Balancing between the two: Are freezing of gait and postural instability in Parkinson's disease connected?

Investigating spatiotemporal and kinematic gait parameters in individuals with Parkinson's disease with a history of freezing of gait and exploring the effects of dopaminergic therapy on freezing of gait subtypes

Introduction

Freezing of Gait (FOG) is a prevalent and debilitating symptom in idiopathic Parkinson's disease (PD). This study evaluated spatiotemporal and kinematic gait parameters in individuals with PD with a history of FOG and explored the effects of dopaminergic therapy on FOG subtypes.

Methods

One hundred and nine individuals with PD underwent clinical assessments and quantitative biomechanical measures during walking cycles before and after dopaminergic therapy. Individuals with FOG were classified into levodopa-responsive and levodopa-unresponsive groups.

Results

Individuals with FOG displayed longer disease duration and higher Unified Parkinson's Disease Rating Scale (UPDRS) II, III, IV scores, and total scores and levodopa equivalent dose, than those without FOG (all p < 0.0001). Following propensity score matching of 15 pairs based on UPDRS total score and disease duration during the off-medication state, the analysis comparing the FOG and non-FOG groups revealed no significant differences in spatiotemporal and kinematic parameters. In 39 cases of FOG, dopaminergic therapy improved gait performance in individuals with PD, enhancing spatiotemporal parameters (speed, stride length, step length, step variability) and kinematic parameters (shoulder and elbow flexion/extension range of motion (ROM), pelvic rotation, and hip abduction/adduction ROM) regardless of FOG responsiveness to dopaminergic therapy. A significant difference in trunk sway ROM (p = 0.029) remained before and after dopaminergic therapy, even after adjusting for disease duration and clinical severity.

Discussion

Dopaminergic therapy had varying effects on PD with FOG, improving several spatiotemporal and kinematic gait parameters but being less effective in levodopa-unresponsive cases. Quantitative biomechanical measures offer detailed insights into gait performance, aiding personalized fall risk assessment and guiding individualized rehabilitation programs.

Correlation between motor function and health-related quality of life in early to mid-stage patients with Parkinson disease: a cross-sectional observational study

Aim

To investigate the correlation between motor function and health-related quality of life (HrQOL) in early to mid-stage patients with Parkinson disease (PwP).

Methods

This cross-sectional study recruited PwP from April 2020 to December 2023 at the outpatient clinic of Peking Union Medical College Hospital in Beijing, China. The motor symptoms were assessed using Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part 3. Balance function was evaluated using the Berg Balance Scale (BBS), and the risk of fall using Timed Up-and-Go test (TUG), and Five Times Sit-to-Stand test (FTSST). Freezing of gait questionnaire (FOGQ) was used to evaluate the severity of gait. The Intelligent Device for Energy Expenditure and Physical Activity (IDEEA) recorded gait cycle parameters, and the isokinetic dynamometer measured muscle strength. The Parkinson's Disease Questionnaire-39 (PDQ-39) was used to measure HrQOL. All assessments were tested during the on state. Spearman correlation was conducted to evaluate the correlation between motor function and HrQOL.

Results

243 patients with mean age of 69.33 years were enrolled. The PDQ-39 score was strongly correlated with FOG in H&Y stage III (r = 0.653, p < 0.001) and moderately correlated in H&Y stage I (r = 0.471, p < 0.001) and H&Y stage II (r = 0.386, p < 0.001). Furthermore, the FOG was strongly correlated with mobility domain at H&Y stage III (r = 0.694, p < 0.001) and moderately correlated at H&Y stage I (r = 0.431, p < 0.001) and H&Y stage II (r = 0.434, p < 0.001). All motor function scores were correlated with PDQ-39 scores at H&Y stage III (p < 0.05).

Conclusion

Motor function correlated with HrQOL in early to mid-stage PwP, and FOG was the main factor, especially affecting mobility, activities of daily life and communication. HrQOL in patients at different disease stages were variously affected by motor function, and HrQOL and multiple dimensions was significantly associated with motor function in patients at H&Y stage III.

Unraveling the threads of stability: A review of the neurophysiology of postural control in Parkinson's disease

Postural instability is a detrimental and often treatment-refractory symptom of Parkinson's disease. While many existing studies quantify the biomechanical deficits among various postural domains (static, anticipatory, and reactive) in this population, less is known regarding the neural network dysfunctions underlying these phenomena. This review will summarize current studies on the cortical and subcortical neural activities during postural responses in healthy subjects and those with Parkinson's disease. We will also review the effects of current therapies, including neuromodulation and feedback-based wearable devices, on postural instability symptoms. With recent advances in implantable devices that allow chronic, ambulatory neural data collection from patients with Parkinson's disease, combined with sensors that can quantify biomechanical measurements of postural responses, future work using these devices will enable better understanding of the neural mechanisms of postural control. Bridging this knowledge gap will be the critical first step towards developing novel neuromodulatory interventions to enhance the treatment of postural instability in Parkinson's disease.

Dynamic evaluation of spine kinematics in individuals with Parkinson's disease and freezing of gait

BACKGROUND

Freezing of gait (FoG) is an episodic failure of gait exposing people with Parkinson's disease (PD) to a high risk of falling. Despite growing evidence of the interconnection between impaired trunk control and FoG, a detailed description of spinal kinematics during walking is still lacking in this population.

RESEARCH QUESTION

Do spinal alterations impact gait performance in individuals with PD and FoG?

METHODS

We analyzed kinematic data of 47 PD participants suffering (PD-FOG, N = 24) or not suffering from FoG (PD-NFOG, N = 23) and 15 healthy controls (HCO) during quiet standing and unperturbed walking. We estimated the main spinal variables (i.e., spinal length, lordosis and kyphosis angles, trunk inclination), the pelvis angles, and the shoulder-pelvis angles during gait and standing. We studied differences across conditions and groups and the relationships between postural and gait parameters using linear regression methods.

RESULTS

During standing and walking, both PD groups showed increased trunk inclination and decreased lordosis angle with respect to HCO, as well as a decreased range in variation of kyphosis angle, pelvic obliquity, and shoulder-pelvis angles. Only PD-FOG participants showed reduced range of lordosis angle and spinal length compared to HCO. PD-FOG individuals were also not able to straighten their spine during walking compared to standing. Stride length and velocity were decreased in both patient groups compared to HCO, while swing duration was reduced only in the PD-FOG group. In individuals with FoG, trunk inclination and lordosis angle showed moderate but significant positive correlations with all gait alterations.

SIGNIFICANCE

Spine alterations impacted gait performance in individuals with PD suffering from FoG. Excessive trunk inclination and poor mastering of the lordosis spinal region may create an unfavourable postural precondition for forward walking. Physical therapy should target combined spinal and stepping alterations in these individuals.

Soft robotic apparel to avert freezing of gait in Parkinson's disease

Freezing of gait (FoG) is a profoundly disruptive gait disturbance in Parkinson's disease, causing unintended stops while walking. Therapies for FoG reveal modest and transient effects, resulting in a lack of effective treatments. Here we show proof of concept that FoG can be averted using soft robotic apparel that augments hip flexion. The wearable garment uses cable-driven actuators and sensors, generating assistive moments in concert with biological muscles. In this n-of-1 trial with five repeated measurements spanning 6 months, a 73-year-old male with Parkinson's disease and substantial FoG demonstrated a robust response to robotic apparel. With assistance, FoG was instantaneously eliminated during indoor walking (0% versus 39 ± 16% time spent freezing when unassisted), accompanied by 49 ± 11 m (+55%) farther walking compared to unassisted walking, faster speeds (+0.18 m s-1) and improved gait quality (-25% in gait variability). FoG-targeting effects were repeatable across multiple days, provoking conditions and environment contexts, demonstrating potential for community use. This study demonstrated that FoG was averted using soft robotic apparel in an individual with Parkinson's disease, serving as an impetus for technological advancements in response to this serious yet unmet need.

