studies are required to increase the level of evidence, especially in the case of globus pallidus internus DBS, pedunculopontine nucleus DBS, and the ventral intermediate nucleus of thalamus DBS, and more long-term studies are required for all respective targets.

Short and Long-Term Cognitive Effects of Subthalamic Deep Brain Stimulation in Parkinson's Disease and Identification of Relevant Factors

BACKGROUND

Subthalamic nucleus deep brain stimulation (STN-DBS) successfully controls the motor symptoms of Parkinson's disease (PD) but has associated cognitive side-effects.

OBJECTIVE

Establish the short- and long-term cognitive effects of STN-DBS in PD.

METHODS

Both the short-term and long-term effects of STN-DBS on cognition were examined through evaluation of the controlled studies that compared patients with STN-DBS to unoperated PD patients, thus controlling for illness progression. We also reviewed the literature to identify the factors that influence cognitive outcome of STN-DBS in PD.

RESULTS

The meta-analysis of the short-term cognitive effects of STN-DBS revealed moderate effect sizes for semantic and phonemic verbal fluency and small effect sizes for psychomotor speed and language, indicating greater decline in the STN-DBS operated than the unoperated patients in these cognitive domains. The longer-term STN-DBS results from controlled studies indicated rates of cognitive decline/dementia up to 32%; which are no different from the rates from the natural progression of PD. Greater executive dysfunction and poorer memory pre-operatively, older age, higher pre-operative doses of levodopa, and greater axial involvement are some of the factors associated with worse cognition after STN-DBS in PD.

CONCLUSION

This evidence can be used to inform patients and their families about the short-term and long-term risks of cognitive decline following STN-DBS surgery and aid the team in selection of suitable candidates for surgery.

Predictors of multi-domain cognitive decline following DBS for treatment of Parkinson's disease

BACKGROUND

Statistically and clinically significant cognitive declines are observed in a small subset of individuals with Parkinson's Disease (PD) following treatment with Deep Brain Stimulation (DBS).

OBJECTIVES

We examine the association between multi-domain cognitive decline (MCD) and demographic and baseline clinical variables and the incidence of serious adverse events (SAE) arising within a six-month interval following DBS for PD.

METHOD

Study participants with PD who displayed MCD at 6-month follow-up evaluation after DBS (n = 18) were contrasted with individuals with PD from the same study who did not show cognitive decline after DBS (n = 146). Logistic regression analyses were employed to assess relationship between predictors, including age (>70 years old), pre-DBS cognitive screening test performance, SAE, and MCD. MCD+ and MCD-groups were also compared on other baseline clinical and demographic variables.

RESULTS

MCD showed modest association with older age and lower baseline neurocognitive screening performance, whereas the groups did not differ on most other baseline clinical and demographic variables. SAEs during the study interval were the most robust predictor of MCD in the DBS group. A variety of SAEs were documented in study participants experiencing MCD after DBS surgery, including, but not limited to, infections and small intracranial hemorrhages.

CONCLUSIONS

Older age and lower baseline cognition measured prior to treatment are associated with MCD measured at six-months after DBS. SAE occurring following DBS surgery are also predictive of MCD. These predictors may reflect aspects of "frailty" in advanced PD. Risk factors for SAE warrant careful consideration in clinical trials.

Anterior lead location predicts verbal fluency decline following STN-DBS in Parkinson's disease

INTRODUCTION

Verbal fluency (VF) decline is a well-documented cognitive effect of Deep Brain Stimulation of the subthalamic nucleus (STN-DBS) in patients with Parkinson's disease (PD). This decline may be associated with disruption to left-sided frontostriatal circuitry involving the anteroventral non-motor area of the STN. While recent studies have examined the impact of lead location in relation to functional STN subdivisions on VF outcomes, results have been mixed and methods have been limited by atlas-based location mapping.

METHODS

Participants included 59 individuals with PD who underwent bilateral STN-DBS. Each participant's active contact location was determined in an atlas-independent fashion, relative to their individual MR-visualized STN midpoint. Multiple linear regression was used to examine lead location in each direction as a predictor of phonemic and semantic VF decline, controlling for demographic and disease variables.

RESULTS

More anterior lead locations relative to the STN midpoint in the left hemisphere predicted greater phonemic VF decline (B = -2.34, B SE = 1.08, β = -0.29, sr² = 0.08). Lead location was not a significant predictor of semantic VF decline.

CONCLUSION

Using an individualized atlas-independent approach, present findings suggest that more anterior stimulation of the left STN may uniquely contribute to post-DBS VF decline. This is consistent with models in which the anterior STN represents a "non-motor" functional subdivision with connections to frontal regions, e.g., the left dorsal prefrontal cortex. Future studies should investigate the effect of DBS lead trajectory on VF outcomes.

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.

Deep brain stimulation effects on verbal fluency dissociated by target and active contact location

OBJECTIVE

Deep brain stimulation (DBS) improves motor symptoms in Parkinson's disease (PD), but it can also disrupt verbal fluency with significant costs to quality of life. The current study investigated how variability of bilateral active electrode coordinates along the superior/inferior, anterior/posterior, and lateral/medial axes in the subthalamic nucleus (STN) or the globus pallidus interna (GPi) contribute to changes in verbal fluency. We predicted that electrode location in the left hemisphere would be linked to changes in fluency, especially in the STN.

