Deep Brain Stimulation for Freezing of Gait in Parkinson's Disease With Early Motor Complications

Deep brain stimulation of symptom-specific networks in Parkinson's disease

Deep Brain Stimulation can improve tremor, bradykinesia, rigidity, and axial symptoms in patients with Parkinson's disease. Potentially, improving each symptom may require stimulation of different white matter tracts. Here, we study a large cohort of patients (N = 237 from five centers) to identify tracts associated with improvements in each of the four symptom domains. Tremor improvements were associated with stimulation of tracts connected to primary motor cortex and cerebellum. In contrast, axial symptoms are associated with stimulation of tracts connected to the supplementary motor cortex and brainstem. Bradykinesia and rigidity improvements are associated with the stimulation of tracts connected to the supplementary motor and premotor cortices, respectively. We introduce an algorithm that uses these symptom-response tracts to suggest optimal stimulation parameters for DBS based on individual patient's symptom profiles. Application of the algorithm illustrates that our symptom-tract library may bear potential in personalizing stimulation treatment based on the symptoms that are most burdensome in an individual patient.

Structural connectivity of low-frequency subthalamic stimulation for improving stride length in Parkinson's disease

BACKGROUND

A reduction in stride length is considered a key characteristic of gait kinematics in Parkinson's disease (PD) and has been identified as a predictor of falls. Although low-frequency stimulation (LFS) has been suggested as a method to improve gait characteristics, the underlying structural network is not well understood.

OBJECTIVE

This study aims to investigate the structural correlates of changes in stride length during LFS (85 Hz).

METHODS

Objective gait performance was retrospectively evaluated in 19 PD patients who underwent deep brain stimulation (DBS) at 85 Hz and 130 Hz. Individual DBS contacts and volumes of activated tissue (VAT) were computed using preoperative magnetic resonance imaging (MRI) and postoperative computed tomography (CT) scans. Structural connectivity profiles to predetermined cortical and mesencephalic areas were estimated using a normative connectome.

RESULTS

LFS led to a significant improvement in stride length compared to 130 Hz stimulation. The intersection between VAT and the associative subregion of the subthalamic nucleus (STN) was associated with an improvement in stride length and had structural connections to the supplementary motor area, prefrontal cortex, and pedunculopontine nucleus. Conversely, we found that a lack of improvement was linked to stimulation volumes connected to cortico-diencephalic fibers bypassing the STN dorsolaterally. The robustness of the connectivity model was verified through leave-one-patient-out, 5-, and 10-fold cross cross-validation paradigms.

CONCLUSION

These findings offer new insights into the structural connectivity that underlies gait changes following LFS. Targeting the non-motor subregion of the STN with LFS on an individual level may present a potential therapeutic approach for PD patients with gait disorders.

Analyses of the clinical factors and freezing of gait in association with the quality-of-life indexes in Parkinson's disease subjects with and without STN-DBS therapy

INTRODUCTION

In this research, paying particular attention to freezıng of gait (FOG), we aimed to investigate the associations between the clinical features and quality of lilfe (QOL) indexes comparatively in our PD subjects with and without STN-DBS therapy.

METHODS

All consecutive PD subjects with and without STN-DBS who applied to our movement disorders outpatient clinics between January/2022 and September/2022; and accepted to participate in the study were enrolled. The demographic data and clinical features were noted. Besides, the MDS-UPDRS, the FOG Questionnaire (FOGQ) and the Parkinson's Disease Questionnaire (PDQ-39) have also been performed on all individuals.

RESULTS

Overall, 105 patients with PD participated in this study (34 patients with STN-DBS, 71 patients without STN-DBS). No difference was found in the PDQ-39 scores between patients with and without STN-DBS. The correlation analyses between the PQQ-39 scores and the clinical parameters revealed significant moderate correlations with the FOGQ score and low correlations with MDS-UPDRS scores. The analyses repeated in either patient group showed that there were no correlations between the MDS-UPDRS scores and PDQ-39 indexes in the DBS group. Besides, the correlations between the PDQ-39 scores and the FOG scores were more prominent in patients without DBS therapy.

CONCLUSION

FOG was found to be associated with worse QOL status in both patients with and without STN-DBS therapy. However, the correlations analyses in either group showed that FOG was a more significant determinant in the QOL indexes in patients without DBS. Future studies evaluating the impact of other clinical features such as falls and gait impairment in QOL of patients with STN-DBS may provide contributions to the current evidence.

Long-term safety and efficacy of frameless subthalamic deep brain stimulation in Parkinson's disease

BACKGROUND

Bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) is standard of care for Parkinson's disease (PD) patients and a correct lead placement is crucial to obtain good clinical outcomes. Evidence demonstrating the targeting accuracy of the frameless technique for DBS, along with the advantages for patients and clinicians, is solid, while data reporting long-term clinical outcomes for PD patients are still lacking.

OBJECTIVES

The study aims to assess the clinical safety and efficacy of frameless bilateral STN-DBS in PD patients at 5 years from surgery.

METHODS

Consecutive PD patients undergoing bilateral STN-DBS with a frameless system were included in this single-center retrospective study. Clinical features, including the Unified Parkinson's Disease Rating Scale (UPDRS) in its total motor score and axial sub-scores, and pharmacological regimen were assessed at baseline, 1 year, 3 years, and 5 years after surgery. The adverse events related to the procedure, stimulation, or the presence of the hardware were systematically collected.

RESULTS

Forty-one PD patients undergone bilateral STN-DBS implantation were included in the study and fifteen patients already completed the 5-year observation. No complications occurred during surgery and the perioperative phase, and no unexpected serious adverse event occurred during the entire follow-up period. At 5 years from surgery, there was a sustained motor efficacy of STN stimulation: STN-DBS significantly improved the off-stim UPDRS III score at 5 years by 37.6% (P < 0.001), while the dopaminergic medications remained significantly reduced compared to baseline (- 21.6% versus baseline LEDD; P = 0.036).

