Dopaminergic medication does not improve stepping responses following backward and forward balance perturbations in patients with Parkinson’s disease

Associating white matter microstructural integrity and improvements in reactive stepping in people with Parkinson's Disease

Reactive steps are rapid responses after balance challenges. People with Parkinson's Disease (PwPD) demonstrate impaired reactive stepping, increasing fall-risk. Although PwPD can improve steps through practice, the neural mechanisms contributing to improved reactive stepping are poorly understood. This study investigated white-matter correlates of responsiveness to reactive step training in PwPD. In an eighteen-week multiple-baseline study, participants (n = 22) underwent baseline assessments (B1 and B2 two-weeks apart), a two-week training protocol, and post-training assessments immediately (P1) and two-months (P2) post-training. Assessments involved three backward reactive step trials, measuring anterior-posterior margin of stability (AP MOS), step length, and step latency. Tract-Based Spatial Statistics correlated white-matter integrity (fractional anisotropy (FA) and radial diffusivity (RD)) with retained (P2-B2) and immediate improvements (P1-B2) in stepping. Significant and sustained improvements in step length and AP MOS were observed. Greater retention of step length improvement correlated with increased FA in the left anterior thalamic radiation (ATR), left posterior thalamic radiation (PTR), left superior longitudinal fasciculus (SLF), and right inferior longitudinal fasciculus (ILF). Step latency retention was associated with lower RD in the left posterior corona radiata and left PTR. Immediate improvements in AP MOS correlated with increased FA of the right ILF, right SLF, and right corticospinal tract. Immediate step length improvements were associated with increased FA in right and left ATR and right SLF. These findings highlight the importance of white-matter microstructural integrity in motor learning and retention processes in PD and could aid in identifying individuals with PD who would benefit most from balance rehabilitation.

A backward cycling programme for people with Parkinson's disease: a feasibility and preliminary results study

OBJECTIVE

To assess the feasibility of backward cycling for people with Parkinson's disease. Secondary objectives were to assess changes in gait and balance following a 6-week program.

DESIGN

A single-group prospective pre-test, post-test study with 1-month follow-up.

SUBJECTS/PATIENTS

Twenty-six people with Parkinson's disease (mean age: 69 (7.74) years, gender: 83% males, time since diagnosis: 6 (4.44) years).

METHODS

Participants pedaled backward on a stationary bicycle for 30 minutes at moderate intensity twice a week for 6 weeks. Feasibility was assessed by acceptability, suitability, and burden. Data collected at pre- and post-intervention with 1-month follow-up included backward stepping response variables, forward/backward gait variables, Mini-Balance Evaluation Systems Test (MBT), and 6 Minute Walk Test.

RESULTS

There was a high retention rate (95.8%) and adherence rate (100%) with one adverse event and minimal burden. Significant improvements were seen in step count and excursion distance during backward stepping responses, forward and backward gait velocity, forward step length, and the Mini-BESTest.

CONCLUSION

Backward cycling was a feasible intervention for people with Parkinson's disease, demonstrating low burden with high retention and adherence rates, and it is a safe exercise with the potential for benefits in gait and balance variables.

Extraction of the pull force from inertial sensors during the pull test for Parkinson's disease: A reliability study

OBJECTIVE

To examine the inter- and intra-rater reliability of the pull test in patients with Parkinson's disease (PD) using the extracted pull force.

METHODS

In this inter- and intra-rater reliability study, two raters performed a pull test on 30 patients with PD. The pull force was quantified using inertial sensors attached to the rater's right hand and the patient's lower trunk. In this study, the pull force was calculated as an extracted three-dimensional vector quantity, the resultant acceleration, and was expressed in m/s2. Inter- and intra-rater reliabilities were analyzed using the interclass correlation coefficient (ICC) for the pull force and Cohen's weighted kappa (κw) for the pull test score. Furthermore, Bland-Altman analysis was used to investigate systematic errors.

RESULTS

The inter- and intra-rater reliability of the pull force was very poor (ICC = 0.033-0.214). Bland-Altman analysis revealed no systematic errors in the pull forces between the two test points. Conversely, κw for the pull test scores ranged from 0.763 to 0.920, indicating substantial to almost perfect agreement.

CONCLUSION

The pull test score was reliable despite variations in the quantified pull force for inter- and intra-rater reliability. Our findings suggest that the pull test is a robust tool for evaluating postural instability in patients with PD and that the pull force probably does not affect scoring performance.

Effects of protective step training on proactive and reactive motor adaptations in Parkinson's disease patients

The aim of this study was to investigate to what extent PD affects the ability to walk, respond to balance perturbations in a single training session, and produce acute short-term effects to improve compensatory reactions and control of unperturbed walking stability. Understanding the mechanism of compensation and neuroplasticity to unexpected step perturbation training during walking and static stance can inform treatment of PD by helping to design effective training regimens that remediate fall risk. Current rehabilitation therapies are inadequate at reducing falls in people with Parkinson's disease (PD). While pharmacologic and surgical treatments have proved largely ineffective in treating postural instability and gait dysfunction in people with PD, studies have demonstrated that therapy specifically focusing on posture, gait, and balance may significantly improve these factors and reduce falls. The primary goal of this study was to assess the effectiveness of a novel and promising intervention therapy (protective step training - i.e., PST) to improve balance and reduce falls in people with PD. A secondary goal was to understand the effects of PST on proactive and reactive feedback responses during stance and gait tasks. Multiple-baseline, repeated measures analyses were performed on the multitude of proactive and reactive performance measures to assess the effects of PST on gait and postural stability parameters. In general, the results indicate that participants with PD were able to use experiences with perturbation training to integrate and adapt feedforward and feedback behaviors to reduce falls. The ability of the participants with PD to adapt to changes in task demands suggests that individuals with PD could benefit from the protective step training to facilitate balance control during rehabilitation.