METHODS

Forty PD participants treated with bilateral DBS targeting STN (n = 23) or GPi (n = 17) completed verbal fluency testing in their optimally treated state before and after DBS therapy. Normalized atlas coordinates from left and right active electrode positions along superior/inferior, anterior/posterior, and lateral/medial axes were used to predict changes in fluency postoperatively, separately for patients with STN and GPi targets.

RESULTS

Consistent with prior studies, fluency significantly declined pre- to postsurgery (in both DBS targets). In STN-DBS patients, electrode position along the inferior to superior axis in the left STN was a significant predictor of fluency changes; relatively more superior left active electrode was associated with the largest fluency declines in STN. Electrode coordinates in right STN or GPi (left or right) did not predict fluency changes.

INTERPRETATION

We discuss these findings in light of putative mechanisms and potential clinical impact.

Long-term Parkinson's disease quality of life after staged DBS: STN vs GPi and first vs second lead

Deep brain stimulation (DBS) for Parkinson's disease (PD) improves quality of life (QoL), but longitudinal follow-up data are scarce. We sought to quantify long-term benefits of subthalamic nucleus (STN) vs globus pallidus internus (GPi), and unilateral vs staged bilateral PD-DBS on postoperative QoL. This is a retrospective, longitudinal, non-randomized study using the PD QoL questionnaire (PDQ)-39 in patients with STN- or GPi-DBS, and with unilateral (N = 191) or staged bilateral (an additional contralateral lead implant) surgery (N = 127 and 156 for the first and second lead, respectively). Changes in PDQ-39 summary index (PDQ-39SI) and subscores throughout 60 months of follow-up were used as the primary analysis. We applied mixed models that included levodopa and covariates that differed at baseline across groups. For unilateral implantation, we observed an initial improvement in PDQ-39SI of 15.55 ± 3.29% (µ ± SE) across both brain targets at 4 months postoperatively. Unilateral STN patients demonstrated greater improvement in PDQ-39SI than GPi patients at 4 and 18 months postoperatively. Analysis of patients with staged bilateral leads revealed an initial 25.34 ± 2.74% (µ ± SE) improvement in PDQ-39SI at 4 months after the first lead with further improvement until 18 months, with no difference across targets. Scores did not improve after the second lead with gradual worsening starting at 18 months postoperatively. STN-DBS provided greater short-term QoL improvement than GPi-DBS for unilateral surgery. For staged bilateral DBS, overall QoL improvement was explained primarily by the first lead. Decision-making for patients considering DBS should include a discussion surrounding the potential risks and benefits from a second DBS lead.

Depression, quality of life, activities of daily living, and subjective memory after deep brain stimulation in Parkinson disease-A reliable change index analysis

OBJECTIVES

In the field of Parkinson disease (PD) research, many studies have shown that deep brain stimulation (DBS) can soften side effects, which arise during long-term medical therapy. This study focuses on the changes in depressive symptoms, quality of life (with the subdivisions physical and mental health), activities of daily living, and subjective memory functioning in PD patients testing the baseline and the outcome 1 year after DBS.

METHODS

For the first time, the reliable change index (RCI) methodology was applied to compare PD-DBS patients (n = 22) with best medically treated PD patients (PD-BMT; n = 28), subjects with mild cognitive impairment (MCI, n = 43) and healthy controls (n = 25) in the above-mentioned domains. The used questionnaires included the revised Beck Depression Inventory (BDI-II), the Short Form (36) Health Survey (SF-36), the Bayer Activities of Daily Living Scale (B-ADL), and the Forgetfulness Assessment Inventory (FAI).

RESULTS

The reliable change indices show high constant or improved results of the PD-DBS patients in the domains subjective memory (85.7%-100.0%), activities of daily living (60.0%-90.0%), physical health summary (77.8%), depressive symptoms (61.9%), and mental health summary (50.0%) in comparison with the PD-BMT, MCI, and control group.

CONCLUSIONS

DBS is an established alternative to best medical treatment of PD. The comparisons between the PD-DBS and PD-BMT groups do suggest that the domains mental health, depressive symptoms, and physical health benefit most, while the domains activities of daily living and subjective memory functioning are rather constant. Nevertheless, further research is needed to identify mechanisms and predictors that lead to improvement in individual cases.

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.

Longitudinal neuropsychological outcomes in treatment-resistant depression following bed nucleus of the stria terminalis-area deep brain stimulation: a case review

Studies have demonstrated the effectiveness of deep brain stimulation (DBS) as a treatment modality for psychiatric conditions. We present a case reviewing the longitudinal neuropsychological performance outcomes following bed nucleus of the stria terminalis-area (BNST) DBS in a patient with treatment-resistant depression (TRD). The cognitive safety of DBS is well documented for various targets, however cognitive outcomes of BNST-area DBS have not been extensively reported for patients with TRD. Neuropsychological assessment was conducted pre- and post-DBS. Twelve months following DBS, augmented general cognitive performance was observed with significant changes in specific domains.