CONCLUSIONS

Our data support the use of the frameless system for STN-DBS in PD patients, as a safe and well-tolerated technique, with long-term clinical benefits and persistent motor efficacy at 5 years from the surgery.

Bilateral deep transcranial magnetic stimulation of motor and prefrontal cortices in Parkinson's disease: a comprehensive review

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by both motor and non-motor symptoms, many of which are resistant to currently available treatments. Since the discovery that non-invasive transcranial magnetic stimulation (TMS) can cause dopamine release in PD patients, there has been growing interest in the use of TMS to fill existing gaps in the treatment continuum for PD. This review evaluates the safety and efficacy of a unique multifocal, bilateral Deep TMS protocol, which has been evaluated as a tool to address motor and non-motor symptoms of PD. Six published clinical trials have delivered a two-stage TMS protocol with an H-Coil targeting both the prefrontal cortex (PFC) and motor cortex (M1) bilaterally (220 PD patients in total; 108 from two randomized, sham-controlled studies; 112 from open label or registry studies). In all studies TMS was delivered to M1 bilaterally (Stage 1) and then to the PFC bilaterally (Stage 2) with approximately 900 pulses per stage. For Stage 1 (M1), two studies delivered 10 Hz at 90% motor threshold (MT) while four studies delivered 1 Hz at 110% MT. For Stage 2 (PFC), all studies delivered 10 Hz at 100% MT. The results suggest that this two-stage Deep TMS protocol is a safe, moderately effective treatment for motor symptoms of PD, and that severely impaired patients have the highest benefits. Deep TMS also improves mood symptoms and cognitive function in these patients. Further research is needed to establish optimal dosing and the long-term durability of treatment effects.

Subthalamic functional connectivity associated with freezing of gait dopa-response

INTRODUCTION

Freezing of gait (FOG) is a prevalent and debilitating feature of Parkinson's Disease (PD). The subthalamic nucleus (STN) is a center for controlled locomotion and a common DBS target. The objective of this study was to identify STN circuitry associated with FOG response to dopaminergic medication. In this study, we compare BOLD functional connectivity of the subthalamic nucleus (STN) in participants with and without dopa-responsive FOG.

METHODS

55 PD participants either with FOG (n = 38) or without FOG (n = 17) were recruited. Among FOG participants 22 were dopa-responsive and 16 were dopa-unresponsive. STN whole-brain connectivity was performed using CONN toolbox. The relationship between the degree of self-reported FOG dopa-response and STN connectivity was evaluated using partial correlations corrected for age, disease duration, and levodopa equivalent daily dose.

RESULTS

Right STN connectivity with the cerebellar locomotor region and the temporal/occipital cortex was greater in the dopa-responsive FOG group (voxel threshold p < 0.01, FWE corrected p < 0.05). Left STN connectivity with the occipital cortex was greater in the dopa-responsive FOG group and connectivity with the postcentral gyrus was greater in the dopa-unresponsive FOG group. Strength of connectivity to these regions correlated with l-dopa induced improvement in UPDRS Item-14 (FOG), but not UPDRS Part-III (overall motor score).

DISCUSSION

We demonstrate that dopa-unresponsive FOG is associated with changes in BOLD functional connectivity between the STN and locomotor as well as sensory processing regions. This finding supports the conceptual framework that effective treatment for freezing of gait likely requires the engagement of both locomotor and sensory brain regions.

Deep brain stimulation of the subthalamic nucleus in severe Parkinson's disease: relationships between dual-contact topographic setting and 1-year worsening of speech and gait

BACKGROUND

Subthalamic nucleus (STN) deep brain stimulation (DBS) alleviates severe motor fluctuations and dyskinesia in Parkinson's disease, but may result in speech and gait disorders. Among the suspected or demonstrated causes of these adverse effects, we focused on the topography of contact balance (CB; individual, right and left relative dual positions), a scantly studied topic, analyzing the relationships between symmetric or non-symmetric settings, and the worsening of these signs.

METHOD

An observational monocentric study was conducted on a series of 92 patients after ethical approval. CB was specified by longitudinal and transversal positions and relation to the STN (CB sub-aspects) and totalized at the patient level (patient CB). CB was deemed symmetric when the two contacts were at the same locations relative to the STN. CB was deemed asymmetric when at least one sub-aspect differed in the patient CB. Baseline and 1-year characteristics were routinely collected: (i) general, namely, Unified Parkinson's Disease Rating Scores (UPDRS), II, III motor and IV, daily levodopa equivalent doses, and Parkinson's Disease Questionnaire of Quality of Life (PDQ39) scores; (ii) specific, namely scores for speech (II-5 and III-18) and axial signs (II-14, III-28, III-29, and III-30). Only significant correlations were considered (p < 0.05).

RESULTS

Baseline characteristics were comparable (symmetric versus asymmetric). CB settings were related to deteriorations of speech and axial signs: communication PDQ39 and UPDRS speech and gait scores worsened exclusively with symmetric settings; the most influential CB sub-aspect was symmetric longitudinal position.

CONCLUSION

Our findings suggest that avoiding symmetric CB settings, whether by electrode positioning or shaping of electric fields, could reduce worsening of speech and gait.

Advances in DBS Technology and Novel Applications: Focus on Movement Disorders

PURPOSE OF REVIEW

Deep brain stimulation (DBS) is an established treatment in several movement disorders, including Parkinson's disease, dystonia, tremor, and Tourette syndrome. In this review, we will review and discuss the most recent findings including but not limited to clinical evidence.