Distinct cortico-muscular coupling between step and stance leg during reactive stepping responses

Balance recovery often relies on successful stepping responses, which presumably require precise and rapid interactions between the cerebral cortex and the leg muscles. Yet, little is known about how cortico-muscular coupling (CMC) supports the execution of reactive stepping. We conducted an exploratory analysis investigating time-dependent CMC with specific leg muscles in a reactive stepping task. We analyzed high density EEG, EMG, and kinematics of 18 healthy young participants while exposing them to balance perturbations at different intensities, in the forward and backward directions. Participants were instructed to maintain their feet in place, unless stepping was unavoidable. Muscle-specific Granger causality analysis was conducted on single step- and stance-leg muscles over 13 EEG electrodes with a midfrontal scalp distribution. Time-frequency Granger causality analysis was used to identify CMC from cortex to muscles around perturbation onset, foot-off and foot strike events. We hypothesized that CMC would increase compared to baseline. In addition, we expected to observe different CMC between step and stance leg because of their functional role during the step response. In particular, we expected that CMC would be most evident for the agonist muscles while stepping, and that CMC would precede upregulation in EMG activity in these muscles. We observed distinct Granger gain dynamics over theta, alpha, beta, and low/high-gamma frequencies during the reactive balance response for all leg muscles in each step direction. Interestingly, between-leg differences in Granger gain were almost exclusively observed following the divergence of EMG activity. Our results demonstrate cortical involvement in the reactive balance response and provide insights into its temporal and spectral characteristics. Overall, our findings suggest that higher levels of CMC do not facilitate leg-specific EMG activity. Our work is relevant for clinical populations with impaired balance control, where CMC analysis may elucidate the underlying pathophysiological mechanisms.

Dopamine replacement therapy normalizes reactive step length to postural perturbations in Parkinson's disease

BACKGROUND

Postural instability is one of the most disabling motor symptoms of Parkinson's disease (PD) given its association with falls and loss of independence. Previous studies have assessed biomechanical measures of reactive stepping in response to perturbations, showing that individuals with PD exhibit inadequate postural responses to regain balance.

RESEARCH QUESTION

Does dopamine replacement therapy normalize step length in response to balance perturbations?

METHODS

In this study, we estimated reactive step length, to a postural perturbation, retrospectively from a dataset of frontal plane video using 2D motion tracking and direct linear transform methods. We compared two perturbation methods: support surface translation and shoulder pull (the clinical standard) in 14 individuals with PD and 13 without PD (on and off medication), with and without partial body weight support (BWS). The primary outcome was the length of the first step taken to regain balance after the perturbation analyzed with mixed effects ANOVA, with post hoc analysis of anteroposterior (AP) and mediolateral (ML) components.

RESULTS

PD OFF medication exhibited shorter reactive step length compared to PD ON and compared to control groups for the surface translation perturbations, but no significant difference was observed for the shoulder pull perturbations.

SIGNIFICANCE

Dopamine replacement therapy affects step length in response to perturbation more robustly for surface translations than for a pull by the shoulders.

Postural instability in Parkinson's disease assessed with clinical "pull test" and standardized postural perturbations: effect of medication and body weight support

OBJECTIVE

This experiment tested if balance performance differed between a standardized treadmill surface perturbation task and a clinical pull test and was affected by medication or the presence of body weight support in people with Parkinson's disease (PD).

METHODS

Twenty-seven individuals were tested (14 PD in both ON- and OFF-medication states). Clinical pull test and rapid forward (backward fall) translations of the support surface were applied to induce postural reactions requiring at least 1 step to restore balance. The effects of pull type (clinical vs. treadmill), partial bodyweight support (0 vs 20% body weight) and group (control, PD ON-meds and PD OFF-meds) on reactive stepping as well as practice/learning effect were examined. The number of steps taken and the first step duration were entered in linear repeated-measures mixed-effect models separately.

RESULTS

The effects of pull type, group, and bodyweight support were all significant in both metrics, as was ON- vs. OFF-medication. A significant interaction term (group x pull type) was found in the first step duration, showing that the group difference was greater in treadmill compared to the clinical pull test. A significant practice effect was also observed within and across testing sessions.

CONCLUSIONS

A standardized treadmill perturbation performed slightly better than the classical pull test in distinguishing between groups, and partial weight support did not substantially degrade the test's performance to detect the balance deficits in people with PD.

Machine Learning and Wearable Sensors for the Early Detection of Balance Disorders in Parkinson's Disease

Dynamic posturography combined with wearable sensors has high sensitivity in recognizing subclinical balance abnormalities in patients with Parkinson's disease (PD). However, this approach is burdened by a high analytical load for motion analysis, potentially limiting a routine application in clinical practice. In this study, we used machine learning to distinguish PD patients from controls, as well as patients under and not under dopaminergic therapy (i.e., ON and OFF states), based on kinematic measures recorded during dynamic posturography through portable sensors. We compared 52 different classifiers derived from Decision Tree, K-Nearest Neighbor, Support Vector Machine and Artificial Neural Network with different kernel functions to automatically analyze reactive postural responses to yaw perturbations recorded through IMUs in 20 PD patients and 15 healthy subjects. To identify the most efficient machine learning algorithm, we applied three threshold-based selection criteria (i.e., accuracy, recall and precision) and one evaluation criterion (i.e., goodness index). Twenty-one out of 52 classifiers passed the three selection criteria based on a threshold of 80%. Among these, only nine classifiers were considered "optimum" in distinguishing PD patients from healthy subjects according to a goodness index ≤ 0.25. The Fine K-Nearest Neighbor was the best-performing algorithm in the automatic classification of PD patients and healthy subjects, irrespective of therapeutic condition. By contrast, none of the classifiers passed the three threshold-based selection criteria in the comparison of patients in ON and OFF states. Overall, machine learning is a suitable solution for the early identification of balance disorders in PD through the automatic analysis of kinematic data from dynamic posturography.