Individual cognitive change after DBS-surgery in Parkinson's disease patients using Reliable Change Index Methodology

Long-term therapy of Parkinson's disease (PD) with levodopa (L-DOPA) is associated with a high risk of developing motor fluctuations and dyskinesia. Deep brain stimulation (DBS) in PD patients of the subthalamic nucleus can improve these motor complications. Although the positive effect on motor symptoms has been proven, postoperative cognitive decline has been documented. To tackle the impact of PD-DBS on cognition, 18 DBS patients were compared to 25 best medically treated Parkinson's patients, 24 Mild Cognitive Impairment (MCI) patients and 12 healthy controls using the Neuropsychological Test Battery Vienna-long (NTBV-long) for cognitive outcome 12 months after first examination. Reliable change index methodology was used. Overall, there was cognitive change in individual patients, but the change was very heterogeneous with gains and losses. Further research is needed to identify the mechanisms that lead to improvement or deterioration of cognitive functions in individual cases.

Working Memory Deficits After Lesions Involving the Supplementary Motor Area

The Supplementary Motor Area (SMA)—located in the superior and medial aspects of the superior frontal gyrus—is a preferential site of certain brain tumors and arteriovenous malformations, which often provoke the so-called SMA syndrome. The bulk of the literature studying this syndrome has focused on two of its most apparent symptoms: contralateral motor and speech deficits. Surprisingly, little attention has been given to working memory (WM) even though neuroimaging studies have implicated the SMA in this cognitive process. Given its relevance for higher-order functions, our main goal was to examine whether WM is compromised in SMA lesions. We also asked whether WM deficits might be reducible to processing speed (PS) difficulties. Given the connectivity of the SMA with prefrontal regions related to executive control (EC), as a secondary goal we examined whether SMA lesions also hampered EC. To this end, we tested 12 patients with lesions involving the left (i.e., the dominant) SMA. We also tested 12 healthy controls matched with patients for socio-demographic variables. To ensure that the results of this study can be easily transferred and implemented in clinical practice, we used widely-known clinical neuropsychological tests: WM and PS were measured with their respective Wechsler Adult Intelligence Scale indexes, and EC was tested with phonemic and semantic verbal fluency tasks. Non-parametric statistical methods revealed that patients showed deficits in the executive component of WM: they were able to sustain information temporarily but not to mentally manipulate this information. Such WM deficits were not subject to patients' marginal PS impairment. Patients also showed reduced phonemic fluency, which disappeared after controlling for the influence of WM. This observation suggests that SMA damage does not seem to affect cognitive processes engaged by verbal fluency other than WM. In conclusion, WM impairment needs to be considered as part of the SMA syndrome. These findings represent the first evidence about the cognitive consequences (other than language) of damage to the SMA. Further research is needed to establish a more specific profile of WM impairment in SMA patients and determine the consequences of SMA damage for other cognitive functions.

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.

Measures of impulsivity in Parkinson's disease decrease after DBS in the setting of stable dopamine therapy

INTRODUCTION

Recent evidence suggests deep brain stimulation can alter impulse control. Our objective was to prospectively evaluate the effects of subthalamic nucleus (STN) and globus pallidus internus (GPi) deep brain stimulation on impulse control disorders (ICDs) in the setting of a conservative dopamine reduction strategy.

METHODS

Patients (n = 37) undergoing de novo, unilateral STN or GPi DBS lead implantation were evaluated pre-operatively and 6-12 months post-operatively for the presence of ICDs using the Questionnaire for Impulsivity in Parkinson's disease (QUIP) and by clinical interview.

RESULTS

Of the patients enrolled, 23 underwent electrode implantation in the globus pallidus internus and 14 were implanted in the subthalamic nucleus. Mean time to long term follow-up was 9.7 ± 2.4 months. Post-operative LEDD was not significantly lower than pre-operative LEDD (pre-op: 1238.53 ± 128.47 vs. post-op: 1178.18 ± 126.43, p = 0.2972, paired t-test). Mean QUIP scores were significantly lower at follow up compared to pre-operative baseline (1.51 ± 0.45 vs. 2.51 ± 0.58, p = 0.0447, paired t-test). Patients with ICDs pre-operatively (n = 14, 37.8%) had significant improvement in QUIP scores at follow-up (6.00 ± 0.94 vs. 2.64 ± 0.98, p = 0.0014, paired t-test). Improvement was not uniform across the cohort: 1 patient with ICD at baseline developed worsening symptoms, and 4 patients with no ICD pre-operatively developed clinically significant ICDs post-operatively.

CONCLUSION

When LEDD is relatively unchanged following STN or GPi DBS for PD, ICD symptoms tend toward improvement, although worsening and emergence of new ICDs can occur. In the setting of stable LEDD, these findings suggest that the intrinsic effects of DBS may play a significant role in altering impulsive behavior.

Assessment of individual cognitive changes after deep brain stimulation surgery in Parkinson's disease using the Neuropsychological Test Battery Vienna short version

Long-term therapy of Parkinson’s disease with L‑DOPA is associated with a high risk of developing motor fluctuations and dyskinesia. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) can improve these motor complications. Although the positive effect on motor symptoms has been proven, postoperative cognitive decline has been documented. To tackle the impact of DBS on cognition, 18 DBS patients were compared to 25 best medically treated Parkinson’s patients, 24 patients with mild cognitive impairment (MCI) and 12 healthy controls using the Neuropsychological Test Battery Vienna short version (NTBV-short) for cognitive outcome 12 months after the first examination. Reliable change index methodology was used. Roughly 10% of DBS patients showed cognitive decline mainly affecting the domains attention and executive functioning (phonemic fluency). Further research is needed to identify the mechanisms that lead to improvement or deterioration of cognitive functions in individual cases.

