The influence of dopaminergic medication on balance automaticity in Parkinson's disease

Multi-muscle synergies in preparation for gait initiation in Parkinson's disease

OBJECTIVE

We investigated changes in indices of muscle synergies prior to gait initiation and the effects of gaze shift in patients with Parkinson's disease (PD). A long-term objective of the study is to develop a method for quantitative assessment of gait-initiation problems in PD.

METHODS

PD patients without clinical signs of postural instability and two control groups (age-matched and young) performed a gait initiation task in a self-paced manner, with and without a quick prior gaze shift produced by turning the head. Muscle groups with parallel scaling of activation levels (muscle modes) were identified as factors in the muscle activation space. Synergy index stabilizing center of pressure trajectory in the anterior-posterior and medio-lateral directions (indices of stability) was quantified in the muscle mode space. A drop in the synergy index in preparation to gait initiation (anticipatory synergy adjustment, ASA) was quantified.

RESULTS

Compared to the control groups, PD patients showed significantly smaller synergy indices and ASA for both directions of the center of pressure shift. Both PD and age-matched controls, but not younger controls, showed detrimental effects of the prior gaze shift on the ASA indices.

CONCLUSIONS

PD patients without clinically significant posture or gait disorders show impaired stability of the center of pressure and its diminished adjustment during gait initiation.

SIGNIFICANCE

The indices of stability and ASA may be useful to monitor pre-clinical gait disorders, and lower ASA may be relevant to emergence of freezing of gait in PD.

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.

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.

Incongruity of Geometric and Spectral Markers in the Assessment of Body Sway

Different measurements of body oscillations in the time or frequency domain are being employed as markers of gait and balance abnormalities. This study investigates basic relationships within and between geometric and spectral measures in a population of young adult subjects. Twenty healthy subjects stood with parallel feet on a force platform with and without a foam pad. Adaptation effects to prolonged stance were assessed by comparing the first and last of a series of eight successive trials. Centre of Foot Pressure (CoP) excursions were recorded with Eyes Closed (EC) and Open (EO) for 90s. Geometric measures (Sway Area, Path Length), standard deviation (SD) of the excursions, and spectral measure (mean power Spectrum Level and Median Frequency), along the medio-lateral (ML) and antero-posterior (AP) direction were computed. Sway Area was more strongly associated than Path Length with CoP SD and, consequently, with mean Spectrum Level for both ML and AP, and both visual and surface conditions. The squared-SD directly specified the mean power Spectrum Level of CoP excursions (ML and AP) in all conditions. Median Frequency was hardly related to Spectrum Level. Adaptation had a confounding effect, whereby equal values of Sway Area, Path Length, and Spectrum Level corresponded to different Median Frequency values. Mean Spectrum Level and SDs of the time series of CoP ML and AP excursions convey the same meaning and bear an acceptable correspondence with Sway Area values. Shifts in Median Frequency values represent important indications of neuromuscular control of stance and of the effects of vision, support conditions, and adaptation. The Romberg Quotient EC/EO for a given variable is contingent on the compliance of the base of support and adaptation, and different between Sway Area and Path Length, but similar between Sway Area and Spectrum Level (AP and ML). These measures must be taken with caution in clinical studies, and considered together in order to get a reliable indication of overall body sway, of modifications by sensory and standing condition, and of changes with ageing, medical conditions and rehabilitation treatment. However, distinct measures shed light on the discrete mechanisms and complex processes underpinning the maintenance of stance.

Increased 18F-FDG Uptake in the Axillary Lymph Nodes of the Vaccinated Side Associated with COVID-19 Vaccination

A 50-year-old female patient underwent (¹⁸fluorine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) following modified radical mastectomy for cancer of the left breast. Ten days before the PET/CT, the coronavirus disease-2019 (COVID-19) vaccine was injected intramuscularly into the right deltoid muscle. Increased (¹⁸F-FDG uptake of maximum standardized uptake value (11.0) was observed in the lymph nodes of the right axilla, which had not been observed in the previous PET/CT. The size of the oval-shaped lymph nodes was up to approximately 11×9 mm; however, it was larger than that observed on the previous PET/CT. We contemplate that the increased (¹⁸F-FDG uptake was a reactive change in the lymph nodes associated with the COVID-19 vaccine.