Acceptability and Preliminary Results of Technology-Assisted Balance Training in Parkinson's Disease

(1) Background: Parkinson’s Disease (PD) is one of the most common causes of disability among older individuals. The advanced stages of PD are usually characterized by postural instability and, as a consequence, falls. Those are among the main factors that determine the quality of life, as well as the morbidity and mortality of a person with PD. In the field of PD rehabilitation, robotics is also rapidly gaining ground. As a primary aim, we evaluate the acceptability of the technology integrated intervention, using the Psychosocial Impact of Assistive Devices Scale (PIADS), in order to analyze the attitude of the participants towards the Tymo^® system. As a secondary outcome, we assess the result of the rehabilitation treatment integrated with the Tymo^® system on several patient’s features. (2) Methods: We studied a population of 16 patients with Parkinson’s Disease. Each recruited subject completed 10 treatment sessions, organized as two training sessions per week, for 5 weeks. The intervention included 30 min of traditional therapy and 20 min of technological treatment with a robotic system. PIADS is composed of three subscales (Competence subscale, Adaptability subscale, Self-esteem subscale) ranging from −3 to +3, reflecting, respectively, a negative or positive feeling towards the device. (3) Results: The Competence subscale, measuring feelings of competence and usefulness, obtained a score of 1.24 (SD = 0.78). The score of Adaptability subscale, indicating a willingness to try out new things and to take risks, was 1.83 (SD = 0.65). Finally, the Self-esteem subscale, indicating feelings of emotional health and happiness, reached a score of 1.31 (SD = 0.72). Moreover, statistical analysis reveals a significant effect on balance performance after intervention. (4) Conclusions: This feasibility study represents a starting point in the use of technology in the rehabilitation pathway of patients affected by Parkinson’s Disease. In fact, our results suggest that a standard therapy combined with an innovative treatment using Tymo^® may be accepted by PD patients, which may benefit especially from preserving balance.

Predicting Axial Impairment in Parkinson's Disease through a Single Inertial Sensor

Background: Current telemedicine approaches lack standardised procedures for the remote assessment of axial impairment in Parkinson’s disease (PD). Unobtrusive wearable sensors may be a feasible tool to provide clinicians with practical medical indices reflecting axial dysfunction in PD. This study aims to predict the postural instability/gait difficulty (PIGD) score in PD patients by monitoring gait through a single inertial measurement unit (IMU) and machine-learning algorithms. Methods: Thirty-one PD patients underwent a 7-m timed-up-and-go test while monitored through an IMU placed on the thigh, both under (ON) and not under (OFF) dopaminergic therapy. After pre-processing procedures and feature selection, a support vector regression model was implemented to predict PIGD scores and to investigate the impact of L-Dopa and freezing of gait (FOG) on regression models. Results: Specific time- and frequency-domain features correlated with PIGD scores. After optimizing the dimensionality reduction methods and the model parameters, regression algorithms demonstrated different performance in the PIGD prediction in patients OFF and ON therapy (r = 0.79 and 0.75 and RMSE = 0.19 and 0.20, respectively). Similarly, regression models showed different performances in the PIGD prediction, in patients with FOG, ON and OFF therapy (r = 0.71 and RMSE = 0.27; r = 0.83 and RMSE = 0.22, respectively) and in those without FOG, ON and OFF therapy (r = 0.85 and RMSE = 0.19; r = 0.79 and RMSE = 0.21, respectively). Conclusions: Optimized support vector regression models have high feasibility in predicting PIGD scores in PD. L-Dopa and FOG affect regression model performances. Overall, a single inertial sensor may help to remotely assess axial motor impairment in PD patients.

The power of instruction on retropulsion: A pilot randomized controlled trial of therapeutic exercise focused on ankle joint movement in Parkinson’s disease

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Retropulsion in PD may involve the lack of push-off for a backward step.

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Exercise with ankle-movement instruction can improve backward response.

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Toe-landing instruction may facilitate treatment of retropulsion in PD.

Introduction

Although retropulsion is a serious complication of Parkinson’s disease (PD), it is unknown whether ankle joint movement patterns can be targeted to treat retropulsion. The primary aim of this study was to investigate the effectiveness of therapeutic exercise focused on instructions regarding ankle joint movement on retropulsion in PD.

Methods

Twenty patients with moderate PD were randomly allocated to the experimental intervention (INSTR) or control groups. The INSTR group received a 2-week therapeutic exercise program (40 min/day, five times/week) that involved repeated backward pulls on the shoulders with instructions to land on the toes as a response, and the control group received the same intervention without the instructions. The primary outcome was the difference in changes from baseline in the Movement Disorder Society-sponsored revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS part III) score between the study groups at weeks 1 and 2.

Results

The improvement in the MDS-UPDRS part III scores was significantly greater for the INSTR group in the week 1 (p = 0.033, _pη² = 0.241) and week 2 (p = 0.004, _pη² = 0.401) assessments. However, the provision of instructions to land on the toes as a backward response induced improvement in the only scores related to the backward response, and no significant between-group differences were observed in the other outcomes.

Conclusion

The 2-week therapeutic exercise program with instructions to treat retropulsion improved the backward response.

Trial registration

UMIN-CTR, UMIN000042722.

Assessing the impact of dual-task reactive step practice in people with Parkinson's disease: A feasibility study

Reactive stepping is impaired in people with Parkinson's Disease (PD) but can be improved with training. However, it is unclear if reactive steps can be improved when performing a concurrent cognitive task, a common and fall-relevant circumstance. We assessed the feasibility and preliminary effectiveness of dual-task reactive step training. Specifically, we measured whether stepping and cognitive reaction time are improved after one day of dual-task reactive step practice and if improvements are retained 24 h later. Sixteen people with PD and 13 age-matched healthy controls (HC) underwent repeated from-stance support surface perturbations that elicited a reactive step while performing an auditory Stroop task. Participants returned the following day to reassess dual-task reactive stepping performance. Cognitive, neuromuscular, and stepping outcomes were calculated. Increased step lengths were observed for both groups after practice (p < 0.001). Cognitive reaction times also improved through practice; however, this was more pronounced in the HC group (group by time interaction- p < 0.001). No changes were observed for step latency, margin of stability, or EMG onset through practice. Step length and cognitive reaction time improvements were retained 24 h after practice in both groups (step length: p < 0.001; cognitive reaction time: p = 0.05). This study provides preliminary evidence for the effectiveness of dual-task reactive step training to improve step length in people with PD. The improvements in step length without compromising cognitive reaction times suggest that participants improved reactive stepping without a robust attention shift toward the postural task. Future research is necessary to determine optimal training protocols and determine if such training protocols impact falls in PD patients.