Worsening of Verbal Fluency After Deep Brain Stimulation in Parkinson's Disease: A Focused Review

Worsening of verbal fluency after treatment with deep brain stimulation in Parkinson's disease patients is one of the most often reported cognitive adverse effect. The underlying mechanisms of this decline are not well understood. The present focused review assesses the evidence for the reliability of the often-reported decline of verbal fluency, as well as the evidence for the suggested mechanisms including disease progression, reduced medication levels, electrode positions, and stimulation effect vs. surgical effects. Finally, we highlight the need for more systematic investigations of the large degree of heterogeneity in the prevalence of verbal fluency worsening after DBS, as well as provide suggestions for future research.

Deep brain stimulation of the subthalamic nucleus alters frontal activity during spatial working memory maintenance of patients with Parkinson's disease

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves the motor symptoms of Parkinson's disease (PD). The STN may represent an important relay station not only in the motor but also the associative cortico-striato-thalamocortical pathway. Therefore, STN stimulation may alter cognitive functions, such as working memory (WM). We examined cortical effects of STN-DBS on WM in early PD patients using functional near-infrared spectroscopy. The effects of dopaminergic medication on WM were also examined. Lateral frontal activity during WM maintenance was greater when patients were taking dopaminergic medication. STN-DBS led to a trend-level worsening of WM performance, accompanied by increased lateral frontal activity during WM maintenance. These findings suggest that STN-DBS in PD might lead to functional modifications of the basal ganglia-thalamocortical pathway during WM maintenance.

Verbal Fluency in Parkinson's Patients with and without Bilateral Deep Brain Stimulation of the Subthalamic Nucleus: A Meta-analysis

OBJECTIVES

Patients with Parkinson's disease often experience significant decline in verbal fluency over time; however, deep brain stimulation of the subthalamic nucleus (STN-DBS) is also associated with post-surgical declines in verbal fluency. The purpose of this study was to determine if Parkinson's patients who have undergone bilateral STN-DBS have greater impairment in verbal fluency compared to Parkinson's patients treated by medication only.

METHODS

A literature search yielded over 140 articles and 10 articles met inclusion criteria. A total of 439 patients with Parkinson's disease who underwent bilateral STN-DBS and 392 non-surgical patients were included. Cohen's d, a measure of effect size, was calculated using a random effects model to compare post-treatment verbal fluency in patients with Parkinson's disease who underwent STN-DBS versus those in the non-surgical comparison group.

RESULTS

The random effects model demonstrated a medium effect size for letter fluency (d=-0.47) and a small effect size for category fluency (d=-0.31), indicating individuals with bilateral STN-DBS had significantly worse verbal fluency performance than the non-surgical comparison group.

CONCLUSIONS

Individuals with Parkinson's disease who have undergone bilateral STN-DBS experience greater deficits in letter and category verbal fluency compared to a non-surgical group.

Deep Brain Stimulation Target Selection for Parkinson’s Disease

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

Neuropsychological changes following deep brain stimulation surgery for Parkinson's disease: comparisons of treatment at pallidal and subthalamic targets versus best medical therapy

BACKGROUND

Deep brain stimulation (DBS) improves motor symptoms in Parkinson's disease (PD), but questions remain regarding neuropsychological decrements sometimes associated with this treatment, including rates of statistically and clinically meaningful change, and whether there are differences in outcome related to surgical target.

METHODS

Neuropsychological functioning was assessed in patients with Parkinson's disease (PD) at baseline and after 6 months in a prospective, randomised, controlled study comparing best medical therapy (BMT, n=116) and bilateral deep brain stimulation (DBS, n=164) at either the subthalamic nucleus (STN, n=84) or globus pallidus interna (GPi, n=80), using standardised neuropsychological tests. Measures of functional outcomes were also administered.

RESULTS

Comparison of the two DBS targets revealed few significant group differences. STN DBS was associated with greater mean reductions on some measures of processing speed, only one of which was statistically significant in comparison with stimulation of GPi. GPi DBS was associated with lower mean performance on one measure of learning and memory that requires mental control and cognitive flexibility. Compared to the group receiving BMT, the combined DBS group had significantly greater mean reductions at 6-month follow-up in performance on multiple measures of processing speed and working memory. After calculating thresholds for statistically reliable change from data obtained from the BMT group, the combined DBS group also displayed higher rates of decline in neuropsychological test performance. Among study completers, 18 (11%) study participants receiving DBS displayed reliable decline by multiple indicators in two or more cognitive domains, a significantly higher rate than in the BMT group (3%). This multi-domain cognitive decline was associated with less beneficial change in subjective ratings of everyday functioning and quality of life (QOL). The multi-domain cognitive decline group continued to function at a lower level at 24-month follow-up.

CONCLUSIONS

In those with PD, the likelihood of significant decline in neuropsychological functioning increases with DBS, affecting a small minority of patients who also appear to respond less optimally to DBS by other indicators of QOL.

TRIAL REGISTRATION NUMBER

NCT00056563 and NCT01076452.