Effect of concurrent transcranial direct current stimulation on instrumented timed up and go task performance in people with Parkinson's disease: A double-blind and cross-over study

Transcranial direct current stimulation (tDCS) delivered to the dorsolateral prefrontal cortex (DLPFC) can improve mobility among people with Parkinson's disease (PD). Previous studies suggest that delivering tDCS during task performance might be beneficial. However, only a few studies explored the effect of combining tDCS with task. We investigated the effect of stimulating the DLPFC using anodal tDCS while performing a timed up and go (TUG) test and its sustained effects. In this sham-controlled, cross-over, and double-blind study, twenty participants with PD (age = 67.8 ± 8.3 years and 6 females) completed two sessions (anodal or sham tDCS), conducted in the randomized and counterbalanced manner, with at least a 1-week gap. Stimulation involved transferring 2 mA current through the DLPFC for 30 min. Single-trial of TUG test was performed under single- and dual-task conditions before, during, immediately after, 15 and 30 min after stimulation ceased. We estimated durations of completing different components of TUG. Phoneme verbal fluency task was given as the cognitive distractor during the dual-tasking. An improvement was observed in cognitive performance due to the tDCS condition (d = 0.7, p < 0.01) over time. However, we found no effect of tDCS condition on iTUG related outcomes under single- or dual-task conditions. In conclusion, DLPFC stimulation combined with task improved cognitive performance only, and the improvement was sustained after tDCS ceased. Future studies may investigate stimulating multiple brain regions to improve motor and cognitive performance.

Factors affecting postural instability after more than one-year bilateral subthalamic stimulation in Parkinson's disease: A cross-sectional study

Background

Balance impairment in Parkinson’s disease is multifactorial and its changes due to subthalamic stimulation vary in different studies.

Objective

We aimed to analyze the combination of predictive clinical factors of balance impairment in patients with Parkinson’s disease treated with bilateral subthalamic stimulation for at least one year.

Methods

We recruited 24 patients with Parkinson’s disease treated with bilateral subthalamic stimulation and 24 healthy controls. They wore an Opal monitor (APDM Inc.) consisting of three-dimensional gyroscopes and accelerometers in the lumbar region. We investigated four stimulation conditions (bilateral stimulation OFF, bilateral stimulation ON, and unilateral right- and left-sided stimulation ON) with four tests: stance on a plain ground with eyes open and closed, stance on a foam platform with eyes open and closed. Age, disease duration, the time elapsed after implantation, levodopa, and stimulation responsiveness were analyzed. The distance of stimulation location from the subthalamic motor center was calculated individually in each plane of the three dimensions. We analyzed the sway values in the four stimulation conditions in the patient group and compared them with the control values. We explored factor combinations (with age as confounder) in the patient group predictive for imbalance with cluster analysis and a machine‐learning‐based multiple regression method.

Results

Sway combined from the four tasks did not differ in the patients and controls on a group level. The combination of the disease duration, the preoperative levodopa responsiveness, and the stimulation responsiveness predicted individual stimulation-induced static imbalance. The more affected patients had more severe motor symptoms; primarily, the proprioceptive followed by visual sensory feedback loss provoked imbalance in them when switching on the stimulation.

Conclusions

The duration of the disease, the severity of motor symptoms, the levodopa responsiveness, and additional sensory deficits should be carefully considered during preoperative evaluation to predict subthalamic stimulation-induced imbalance in Parkinson’s disease.

Temporal dynamics of cortical activity and postural control in response to the first levodopa dose of the day in people with Parkinson's disease

BACKGROUND

Our understanding of how balance control responds to levodopa over the course of a single day in people with Parkinson's disease (PD) is limited with the majority of studies focused on isolated comparisons of ON vs. OFF levodopa medication.

OBJECTIVE

To evaluate the temporal dynamics of postural control following the first levodopa dose of the day during a challenging standing task in a group of people with PD.

METHODS

Changes in postural control were evaluated by monitoring cortical activity (covering frontal, motor, parietal and occipital areas), body sway parameters (force platform), and lower limb muscle activity (tibialis anterior and gastrocnemius medialis) in 15 individuals with PD during a semi-tandem standing task. Participants were assessed during two 60 second trials every 30 minutes (ON-30 ON-60 etc.) for 3 hours after the first matinal dose (ON-180).

RESULTS

Compared to when tested OFF-medication, cortical activity was increased across all four regions from ON-60 to ON-120 with early increases in alpha and beta band activity observed at ON-30. Levodopa was associated with increased gastrocnemius medialis activity (ON-30 to ON-120) and ankle co-contraction (ON-60 to ON-120). Changes in body sway outcomes (particularly in the anterior-posterior direction) were evident from ON-60 to ON-120.

CONCLUSIONS

Our results reveal a 60-minute window within which postural control outcomes may be obtained that are different compared to OFF-state and remain stable (from 60-minutes to 120-minutes after levodopa intake). Identifying a window of opportunity for measurement when individuals are optimally medicated is important for observations in a clinical and research setting.