Investigating gait-responsive somatosensory cueing from a wearable device to improve walking in Parkinson's disease

Freezing-of-gait (FOG) and impaired walking are common features of Parkinson's disease (PD). Provision of external stimuli (cueing) can improve gait, however, many cueing methods are simplistic, increase task loading or have limited utility in a real-world setting. Closed-loop (automated) somatosensory cueing systems have the potential to deliver personalised, discrete cues at the appropriate time, without requiring user input. Further development of cue delivery methods and FOG-detection are required to achieve this. In this feasibility study, we aimed to test if FOG-initiated vibration cues applied to the lower-leg via wearable devices can improve gait in PD, and to develop real-time FOG-detection algorithms. 17 participants with Parkinson's disease and daily FOG were recruited. During 1 h study sessions, participants undertook 4 complex walking circuits, each with a different intervention: continuous rhythmic vibration cueing (CC), responsive cueing (RC; cues initiated by the research team in response to FOG), device worn with no cueing (NC), or no device (ND). Study sessions were grouped into 3 stages/blocks (A-C), separated by a gap of several weeks, enabling improvements to circuit design and the cueing device to be implemented. Video and onboard inertial measurement unit (IMU) data were analyzed for FOG events and gait metrics. RC significantly improved circuit completion times demonstrating improved overall performance across a range of walking activities. Step frequency was significantly enhanced by RC during stages B and C. During stage C, > 10 FOG events were recorded in 45% of participants without cueing (NC), which was significantly reduced by RC. A machine learning framework achieved 83% sensitivity and 80% specificity for FOG detection using IMU data. Together, these data support the feasibility of closed-loop cueing approaches coupling real-time FOG detection with responsive somatosensory lower-leg cueing to improve gait in PD.

Prevention of Falls in Parkinson's Disease: Guidelines and Gaps

Background

People living with Parkinson's disease (PD) have a high risk for falls.

Objective

To examine gaps in falls prevention targeting people with PD as part of the Task Force on Global Guidelines for Falls in Older Adults.

Methods

A Delphi consensus process was used to identify specific recommendations for falls in PD. The current narrative review was conducted as educational background with a view to identifying gaps in fall prevention.

Results

A recent Cochrane review recommended exercises and structured physical activities for PD; however, the types of exercises and activities to recommend and PD subgroups likely to benefit require further consideration. Freezing of gait, reduced gait speed, and a prior history of falls are risk factors for falls in PD and should be incorporated in assessments to identify fall risk and target interventions. Multimodal and multi-domain fall prevention interventions may be beneficial. With advanced or complex PD, balance and strength training should be administered under supervision. Medications, particularly cholinesterase inhibitors, show promise for falls prevention. Identifying how to engage people with PD, their families, and health professionals in falls education and implementation remains a challenge. Barriers to the prevention of falls occur at individual, environmental, policy, and health system levels.

Conclusion

Effective mitigation of fall risk requires specific targeting and strategies to reduce this debilitating and common problem in PD. While exercise is recommended, the types and modalities of exercise and how to combine them as interventions for different PD subgroups (cognitive impairment, freezing, advanced disease) need further study.

Digital measures of freezing of gait across the spectrum of normal, non-freezers, possible freezers and definite freezers

Over the course of the disease, freezing of gait (FoG) will gradually impact over 80% of people with Parkinson's disease (PD). Clinical decision-making and research design are often based on classification of patients as 'freezers' or 'non-freezers'. We derived an objective measure of FoG severity from inertial sensors on the legs to examine the continuum of FoG from absent to possible and severe in people with PD and in healthy controls. One hundred and forty-seven people with PD (Off-medication) and 83 healthy control subjects turned 360° in-place for 1 minute while wearing three wearable sensors used to calculate a novel Freezing Index. People with PD were classified as: 'definite freezers', new FoG questionnaire (NFOGQ) score > 0 and clinically observed FoG; 'non-freezers', NFOGQ = 0 and no clinically observed FoG; and 'possible freezers', either NFOGQ > 0 but no FoG observed or NFOGQ = 0 but FoG observed. Linear mixed models were used to investigate differences in participant characteristics among groups. The Freezing Index significantly increased from healthy controls to non-freezers to possible freezers and to definite freezers and showed, in average, excellent test-retest reliability (ICC = 0.89). Unlike the Freezing Index, sway, gait and turning impairments were similar across non-freezers, possible and definite freezers. The Freezing Index was significantly related to NFOG-Q, disease duration, severity, balance confidence, and the SCOPA-Cog (p < 0.01). An increase in the Freezing Index, objectively assessed with wearable sensors during a turning- in-place test, may help identify prodromal FoG in people with PD prior to clinically-observable or patient-perceived freezing. Future work should follow objective measures of FoG longitudinally.

A cholinergic contribution to postural control and freezing of gait in Parkinson's disease

This scientific commentary refers to ‘Cholinergic system correlates of postural control changes in Parkinson's disease freezers’ by Roytman et al. (https://doi.org/10.1093/brain/awad134).

Cholinergic system correlates of postural control changes in Parkinson's disease freezers

Postural instability and freezing of gait are the most debilitating dopamine-refractory motor impairments in advanced stages of Parkinson's disease because of increased risk of falls and poorer quality of life. Recent findings suggest an inability to efficaciously utilize vestibular information during static posturography among people with Parkinson's disease who exhibit freezing of gait, with associated changes in cholinergic system integrity as assessed by vesicular acetylcholine transporter PET. There is a lack of adequate understanding of how postural control varies as a function of available sensory information in patients with Parkinson's disease with freezing of gait. The goal of this cross-sectional study was to examine cerebral cholinergic system changes that associate with inter-sensory postural control processing features as assessed by dynamic computerized posturography and acetylcholinesterase PET. Seventy-five participants with Parkinson's disease, 16 of whom exhibited freezing of gait, underwent computerized posturography on the NeuroCom© Equitest sensory organization test platform, striatal dopamine, and acetylcholinesterase PET scanning. Findings demonstrated that patients with Parkinson's disease with freezing of gait have greater difficulty maintaining balance in the absence of reliable proprioceptive cues as compared to those without freezing of gait [β = 0.28 (0.021, 0.54), P = 0.034], an effect that was independent of disease severity [β = 0.16 (0.062, 0.26), P < 0.01] and age [β = 0.092 (-0.005, 0.19), P = 0.062]. Exploratory voxel-based analysis revealed an association between postural control and right hemispheric cholinergic network related to visual-vestibular integration and self-motion perception. High anti-cholinergic burden predicted postural control impairment in a manner dependent on right hemispheric cortical cholinergic integrity [β = 0.34 (0.065, 0.61), P < 0.01]. Our findings advance the perspective that cortical cholinergic system might play a role in supporting postural control after nigro-striatal dopaminergic losses in Parkinson's disease. Failure of cortex-dependent visual-vestibular integration may impair detection of postural instability in absence of reliable proprioceptive cues. Better understanding of how the cholinergic system plays a role in this process may augur novel treatments and therapeutic interventions to ameliorate debilitating symptoms in patients with advanced Parkinson's disease.