Early balance impairment in Parkinson's Disease: Evidence from Robot-assisted axial rotations

OBJECTIVE

Early postural instability (PI) is a red flag for the diagnosis of Parkinson's disease (PD). Several patients, however, fall within the first three years of disease, particularly when turning. We investigated whether PD patients, without clinically overt PI, manifest abnormal reactive postural responses to ecological perturbations resembling turning.

METHODS

Fifteen healthy subjects and 20 patients without clinically overt PI, under and not under L-Dopa, underwent dynamic posturography during axial rotations around the longitudinal axis, provided by a robotic mechatronic platform. We measured reactive postural responses, including body displacement and reciprocal movements of the head, trunk, and pelvis, by using a network of three wearable inertial sensors.

RESULTS

Patients showed higher body displacement of the head, trunk and pelvis, and lower joint movements at the lumbo-sacral junction than controls. Conversely, movements at the cranio-cervical junction were normal in PD. L-Dopa left reactive postural responses unchanged.

CONCLUSIONS

Patients with PD without clinically overt PI manifest abnormal reactive postural responses to axial rotations, unresponsive to L-Dopa. The biomechanical model resulting from our experimental approach supports novel pathophysiological hypotheses of abnormal axial rotations in PD.

SIGNIFICANCE

PD patients without clinically overt PI present subclinical balance impairment during axial rotations, unresponsive to L-Dopa.

Change in 'first-trial' performance after protective step practice in people with multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a debilitating, neurodegenerative disorder causing considerable gait and balance dysfunction. Reactive balance (i.e., quick movements in response to a loss of balance) is particularly important for fall risk and is impaired in people with MS compared to neurotypical peers. Therefore, improving reactive balance among those with MS is critical. However, for maximum ecological validity, improvements in reactive balance through training would be demonstrable upon first loss-of-balance, rather than an average of several trials as is typically reported. This study evaluated changes in performance on the first stepping trial in people with MS after one day of practice.

METHODS

Fourteen people with MS underwent two, consecutive days of support-surface perturbations from stance. On day 1, participants underwent a single backward-stepping trial, followed by 35 practice trails (forward and backward). Approximately 24 h later, participants were again exposed to a single backward stepping perturbation. Protective stepping outcomes were step length, step latency, and margin of stability at first foot contact. The backward step performance on the first trial of days one and two were compared, and difference scores were evaluated for relationships with correlates based on theoretical considerations.

FINDINGS

First-trial margin of stability increased (improved) from day 1 to day 2 (P = .016). Steps were also faster on average by approximately 5 ms on day 2, although this improvement was not significant (P = .062).

INTERPRETATIONS

Although preliminary, these findings provide evidence that individuals with MS may be able to experience first-trial improvements after a low dose of perturbation training.

Does the impaired postural control in Parkinson's disease affect the habituation to non-sequential external perturbation trials?

BACKGROUND

How people with Parkinson's disease habituate their postural response to unpredictable translation perturbation is not totally understood. We compared the capacity to change the postural responses after unexpected external perturbation and investigated the habituation plateaus of postural responses to non-sequential perturbation trials in people with Parkinson's disease and healthy older adults.

METHODS

In people with Parkinson's disease (n = 37) and older adults (n = 20), sudden posterior support-surface translational were applied in 7 out of 17 randomized trials to ensure perturbation unpredictability. Electromyography and center of pressure parameters of postural response were analyzed by ANOVAs (Group vs. Trials). Two simple planned contrasts were performed to determine at which trial the responses first significantly habituate, and by which trials the habituation plateaus.

FINDINGS

Older adults demonstrated a first response change in trial 5 and habituation plateaus after trial 4, while for people with Parkinson's disease, the first change occurred in trial 2 and habituation plateau after trial 5 observed by center of pressure range. People with Parkinson's disease demonstrated a greater center of pressure range in trial 1 compared to older adults. Independent of trial, people with Parkinson's disease vs. older adults demonstrated a greater ankle muscle co-activation and recovery time.

INTERPRETATION

Despite the greater center of pressure range in the first trial, people with Parkinson's disease can habituate to unpredictable perturbations. This is reflected by little, to no difference in the time-course of adaptation for all but 2 parameters that showed only marginal differences between people with Parkinson's disease and older adults.

Comparison of forward and backward postural perturbations in mild-to-moderate Parkinson's disease

BACKGROUND

Assessing postural stability in Parkinson's disease (PD) often relies on measuring the stepping response to an imposed postural perturbation. The standard clinical technique relies on a brisk backwards pull at the shoulders by the examiner and judgement by a trained rater. In research settings, various quantitative measures and perturbation directions have been tested, but it is unclear which metrics and perturbation direction differ most between people with PD and controls.

OBJECTIVES

(1) Use standardized forward vs. backward perturbations of a support surface to evaluate reactive stepping performance between PD and control participants. (2) Evaluate the utility of using principal components analysis to capture the dynamics of the reactive response and differences between groups.

METHODS

Sixty-two individuals participated (40 mild-to-moderate PD, off medication). Standardized rapid translations of the support surface were applied, requiring at least one step, backward or forward, to restore balance. The number of steps taken and the projection of the first principal component (PC1) of the center of pressure (COP) time series were entered in linear repeated-measures mixed effect models.

RESULTS

Forward falls required significantly fewer steps to recover than backward falls. PC1 captured more than half of the variance in the COP trajectory. Analysis of the PC1 projection revealed a significant interaction effect of group (PD vs. controls) by direction, such that there was a group difference in forward stepping, but not backward.

SIGNIFICANCE

Forward reactive stepping in PD differed from controls more than backward-stepping. PC1 projections of the COP trajectory capture the dynamics of the postural response and differ between PD and controls.