Apathy in Parkinson's disease: clinical features, neural substrates, diagnosis, and treatment

Normal maintenance of human motivation depends on the integrity of subcortical structures that link the prefrontal cortex with the limbic system. Structural and functional disruption of different networks within these circuits alters the maintenance of spontaneous mental activity and the capacity of affected individuals to associate emotions with complex stimuli. The clinical manifestations of these changes include a continuum of abnormalities in goal-oriented behaviours known as apathy. Apathy is highly prevalent in Parkinson's disease (and across many neurodegenerative disorders) and can severely affect the quality of life of both patients and caregivers. Differentiation of apathy from depression, and discrimination of its cognitive, emotional, and auto-activation components could guide an individualised approach to the treatment of symptoms. The opportunity to manipulate dopaminergic treatment in Parkinson's disease allows researchers to study a continuous range of motivational states, from apathy to impulse control disorders. Parkinson's disease can thus be viewed as a model that provides insight into the neural substrates of apathy.

Swallowing outcomes following unilateral STN vs. GPi surgery: a retrospective analysis

The adverse effects of deep brain stimulation (DBS) surgery on swallowing could potentially exacerbate the natural deterioration of airway protection associated with Parkinson's disease (PD) degeneration and increase the incidence of aspiration pneumonia and associated death. There are no studies that compare swallowing outcomes associated with subthalamic nucleus (STN) versus globus pallidus interna (GPi) DBS surgery; therefore, we completed a retrospective study comparing swallowing outcomes in a cohort of patients with PD who underwent unilateral DBS surgery in either the STN or GPi. A chart review was completed to identify all patients with a diagnosis of PD who received videofluoroscopic swallowing evaluations before DBS and after unilateral DBS in the STN or GPi. The retrospective search yielded 33 patients (STN = 14, GPi = 19) with idiopathic PD who met the inclusion criteria. Mean penetration-aspiration (PA) scores did not change significantly for participants who underwent GPi surgery (z = -.181, p = .857), but mean PA scores significantly worsened for participants who underwent STN DBS (z = -2.682, p = .007). There was a significant improvement in Unified PD Rating Scale (UPDRS) scores off medication before surgery, to off medication and on stimulation after surgery for both groups (F = 23.667, p < .001). Despite the limitations of a retrospective analysis, this preliminary study suggests that unilateral STN DBS may have an adverse effect on swallowing function, while unilateral GPi DBS does not appear to have a similar deleterious effect. This study and other future studies should help to elucidate the mechanisms underpinning the effects of DBS on swallowing function.

Influence of deep brain stimulation of the subthalamic nucleus on cognitive function in patients with Parkinson's disease

Deep brain stimulation (DBS) is an effective technique for treating Parkinson's disease (PD) in the middle and advanced stages. The subthalamic nucleus (STN) is the most common target for clinical treatment using DBS. While STN-DBS can significantly improve motor symptoms in PD patients, adverse cognitive effects have also been reported. The specific effects of STN-DBS on cognitive function and the related mechanisms remain unclear. Thus, it is imperative to identify the influence of STN-DBS on cognition and investigate the potential mechanisms to provide a clearer view of the various cognitive sequelae in PD patients. For this review, a literature search was performed using the following inclusion criteria: (1) at least 10 patients followed for a mean of at least 6 months after surgery since the year 2006; (2) pre- and postoperative cognitive data using at least one standardized neuropsychological scale; and (3) adequate reporting of study results using means and standard deviations. Of ∼170 clinical studies identified, 25 cohort studies (including 15 self-controlled studies, nine intergroup controlled studies, and one multi-center, randomized control experiment) and one meta-analysis were eligible for inclusion. The results suggest that the precise mechanism of the changes in cognitive function after STN-DBS remains obscure, but STN-DBS certainly has effects on cognition. In particular, a progressive decrease in verbal fluency after STN-DBS is consistently reported and although executive function is unchanged in the intermediate stage postoperatively, it tends to decline in the early and later stages. However, these changes do not affect the improvements in quality of life. STN-DBS seems to be safe with respect to cognitive effects in carefully-selected patients during a follow-up period from 6 months to 9 years.

Neuropsychological effects of deep brain stimulation for Parkinson's disease

BACKGROUND

Putative changes of cognition after deep brain stimulation (DBS) in patients with Parkinson's disease (PD) are a matter of debate. The aim of this study was to assess cognitive abilities before and following bilateral subthalamic nucleus (STN) DBS and to review the available literature.

METHODS

Twenty patients underwent bilateral DBS of the STN. Cognitive skills were assessed in a standardized fashion before and at least at 12 months after the surgical intervention.

RESULTS

There was a significant decline of both semantic and phonematic verbal fluency and a mild trend for a deterioration of verbal memory after DBS. Mood, general cognitive screening, and visospatial abilities remained unchanged.

CONCLUSION

STN DBS in the treatment of PD has resulted in a significant reduction of motor symptoms and improved independence and quality of life in appropriately selected patients. However, it may have isolatable effects on verbal fluency and related function. Case series in the literature reported similar findings. Potential candidates for DBS should be counseled about the risk of mild cognitive declines.

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.

Stimulation region within the globus pallidus does not affect verbal fluency performance

BACKGROUND

Subthalamic (STN) and globus pallidus (GP) deep brain stimulation (DBS) have been previously shown to be efficacious in the treatment of selected Parkinson patients with medication resistant motor fluctuations and/or tremor. Deep brain stimulation of the STN has been implicated with more cognitive and mood side effects as compared to GP DBS; however, more studies are needed to better understand possible target differences. Previously, Mikos et al. [1] reported worsening of verbal fluency depending on the stimulation location within the STN region.