Neural underpinnings of freezing-related dynamic balance control in people with Parkinson's disease

INTRODUCTION

People with Parkinson's disease (PD) with freezing of gait (FOG; freezers) show impaired dynamic balance and experience falls more frequently compared to those without (non-freezers). Here, we explore the neural underpinnings of these freezing-related balance problems.

METHODS

12 freezers, 16 non-freezers and 14 controls performed a dynamic balance task in the lab. The next day, the same task was investigated in the MRI-scanner through motor imagery (MI). A visual imagery (VI) control task was also performed. Imagery engagement was determined by comparing the performance times between the dynamic balance task, and its MI- and VI-variants. Balance-related brain activations in regions of interest were contrasted between groups based on an MI > rest versus VI > rest contrast.

RESULTS

Freezers and non-freezers were matched for age, cognition and disease severity. Similar performance times between the balance control task and the MI-conditions revealed excellent imagery engagement. Compared to non-freezers, freezers showed decreased activation in regions of interest located in the left mesencephalic locomotor region (MLR; p = 0.006), right anterior cerebellum (p = 0.017) and cerebellar vermis (p < 0.001). Intriguingly, non-freezers showed higher activations in the cerebellar vermis than controls (p = 0.010).

CONCLUSION

Overall, we showed that decreased activation in the left MLR, and cerebellar regions in freezers relative to non-freezers could explain why dynamic balance is more affected in freezers. As non-freezers displayed increased cerebellar vermis activation compared to controls, it is possible that freezers show an inability to recruit sufficient compensatory cerebellar activity for effective dynamic balance control.

Effects of freezing of gait on balance in patients with Parkinson's disease

OBJECTIVES

The aim of the study was to evaluate the effects of freezing of gait (FOG) on static and dynamic balance.

METHODS

Twenty patients with Parkinson's disease with and without FOG [PD+FOG (68,6±6,39 years) and PD-FOG group (70,6±4,57 years)] and 10 healthy individuals (68,4±4,92 years) with similar demographic characteristics were included in the study. Balance was compared between the three groups. Balance was evaluated with clinical tests Limits of stability (LoS) and body sway were measured using the E-LINK FP3 Force Plate and the Korebalance Balance Evaluation System, which measure the balance in static and dynamic conditions. Center of pressure (COP) change and average sway velocity were evaluated with the Zebris RehaWalk system.

RESULTS

Total and subscale scores of the Unified Parkinson's Disease Rating Scale were significantly higher in the PD+FOG group (p<0.05). The balance test results for both groups were similar (p>0.05). The PD+FOG group performed worse on the computerized static balance tests, the COP analysis, and the dynamic balance total score than the other two groups (p<0.05). The PD+FOG group had significantly greater sustained weight deviation than the healthy controls (p<0.05). Patients with Parkinson's disease had a lower LoS in the posterior direction than healthy controls (p<0.05).

DISCUSSION

FOG affects the dynamic balance more negatively than the static balance. In addition, FOG reduces LoS in the posterior direction and increases body sway in the anterior-posterior direction, which can lead to falls.

Effects of Oral Levodopa on Balance in People with Idiopathic Parkinson's Disease

BACKGROUND

Balance impairment is a frequent cause of morbidity and mortality in people with Parkinson's disease (PD). As opposed to the effects of appendicular motor symptoms, the effects of Levodopa on balance impairment in idiopathic PD are less clear.

OBJECTIVE

To review the literature on the effects of oral Levodopa on clinical balance test performance, posturography, step initiation, and responses to perturbation in people with idiopathic PD (PwPD).

METHODS

A systematic search of three scientific databases (Pubmed, Embase, and Web of Science) was conducted in accordance with PRISMA guidelines. For the pilot meta-analysis, standardized mean differences with 95% confidence intervals were calculated using an inverse variance random effects model. Data not suitable for implementation in the meta-analysis (missing means or standard deviations, and non-independent outcomes) were analyzed narratively.

RESULTS

A total of 2772 unique studies were retrieved, of which 18 met the eligibility criteria and were analyzed, including data of 710 idiopathic PwPD. Levodopa had a significant positive effect on the Berg Balance Scale, the Push and Release test, and jerk and frequency parameters during posturography. In contrast, some significant negative effects on velocity-based sway parameters were found during posturography and step initiation. However, Levodopa had no significant effect on most step initiation- and all perturbation parameters.

CONCLUSION

The effects of Levodopa on balance in PwPD vary depending on the outcome parameters and patient inclusion criteria. A systematic approach with well-defined outcome parameters, and prespecified, sensitive and reliable tests is needed in future studies to unravel the effects of oral Levodopa on balance.

Postural control of Parkinson's disease: A visualized analysis based on Citespace knowledge graph

Postural control impairment is one of the primary motor symptoms in patients with Parkinson's disease, leading to an increased risk of falling. Several studies have been conducted on postural control disorders in Parkinson's disease patients, but no relevant bibliometric analysis has been found. In this paper, the Web of Science Core Collection database was searched for 1,295 relevant papers on postural control in Parkinson's disease patients from December 2011 to December 2021. Based on the Citespace knowledge graph, these relevant papers over the last decade were analyzed from the perspectives of annual publication volume, countries and institutes cooperation, authors cooperation, dual-map overlay of journals, co-citation literature, and keywords. The purpose of this study was to explore the current research status, research hotspots, and frontiers in this field, and to provide a reference for further promoting the research on postural control in Parkinson's disease patients.

Feasibility of Combining Disease-Specific and Balance-Related Measures as Risk Predictors of Future Falls in Patients with Parkinson's Disease

Evidence supports the view that postural sway in a quiet stance increases with clinical disease severity and dopaminergic therapy in idiopathic Parkinson’s disease (PD), which, in turn, increases the risk of falling. This study evaluated the feasibility of combining disease-specific and balance-related measures as risk predictors for future falls in patients with PD. The patients with PD underwent postural sway measurements (area, length, and velocity traveled by the excursion of the center of pressure) and clinical functional scores (Parkinson’s Disease Rating Scale [UPDRS] and Tinetti balance and gait score assessment) in both the on- and off-states of dopaminergic therapy. The outcome was defined as the development of a new fall. The sway area, velocity, and length increased after the medication administration. The Cox proportional hazards model showed that only previous fall history, Tinetti balance and gait score (on-state), and levodopa equivalent daily dose (LEDD) were associated with the development of future falls. The cumulative risk of fall development showed that the sway length and velocity were associated with future falls after more than six months. The combined LEDD, Tinetti balance and gait score (on-state), and velocity and length of postural sway (on-state) had the highest diagnostic accuracy (area under the curve = 0.9, p < 0.0001). Dopaminergic therapy can improve clinical functional scores but worsen balance-related measures. Increased sway length and velocity during the medication state are hallmarks of future falls, particularly in advanced PD. Combining disease-specific and balance-related measures can serve as an auxiliary diagnosis as risk predictors for future falls.

Vestibular Sensory Conflict During Postural Control, Freezing of Gait, and Falls in Parkinson's Disease

BACKGROUND

The vestibular system has been implicated in the pathophysiology of episodic motor impairments in Parkinson's disease (PD), but specific evidence remains lacking.