RECENT FINDINGS

New DBS technologies include novel hardware design (electrodes, cables, implanted pulse generators) enabling new stimulation patterns and adaptive DBS which delivers potential stimulation tailored to moment-to-moment changes in the patient's condition. Better understanding of movement disorders pathophysiology and functional anatomy has been pivotal for studying the effects of DBS on the mesencephalic locomotor region, the nucleus basalis of Meynert, the substantia nigra, and the spinal cord. Eventually, neurosurgical practice has improved with more accurate target visualization or combined targeting. A rising research domain emphasizes bridging neuromodulation and neuroprotection. Recent advances in DBS therapy bring more possibilities to effectively treat people with movement disorders. Future research would focus on improving adaptive DBS, leading more clinical trials on novel targets, and exploring neuromodulation effects on neuroprotection.

Troubleshooting Gait Disturbances in Parkinson's Disease With Deep Brain Stimulation

Deep brain stimulation (DBS) of the subthalamic nucleus or the globus pallidus is an established treatment for Parkinson's disease (PD) that yields a marked and lasting improvement of motor symptoms. Yet, DBS benefit on gait disturbances in PD is still debated and can be a source of dissatisfaction and poor quality of life. Gait disturbances in PD encompass a variety of clinical manifestations and rely on different pathophysiological bases. While gait disturbances arising years after DBS surgery can be related to disease progression, early impairment of gait may be secondary to treatable causes and benefits from DBS reprogramming. In this review, we tackle the issue of gait disturbances in PD patients with DBS by discussing their neurophysiological basis, providing a detailed clinical characterization, and proposing a pragmatic programming approach to support their management.

How Does Deep Brain Stimulation Change the Course of Parkinson's Disease?

A robust body of evidence from randomized controlled trials has established the efficacy of deep brain stimulation (DBS) in reducing off time and dyskinesias in levodopa‐treated patients with Parkinson's disease (PD). These effects go along with improvements in on period motor function, activities of daily living, and quality of life. In addition, subthalamic DBS is effective in controlling drug‐refractory PD tremor. Here, we review the available data from long‐term observational and controlled follow‐up studies in DBS‐treated patients to re‐examine the persistence of motor and quality of life benefits and evaluate the effects on disease progression, major disability milestones, and survival. Although there is consistent evidence from observational follow‐up studies in DBS‐treated patients over 5–10 years and beyond showing sustained improvement of motor control, the long‐term impact of DBS on overall progression of disability in PD is less clear. Whether DBS reduces or delays the development of later motor and non‐motor disability milestones in comparison to best medical management strategies is difficult to answer by uncontrolled observational follow‐up, but there are signals from controlled long‐term observational studies suggesting that subthalamic DBS may delay some of the late‐stage disability milestones including psychosis, falls, and institutionalization, and also slightly prolongs survival compared with matched medically managed patients. These observations could be attributable to the sustained improvements in motor function and reduction in medication‐induced side effects, whereas there is no clinical evidence of direct effects of DBS on the underlying disease progression. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Parkinson's Disease Symptoms Associated with Developing On-State Axial Symptoms Early after Subthalamic Deep Brain Stimulation

Background: The relationship between axial symptoms in Parkinson’s disease (PD) and subthalamic deep brain stimulation (STN-DBS) is still unclear. Purpose: We searched for particular clinical characteristics before STN-DBS linked to on-state axial problems after surgery. Methods: We retrospectively analyzed baseline motor, emotional and cognitive features from PD patients with early axial symptoms (within 4 years after STN-DBS) and late axial symptoms (after 4 years). We also considered a group of PD patients without axial symptoms for at least 4 years after surgery. Results: At baseline, early-axial PD patients (n = 28) had a higher on-state Unified Parkinson’s Disease Rating Scale III (15.0 ± 5.6 to 11.6 ± 6.2, p = 0.020), higher axial score (2.4 ± 1.8 to 0.7 ± 1.0, p < 0.001) and worse dopaminergic response (0.62 ± 0.12 to 0.70 ± 0.11, p = 0.005), than non-axial PD patients (n = 51). Early-axial PD patients had short-term recall impairment, not seen in non-axial PD (36.3 ± 7.6 to 40.3 ± 9.3, p = 0.041). These variables were similar between late-axial PD (n = 18) and non-axial PD, but late-axial PD showed worse frontal dysfunction. Conclusions: PD patients with early axial symptoms after DBS may have a significantly worse presurgical motor phenotype, poorer dopaminergic response and memory impairment. This may correspond to a more severe form of PD.

Subthalamic Deep Brain Stimulation Lead Asymmetry Impacts the Parkinsonian Gait Disorder

Background

The preferable position of Deep Brain Stimulation (DBS) electrodes is proposed to be located in the dorsolateral subthalamic nucleus (STN) to improve general motor performance. The optimal DBS electrode localization for the post-operative improvement of balance and gait is unknown.

Methods

In this single-center, retrospective analyses, 66 Parkinson’s disease (PD) patients (24 female, age 63 ± 7 years) were assessed pre- and post-operatively (8.45 ± 4.2 months after surgery) by using MDS-UPDRS, freezing of gait (FoG) score, Giladi’s gait and falls questionnaire and Berg balance scale. The clinical outcome was related to the DBS electrode coordinates in x, y, z plane as revealed by image-based reconstruction (SureTune™). Binomial generalized linear mixed models with fixed-effect variables electrode asymmetry, parkinsonian subtype, medication, age class and clinical DBS induced changes were analyzed.

Results

Subthalamic nucleus-deep brain stimulation improved all motor, balance and FoG scores in MED OFF condition, however there were heterogeneous results in MED ON condition. DBS electrode reconstructed coordinates impacted the responsiveness of axial symptoms. FoG and balance responders showed slightly more medially located STN electrode coordinates and less medio-lateral asymmetry of the electrode reconstructed coordinates across hemispheres compared to non-responders.

Conclusion

Deep brain stimulation electrode reconstructed coordinates, particularly electrode asymmetry on the medio-lateral axis affected the post-operative responsiveness of balance and FoG symptoms in PD patients.