OBJECTIVE/HYPOTHESIS

The current study applied the methods used by Mikos et al. (2011) to a different sample of Parkinson patients who underwent GP DBS. Based on differences in the size and functional somatotopy between structures (GP 412 mm(3) vs. STN 167 mm(3)), we hypothesized that there would be a less robust relationship between volume of tissue activated, fluency performance, and stimulation contact within the GP compared to what was reported in the STN.

METHODS

Patient-specific DBS models were created and the volume of tissue activated within the GP was calculated. These data were correlated with patients' verbal fluency performance at dorsal, optimal, and ventral stimulation contacts.

RESULTS

In contrast to STN findings, there was no significant relationship between stimulation location and fluency performance in patients who received GP DBS.

CONCLUSION(S)

These results suggest that fluency may be less sensitive to stimulation location in the globus pallidus and thus there may be more flexibility in terms of DBS programming with GP DBS patients.

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.

Evidence-based indicators of neuropsychological change in the individual patient: relevant concepts and methods

Repeated assessments are a relatively common occurrence in clinical neuropsychology. The current paper will review some of the relevant concepts (e.g., reliability, practice effects, alternate forms) and methods (e.g., reliable change index, standardized based regression) that are used in repeated neuropsychological evaluations. The focus will be on the understanding and application of these concepts and methods in the evaluation of the individual patient through examples. Finally, some future directions for assessing change will be described.

Assessing reliable change using the repeatable battery for the assessment of neuropsychological status (RBANS) for patients with Parkinson's Disease undergoing deep brain stimulation (DBS) surgery

Parkinson's disease (PD) is progressive neurological disease characterized by resting tremor, rigidity, akinesia, postural instability and cognitive changes. The symptoms of PD are debilitating and often become unsatisfactorily treated by medication. Deep brain stimulation (DBS) is an effective treatment to significantly reduce the cardinal motor symptoms of PD. However, the neuropsychological effects of this treatment are less clear. This study examined pre- to post-DBS scores on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) using Reliable Change Indices (RCIs) derived from 20 patients with PD who were medically managed, and then compared to 20 patients with PD treated with DBS and medication. When using group statistical analyses and false discovery rate correction, no significant differences between or within groups were evident at baseline or at follow-up. However, when using the RCIs more patients in the DBS group exhibited reliable change in RBANS scores than did the Med Tx group. Although preliminary, these RCIs provide clinicians and researchers a foundational tool for assessing the effects of interventions (e.g., DBS) independent of the effects of PD and measurement error when using the RBANS.

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.

Prospect of cell therapy for Parkinson's disease

The hallmark of Parkinson's disease is on-going degeneration of dopaminergic neurons in the substantia nigra, which may be due to various etiologies. Various approaches to alleviate symptoms are available, such as life-long pharmacological intervention, deep brain stimulation, and transplantation of dopaminergic neuron-containing fetal tissue. However, each of these approaches has a disadvantage. Several studies have shown that various kinds of stem cells, induced pluripotent stem cells, and other cells can differentiate into dopaminergic neurons and may be promising for treating Parkinson's disease in the future. Therefore, this review addresses those cells in terms of their prospects in cell therapy for Parkinson's disease. In addition, the need for safety and efficacy studies, various cell delivery modes and sites, and possible side effects will be discussed.

A gamma band specific role of the subthalamic nucleus in switching during verbal fluency tasks in Parkinson's disease

OBJECTIVE

Decline in verbal fluency is the most consistent and persistent cognitive impairment documented after deep brain stimulation of the subthalamic nucleus in Parkinson's disease. The mechanisms of this deficit are unclear. We aimed to identify and characterise verbal fluency related processing within the subthalamic nucleus through analysis of local field potentials.

METHODS

Local field potentials were recorded from deep brain stimulation electrodes implanted in the subthalamic nuclei of 8 patients (16 sides) with Parkinson's disease, when patients were on medication. Patients performed phonemic and semantic verbal fluency tasks and a control word repetition task to control for the motor output involved in response generation.

RESULTS

Significant increases in local field potential Power (p ≤ 0.05) were seen across a broad gamma frequency band (30-95 Hz) during both verbal fluency tasks, after controlling for motor output. Increases in gamma local field potential Power of +7.5% ± 2.3% (SEM) in the semantic fluency task and +6.9% ± 2.0% in the phonemic fluency task were derived when averaging across all electrode contact pairs. Gamma changes recorded from contacts lying in the left hemisphere (dominant in verbal fluency) correlated with average number of correct responses generated (r=0.81 p=0.015) and measures of 'switching' (r=0.79 p=0.020) particularly strongly in the semantic fluency task.

INTERPRETATION

Frequency specific power changes observed during task performance are consistent with involvement of the subthalamic nucleus in switching during verbal fluency. Antagonism of such task-related activity with high frequency stimulation of this nucleus may explain the impairments reported.

Feasibility and acceptance of a nonpharmacological cognitive remediation intervention for patients with Parkinson disease

Many patients with idiopathic Parkinson disease (PD) experience deficits in executive skills (ES; eg, attentional control, self-monitoring), which are associated with a range of impairing symptoms such as visual hallucinations, decreased motor control, and increased apathy. Pharmacological methods for improving ES in PD have shown to be somewhat unreliable. The goal of this study was to evaluate the feasibility and patient acceptance of a nonpharmacological cognitive remediation program that aimed to improve sustained, selective, alternating, and divided attentional abilities in a sample of 16 nondemented PD patients. Based on ratings of 4 feasibility dimensions (fatigue, effort, progress, enjoyment), patients with PD demonstrated a high degree of acceptance and successfully engaged in the program. As predicted, ratings of progress differed significantly across tasks according to difficulty level and were positively related to posttraining improvement in ES. Fatigue ratings showed negative associations with other indices across task types, suggesting that monitoring fatigue during cognitive remediation is essential. Patients' ratings of enjoyment did not correspond to task difficulty, indicating that tasks could be simultaneously challenging and rewarding. Males reported exerting greater effort during the training than females. It was concluded that the intervention is appropriate for testing in a randomized controlled trial.