OBJECTIVE

We investigated the relationship between the presence of freezing of gait and falls and postural failure during the performance on Romberg test condition 4 in patients with PD.

METHODS

Modified Romberg sensory conflict test, fall, and freezing-of-gait assessments were performed in 92 patients with PD (70 males/22 females; mean age, 67.6 ± 7.4 years; Hoehn and Yahr stage, 2.4 ± 0.6; mean Montreal Cognitive Assessment, 26.4 ± 2.8).

RESULTS

Failure during Romberg condition 4 was present in 33 patients (35.9%). Patients who failed the Romberg condition 4 were older and had more severe motor and cognitive impairments than those without. About 84.6% of all patients with freezing of gait had failure during Romberg condition 4, whereas 13.4% of patients with freezing of gait had normal performance (χ²  = 15.6; P < 0.0001). Multiple logistic regression analysis showed that the regressor effect of Romberg condition 4 test failure for the presence of freezing of gait (Wald χ²  = 5.0; P = 0.026) remained significant after accounting for the degree of severity of parkinsonian motor ratings (Wald χ²  = 6.2; P = 0.013), age (Wald χ²  = 0.3; P = 0.59), and cognition (Wald χ²  = 0.3; P = 0.75; total model: Wald χ²  = 16.1; P < 0.0001). Patients with PD who failed the Romberg condition 4 (45.5%) did not have a statistically significant difference in frequency of patients with falls compared with patients with PD without abnormal performance (30.5%; χ²  = 2.1; P = 0.15).

CONCLUSIONS

The presence of deficient vestibular processing may have specific pathophysiological relevance for freezing of gait, but not falls, in PD. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Levodopa ONOFF-state freezing of gait: Defining the gait and non-motor phenotype

Background

Freezing in the levodopa-medicated-state (ON-state) is a debilitating feature of Parkinson’s disease without treatment options. Studies detailing the distinguishing features between people with freezing of gait that improves with levodopa and those whose freezing continues even on levodopa are lacking.

Objective

To characterize the gross motor, gait, and non-motor features of this phenotype.

Methods

Instrumented continuous gait was collected in the levodopa-medicated-state in 105 patients: 43 non-freezers (no-FOG), 36 with freezing only OFF-levodopa (OFF-FOG) and 26 with freezing both ON- and OFF-levodopa (ONOFF-FOG). Evaluation of motor and non-motor disease features was undertaken using validated scales. A linear mixed model with age, sex, disease duration, and motor UPDRS scores as covariates was used to determine differences in spatiotemporal gait and non-motor disease features among the groups.

Results

Compared to OFF-FOG, the ONOFF-FOG group had greater disease severity (on the Unified Parkinson’s disease Rating Scale) and worse cognition (on the Montreal Cognitive Assessment, Frontal Assessment Battery and Scales for Outcome in Parkinson’s disease-Cognition scales) and quality of life (on the PDQ-39), but similar mood (on the Hamilton depression and anxiety scales) and sleep quality (on Epworth sleepiness scale and RBD questionnaire). For several gait features, differences between the ONOFF-OFF groups were at least as large and in the opposite direction as differences between OFF-no groups, controlling for disease severity. Variability in ONOFF-FOG was greater than in other groups. Using results from our study and others, a power analysis for a potential future study reveals sample sizes of at least 80 ONOFF and 80 OFF-FOG patients would be needed to detect clinically meaningful differences.

Conclusions

Intra-patient variability in spatiotemporal gait features was much greater in ONOFF-FOG than in the other two groups. Our results suggest that multifactorial deficits may lead to ONOFF-FOG development.

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.

Clinical Disease Severity Mediates the Relationship between Stride Length and Speed and the Risk of Falling in Parkinson’s Disease

The shuffling gait with slowed speed and reduced stride length has been considered classic clinical features in idiopathic Parkinson’s disease (PD), and the risk of falling increases as the disease progresses. This raises the possibility that clinical disease severity might mediate the relationship between stride length and speed and the risk of falling in patients with PD. Sixty-one patients with PD patients underwent the clinical scores as well as quantitative biomechanical measures during walking cycles before and after dopamine replacement therapy. Mediation analysis tests whether the direct effect of an independent variable (stride length and speed) on a dependent variable (three-step fall prediction model score) can be explained by the indirect influence of the mediating variable (Unified Parkinson’s Disease Rating Scale (UPDRS) total scores). The results demonstrate that decreased stride length, straight walking speed, and turning speed is associated with increased three-step fall prediction model score (r = −0.583, p < 0.0001, r = −0.519, p < 0.0001, and r = −0.462, p < 0.0001, respectively). We further discovered that UPDRS total scores value is negatively correlated with stride length, straight walking, and turning speed (r = −0.651, p < 0.0001, r = −0.555, p < 0.0001, and r = −0.372, p = 0.005, respectively) but positively correlated with the fall prediction model score value (r = 0.527, p < 0.0001). Further mediation analysis shows that the UPDRS total score values serve as mediators between lower stride length, straight walking, and turning speed and higher fall prediction model score values. Our results highlighted the relationship among stride length and speed, clinical disease severity, and risk of falling. As decreased stride length and speed are hallmarks of falls, monitoring the changes of quantitative biomechanical measures along with the use of wearable technology in a longitudinal study can provide a scientific basis for pharmacology, rehabilitation programs, and selecting high-risk candidates for surgical treatment to reduce future fall risk.

Longitudinal Prediction of Freezing of Gait in Parkinson's Disease: A Prospective Cohort Study

Objective: Freezing of gait (FOG) is a disabling complication in Parkinson's disease (PD). Yet, studies on a validated model for the onset of FOG based on longitudinal observation are absent. This study aims to develop a risk prediction model to predict the probability of future onset of FOG from a multicenter cohort of Chinese patients with PD.

Methods: A total of 350 patients with PD without FOG were prospectively monitored for ~2 years. Demographic and clinical data were investigated. The multivariable logistic regression analysis was conducted to develop a risk prediction model for FOG.

Results: Overall, FOG was observed in 132 patients (37.70%) during the study period. At baseline, longer disease duration [odds ratio (OR) = 1.214, p = 0.008], higher total levodopa equivalent daily dose (LEDD) (OR = 1.440, p < 0.001), and higher severity of depressive symptoms (OR = 1.907, p = 0.028) were the strongest predictors of future onset of FOG in the final multivariable model. The model performed well in the development dataset (with a C-statistic = 0.820, 95% CI: 0.771–0.865), showed acceptable discrimination and calibration in internal validation, and remained stable in 5-fold cross-validation.

Conclusion: A new prediction model that quantifies the risk of future onset of FOG has been developed. It is based on clinical variables that are readily available in clinical practice and could serve as a small tool for risk counseling.

Neural correlates of dual-task walking in people with central neurological disorders: a systematic review

BACKGROUND

People with central neurological disorders experience difficulties with dual-task walking due to disease-related impairments. The objective of this review was to provide a comprehensive examination of the neural correlates (structural/functional brain changes) of dual-task walking in people with Parkinson's disease (PD), multiple sclerosis (MS), stroke, and Alzheimer's disease (AD).

METHODS

A systematic review of the literature was conducted, following PRISMA guidelines, on Medline, Embase, and Scopus. Included studies examined the relationship between structural and functional brain imaging and dual-task walking performance in people with PD, MS, stroke, and AD. Articles that met the inclusion criteria had baseline characteristics, study design, and behavioral and brain outcomes extracted. Twenty-three studies were included in this review.