Backward Protective Stepping During Dual-Task Scenarios in People With Parkinson's Disease: A Pilot Study

Introduction. Reactive movements in response to a loss of balance are altered in people with Parkinson's disease (PD) and are critical for fall prevention. Further, falls are more common while attention is divided. Although divided attention has been shown to impact postural responses in healthy older adults, the impact of dividing attention on reactive balance, and the natural prioritization across postural and cognitive tasks in people with PD is largely unknown. Objectives. To characterize (1) the impact of a secondary cognitive task on reactive postural control and (2) the prioritization across stepping and cognitive tasks in people with PD. Methods. Sixteen people with PD and 14 age-matched controls underwent step-inducing, support-surface perturbations from stance, with and without an auditory Stroop secondary cognitive task. Cognitive, neuromuscular, and protective stepping performance were calculated for single and dual task scenarios. Results. In PD and control participants, cognitive reaction times (P = .001) and muscle onset latency (P = .007), but not protective step outcomes (P > .12 for all) were worse during dual tasking compared with single-task scenarios. Both PD and control groups prioritized the protective stepping task over the cognitive task. Overall, people with PD exhibited worse first-step margin of stability (a measure of protective step performance) than controls (P = .044). Conclusion. This study provides preliminary evidence that people with PD, like age-matched controls, exhibit cognitive and neuromuscular, but not protective step, dual-task interference. The lack of dual-task interference on step performance indicates a postural prioritization for PD and healthy older adults during dual-task protective stepping.

Co-treatment with rivastigmine and idalopirdine reduces the propensity for falls in a rat model of falls in Parkinson's disease

RATIONALE

Falls in patients with Parkinson's disease (PD) are associated with cognitive, specifically attentional impairments and with losses in cholinergic projection systems. We previously established an animal model of the combined basal forebrain cholinergic-striatal dopaminergic losses of PD fallers (Dual Lesioned, DL, rats) and demonstrated that treating DL rats with an acetylcholinesterase inhibitor (AChEI), donepezil, together with a 5HT₆ receptor antagonist, idalopirdine, reduced fall frequency and improved associated aspects of the performance of DL rats traversing rotating rods.

OBJECTIVES

Here, we employed a longer and more taxing rotating beam apparatus to determine the potential therapeutic efficacy of idalopirdine when combined with the pseudo-irreversible, and thus relatively long-acting, AChE- and butyrylcholinesterase- (BuChE) inhibitor rivastigmine.

RESULTS

As before, vehicle-treated DL rats fell more frequently, committed more slips, and exhibited more movement stoppages than intact control rats. Repeated intermittent administration of rivastigmine and idalopirdine significantly improved the performance of DL rats. Rivastigmine alone also produced strong trends for reducing falls and slips. The combination treatment was more effective than rivastigmine alone in reducing stoppages and stoppage-associated falls. As before, idalopirdine treatment alone was ineffective.

CONCLUSIONS

These results extend the prediction that the combined treatment with idalopirdine and an AChEI improves complex movement control and reduces the propensity for falls in patients with movement disorders. Because of the importance of finding better treatments for gait and balance deficits in PD, the present results may further motivate a clinical exploration of the usefulness of this combination treatment.

Gait festination in parkinsonism: introduction of two phenotypes

Gait festination is one of the most characteristic gait disturbances in patients with Parkinson’s disease or atypical parkinsonism. Although festination is common and disabling, it has received little attention in the literature, and different definitions exist. Here, we argue that there are actually two phenotypes of festination. The first phenotype entails a primary locomotion disturbance, due to the so-called sequence effect: a progressive shortening of step length, accompanied by a compensatory increase in cadence. This phenotype strongly relates to freezing of gait with alternating trembling of the leg. The second phenotype results from a postural control problem (forward leaning of the trunk) combined with a balance control deficit (inappropriately small balance-correcting steps). In this viewpoint, we elaborate on the possible pathophysiological substrate of these two phenotypes of festination and discuss their management in daily clinical practice.

Relating Anticipatory Postural Adjustments to Step Outcomes During Loss of Balance in People With Parkinson's Disease

BACKGROUND

Effective protective steps are critical for fall prevention, and anticipatory postural adjustments (APAs) after a perturbation but prior to protective steps affect step performance. Although APAs prior to protective steps are altered in people with Parkinson's disease (PD), whether these changes affect subsequent step performance is poorly understood.

OBJECTIVE

Characterize the relationship between mediolateral APA size and protective step outcomes in response to anteroposterior balance perturbations in people with PD.

METHODS

Twenty-eight individuals with PD completed 25 forward and 25 backward protective steps in response to support surface translations. Multilevel linear models related mediolateral APA size to protective step outcomes.

RESULTS

During forward protective stepping, larger mediolateral APAs were associated with delayed ( P < .001) and larger ( P = .004) steps. Larger APAs were also associated with smaller mediolateral ( P < .001) but larger anterior-posterior center of mass movement at foot off ( P < .001). During backward stepping, larger APAs were associated with later steps ( P < .001) and smaller anterior-posterior margin of stability at first foot contact ( P < .001). During backward stepping, larger APAs were also associated with worse clinical (ie, UPDRS [Unified Parkinson's Disease Rating Scale]; P = .005) and balance (ie, MiniBEST [Mini-Balance Evaluation Systems Test]; P = .021) outcomes.

CONCLUSIONS

During forward protective stepping, larger APAs were associated with larger and later steps, suggesting APA size may have mixed effects on the subsequent step. During backward stepping, larger APAs were associated with worse stepping outcomes (ie, later steps, smaller anterior-posterior margin of stability, worse clinical outcomes). Interventions aimed at improving APAs in PD should monitor spatial and temporal protective step outcomes to ensure treatment does not negatively affect protective steps, particularly for forward stepping.

Paradoxical Decision-Making: A Framework for Understanding Cognition in Parkinson's Disease

People with Parkinson's disease (PD) show impaired decision-making when sensory and memory information must be combined. This recently identified impairment results from an inability to accumulate the proper amount of information needed to make a decision and appears to be independent of dopamine tone and reinforcement learning mechanisms. Although considerable work focuses on PD and decisions involving risk and reward, in this Opinion article we propose that the emerging findings in perceptual decision-making highlight the multisystem nature of PD, and that unraveling the neuronal circuits underlying perceptual decision-making impairment may help in understanding other cognitive impairments in people with PD. We also discuss how a decision-making framework may be extended to gain insights into mechanisms of motor impairments in PD.

Maximum Step Length Test Performance in People With Parkinson Disease: A Cross-sectional Study

BACKGROUND AND PURPOSE

The Maximum Step Length Test (MSLT), a measure of one's capacity to produce a large step, has been studied in older adults, but not in people with Parkinson disease (PD). We characterized performance and construct validity of the MSLT in PD.