Pre- and post- GPi DBS neuropsychological profiles in a case of X-linked dystonia-Parkinsonism

We present the pre to post bilateral globus pallidus interna (GPi) deep brain stimulation neuropsychological profiles of a 69-year-old patient with a 12-year history of X-linked dystonia-Parkinsonism (XDP). Pre-operative cognitive function was impaired in almost all domains and this impaired performance was not dependent on his medications. Following DBS, changes in neuropsychological functioning were examined using Reliable Change Indices and standardized z-score comparisons. Results showed reductions in processing speed in the context of stable performance in language and visuospatial domains. Post-operative improvements occurred on a cognitive screening measure, verbal memory, and a test of problem-solving skills. This is the first report on an individual with XDP who was cognitively impaired, but had good outcome following GPi bilateral stimulation to treat debilitating motor symptoms. The possible mechanisms for his stable cognitive performance include the target of his DBS, reduced medication dosage, and improvement in dystonia that may in turn have reduced patient's pain.

Parkinson’s disease DBS: what, when, who and why? The time has come to tailor DBS targets

Deep brain stimulation (DBS) has recently been proven to be an effective therapy for medication refractory symptoms of Parkinson's disease. As the evidence base continues to evolve, many important issues have surfaced, including: what operation should be performed (brain target[s],unilateral vs bilateral, simultaneous vs staged); when to operate (how early is too early to intervene?), who should be operated on (disease duration, age, symptom profiles and the use of the interdisciplinary screening team); and finally, why to operate (the rationale of surgery vs medication/apomorphine pumps/duodopa pumps/stem cell trials/gene therapy trials). We will address each of these critical issues, as well make the argument that a tailored approach to DBS and DBS targeting will best serve each potential candidate. We will review the multiple peer reviewed studies and we will emphasize the recently available data from randomized DBS studies.We will argue that moving away from a single DBS target (e.g., subthalamic nucleus DBS) and a single approach to DBS methodology (e.g., bilateral simultaneous operations) is a reasonable next step for the Parkinson's disease community. Following careful interdisciplinary DBS screening, a physician-patient discussion has the potential to establish a patient-centered and symptom-specific outcome for each potential DBS candidate. The interdisciplinary DBS team can function together to formulate and to consider an optimal and tailored approach. A tailored approach will allow for the consideration of the complex and numerous variables that may contribute to a positive or negative overall DBS outcome. We will review and provide expert commentary on a potential interdisciplinary approach to selecting unilateral or alternatively bilateral subthalamic nucleus or globus pallidus internus DBS. Our approach is aimed to maximize benefit(s) and minimize risk(s) in order to best tailor therapy for an individual patient.

Cognitive outcome and reliable change indices two years following bilateral subthalamic nucleus deep brain stimulation

Subthalamic nucleus deep brain stimulation (STN-DBS) is currently the treatment of choice for medication-resistant levodopa-related motor complications in patients with Parkinson's disease (PD). While STN-DBS often results in meaningful motor improvements, consensus regarding long-term neuropsychological outcome continues to be debated. We assessed the cognitive outcomes of 19 STN-DBS patients compared to a group of 18 medically-managed PD patients on a comprehensive neuropsychological battery at baseline and two years post-surgery. Patients did not demonstrate changes in global cognitive functioning on screening measures. However, neuropsychological results revealed impairments in nonverbal recall, oral information processing speed, and lexical and semantic fluency in STN-DBS patients compared to PD controls 2 years post-surgery in these preliminary analyses. Additionally, reliable change indices revealed that approximately 50% of STN-DBS patients demonstrated significant declines in nonverbal memory and oral information processing speed compared to 25-30% of PD controls, and 26% of STN-DBS patients declined on lexical fluency compared to 11% of PD patients. Approximately 30% of both groups declined on semantic fluency. The number of STN-DBS patients who converted to dementia 2 years following surgery was not significantly different from the PD participants (32% versus 16%, respectively). Our results suggest that neuropsychological evaluations may identify possible mild cognitive changes following surgery.

Stuck in a rut: rethinking depression and its treatment

The current definition of major depressive disorder (MDD) emerged from efforts to create reliable diagnostic criteria for clinical and research use. However, despite decades of research, the neurobiology of MDD is largely unknown, and treatments are no more effective today than they were 50-70 years ago. Here, we propose that the current conception of depression is misguiding basic and clinical research. Redefinition is necessary and could include a focus on a more narrowly defined set of core symptoms. However, we conclude that depression is better defined as the tendency to enter into, and inability to disengage from, a negative mood state rather than the mood state per se. We also discuss the implications of this revised definition for future clinical and basic research.