RESULTS

Most structural imaging studies (75%) found an association between decreased brain integrity and poor dual-task performance. Specific brain regions that showed this association include the striatum regions and hippocampus in PD and supplementary motor area in MS. Functional imaging studies reported an association between increased prefrontal activity and maintained (compensatory recruitment) or decreased dual-task walking performance in PD and stroke. A subset (n = 2) of the stroke papers found no significant correlations. Increased supplementary motor area activity was associated with decreased performance in MS and stroke. No studies on AD were identified.

CONCLUSION

In people with PD, MS, and stroke, several neural correlates of dual-task walking have been identified, however, the direction of the association between neural and performance outcomes varied across the studies. The type of cognitive task used and presentation modality (e.g., visual) may have contributed to these mixed findings.

Impaired Weight-Shift Amplitude in People with Parkinson's Disease with Freezing of Gait

BACKGROUND

People with Parkinson's disease and freezing of gait (FOG; freezers) suffer from pronounced postural instability. However, the relationship between these phenomena remains unclear and has mostly been tested in paradigms requiring step generation.

OBJECTIVE

To determine if freezing-related dynamic balance deficits are present during a task without stepping and determine the influence of dopaminergic medication on dynamic balance control.

METHODS

Twenty-two freezers, 16 non-freezers, and 20 healthy age-matched controls performed mediolateral weight-shifts at increasing frequencies when following a visual target projected on a screen (MELBA task). The amplitude and phase shift differences between center of mass and target motion were measured. Balance scores (Mini-BESTest), 360° turning speed and the freezing ratio were also measured. Subjects with Parkinson's disease were tested ON and partial OFF (overnight withdrawal) dopaminergic medication.

RESULTS

Freezers had comparable turning speed and balance scores to non-freezers and took more levodopa. Freezers produced hypokinetic weight-shift amplitudes throughout the MELBA task compared to non-freezers (p = 0.002), which were already present at task onset (p < 0.001). Freezers also displayed an earlier weight-shift breakdown than controls when OFF-medication (p = 0.008). Medication improved mediolateral weight-shifting in freezers and non-freezers. Freezers decreased their freezing ratio in response to medication.

CONCLUSION

Hypokinetic weight-shifting proved a marked postural control deficit in freezers, while balance scores and turning speed were similar to non-freezers. Both weight-shift amplitudes and the freezing ratio were responsive to medication in freezers, suggesting axial motor vigor is levodopa-responsive. Future work needs to test whether weight-shifting and freezing severity can be further ameliorated through training.

Functional limits of stability and standing balance in people with Parkinson's disease with and without freezing of gait using wearable sensors

BACKGROUND

People with from Parkinson's disease (PD) and freezing of gait (FoG) have more frequent falls compared to those who do not freeze but there is no consensus on which, specific objective measures of postural instability are worse in freezers (PD + FoG) than non-freezers (PD-FoG).

RESEARCH QUESTION

Are functional limits of stability (fLoS) or postural sway during stance measured with wearable inertial sensors different between PD + FoG versus PD-FoG, as well as between PD versus healthy control subjects (HC)?

METHODS

Sixty-four PD subjects with FoG (MDS-UPDRS Part III: 45.9 ± 12.5) and 80 PD subjects without FoG (MDS-UPDRS Part III: 36.2 ± 10.9) were tested Off medication and compared with 79 HC. Balance was quantified with inertial sensors worn on the lumbar spine while performing the following balance tasks: 1) fLoS as defined by the maximum displacement in the forward and backward directions and 2) postural sway area while standing with eyes open on a firm and foam surface. An ANOVA, controlling for disease duration, compared postural control between groups.

RESULTS

PD + FoG had significantly smaller fLoS compared to PD-FoG (p =  0.004) and to healthy controls (p <  0.001). However, PD-FoG showed similar fLoS compared to healthy controls (p =  0.48). Both PD+FoG and PD-FoG showed larger postural sway on a foam surface compared to healthy controls (p =  0.001) but there was no significant difference in postural sway between PD+FoG and PD-FoG.

SIGNIFICANCE

People with PD and FoG showed task-specific, postural impairments with smaller fLoS compared to non-freezers, even when controlling for disease duration. However, individuals with PD with or without FoG had similar difficulties standing quietly on an unreliable surface compared to healthy controls. Wearable inertial sensors can reveal worse fLoS in freezers than non-freezers that may contribute to FoG and help explain their more frequent falls.

Recovery of dynamic stability during slips unaffected by arm swing in people with Parkinson's Disease

The arm elevation strategy assists in recovering stability during slips in healthy young and elderly individuals. However, in people with Parkinson's Disease, one of the main motor symptoms affecting the upper limbs is reduced arm swing which intensifies throughout the course of the disease before becoming absent. This holds direct implications for these individuals when encountering slips as the arm elevation strategy is an integral component in the interlimb slip response to restore stability. Arm swing's effect in recovering from slips in people with Parkinson's Disease though remains unexamined. Twenty people with Parkinson's Disease (63.78 ± 8.97 years) walked with restricted and unrestricted arm swing conditions on a dual-belt treadmill where slips were induced on the least and most affected sides. Data were collected on the CAREN Extended System (Motek Medical, Amsterdam, NL). The Margin of Stability, linear and angular trunk velocities, as well as step length, time, and width were calculated. Data were examined during the slipped step and recovery step. The restricted arm swing condition, compared to unrestricted, caused a faster step time during the slipped step. Compared to the most affected leg, the least affected had a wider step width during the slipped step. During the recovery step, the least affected leg had a larger anteroposterior Margin of Stability and longer step time than the most affected. No differences between our arm swing conditions suggests that the normal arm swing in our participants was not more effective at restoring stability after an induced slip compared to when their arm motion was restricted. This may be due to the arm elevation strategy being ineffective in counteracting the slip's backward destabilization in these individuals. Differences between the legs revealed that our participants were asymmetrically impaired in their slip recovery response.

A vicious cycle of fear of falling avoidance behavior in Parkinson's disease: A path analysis

BACKGROUND

Postural instability (PI) in Parkinson's disease (PD) is associated with several negative downstream consequences.

OBJECTIVE

The purpose was to explore the validity of a theoretical model of these downstream consequences arranged in a vicious cycle wherein PI leads to decreased balance confidence, which in turn leads to increased fear of falling (FOF) avoidance behavior, which in turn leads to decreased physical conditioning, which then feeds back and negatively affects PI.

METHODS

A path analysis of cross-sectional data from 55 participants with PD was conducted. The four constructs in the model connected in succession were: 1. PI (principal components analysis (PCA) composite of the Unified Parkinson's Disease Rating Scale PI and Gait Difficulty score, Timed Up and Go test, and Berg Balance Scale); 2. balance confidence (Activities-Specific Balance Confidence Scale); 3. FOF avoidance behavior (PCA composite of the FOF Avoidance Behavior Questionnaire and average number of steps per day); and, 4. physical conditioning (2-Minute Step Test).

RESULTS

The path model was an excellent fit to the data, χ2 (7) = 7.910, p = .341, CFI = 0.985, TLI = 0.968, RMSEA = 0.049 (90% CI: 0.000 to 0.179). The moderate to strong and uniformly significant parameter estimates were -0.519, -0.651, -0.653, and -0.570, respectively (ps < 0.01).