METHODS

Forty participants (mean age: 65.12 ± 8.20 years; 45% female) with idiopathic PD completed the MSLT while "OFF" and "ON" anti-PD medication. Construct validity was investigated by examining relationships between MSLT and measures of motor performance. The following measures were collected: Mini-Balance Evaluation Systems Test (Mini-BESTest), Activities-specific Balance Confidence (ABC) scale, gait velocity, 6-minute walk test (6MWT), Movement Disorder Society-Unified Parkinson Disease Rating Scale subsection III (MDS-UPDRS III), and Timed Up and Go (TUG) test. A repeated-measures analysis of variance tested for main effects of medication and stepping direction and the interaction between the 2. Pearson or Spearman correlations were used to assess the relationships between MSLT and motor performance measures (α = 0.05).

RESULTS

Regardless of medication status, participants stepped further in the forward direction compared with the backward and lateral directions (P < 0.001). Participants increased MSLT performance when ON-medication compared with OFF-medication (P = 0.004). Regardless of medication status, MSLT was moderately to strongly related to Mini-BESTest, TUG, and 6MWT.

DISCUSSION AND CONCLUSIONS

People with PD stepped furthest in the forward direction when performing the MSLT. Increased MSLT performance was observed in the ON-medication state compared with OFF-medication; however, the small increase may not be clinically meaningful. Given the relationships between the MSLT and the Mini-BESTest, 6MWT, and TUG, MSLT performance appears to be associated with balance and gait hypokinesia in people with PD.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A186).

First-trial protective step performance before and after short-term perturbation practice in people with Parkinson's disease

BACKGROUND

Protective steps are critical for fall prevention and are altered in people with Parkinson's disease (PD). Previous work suggests that perturbation training, in which patients are exposed to repeated slips, may improve protective postural responses. However, these studies typically take the average performance of several postural responses before and after training. To reduce falls in the community, training must improve protective stepping after the first perturbation exposure. To date, no investigations have examined whether first-trial protective stepping is improved after training in people with PD.

METHODS

First-trial protective stepping was measured in 14 people with PD and 9 healthy adults before and 24 h after 1 day of perturbation training. The primary outcome was margin of stability after a perturbation, a measure of protective stepping effectiveness.

RESULTS

Margin of stability for the first perturbation was significantly (p = 0.001) improved on day 2 compared to before perturbation practice (day 1) in both groups. Furthermore, improvement in margin of stability was correlated with age and baseline stepping performance, such that older individuals and people with worse baseline performance showed the most pronounced improvement.

CONCLUSIONS

Improving the first loss of balance after training is critical if such training is to reduce falls in people with PD. The observed improvement in first-trial protective stepping provides further support for perturbation training as a potential tool to improve protective steps and reduce falls in people with PD.

Motor learning in people with Parkinson's disease: Implications for fall prevention across the disease spectrum

BACKGROUND

Falls are a significant burden for people with Parkinson's disease (PD), however, individuals across the spectrum of disease severity respond differently to fall prevention interventions. Despite the multifactorial causes of falls in people with PD, recent work has provided insight into interventions that hold promise for fall prevention. Further, studies have begun to identify patient characteristics that may predict responsiveness to such interventions.

RESEARCH QUESTION

We discuss (i) the postural motor learning abilities of people with mild versus severe PD that could affect their ability to benefit from fall prevention interventions, (ii) how people with different severity of PD respond to such interventions, and (iii) the practical considerations of providing effective fall prevention interventions for people with PD across the spectrum of disease severity.

METHODS

This narrative review consolidates recent work on postural motor learning and fall prevention rehabilitation involving exercise in people with PD.

RESULTS

People with PD are able to improve postural motor control through practice, enabling them to benefit from exercise which challenges their gait and balance to reduce falling. Worsening of axial and cognitive symptoms may result in diminished learning, and those with more severe PD may require fully supervised, high intensity programs to reduce falls.

SIGNIFICANCE

Understanding how people with PD across the spectrum of disease severity differ in their postural motor learning ability and response to different fall prevention interventions will enable researchers and clinicians to refine such interventions and their delivery to minimize falls and their negative sequelae in people with PD.

The effects of anxiety and external attentional focus on postural control in patients with Parkinson's disease

Background

Although anxiety is a common non-motor outcome of Parkinson's disease (PD) affecting 40% of patients, little attention has been paid so far to its effects on balance impairment and postural control. Improvement of postural control through focusing on the environment (i.e. external focus) has been reported, but the role of anxiety, as a confounding variable, remains unclear.

Objectives

This study aimed to investigate the influence of anxiety and attentional focus instruction on the standing postural control of PD patients.

Methods

Thirty-four patients with PD (17 with high anxiety (HA-PD) and 17 with low anxiety (LA-PD)), as well as 17 gender- and age-matched healthy control subjects (HC) participated in the study. Postural control was evaluated using a combination of two levels of postural difficulty (standing on a rigid force plate surface with open eyes (RO) and standing on a foam surface with open eyes (FO)), as well as three attentional focus instructions (internal, external and no focus).

Results

Only the HA-PD group demonstrated significant postural control impairment as compared to the control, as indicated by significantly greater postural sway measures. Moreover, external focus significantly reduced postural sway in all participants especially during the FO condition.

Conclusion

The results of the current study provide evidence that anxiety influences balance control and postural stability in patients with PD, particularly those with high levels of anxiety. The results also confirmed that external focus is a potential strategy that significantly improves the postural control of these patients. Further investigation of clinical applicability is warranted towards developing effective therapeutic and rehabilitative treatment plans.

Adaptation of Stability during Perturbed Walking in Parkinson's Disease

Gait and balance disorders are major problems that contribute to falls among subjects with Parkinson's disease (PD). Strengthening the compensatory responses through the use of balance perturbations may improve balance in PD. To date, it is unclear how PD affects the ability to react and adapt to perturbations delivered while walking. This study aims to investigate how PD affects the ability to walk, respond to balance perturbations, and produce acute short-term effects to improve compensatory reactions and gait stability. A cable-driven robot was used to train nine patients with PD and nine age-matched controls with multidirectional waist-pull perturbations while walking on a treadmill. Margin of stability and base of support were evaluated while walking without cables and reacting to the perturbations. PD was associated with a reduced stability in the forward direction and the inability to produce proactive anticipatory adjustments. Both groups were able to improve the response to the disturbances and produce short-term aftereffects of increased gait stability once the cables were removed. A single session of perturbation-based balance training produced acute effects that ameliorated gait instability in PD. This result is encouraging for designing new therapeutic interventions that remediate falls risk.