People With Parkinson’s Disease and Freezing of Gait Show Abnormal Low Frequency Activity of Antagonistic Leg Muscles

Objective

Freezing of gait is detrimental to patients with idiopathic Parkinson’s disease (PD). Its pathophysiology represents a multilevel failure of motor processing in the cortical, subcortical, and brainstem circuits, ultimately resulting in ineffective motor output of the spinal pattern generator. Electrophysiological studies pointed to abnormalities of oscillatory activity in freezers that covered a broad frequency range including the theta, alpha, and beta bands. We explored muscular frequency domain activity with respect to freezing, and used deep brain stimulation to modulate these rhythms thereby evaluating the supraspinal contributions to spinal motor neuron activity.

Methods

We analyzed 9 PD freezers and 16 healthy controls (HC). We studied the patients after overnight withdrawal of dopaminergic medication with stimulation off, stimulation of the subthalamic nucleus (STN-DBS_only) or the substantia nigra pars reticulate (SNr-DBS_only), respectively. Patients performed a walking paradigm passing a narrow obstacle. We analyzed the frequency-domain spectra of the tibialis anterior (TA) and gastrocnemius (GA) muscles in ‘regular gait’ and during the ‘freezing’ episodes.

Results

In stimulation off, PD freezers showed increased muscle activity of the alpha and low-beta band compared to HC in both TA and GA. This activity increase was present during straight walking and during the freezes to similar extent. STN- but not SNr-DBS decreased this activity and paralleled the clinical improvement of freezing.

Conclusion

We found increased muscle activation of the alpha and lower beta band in PD freezers compared to HC, and this was attenuated with STN-DBS. Future studies may use combined recordings of local field potentials, electroencephalography (EEG), and electromyography (EMG) to interrogate the supraspinal circuit mechanisms of the pathological activation pattern of the spinal pattern generator.

Structural Connectivity of Subthalamic Nucleus Stimulation for Improving Freezing of Gait

BACKGROUND

Freezing of gait (FOG) is among the most common and disabling symptoms of Parkinson's disease (PD). Studies show that deep brain stimulation (DBS) of the subthalamic nucleus (STN) can reduce FOG severity. However, there is uncertainty about pathways that need to be modulated to improve FOG.

OBJECTIVE

To investigate whether STN-DBS effectively reduces FOG postoperatively and whether structural connectivity of the stimulated tissue explains variance of outcomes.

METHODS

We investigated 47 patients with PD and preoperative FOG. Freezing prevalence and severity was primarily assessed using the Freezing of Gait Questionnaire (FOG-Q). In a subset of 18 patients, provoked FOG during a standardized walking course was assessed. Using a publicly available model of basal-ganglia pathways we determined stimulation-dependent connectivity associated with postoperative changes in FOG. A region-of-interest analysis to a priori defined mesencephalic regions was performed using a disease-specific normative connectome.

RESULTS

Freezing of gait significantly improved six months postoperatively, marked by reduced frequency and duration of freezing episodes. Optimal stimulation volumes for improving FOG structurally connected to motor areas, the prefrontal cortex and to the globus pallidus. Stimulation of the lenticular fasciculus was associated with worsening of FOG. This connectivity profile was robust in a leave-one-out cross-validation. Subcortically, stimulation of fibers crossing the pedunculopontine nucleus and the substantia nigra correlated with postoperative improvement.

CONCLUSION

STN-DBS can alleviate FOG severity by modulating specific pathways structurally connected to prefrontal and motor cortices. More differentiated FOG assessments may allow to differentiate pathways for specific FOG subtypes in the future.

Neurodegeneration of the Globus Pallidus Internus as a Neural Correlate to Dopa-Response in Freezing of Gait

BACKGROUND

Background: Parkinson's disease (PD) patients who develop freezing of gait (FOG) have reduced mobility and independence. While some patients experience improvement in their FOG symptoms with dopaminergic therapies, a subset of patients have little to no response. To date, it is unknown what changes in brain structure underlie dopa-response and whether this can be measured using neuroimaging approaches.

OBJECTIVE

We tested the hypothesis that structural integrity of brain regions (subthalamic nucleus and globus pallidus internus, GPi) which link basal ganglia to the mesencephalic locomotor region (MLR), a region involved in automatic gait, would be associated with FOG response to dopaminergic therapy.

METHODS

In this observational study, thirty-six participants with PD and definite FOG were recruited to undergo diffusion kurtosis imaging (DKI) and multiple assessments of dopa responsiveness (UPDRS scores, gait times ON versus OFF medication).

RESULTS

The right GPi in participants with dopa-unresponsive FOG showed reduced fractional anisotropy, mean kurtosis (MK), and increased radial diffusivity relative to those with dopa-responsive FOG. Furthermore, using probabilistic tractography, we observed reduced MK and increased mean diffusivity along the right GPi-MLR tract in dopa-unresponsive FOG. MK in the right GPi was associated with a subjective dopa-response for FOG (r = -0.360, df = 30, p = 0.043) but not overall motor dopa-response.

CONCLUSION

These results support structural integrity of the GPi as a correlate to dopa-response in FOG. Additionally, this study suggests DKI metrics may be a sensitive biomarker for clinical studies targeting dopaminergic circuitry and improvements in FOG behavior.

Discussion of Research Priorities for Gait Disorders in Parkinson's Disease

Gait and balance abnormalities develop commonly in Parkinson's disease and are among the motor symptoms most disabling and refractory to dopaminergic or other treatments, including deep brain stimulation. Efforts to develop effective therapies are challenged by limited understanding of these complex disorders. There is a major need for novel and appropriately targeted research to expedite progress in this area. The Scientific Issues Committee of the International Parkinson and Movement Disorder Society has charged a panel of experts in the field to consider the current knowledge gaps and determine the research routes with highest potential to generate groundbreaking data. © 2021 International Parkinson and Movement Disorder Society.