Arm swing responsiveness to dopaminergic medication in Parkinson's disease depends on task complexity

The evidence of the responsiveness of dopaminergic medication on gait in patients with Parkinson’s disease is contradicting. This could be due to differences in complexity of the context gait was in performed. This study analysed the effect of dopaminergic medication on arm swing, an important movement during walking, in different contexts. Forty-five patients with Parkinson’s disease were measured when walking at preferred speed, fast speed, and dual-tasking conditions in both OFF and ON medication states. At preferred, and even more at fast speed, arm swing improved with medication. However, during dual-tasking, there were only small or even negative effects of medication on arm swing. Assuming that dual-task walking most closely reflects real-life situations, the results suggest that the effect of dopaminergic medication on mobility-relevant movements, such as arm swing, might be small in everyday conditions. This should motivate further studies to look at medication effects on mobility in Parkinson’s disease, as it could have highly relevant implications for Parkinson’s disease treatment and counselling.

Effects of dual-tasking on time-to-boundary during stance in people with PD: A preliminary study

BACKGROUND

Quiet stance is impacted by Parkinson's disease and dual-tasking. Recently developed outcomes such as the time-to-boundary provide unique insight into balance by integrating center of pressure position with base of support. However, little is known about the effects of Parkinson's disease on time-to-boundary. In particular, the effects of distracting cognitive tasks, and how people with Parkinson's disease prioritize balance and cognitive tasks are poorly understood.

METHODS

14 people with Parkinson's disease and 13 controls completed quiet standing and cognitive Stroop tasks separately (single-task) and together (dual-task). 2-dimentional, medio-lateral, and anterior-posterior time-to-boundary were calculated via force-plate data. Traditional sway outcomes, including sway area and path length, were also calculated. Cognitive performance was measured as the verbal reaction time after auditory stimulus delivery. Prioritization was assessed by taking the difference between cognitive and postural dual-task interference.

FINDINGS

Time-to-boundary was worse in Parkinson's disease compared to controls (2-dimentional: p = .019; anterior-posterior: p = .062; medio-lateral: p = .012). Medio-lateral time-to-boundary, but not anterior-posterior, was significantly worse during dual-tasking than single-tasking (p = .024). Neurotypical adults tended to prioritize cognition over medio-lateral postural outcomes.

INTERPRETATION

People with Parkinson's disease exhibit worse time-to-boundary than their neurotypical peers, and medio-lateral outcomes were sensitive to single to dual-task performance changes. Further, participants generally showed cognitive prioritization, such that cognitive performance was less impacted than medio-lateral postural outcomes by dual-tasking.

The assessment of center of mass and center of pressure during quiet stance: Current applications and future directions

This perspective article provides a brief review of our understanding of how center of pressure (CoP) and center of mass (CoM) are traditionally utilized to measure quiet standing and how technological advancements are allowing for measurements to be derived outside the confines of a laboratory setting. Furthermore, this viewpoint provides descriptions of what CoP and CoM outcomes may reflect, a discussion of recent developments in selected balance outcomes, the importance of measuring instantaneous balance outcomes, and directions for future questions/research. Considering the enormous number and cost of falls annually, conclusions drawn from this perspective underscore the need for more cohesive efforts to advance our understanding of balance performance. As we refine the technology and algorithms used to portably assess postural stability, the question of which measurement (i.e. CoP or CoM) to utilize seems to be highly dependent on the question being asked. Further, the complexity of the question appears to span multiple disciplines and cultivate exploration of the intrinsic mechanisms of stability. Recently developed multi-dimensional methods for assessing balance performance may provide additional insight into balance, improving our ability to predict balance impairments and falls outside the laboratory and in the clinic. However, additional work will be necessary to understand the clinical significance and predictive capacity of these outcomes in various fall-prone populations.

Synergic control of action in levodopa-naïve Parkinson's disease patients: II. Multi-muscle synergies stabilizing vertical posture