Dopaminergic modulation of multi-muscle synergies in postural tasks performed by patients with Parkinson's disease

BACKGROUND

Postural instability is one of most disabling motor symptoms in Parkinson's disease. Indices of multi-muscle synergies are new measurements of postural stability.

OBJECTIVES

We explored the effects of dopamine-replacement drugs on multi-muscle synergies stabilizing center of pressure coordinate and their adjustments prior to a self-triggered perturbation in patients with Parkinson's disease. We hypothesized that both synergy indices and synergy adjustments would be improved on dopaminergic drugs.

METHODS

Patients at Hoehn-Yahr stages II and III performed whole-body tasks both off- and on-drugs while standing. Muscle modes were identified as factors in the muscle activation space. Synergy indices stabilizing center of pressure in the anterior-posterior direction were quantified in the muscle mode space during a load-release task.

RESULTS

Dopamine-replacement drugs led to more consistent organization of muscles in stable groups (muscle modes). On-drugs patients showed larger indices of synergies and anticipatory synergy adjustments. In contrast, no medication effects were seen on anticipatory postural adjustments or other performance indices.

CONCLUSIONS

Dopamine-replacement drugs lead to significant changes in characteristics of multi-muscle synergies in Parkinson's disease. Studies of synergies may provide a biomarker sensitive to problems with postural stability and agility and to efficacy of dopamine-replacement therapy.

Effects of freezing of gait on postural motor learning in people with Parkinson's disease

Protective postural responses, including stepping, to recover equilibrium are critical for fall prevention and are impaired in people with Parkinson's disease (PD) with freezing of gait (FoG). Improving protective postural responses through training may reduce falls in this population. However, motor learning, the basis of neurorehabilitation, is also impaired in people with PD and, in particular, people with PD who experience freezing. It is unknown whether people with PD who freeze can improve protective postural responses, and whether these improvements are similar to nonfreezers. Our goal was to assess whether people with freezing can improve protective postural responses and retain these improvements similarly to nonfreezers. Twenty-eight people with PD (13 freezers, 15 nonfreezers) were enrolled. Improvement in protective postural responses was assessed over the course of 25 forward and 25 backward support surface translations (delivered in pseudo-random order). Postural responses were re-assessed 24h later to determine whether improvements were retained. People who freeze did not improve or retain improvement in protective postural responses as well as nonfreezers in our primary outcome variable, center of mass (COM) displacement after perturbations (post hoc across group assessments: freezers- p=0.14 and nonfreezers- p=0.001, respectively). However, other protective stepping outcomes, including margin of stability, step length, and step time, improved similarly across groups. Significant improvements were retained in both groups. In conclusion, people with PD who freeze exhibited reduced ability to improve protective postural responses in some, but not all, outcome variables. Additional training may be necessary to improve protective postural responses in people with PD who freeze.

Unmasking levodopa resistance in Parkinson's disease

Some motor and nonmotor features associated with Parkinson's disease (PD) do not seem to respond well to levodopa (or other forms of dopaminergic medication) or appear to become resistant to levodopa treatment with disease progression and longer disease duration. In this narrative review, we elaborate on this issue of levodopa resistance in PD. First, we discuss the possibility of pseudoresistance, which refers to dopamine-sensitive symptoms or signs that falsely appear to be (or have become) resistant to levodopa, when in fact other mechanisms are at play, resulting in suboptimal dopaminergic efficacy. Examples include interindividual differences in pharmacodynamics and pharmacokinetics and underdosing because of dose-limiting side effects or because of levodopa phobia. Moreover, pseudoresistance can emerge as not all features of PD respond adequately to the same dosage of levodopa. Second, we address that for several motor features (eg, freezing of gait or tremor) and several nonmotor features (eg, specific cognitive functions), the response to levodopa is fairly complex, with a combination of levodopa-responsive, levodopa-resistant, and even levodopa-induced characteristics. A possible explanation relates to the mixed presence of underlying dopaminergic and nondopaminergic brain lesions. We suggest that clinicians take these possibilities into account before concluding that symptoms or signs of PD are totally levodopa resistant. © 2016 International Parkinson and Movement Disorder Society.

Postural motor learning in people with Parkinson's disease

Protective postural responses to external perturbations are hypokinetic in people with Parkinson's disease (PD), and improving these responses may reduce falls. However, the ability of people with PD to improve postural responses with practice is poorly understood. Our objective was to determine whether people with PD can improve protective postural responses similarly to healthy adults through repeated perturbations, and whether improvements are retained or generalize to untrained perturbations. Twelve healthy adults and 15 people with PD underwent 25 forward and 25 backward translations of the support surface, eliciting backward, and forward protective steps, respectively. We assessed whether: (1) performance improved over one day of practice, (2) changes were retained 24 h later, and (3) improvements generalized to untrained (lateral) postural responses. People with PD and healthy adults improved postural response characteristics, including center of mass displacement after perturbations (p < 0.001), margin of stability at first footfall (p = 0.001), step latency (p = 0.044), and number of steps (p = 0.001). However, unlike controls, improvements in people with PD occurred primarily in the first block of trials. Improvements were more pronounced during backward protective stepping than forward, and with the exception of step latency, were retained 24 h later. Improvements in forward-backward stepping did not generalize to lateral protective stepping. People with PD can improve protective stepping over the course of 1 day of perturbation practice. Improvements were generally similar to healthy adults, and were retained in both groups. Perturbation practice may represent a promising approach to improving protective postural responses in people with PD; however, additional research is needed to understand how to enhance generalization.