Factors correlated with therapeutic effects of globus pallidus deep brain stimulation on freezing of gait in advanced Parkinson's disease: A pilot study

INTRODUCTION

Deep brain stimulation (DBS) has showed variable therapeutic effect on freezing of gait (FOG) in Parkinson's disease (PD). It is unclear which factors associated with the effect of DBS on FOG in patients with advanced PD. In this study, we investigated the correlation of pre and postoperative factors with the therapeutic effect of globus pallidus interna (GPi) DBS on FOG in PD patients.

METHODS

We retrospectively analyzed PD patients with FOG (N = 20) who underwent GPi DBS surgery. Postoperatively, video-based analysis for FOG severity was performed at the first DBS programming and patients were categorized into two groups according to DBS effect on FOG (11 FOG responders and 9 FOG non-responders) at medication-off state. We analyzed preoperative clinical characteristics, cognitive function, striatal dopamine transporter availability, postoperative DBS programming parameters, lead locations, and volume of tissue activated in functional subregions of GPi. Bootstrap enhanced Elastic-Net logistic regression was used to select pre and postoperative factors associated with the effect of GPi DBS.

RESULTS

Therapeutic effect of GPi DBS on FOG were correlated with the disease duration of PD before DBS surgery, preoperative improvement in FOG severity by levodopa medication, and the distance from active contact of DBS electrode to the prefrontal region of GPi anatomical site.

CONCLUSIONS

Our study results suggest that the effect of GPi DBS on FOG is correlated with disease duration, levodopa responsiveness on FOG before DBS surgery and DBS electrode location, providing useful information to predict FOG outcome after GPi DBS in PD patients.

Controlling Clinical States Governed by Different Temporal Dynamics With Closed-Loop Deep Brain Stimulation: A Principled Framework

Closed-loop strategies for deep brain stimulation (DBS) are paving the way for improving the efficacy of existing neuromodulation therapies across neurological disorders. Unlike continuous DBS, closed-loop DBS approaches (cl-DBS) optimize the delivery of stimulation in the temporal domain. However, clinical and neurophysiological manifestations exhibit highly diverse temporal properties and evolve over multiple time-constants. Moreover, throughout the day, patients are engaged in different activities such as walking, talking, or sleeping that may require specific therapeutic adjustments. This broad range of temporal properties, along with inter-dependencies affecting parallel manifestations, need to be integrated in the development of therapies to achieve a sustained, optimized control of multiple symptoms over time. This requires an extended view on future cl-DBS design. Here we propose a conceptual framework to guide the development of multi-objective therapies embedding parallel control loops. Its modular organization allows to optimize the personalization of cl-DBS therapies to heterogeneous patient profiles. We provide an overview of clinical states and symptoms, as well as putative electrophysiological biomarkers that may be integrated within this structure. This integrative framework may guide future developments and become an integral part of next-generation precision medicine instruments.

Future Therapeutic Strategies for Freezing of Gait in Parkinson's Disease

Freezing of gait (FOG) is a common and challenging clinical symptom in Parkinson’s disease. In this review, we summarise the recent insights into freezing of gait and highlight the strategies that should be considered to improve future treatment. There is a need to develop individualised and on-demand therapies, through improved detection and wearable technologies. Whilst there already exist a number of pharmacological (e.g., dopaminergic and beyond dopamine), non-pharmacological (physiotherapy and cueing, cognitive training, and non-invasive brain stimulation) and surgical approaches to freezing (i.e., dual-site deep brain stimulation, closed-loop programming), an integrated collaborative approach to future research in this complex area will be necessary to systematically investigate new therapeutic avenues. A review of the literature suggests standardising how gait freezing is measured, enriching patient cohorts for preventative studies, and harnessing the power of existing data, could help lead to more effective treatments for freezing of gait and offer relief to many patients.

Projections and the Potential Societal Impact of the Future of Neurotechnologies

Traditionally, recording from and stimulating the brain with high spatial and temporal resolution required invasive means. However, recently, the technical capabilities of less invasive and non-invasive neuro-interfacing technology have been dramatically improving, and laboratories and funders aim to further improve these capabilities. These technologies can facilitate functions such as multi-person communication, mood regulation and memory recall. We consider a potential future where the less invasive technology is in high demand. Will this demand match that the current-day demand for a smartphone? Here, we draw upon existing research to project which particular neuroethics issues may arise in this potential future and what preparatory steps may be taken to address these issues.

Executive function and dopamine response in Parkinson's disease freezing of gait

BACKGROUND

This investigation examined whether aspects of attention and executive functioning differed between Parkinson's Disease (PD) patients with freezing of gait (FOG) based on responsiveness to dopamine. We also explored association of cognition with FOG severity and gait metrics.

METHODS

Fifty-four individuals with PD completed the study protocol: 17 without freezing (PDC), 23 with dopa-responsive FOG (RFOG), and 14 with dopa-unresponsive (URFOG). Standardized neuropsychological tests assessed attention (focused and sustained), psychomotor speed, and set-switching (time and errors). FOG severity was measured using the new FOG Questionnaire (nFOG-Q). Metrics from timed up and go (TUG) tasks were obtained while "on" and "off" dopamine, with and without dual cognitive tasks.

RESULTS

After controlling for clinical and demographic factors, analysis of covariance revealed a significant between-group difference for set-switching errors; planned contrasts revealed increased set-switching errors in URFOG relative to RFOG and PD control groups. Groups were not different in other cognitive domains. FOG severity was modestly associated with set-switching errors in RFOG but not URFOG. TUG performances while "on" were associated with set-switching errors in PD controls, and with focused attention in RFOG.

CONCLUSION

PD patients with dopa-unresponsive FOG are more prone to set-switching errors than those who respond to treatment. Furthermore, executive function appears relevant to FOG severity only in patients who show dopamine response. Together, these findings suggest disruption of a common dopamine-mediated pathway for FOG and ability to monitor rules while alternating cognitive processes. Consideration of dopa-response could be useful in characterizing cohorts and treating FOG in PD.