Patient-specific analysis of the relationship between the volume of tissue activated during DBS and verbal fluency

Deep brain stimulation (DBS) for the treatment of advanced Parkinson's disease involves implantation of a lead with four small contacts usually within the subthalamic nucleus (STN) or globus pallidus internus (GPi). While generally safe from a cognitive standpoint, STN DBS has been commonly associated with a decrease in the speeded production of words, a skill referred to as verbal fluency. Virtually all studies comparing presurgical to postsurgical verbal fluency performance have detected a decrease with DBS. The decline may be attributable in part to the surgical procedures, yet the relative contributions of stimulation effects are not known. In the present study, we used patient-specific DBS computer models to investigate the effects of stimulation on verbal fluency performance. Specifically, we investigated relationships of the volume and locus of activated STN tissue to verbal fluency outcome. Stimulation of different electrode contacts within the STN did not affect total verbal fluency scores. However, models of activation revealed subtle relationships between the locus and volume of activated tissue and verbal fluency performance. At ventral contacts, more tissue activation inside the STN was associated with decreased letter fluency performance. At optimal contacts, more tissue activation within the STN was associated with improved letter fluency performance. These findings suggest subtle effects of stimulation on verbal fluency performance, consistent with the functional nonmotor subregions/somatotopy of the STN.

Neurosurgical treatment for Gilles de la Tourette syndrome: the Italian perspective

Despite the availability of both pharmacological and behavioral therapies for Gilles de la Tourette Syndrome (GTS), a subgroup of patients suffer intractable disease and require treatment through non-conservative means. Since 1955, various neurosurgical procedures have been considered as a potential resort for this severely affected sub-group; this article reviews the neurosurgical treatment for GTS, with in-depth discussion on deep brain stimulation (DBS). Internationally, 39 cases of GTS undergoing DBS treatment have been published. Yet, despite the small numbers of patients assessed in centers involved and the inconsistency of postoperative assessment between centres, DBS has been considered the most promising neurosurgical procedure. Patients resorting to surgical measures often carry the additional burden of a diverse range of behavioral disturbances found to significantly impair health-related quality of life; comorbid psychopathologies must be considered when postoperatively evaluating the benefits of DBS. The authors acknowledge that out of the 39 documented cases of GTS treated with DBS, 18 cases originate from Italy; thus, it seems both relevant and pertinent to recount and present the lived Italian experience of that subgroup of GTS treated by DBS, for the first time. Recommendations from such experience are presented.

Cognitive declines after unilateral deep brain stimulation surgery in Parkinson's disease: a controlled study using Reliable Change, part II

Deep brain stimulation (DBS) surgery, an effective treatment for medication-refractory Parkinson's disease (PD), may also lead to selective cognitive declines. In this continuation of a report by Zahodne et al. (2009), we compare cognitive performance of 24 PD patients who underwent unilateral implantation of the globus pallidus internal segment (GPi) or subthalamic nucleus (STN) to that of 19 PD controls. We used group statistical comparisons as well as Reliable Change Indexes (RCIs) to examine performance on measures of memory, processing speed, executive function, and visuospatial perception at baseline and 16 months after surgery. Significant between-group differences were noted on a psychomotor processing speed task. However, a significantly higher proportion of DBS patients than controls demonstrated reliable individual decline on a word list recall task (HVLT-R) and on several processing speed tests. Reliable improvements were noted on tests of visuospatial functioning. There was variability in individual outcome on executive functioning tests, with a small proportion of DBS patients demonstrating reliable decline and some demonstrating reliable improvement. Use of Reliable Change highlights the occurrence of individual variability, revealing declines and improvements in a small proportion of unilateral DBS patients that were not evident upon group comparison. These findings must be interpreted in light of group-level differences between the PD control and DBS patients on demographic and disease-related factors.

Greater improvement in quality of life following unilateral deep brain stimulation surgery in the globus pallidus as compared to the subthalamic nucleus

While deep brain stimulation (DBS) surgery is a well-accepted treatment for Parkinson disease (PD) that improves overall quality of life (QoL), its effects across different domains of QoL are unclear. The study reported here directly compared the effects of unilateral DBS in subthalamic nucleus (STN) or globus pallidus (GPi) on QoL in 42 non-demented patients with medication-refractory PD. Patients were enrolled in the COMPARE trial, a randomized clinical trial of cognitive and mood effects of STN versus GPi DBS conducted at the University of Florida Movement Disorders Center. Patients underwent motor, mood, verbal fluency and QoL (Parkinson disease questionnaire: PDQ-39) measures before and 6 months following surgery. Groups experienced motor and mood improvements that did not differ by target. Patients with STN DBS evidenced a slight decrement on letter fluency. On average, all patients endorsed better overall QoL after surgery. However, despite similar motor and mood improvements, GPi patients improved more than STN patients (38 vs. 14%, respectively; P = 0.03). Patients reported better QoL on subscales of mobility, activities of daily living (ADLs), emotional well-being, stigma, cognition and discomfort, but not on those of social support and communication. Improvements on the mobility, ADLs, stigma and social support subscales were greater amongst GPi patients. In regression analyses, only depression changes independently predicted changes in overall QoL as well as emotional well-being and social support changes. Within the STN group only, declining category fluency scores correlated with poorer QoL on the communication subscale. Unilateral DBS in both STN and GPi improved QoL overall and in disparate domains 6 months after surgery. Patients receiving GPi DBS reported greater improvements that cannot be explained by differential mood or motor effects; however, verbal fluency changes may have partially contributed to lesser QoL improvements amongst STN patients.