The Effect of Levodopa on Improvements in Protective Stepping in People With Parkinson's Disease

Background The effect of levodopa on postural motor learning in people with Parkinson's disease is poorly understood. In particular, it is unknown whether levodopa affects improvement in protective postural responses after external perturbations such as a slip or trip, a critical aspect of fall prevention. Objective Determine the effect of levodopa on postural motor learning in people with Parkinson's disease. Methods We assessed improvement in protective postural responses in people with Parkinson's disease over short-term (1 day) perturbation training on and off levodopa. We also assessed retention and generalization of improvement. Participants were 22 individuals with Parkinson's disease. The primary outcome was total center of mass (COM) displacement after perturbation. Secondary outcomes assessed first step performance and included margin of stability at first foot contact. Results People with Parkinson's disease improved COM displacement (P = .011) and margin of stability (P = .016) over training. Improvements in these outcomes were more pronounced after training while on levodopa than off levodopa. Levodopa State × Training interactions were not observed for other step performance variables (eg, step latency, length, total number of steps). Improvements were retained for 24 hours, and for margin of stability, retention was more pronounced while on levodopa than off (P = .018). Conclusions Individuals with Parkinson's disease are able to improve protective postural responses through short-term perturbation training, and improvements were more pronounced when on levodopa for some variables. Perturbation training may be more effective if completed while optimally medicated with levodopa.

Maintaining balance against force perturbations: impaired mechanisms unresponsive to levodopa in Parkinson's disease

We introduce a new method to investigate postural instability in Parkinson's disease (PD) using computer-controlled motors to deliver precise pulls to the shoulders of subjects while standing. It mimics the clinical pull test but uses forces with unpredictable timing, direction, and magnitude. It revealed a number of balance control deficits in PD. Notably, the identified deficits were not significantly altered by levodopa medication, suggesting that disruption to nondopaminergic systems contributes to postural instability in PD.

There is evidence that postural instability associated with Parkinson's disease (PD) is not adequately improved by levodopa, implying involvement of nondopaminergic pathways. However, the mechanisms contributing to postural instability have yet to be fully identified and tested for their levodopa responsiveness. In this report we investigate balance processes that resist external forces to the body when standing. These include in-place responses and the transition to protective stepping. Forward and backward shoulder pulls were delivered using two force-feedback-controlled motors and were randomized for direction, magnitude, and onset. Sixteen patients with PD were tested OFF and ON levodopa, and 16 healthy controls were tested twice. Response behavior was quantified from 3-dimensional ground reaction forces and kinematic measurements of body segments and total body center-of-mass (CoM) motion. In-place responses resisting the pull were significantly smaller in PD as reflected in reduced horizontal anteroposterior ground reaction force and increased CoM displacement. Ankle, knee, and hip moments contributing to this resistance were smaller in PD, with the knee extensor moment to backward pulls being the most affected. The threshold force needed to evoke a step was also smaller for PD in the forward direction. Protective steps evoked by suprathreshold pulls showed deficits in PD in the backward direction, with steps being shorter and more steps being required to arrest the body. Levodopa administration had no significant effect on either in-place or protective stepping deficits. We conclude that processes employed to maintain balance in the face of external forces show impairment in PD consistent with disruption to nondopaminergic systems.

Neural Control of Walking in People with Parkinsonism

People with Parkinson's disease exhibit debilitating gait impairments, including gait slowness, increased step variability, and poor postural control. A widespread supraspinal locomotor network including the cortex, cerebellum, basal ganglia, and brain stem contributes to the control of human locomotion, and altered activity of these structures underlies gait dysfunction due to Parkinson's disease.

Characterization of Compensatory Stepping in People With Multiple Sclerosis

OBJECTIVE

To characterize postural responses to forward and backward external perturbations in people with multiple sclerosis (PwMS), and to relate performance to commonly used clinical outcomes.

DESIGN

Cross-sectional study. Postural responses were tested during large stepping and smaller feet-in-place perturbations in forward and backward directions.

SETTING

University research laboratory.

PARTICIPANTS

PwMS (n=54) and age-matched controls (n=21) (N=75).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Center of mass displacement and step latency after external perturbations.

RESULTS

PwMS exhibited larger center of mass displacements and step latencies than control participants in response to stepping perturbations (P=.003 and P=.028, respectively). Stepping deficits were more pronounced during backward stepping and were significantly correlated to increased severity on clinical measures (European Database for Multiple Sclerosis disability score and Timed 25-Foot Walk).

CONCLUSIONS

Compensatory stepping is impaired in PwMS and correlates with clinical disability. Measurement of backward compensatory stepping may be more effective at identifying postural dysfunction in PwMS than forward compensatory steps. Prolonged step latencies, large anticipatory postural adjustments, and multiple compensatory steps are especially altered in PwMS, suggesting possible targets for neurorehabilitation.

StartReact effects support different pathophysiological mechanisms underlying freezing of gait and postural instability in Parkinson's disease

Introduction

The pathophysiology underlying postural instability in Parkinson’s disease is poorly understood. The frequent co-existence with freezing of gait raises the possibility of shared pathophysiology. There is evidence that dysfunction of brainstem structures contribute to freezing of gait. Here, we evaluated whether dysfunction of these structures contributes to postural instability as well. Brainstem function was assessed by studying the StartReact effect (acceleration of latencies by a startling acoustic stimulus (SAS)).

Methods

We included 25 patients, divided in two different ways: 1) those with postural instability (HY = 3, n = 11) versus those without (HY<3, n = 14); and 2) those with freezing (n = 11) versus those without freezing (n = 14). We also tested 15 matched healthy controls. We tested postural responses by translating a balance platform in the forward direction, resulting in backward balance perturbations. In 25% of trials, the start of the balance perturbation was accompanied by a SAS.

Results

The amplitude of automatic postural responses and length of the first balance correcting step were smaller in patients with postural instability compared to patients without postural instability, but did not differ between freezers and non-freezers. In contrast, the StartReact effect was intact in patients with postural instability but was attenuated in freezers.

Discussion

We suggest that the mechanisms underlying freezing of gait and postural instability in Parkinson’s disease are at least partly different. Underscaling of automatic postural responses and balance-correcting steps both contribute to postural instability. The attenuated StartReact effect was seen only in freezers and likely reflects inadequate representation of motor programs at upper brainstem level.