Short- and Long-Term Effects of DBS on Gait in Parkinson's Disease

The aim was to compare the short and long-term effects of subthalamic nucleus (STN) deep brain stimulation (DBS) on gait dysfunction and other cardinal symptoms of Parkinson's disease (PD). Two groups of patients were studied. The first group (short-term DBS, n = 8) included patients recently implanted with STN DBS (mean time since DBS 15.8 months, mean age 58.8 years, PD duration 13 years); the second group (long-term DBS, n = 10) included patients with at least 5 years of DBS therapy (mean time since DBS 67.6 months, mean age 61.7 years, PD duration 17.1 years). Both groups were examined using the Unified Parkinson's Disease Rating Scale (UPDRS) and Gait and Balance scale (GABS) during four stimulation/medication states (ON/OFF; OFF/OFF; OFF/ON; ON/ON). Data were analyzed using repeated measures ANOVA with time since implantation (years) between groups and medication or DBS effect (ON, OFF) within groups. In the short-term DBS group, stimulation improved all UPDRS subscores similar to dopaminergic medications. In particular, average gait improvement was over 40% (p = 0.01), as measured by the UPDRS item 29 and GABS II. In the long-term DBS group, stimulation consistently improved all clinical subscores with the exception of gait and postural instability. In these patients, the effect of levodopa on gait was partially preserved. Short-term improvement of gait abnormalities appears to significantly decline after 5 years of STN DBS in PD patients, while effectiveness for other symptoms remains stable. Progressive non-dopaminergic (non-DBS responsive) mechanisms or deleterious effects of high frequency STN stimulation on gait function may play a role.

Axial Impairment Following Deep Brain Stimulation in Parkinson's Disease: A Surgicogenomic Approach

Background:

Postoperative outcome following deep brain stimulation (DBS) of the subthalamic nucleus is variable, particularly with respect to axial motor improvement. We hypothesized a genetic underpinning to the response to surgical intervention, termed “surgicogenomics”.

Objective:

We aimed to identify genetic variants associated with clinical heterogeneity in DBS outcome of Parkinson’s disease (PD) patients that could then be applied clinically to target selection leading to improved surgical outcome.

Methods:

Retrospective clinical data was extracted from 150 patient’s charts. Each individual was genotyped using the genome-wide NeuroX array tailored to study neurologic diseases. Genetic data were clustered based on surgical outcome assessed by comparing pre- and post-operative scores of levodopa equivalent daily dose and axial impairment at one and five years post-surgery. Allele frequencies were compared between patients with excellent vs. moderate/poor outcomes grouped using a priori defined cut-offs. We analyzed common variants, burden of rare coding variants, and PD polygenic risk score.

Results:

NeuroX identified 2,917 polymorphic markers at 113 genes mapped to known PD loci. The gene-burden analyses of 202 rare nonsynonymous variants suggested a nominal association of axial impairment with 14 genes (most consistent with CRHR1, IP6K2, and PRSS3). The strongest association with surgical outcome was detected between a reduction in levodopa equivalent daily dose and common variations tagging two linkage disequilibrium blocks with SH3GL2.

Conclusion:

Once validated in independent populations, our findings may be implemented to improve patient selection for DBS in PD.

A systematic review on exercise and training-based interventions for freezing of gait in Parkinson's disease

Freezing of gait (FOG) in Parkinson's disease (PD) causes severe patient burden despite pharmacological management. Exercise and training are therefore advocated as important adjunct therapies. In this meta-analysis, we assess the existing evidence for such interventions to reduce FOG, and further examine which type of training helps the restoration of gait function in particular. The primary meta-analysis across 41 studies and 1838 patients revealed a favorable moderate effect size (ES = -0.37) of various training modalities for reducing subjective FOG-severity (p < 0.00001), though several interventions were not directly aimed at FOG and some included non-freezers. However, exercise and training also proved beneficial in a secondary analysis on freezers only (ES = -0.32, p = 0.007). We further revealed that dedicated training aimed at reducing FOG episodes (ES = -0.24) or ameliorating the underlying correlates of FOG (ES = -0.40) was moderately effective (p < 0.01), while generic exercises were not (ES = -0.14, p = 0.12). Relevantly, no retention effects were seen after cessation of training (ES = -0.08, p = 0.36). This review thereby supports the implementation of targeted training as a treatment for FOG with the need for long-term engagement.

Focused Vibrotactile Stimulation with Cueing Effect on Freezing of Gait in Parkinson's Disease: Two Case Reports

Freezing of gait (FOG) is a common occurrence in patients with Parkinson’s disease (PD) that leads to significant limitations in mobility and increases risk of falls. Focused vibrotactile stimulation and cueing are two methods used to alleviate motor symptoms, including FOG, in patients with PD. While effective on their own, the effect of combining both focused vibrotactile stimulation and cueing has yet to be investigated. Two patients, both with a history of PD, suffered from frequent FOG episodes that failed to respond adequately to medication. A novel vibrotactile stimulation device that delivered rhythmic kinesthetic stimuli onto the sternum successfully reduced FOG episodes in both patients and drastically improved their mobility as measured by the Timed Up and Go test. We found that a combination of focused vibrotactile stimulation and cueing was effective in reducing FOG episodes in two patients with PD. Further well-designed prospective studies are needed to confirm our observations.