CONCLUSIONS

PI directly and inversely predicted balance confidence, which in turn directly and inversely predicted FOF avoidance behavior. Furthermore, FOF avoidance behavior directly and inversely predicted physical conditioning, which directly and inversely predicted PI, thereby closing the cycle. These findings highlight the downstream consequences of PI in PD and support the notion of a vicious cycle of FOF avoidance behavior.

Initial center of pressure position prior to anticipatory postural adjustments during gait initiation in people with Parkinson's disease with freezing of gait

INTRODUCTION

Freezing of gait (FOG) in Parkinson's disease (PD) is associated with an altered posture during quiet stance as well as an impaired preparation and execution of the gait initiation process. We aimed to investigate whether an altered initial posture impacts anticipatory postural adjustments (APAs) and first-step execution during gait initiation in people with PD with FOG (PD + FOG).

METHODS

Twenty-seven PD+FOG, 30 PD patients without FOG and 27 age-matched healthy controls performed self-generated gait initiation. Initial mean center of pressure (COP) position prior to APA onset, characteristics of APAs and features of first-step execution were investigated.

RESULTS

Contrarily to controls, PD patients showed a COP that was initially positioned more towards the stance leg (p = 0.007). Moreover, significantly smaller backward COP shift, longer duration of swing-foot unloading phase, and lower first-step length and velocity characterized PD+FOG compared to controls. While size and duration of backward COP shift during APA and lateral COP shift during the unloading phase were main predictors of first-step length and velocity in all groups, the medio-lateral shift of the initial COP position in PD+FOG was a main predictor of first-step execution (β = -0.191, p = 0.001 for velocity).

CONCLUSION

In PD+FOG, the more the COP was initially positioned towards the stance foot, the slower and shorter the first step. The initial medio-lateral COP position may be a compensatory strategy to address postural instability of PD+FOG. A specific training regarding postural control prior to gait preparation and execution could improve functional mobility in PD+FOG.

Freezing of Gait in Parkinson's Disease: Risk Factors, Their Interactions, and Associated Nonmotor Symptoms

Background

Freezing of gait (FOG) is a debilitating and incompletely understood symptom in Parkinson's disease (PD).

Objective

To determine the principal clinical factors predisposing to FOG in PD, their interactions, and associated nonmotor symptoms.

Methods

164 PD subjects were assessed in a cross-sectional retrospective study, using the MDS-UPDRS scale, MMSE, and Clinical Dementia Rating Scale. Clinical factors associated with FOG were determined using univariate analysis and nominal logistic regression. Receiver operating characteristic curves were computed, to obtain measures of sensitivity and specificity of predictors of FOG. Subgroups of patients with FOG were compared with those without FOG, based on defining aspects of their clinical phenotype.

Results

Relative to non-FOG patients, those with FOG had a longer disease duration, higher PIGD and balance-gait score, higher LED, and more motor complications (p < 0.0001) and were more likely to exhibit urinary dysfunction (p < 0.0003), cognitive impairment, hallucinations, and psychosis (p=0.003). The balance-gait score and motor complications, at their optimum cutoff values, together predicted FOG with 86% accuracy. Interactions were noted between cognitive dysfunction and both the Bal-Gait score and motor complication status, cognitive impairment or dementia increasing the likelihood of FOG in subjects without motor complications (p=0.0009), but not in those with motor complications.

Conclusions

Both disease and treatment-related factors, notably LED, influence the risk of FOG in PD, with a selective influence of cognitive dysfunction in patients with balance-gait disorder but not in those with motor fluctuations. These findings may help to inform clinical management and highlight distinct subgroups of patients with PD-FOG, which are likely to differ in their network pathophysiology.

Using machine learning-based analytics of daily activities to identify modifiable risk factors for falling in Parkinson's disease

BACKGROUND

Although risk factors that lead to falling in Parkinson's disease (PD) have been previously studied, the established predictors are mostly non-modifiable. A novel method for fall risk assessment may provide more insight into preventable high-risk activities to reduce future falls.

OBJECTIVES

To explore the prediction of falling in PD patients using a machine learning-based approach.

METHOD

305 PD patients, with or without a history of falls within the past month, were recruited. Data including clinical demographics, medications, and balance confidence, scaled by the 16-item Activities-Specific Balance Confidence Scale (ABC-16), were entered into the supervised machine learning models using XGBoost to explore the prediction of fallers/recurrent fallers in two separate models.

RESULTS

99 (32%) patients were fallers and 58 (19%) were recurrent fallers. The accuracy of the model to predict falls was 72% (p = 0.001). The most important factors were item 7 (sweeping the floor), item 5 (reaching on tiptoes), and item 12 (walking in a crowded mall) in the ABC-16 scale, followed by disease stage and duration. When recurrent falls were analysed, the models had higher accuracy (81%, p = 0.02). The strongest predictors of recurrent falls were item 12, 5, and 10 (walking across parking lot), followed by disease stage and current age.

CONCLUSION

Our machine learning-based study demonstrated that predictors of falling combined demographics of PD with environmental factors, including high-risk activities that require cognitive attention and changes in vertical and lateral orientations. This enables physicians to focus on modifiable factors and appropriately implement fall prevention strategies for individual patients.

Is freezing of gait correlated with postural control in patients with moderate-to-severe Parkinson's disease?

Freezing of gait (FoG) is one of the main reasons for movement initiation disorders and abnormal coupling of posture and gait in Parkinson's disease (PD). Patients with FoG have poor postural control when compared to patients without FoG. However, the nature of the interrelationship between FoG and domains of postural control remains unknown. The aim of this study was to estimate the association between different domains of postural control and severity of FoG in patients with moderate-to-severe PD. Thirty patients with idiopathic PD with FoG (age range 45-80 years, Hoehn & Yahr stages 3 and 4) participated in the study. We evaluated objective (FoG-ratio during turning task) and subjective (New Freezing of Gait Questionnaire, NFoG-Q) measures of FoG severity, reactive postural adjustments in response to an external perturbation, first step anticipatory adjustment for step initiation and quiet standing stability. In the multiple regression analysis, step initiation was the strongest significant correlation of the NFoG-Q score explaining 23% of the variance of the assessment. For the objective FoG measure, mediolateral CoP amplitude in quiet standing and mediolateral CoP amplitude in step initiation explained 39% of the variance of the FoG-ratio. As main conclusions, this study identified the association between objective and subjective measure for FoG severity and postural control domains. The results support conducting step initiation training during rehabilitation of individuals with FoG.

Relating Parkinson freezing and balance domains: A structural equation modeling approach

BACKGROUND

People with PD who exhibit freezing of gait (FOG) also exhibit poor balance compared to those who do not freeze. However, balance is a broad construct that can be subdivided into subdomains that include dynamic balance (gait), anticipatory postural adjustments (APAs) & gait initiation, postural sway in stance, and automatic postural responses (e.g., reactive stepping). Few studies have provided a robust investigation on how each of these domains is impacted by FOG, and no studies have compared balance across groups while rigorously controlling for disease severity.

METHODS

Structural equation modeling was used to evaluate the relationships between FOG and balance domains constructed as latent variables and controlling for disease severity. Domains included: dynamic balance (gait), APAs, postural sway, and reactive stepping. Models were run relating domains to both the presence and severity of FOG.

RESULTS

Latent variables reflecting domains of Gait and APAs, but not postural sway or reactive stepping, were significantly related to the severity of FOG. Models for presence of FOG showed the same results, as Gait and APAs, but not postural sway or reactive stepping, were related to presence of FOG.