Postural instability is a major disabling feature in Parkinson's disease (PD). We quantified the organization of leg and trunk muscles into synergies stabilizing the center of pressure (COP) coordinate within the uncontrolled manifold hypothesis in levodopa-naïve patients with PD and age-matched control subjects. The main hypothesis was that changes in the synergic control of posture are present early in the PD process even before levodopa exposure. Eleven levodopa-naïve patients with PD and 11 healthy controls performed whole-body cyclical voluntary sway tasks and a self-initiated load-release task during standing on a force plate. Surface electromyographic activity in 13 muscles on the right side of the body was analyzed to identify muscle groups with parallel scaling of activation levels (M-modes). Data were collected both before ("off-drug") and approximately 60 min after the first dose of 25/100 carbidopa/levodopa ("on-drug"). COP-stabilizing synergies were quantified for the load-release task. Levodopa-naïve patients with PD showed no COP-stabilizing synergy "off-drug", whereas controls showed posture-stabilizing multi-M-mode synergy. "On-drug", patients with PD demonstrated a significant increase in the synergy index. There were no significant drug effects on the M-mode composition, anticipatory postural adjustments, indices of motor equivalence, or indices of COP variability. The results suggest that levodopa-naïve patients with PD already show impaired posture-stabilizing multi-muscle synergies that may be used as promising behavioral biomarkers for emerging postural disorders in PD. Moreover, levodopa modified synergy metrics differently in these levodopa-naïve patients compared to a previous study of patients on chronic antiparkinsonian medications (Falaki et al. in J Electromyogr Kinesiol 33:20-26, 2017a), suggesting different neurocircuitry involvement.

Effect of a Concurrent Cognitive Task, with Stabilizing Visual Information and Withdrawal, on Body Sway Adaptation of Parkinsonian's Patients in an Off-Medication State: A Controlled Study

Background: In persons with Parkinson's disease (pwPD) any additional somatosensory or distractor interference can influence the posture. When deprivation of vision and dual-task are associated, the effect on biomechanical performance is less consistent. The aim of this study was to evaluate the role of the visual deprivation and a cognitive task on the static balance in earlier stage PD subjects. Methods: Fifteen off-medication state pwPD (9 women and 6 men), 67.7 ± 7.3 years old, diagnosed PD since 5.4 ± 3.4 years, only Hoehn and Yahr state 2 and fifteen young control adults (7 women and 8 men) aged 24.9 ± 4.9 years, performed semi-tandem task under four randomized experimental conditions: eyes opened single-task, eyes closed single-task, eyes opened dual-task and eyes closed dual-task. The center of pressure (COP) was measured using a force plate and electromyography signals (EMG) of the ankle/hip muscles were recorded. Traditional parameters, including COP pathway length, ellipse area, mediolateral/anteroposterior root-mean-square and non-linear measurements were computed. The effect of vision privation, cognitive task, and vision X cognitive was investigated by a 2 (eyes opened/eyes closed) × 2 (postural task alone/with cognitive task) repeated-measures ANOVA after application of a Bonferroni pairwise correction for multiple comparisons. Significant interactions were further analyzed using post-hoc tests. Results: In pwPD, both COP pathway length (p < 0.01), ellipse area (p < 0.01) and mediolateral/anteroposterior root-mean-square (p < 0.01) were increased with the eyes closed, while the dual-task had no significant effect when compared to the single-task condition. Comparable results were observed in the control group for who COP pathway was longer in all conditions compared to eyes opened single-task (p < 0.01) and longer in conditions with eyes closed compared to eyes opened dual-task (p < 0.01). Similarly, all differences in EMG activity of pwPD were exclusively observed between eyes opened vs. eyes closed conditions, and especially for the forward leg's soleus (p < 0.01) and backward tibialis anterior (p < 0.01). Conclusions: These results in pwPD without noticeable impairment of static balance encourage the assessment of both visual occlusion and dual-task conditions when the appearance of significant alteration during the dual-task could reveal the subtle worsening onset of the balance control.

Cerebellar Transcranial Direct Current Stimulation in People with Parkinson's Disease: A Pilot Study

People with Parkinson’s disease (PwPD) often experience gait and balance problems that substantially impact their quality of life. Pharmacological, surgical, and rehabilitative treatments have limited effectiveness and many PwPD continue to experience gait and balance impairment. Transcranial direct current stimulation (tDCS) may represent a viable therapeutic adjunct. The effects of lower intensity tDCS (2 mA) over frontal brain areas, in unilateral and bilateral montages, has previously been explored; however, the effects of lower and higher intensity cerebellar tDCS (2 mA and 4 mA, respectively) on gait and balance has not been investigated. Seven PwPD underwent five cerebellar tDCS conditions (sham, unilateral 2 mA, bilateral 2 mA, unilateral 4 mA, and bilateral 4 mA) for 20 min. After a 10 min rest, gait and balance were tested. The results indicated that the bilateral 4 mA cerebellar tDCS condition had a significantly higher Berg Balance Scale score compared to sham. This study provides preliminary evidence that a single session of tDCS over the cerebellum, using a bilateral configuration at a higher intensity (4 mA), significantly improved balance performance. This intensity and cerebellar configuration warrants future investigation in larger samples and over repeated sessions.