Structural Connectivity Patterns of Side Effects Induced by Subthalamic Deep Brain Stimulation for Parkinson's Disease

Background: Tractography based on diffusion-weighted magnetic resonance imaging (DWI) models the structural connectivity of the human brain. Deep brain stimulation (DBS) targeting the subthalamic nucleus is an effective treatment for advanced Parkinson's disease, but may induce adverse effects. This study investigated the relationship between structural connectivity patterns of DBS electrodes and stimulation-induced side effects. Materials and Methods: Twenty-one patients with Parkinson's disease treated with bilateral subthalamic DBS were examined. Overall, 168 electrode contacts were categorized as inducing or noninducing depending on their capability for inducing side effects such as motor effects, paresthesia, dysarthria, oculomotor effects, hyperkinesia, and other complications as assessed during the initial programming session. Furthermore, the connectivity of each contact with target regions was evaluated by probabilistic tractography based on DWI. Finally, stimulation sites and structural connectivity patterns of inducing and noninducing contacts were compared. Results: Inducing contacts differed across the various side effects and from those mitigating Parkinson's symptoms. Although contacts showed a largely overlapping spatial distribution within the subthalamic region, they could be distinguished by their connectivity patterns. In particular, inducing contacts were more likely connected with supplementary motor areas (hyperkinesia, dysarthria), frontal cortex (oculomotor), fibers of the internal capsule (paresthesia), and the basal ganglia-thalamo-cortical circuitry (dysarthria). Discussion: Side effects induced by DBS seem to be associated with distinct connectivity patterns. Cerebellar connections are hardly associated with side effects, although they seem relevant for mitigating motor symptoms in Parkinson's disease. A symptom-specific, connectivity-based approach for target planning in DBS may enhance treatment outcomes and reduce adverse effects.

Prevalence of freezing of gait in Parkinson's disease: a systematic review and meta-analysis

BACKGROUND

Freezing of gait (FOG) is considered one of the most disturbing and least understood symptoms in Parkinson's disease (PD). The reported prevalence rates of FOG in PD vary widely, ranging from 5 to 85.9%.

OBJECTIVE

We conducted a systematic review and meta-analysis to provide a reliable estimate of the average point prevalence of FOG in PD, and we further investigated the study characteristics that might have influenced the estimate.

METHODS

We searched different databases to identify studies that report the prevalence of FOG in PD or include relevant raw data for further calculation. The last inclusion date was February 20, 2020. The modified Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool was used for the quality assessment, and articles that met the predefined criteria were included in the quantitative analysis.

RESULTS

Sixty-six studies were selected from 3392 references. A weighted prevalence of 50.6% in 9072 PD patients experienced FOG based on the special questionnaires (the FOG-Q and NFOG-Q), which was about twice as high as that assessed by the specific items of the clinical rating scales (UPDRS item2.14 and MDS-UPDRS item3.11) (23.2%) or simple clinical questions (25.4%). The weighted prevalence was 37.9% for early stage (≤ 5 years) and 64.6% for advanced stage (≥ 9 years). Moreover, a higher prevalence was calculated from the population-based studies than that in multicenter and single-center studies (47.3% vs. 33.5% and 37.1%, respectively).

CONCLUSION

The result from this systematic review confirms that FOG is very common in PD and its prevalence is usually underestimated in hospital settings. Importantly, a more accurate assessment of FOG in future clinical researches would involve the use of special FOG scale rather than a single item on a scale or a general clinical inquiry.

Freezing of Gait in Parkinson's Disease: Invasive and Noninvasive Neuromodulation

INTRODUCTION

Freezing of gait (FoG) is one of the most disabling yet poorly understood symptoms of Parkinson's disease (PD). FoG is an episodic gait pattern characterized by the inability to step that occurs on initiation or turning while walking, particularly with perception of tight surroundings. This phenomenon impairs balance, increases falls, and reduces the quality of life.

MATERIALS AND METHODS

Clinical-anatomical correlations, electrophysiology, and functional imaging have generated several mechanistic hypotheses, ranging from the most distal (abnormal central pattern generators of the spinal cord) to the most proximal (frontal executive dysfunction). Here, we review the neuroanatomy and pathophysiology of gait initiation in the context of FoG, and we discuss targets of central nervous system neuromodulation and their outcomes so far. The PubMed database was searched using these key words: neuromodulation, freezing of gait, Parkinson's disease, and gait disorders.

CONCLUSION

Despite these investigations, the pathogenesis of this process remains poorly understood. The evidence presented in this review suggests FoG to be a heterogenous phenomenon without a single unifying pathologic target. Future studies rigorously assessing targets as well as multimodal approaches will be essential to define the next generation of therapeutic treatments.

Deep Brain Stimulation Selection Criteria for Parkinson's Disease: Time to Go beyond CAPSIT-PD

Despite being introduced in clinical practice more than 20 years ago, selection criteria for deep brain stimulation (DBS) in Parkinson's disease (PD) rely on a document published in 1999 called 'Core Assessment Program for Surgical Interventional Therapies in Parkinson's Disease'. These criteria are useful in supporting the selection of candidates. However, they are both restrictive and out-of-date, because the knowledge on PD progression and phenotyping has massively evolved. Advances in understanding the heterogeneity of PD presentation, courses, phenotypes, and genotypes, render a better identification of good DBS outcome predictors a research priority. Additionally, DBS invasiveness, cost, and the possibility of serious adverse events make it mandatory to predict as accurately as possible the clinical outcome when informing the patients about their suitability for surgery. In this viewpoint, we analyzed the pre-surgical assessment according to the following topics: early versus delayed DBS; the evolution of the levodopa challenge test; and the relevance of axial symptoms; patient-centered outcome measures; non-motor symptoms; and genetics. Based on the literature, we encourage rethinking of the selection process for DBS in PD, which should move toward a broad clinical and instrumental assessment of non-motor symptoms, quantitative measurement of gait, posture, and balance, and in-depth genotypic and phenotypic characterization.