CONCLUSION

These results are consistent with hypotheses that balance deficits in people with PD who freeze are most pronounced in gait and anticipatory postural adjustments. Reactive stepping and postural sway domains are less effected in PD patients who freeze compared to those who do not. These findings suggest that rehabilitative strategies focused on gait and APAs may be most effective for people with PD who freeze.

The effect of tactile feedback on gait initiation in people with Parkinson's disease: A pilot study

BACKGROUND

Gait initiation and turning are common triggers for Freezing of Gait (FOG) in people with Parkinson's disease (PD). Recently, it has been shown that closed-loop tactile feedback (CLTF) can be effective to improve turning performance in people with FOG.

RESEARCH QUESTION

Does CLTF change the preparation and execution of the first step during gait initiation?

METHODS

People (n = 36) with PD with FOG (PD + FOG) (n = 18) and without FOG (PD-FOG) (n = 18) were included in the study and performed self-initiated gait with or without CLTF under single and dual task conditions. Anticipatory postural adjustments (APAs) and step kinematics were quantified with inertial measurement units (IMUs). Muscle activity of the right and left tensor fasciae latae (TFL) was measured via EMG recordings.

RESULTS

PD + FOG and PD-FOG did not differ in age, gender and disease duration and severity (p > 0.05). PD + FOG performed smaller APAs (F = 4.559, p = 0.04) with a higher amount of TFL co-contraction (F = 6.034, p = 0.02) compared to PD-FOG. CLTF had no effect on APAs but led to an increase in first step duration (F = 7.921, p = 0.008).

CONCLUSIONS

PD + FOG had smaller APAs and higher left and right TFL co-contraction during gait initiation. CLTF did not impact preparation of the first step but led to a slower execution of the first step. We speculate that, similarly to findings from turning, CLTF might result in the participant attending more closely to the first step compared to without CLTF. Whether increased attention on gait initiation is beneficial in diminishing FOG should be investigated in more detail.

Behavioural manifestations and associated non-motor features of freezing of gait: A narrative review and theoretical framework

Over the past decade, non-motor related symptoms and provocative contexts have offered unique opportunities to gain insight into the potential mechanisms that may underpin freezing of gait (FOG) in Parkinson's disease (PD). While this large body of work has informed several theoretical models, to date, few are capable of explaining behavioural findings across multiple domains (i.e. cognitive, sensory-perceptual and affective) and in different behavorial contexts. As such, the exact nature of these interrelationships and their neural basis remain quite enigmatic. Here, the non-motor, behavioural evidence for cognitive, sensory-perceptual and affective contributors to FOG are reviewed and synthesized by systematically examining (i) studies that manipulated contextual environments that provoke freezing of gait, (ii) studies that uncovered factors that have been proposed to contribute to freezing, and (iii) studies that longitudinally tracked factors that predict the future development of freezing of gait. After consolidating the evidence, we offer a novel perspective for integrating these multi-faceted behavioural patterns and identify key challenges that warrant consideration in future work.

Interindividual Balance Adaptations in Response to Perturbation Treadmill Training in Persons With Parkinson Disease

BACKGROUND AND PURPOSE

Perturbation training is a promising approach to reduce fall incidence in persons with Parkinson disease (PwPD). This study aimed to evaluate interindividual differences in balance adaptations in response to perturbation treadmill training (PTT) and identify potential outcome predictors.

METHODS

PwPD (n = 43, Hoehn & Yahr stage 1-3.5) were randomly assigned to either 8 weeks of PTT or conventional treadmill training (CTT) without perturbations. At baseline and following intervention, data from 4 domains of balance function (reactive, anticipatory, dynamic postural control, and quiet stance) were collected. Using responder analysis we investigated interindividual differences (responder rates and magnitude of change) and potential predictive factors.

RESULTS

PTT showed a significantly higher responder rate in the Mini Balance Evaluation Systems Test (Mini-BESTest) subscore reactive postural control, compared with CTT (PTT = 44%; CTT = 10%; risk ratio = 4.22, confidence interval = 1.03-17.28). Additionally, while between-groups differences were not significant, the proportion of responders in the measures of dynamic postural control was higher for PTT compared with CTT (PTT: 22%-39%; CTT: 5%-10%). The magnitude of change in responders and nonresponders was similar in both groups. PTT responders showed significantly lower initial balance performance (4/8 measures) and cognitive function (3/8 measures), and were older and at a more advanced disease stage, based on descriptive evaluation.

DISCUSSION AND CONCLUSIONS

Our findings suggest that PTT is beneficial to improve reactive balance in PwPD. Further, PTT appeared to be effective only for a part of PwPD, especially for those with lower balance and cognitive function, which needs further attention.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A1).

Predicting falls in people with Parkinson's disease: impact of methodological approaches on predictors identified

BACKGROUND

Previous investigations of falls predictors in people with Parkinson's disease (PD) have used various statistical methods and categorization of falls outcomes. The impact of methodological differences on falls predictors has not been investigated.

OBJECTIVES

To describe similarities and differences in predictors modelled for fall rates [negative binomial (NB), Poisson Inverse Gaussian (PIG) and quantile regression] and previously-reported predictors of time to second fall (Cox regression), i.e. past falls, motor fluctuations, disability, levodopa dose and balance impairment. To investigate whether predictors from quantile regression vary across subsets of fallers based on fall frequency.

METHODS

Participants with PD (n = 229) were followed-up for 12 months. NB and PIG regression were used to determine predictors of fall rates, with the best fitting model reported. Quantile regression was used to determine predictors at higher (62nd, 70th, 80th) percentiles of the falls distribution. Univariate and multivariate analyses were performed.

RESULTS

Predictors of fall rates were the same in NB and PIG multivariate models, with the PIG model fitting our data better. Past falls, disability and levodopa dose were associated with fall rates from PIG and quantile regression. Freezing of gait was associated with fall rates from PIG regression. Disease severity predicted less (70th percentile, approximately 2-4) and more (80th percentile, approximately ≥ 5) frequent falls, and anteroposterior stability also predicted less frequent falls (p < 0.05), from quantile regression.

CONCLUSIONS

Not all predictors of time to second fall were predictors of fall rates. Quantile regression revealed some divergent predictors depending on the percentile of fall frequency examined.

Functional neuroimaging of human postural control: A systematic review with meta-analysis

Postural instability is a strong risk factor for falls that becomes more prominent with aging. To facilitate treatment and prevention of falls in an aging society, a thorough understanding of the neural networks underlying postural control is warranted. Here, we present a systematic review of the functional neuroimaging literature of studies measuring posture-related neural activity in healthy subjects. Study methods were overall heterogeneous. Eleven out of the 14 studies relied on postural simulation in a supine position (e.g. motor imagery). The key nodes of human postural control involved the brainstem, cerebellum, basal ganglia, thalamus and several cortical regions. An activation likelihood estimation meta-analysis revealed that the anterior cerebellum was consistently activated across the wide range of postural tasks. The cerebellum is known to modulate the brainstem nuclei involved in the control of posture. Hence, this systematic review with meta-analysis provides insight into the neural correlates which underpin human postural control and which may serve as a reference for future neural network and region of interest analyses.

Absent Arm Swing and Dual Tasking Decreases Trunk Postural Control and Dynamic Balance in People With Parkinson's Disease

Introduction: Falling during walking is a common occurrence in people with Parkinson's disease and is closely associated with severe social and medical consequences. Recent evidence demonstrates that arm swing affects dynamic balance in healthy young adults; however, it remains unexamined what its effect is in people with Parkinson's disease, particularly when combined with a secondary dual task.