Entraining Stepping Movements of Parkinson's Patients to Alternating Subthalamic Nucleus Deep Brain Stimulation

Patients with advanced Parkinson's can be treated by deep brain stimulation (DBS) of the subthalamic nucleus (STN). This affords a unique opportunity to record from this nucleus and stimulate it in a controlled manner. Previous work has shown that activity in the STN is modulated in a rhythmic pattern when Parkinson's patients perform stepping movements, raising the question whether the STN is involved in the dynamic control of stepping. To answer this question, we tested whether an alternating stimulation pattern resembling the stepping-related modulation of activity in the STN could entrain patients' stepping movements as evidence of the STN's involvement in stepping control. Group analyses of 10 Parkinson's patients (one female) showed that alternating stimulation significantly entrained stepping rhythms. We found a remarkably consistent alignment between the stepping and stimulation cycle when the stimulation speed was close to the stepping speed in the five patients that demonstrated significant individual entrainment to the stimulation cycle. Our study suggests that the STN is causally involved in dynamic control of step timing and motivates further exploration of this biomimetic stimulation pattern as a potential basis for the development of DBS strategies to ameliorate gait impairments.SIGNIFICANCE STATEMENT We tested whether the subthalamic nucleus (STN) in humans is causally involved in controlling stepping movements. To this end, we studied patients with Parkinson's disease who have undergone therapeutic deep brain stimulation (DBS), as in these individuals we can stimulate the STNs in a controlled manner. We developed an alternating pattern of stimulation that mimics the pattern of activity modulation recorded in this nucleus during stepping. The alternating DBS (altDBS) could entrain patients' stepping rhythm, suggesting a causal role of the STN in dynamic gait control. This type of stimulation may potentially form the basis for improved DBS strategies for gait.

[The history of Freezing-of-gait in Parkinson's disease - from phenomena to symptom]

The background of the freezing-of-gait (FOG) phenomenon in Parkinson's syndrome is presented in this review. The following issues are addressed: characterization of the symptom freezing and its subtypes that challenge standardized diagnostic procedures; available assessment methods generating freezing-related parameters that not only support clinical studies but can also be applied in everyday care, and current therapy options. FOG exists in different subtypes, and clinical and diagnostic definitions are limited by subjective characterization and semi-standardized tests. FOG-specific drug options are not existing, apart from the optimization of dopaminergic medication, which may also be due to the poor discriminatory power of standardized diagnostics. This is also true for deep brain stimulation. Both of these therapeutic options may be due not only to the complex neural network alterations as a motor-control correlate of FOG, but also because of challenging diagnostic assessments methodologies. Innovative, wearable, sensor-based diagnostic strategies are currently being developed, and supportive therapies using tools and technologies focusing on 'cueing' are becoming increasingly well accepted. Even though high level evidence is missing, they provide a helpful treatment option for individualized therapy. It can be assumed that these options will become particularly popular due to technological progress and likely alter the everyday treatment challenges faced by doctors and therapists.

Intestinal Levodopa/Carbidopa Infusion as a Therapeutic Option for Unresponsive Freezing of Gait after Deep Brain Stimulation in Parkinson's Disease

Background

Treatment of freezing of gait (FOG) is always challenging because of its unpredictable nature and multifactorial physiopathology. Intestinal levodopa infusion has been proposed in recent years as a valuable option for its improvement. FOG in Parkinson's disease (PD) can appear after deep brain stimulation in patients who never had gait symptoms.

Objective

To study the effects of intestinal levodopa/carbidopa infusion in unresponsive-FOG that appears in PD patients treated with subthalamic nucleus deep brain stimulation.

Methods

We retrospectively collected and analyzed demographic, clinical, and therapeutic data from five PD patients treated with subthalamic nucleus stimulation who developed unresponsive-FOG and received intestinal levodopa/carbidopa infusion as an alternative therapy. FOG was measured based on scores in item 14 of the Unified Parkinson's Disease Rating Scale before and after intestinal levodopa infusion.

Results

Administration of intestinal levodopa caused improvement of FOG in the “ON” state in four patients (80%) by 2 or more points in item 14 of the Unified Parkinson's Disease Rating Scale. The improvement was maintained for at least 12 months.

Conclusions

Intestinal levodopa infusion may be a valuable therapeutic option for unresponsive-FOG developed after subthalamic nucleus deep brain stimulation.

Clinical and Kinematic Correlates of Favorable Gait Outcomes From Subthalamic Stimulation

Objective: Gait and freezing of gait (FoG) are highly relevant to the outcomes of subthalamic nucleus deep brain stimulation (STN-DBS) in Parkinson's disease (PD). Previous studies pointed to variable response to combined dopaminergic and STN-DBS treatment. Here, we performed a prospective exploratory study on associations of preoperative clinical and kinematic gait measures with quantitative gait and FoG outcomes after STN-DBS implantation. Methods: We characterized 18 consecutive PD patients (13 freezers) before and after STN-DBS implantation. The patients received preoperative levodopa challenges (MedOff vs. MedOn) and a postoperative reassessment at 6 months from surgery in MedOn/StimOn condition. We correlated the FoG outcome, calculated as improvement of Freezing of Gait Assessment Course (FoG-AC) from baseline MedOff to 6-month follow-up MedOn/StimOn, with the levodopa response of preoperative clinical and kinematic gait measures. We considered measures with significant correlations for a multiple regression model. Results: We found that the postoperative gait and FoG outcomes were associated with the preoperative levodopa response of clinical and kinematic gait measures. In particular, preoperative levodopa sensitivity of FoG showed high correlation with a favorable quantitative FoG outcome. Among kinematic measures, preoperative levodopa response of stride length and range of motion showed high correlation with favorable FoG outcome. In addition, the preoperative levodopa sensitivity of FoG predicted postoperative FoG outcome with high accuracy (R ² = 0.952; 95% CI: 0.95-1.29; P < 0.001). Conclusions: Preoperative clinical and kinematic measures correlated with favorable postoperative gait and FoG outcomes. The findings should be reproduced in larger and independent cohorts to verify their predictive value.