Methods: Twenty people with Parkinson's disease (63.78 ± 8.97) walked with two arm swing conditions (absent and normal) with and without a secondary dual task. Data were collected on a split-belt treadmill CAREN Extended-System (Motek Medical, Amsterdam, NL). Average and standard deviations for trunk linear and angular velocity were calculated along with their instantaneous values (during foot strikes) in all three axes. Averages and coefficient of variations for step length, time, and width; margin of stability; and harmonic ratios were also calculated.

Results: Compared with normal arm swing, absent arm swing reduced the least affected leg's average step length and increased its step length coefficient of variation while increasing step time coefficient of variation in the most affected leg. Further, absent arm swing reduced trunk anteroposterior instantaneous angular velocity (least affected leg) and reduced anteroposterior instantaneous linear velocity (bilaterally). For the vertical axis, absent arm swing increased the trunk's average angular velocity but reduced its instantaneous linear velocity and angular velocity standard deviation (least affected leg). Additionally, the margin of stability increased when the arms were absent (least affected leg). Alternatively, dual tasking reduced average step time (most affected leg) and increased the step width coefficient of variation (bilaterally). Additionally, dual tasking increased the mediolateral average angular velocity, instantaneous linear velocity standard deviation (bilaterally), and instantaneous angular velocity standard deviation (least affected leg). For the vertical axis, dual tasking increased average linear and angular velocity standard deviation as well as instantaneous angular velocity standard deviation (bilaterally).

Conclusion: Findings suggest that participants attempted to control extraneous trunk movement (due to absent arm swing) through compensatory responses in both lower and upper extremities. However, participants appeared to predominately compensate on their least affected side. Contrastingly, modifying mediolateral foot placement appeared to be the main means of maintaining walking stability while dual tasking.

Freezing of gait in Parkinson's disease: pathophysiology, risk factors and treatments

Background

Freezing of gait (FOG) is a common, disabling symptom of Parkinson's disease (PD), but the mechanisms and treatments of FOG remain great challenges for clinicians and researchers. The main focus of this review is to summarize the possible mechanisms underlying FOG, the risk factors for screening and predicting the onset of FOG, and the clinical trials involving various therapeutic strategies. In addition, the limitations and recommendations for future research design are also discussed.

Main body

In the mechanism section, we briefly introduced the physiological process of gait control and hypotheses about the mechanism of FOG. In the risk factor section, gait disorders, PIGD phenotype, lower striatal DAT uptake were found to be independent risk factors of FOG with consistent evidence. In the treatment section, we summarized the clinical trials of pharmacological and non-pharmacological treatments. Despite the limited effectiveness of current medications for FOG, especially levodopa resistant FOG, there were some drugs that showed promise such as istradefylline and rasagiline. Non-pharmacological treatments encompass invasive brain and spinal cord stimulation, noninvasive repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) and vagus nerve stimulation (VNS), and physiotherapeutic approaches including cues and other training strategies. Several novel therapeutic strategies seem to be effective, such as rTMS over supplementary motor area (SMA), dual-site DBS, spinal cord stimulation (SCS) and VNS. Of physiotherapy, wearable cueing devices seem to be generally effective and promising.

Conclusion

FOG model hypotheses are helpful for better understanding and characterizing FOG and they provide clues for further research exploration. Several risk factors of FOG have been identified, but need combinatorial optimization for predicting FOG more precisely. Although firm conclusions cannot be drawn on therapeutic efficacy, the literature suggested that some therapeutic strategies showed promise.

Do Patients With Parkinson's Disease With Freezing of Gait Respond Differently Than Those Without to Treadmill Training Augmented by Virtual Reality?

Background. People with Parkinson's disease and freezing of gait (FOG+) have more falls, postural instability and cognitive impairment compared with FOG-. Objective. To conduct a secondary analysis of the V-TIME study, a randomized, controlled investigation showing a greater reduction of falls after virtual reality treadmill training (TT + VR) compared with usual treadmill walking (TT) in a mixed population of fallers. We addressed whether these treadmill interventions led to similar gains in FOG+ as in FOG-. Methods. A total of 77 FOG+ and 44 FOG- were assigned randomly to TT + VR or TT. Participants were assessed pre- and posttraining and at 6 months' follow-up. Main outcome was postural stability assessed by the Mini Balance Evaluation System Test (Mini-BEST) test. Falls were documented using diaries. Other outcomes included the New Freezing of Gait Questionnaire (NFOG-Q) and the Trail Making Test (TMT-B). Results. Mini-BEST scores and the TMT-B improved in both groups after training (P = .001), irrespective of study arm and FOG subgroup. However, gains were not retained at 6 months. Both FOG+ and FOG- had a greater reduction of falls after TT + VR compared with TT (P = .008). NFOG-Q scores did not change after both training modes in the FOG+ group. Conclusions. Treadmill walking (with or without VR) improved postural instability in both FOG+ and FOG-, while controlling for disease severity differences. As found previously, TT + VR reduced falls more than TT alone, even among those with FOG. Interestingly, FOG itself was not helped by training, suggesting that although postural instability, falls and FOG are related, they may be controlled by different mechanisms.

Treatment options for postural instability and gait difficulties in Parkinson's disease

Introduction: Gait and balance disorders in Parkinson's disease (PD) represent a major therapeutic challenge as frequent falls and freezing of gait impair quality of life and predict mortality. Limited dopaminergic therapy responses implicate non-dopaminergic mechanisms calling for alternative therapies.Areas covered: The authors provide a review that encompasses pathophysiological changes involved in axial motor impairments in PD, pharmacological approaches, exercise, and physical therapy, improving physical activity levels, invasive and non-invasive neurostimulation, cueing interventions and wearable technology, and cognitive interventions.Expert opinion: There are many promising therapies available that, to a variable degree, affect gait and balance disorders in PD. However, not one therapy is the 'silver bullet' that provides full relief and ultimately meaningfully improves the patient's quality of life. Sedentariness, apathy, and emergence of frailty in advancing PD, especially in the setting of medical comorbidities, are perhaps the biggest threats to experience sustained benefits with any of the available therapeutic options and therefore need to be aggressively treated as early as possible. Multimodal or combination therapies may provide complementary benefits to manage axial motor features in PD, but selection of treatment modalities should be tailored to the individual patient's needs.

Functional MRI to Study Gait Impairment in Parkinson's Disease: a Systematic Review and Exploratory ALE Meta-Analysis

PURPOSE OF REVIEW

Whilst gait impairment is a main cause for disability in Parkinson's disease (PD), its neural control remains poorly understood. We performed a systematic review and meta-analysis of neuroimaging studies of surrogate features of gait in PD.

FINDINGS

Assessing the results from PET or SPECT scans after a period of actual walking as well as fMRI during mental imagery or virtual reality (VR) gait paradigms, we found a varying pattern of gait-related brain activity. Overall, a decrease in activation of the SMA during gait was found in PD compared to elderly controls. In addition, the meta-analysis showed that the most consistent gait-related activation was situated in the cerebellar locomotor region (CLR) in PD. Despite methodological heterogeneity, the combined neuroimaging studies of gait provide new insights into its neural control in PD, suggesting that CLR activation likely serves a compensatory role in locomotion.