Meir Plotnik

Is freezing of gait in Parkinson's disease related to asymmetric motor function?

Freezing of gait (FOG) is a disabling phenomenon common in patients with advanced Parkinsons disease (PD). The cause of FOG is unclear. The objective of this study was to explore a novel hypothesis stating that FOG is related to asymmetric motor performance. We compared PD patients that experience FOG episodes (PD+FOG) with PD patients that do not (PD−FOG) and studied the relationship of FOG to asymmetry in gait and in rhythmic hand movement performance to determine whether potential FOG‐related gait asymmetry is unique to walking or whether it is systemic. Subjects were tested in an “off” (unmedicated) and again in an “on” (medicated) state. Gait was more asymmetric in PD+FOG than in PD−FOG during “off” state (p = 0.005) and during “on” (p = 0.016). Rhythmicity of foot swing in one leg was correlated with the other leg in PD−FOG but not in PD+FOG. There was no difference in asymmetry in performance of rhythmic hand movements between the two groups. No correlation was found between asymmetry of clinical symptoms and gait asymmetry. Taken together, the results of this study suggest that bilateral uncoordinated gait and marked gait asymmetry, but not asymmetry in motor performance in general, are associated with FOG. Ann Neurol 2005;57:656–663

Can an accelerometer enhance the utility of the Timed Up & Go Test when evaluating patients with Parkinson's disease?

INTRODUCTION The Timed Up and Go (TUG) test is a widely used measure of mobility and fall risk in older adults and in Parkinsons disease (PD). We tested the hypothesis that body-fixed accelerometers can provide insight into TUG performance in PD patients. METHODS We examined 17 patients with PD (Hoehn and Yahr score: 2.7+/-0.7; ON state) and 15 age-matched healthy controls; mean ages were 66.8+/-5.9 years, 67.6+/-9.6 years, respectively. Subjects wore a 3D-accelerometer (ADXL330, Analog Devices) on the lower back while performing the TUG test. Sit-to-Stand and Stand-to-Sit times were extracted from the anterior-posterior (AP) signal. Parameters included Sit-to-Stand, Stand-to-Sit durations, amplitude range (Range) and slopes (Jerk). Acceleration median and standard deviation (SD) were also calculated. RESULTS Stopwatch-based TUG duration tended to be higher for the PD patients compared to the control group, although not significantly (p=0.08). In contrast, the TUG duration that was extracted from the acceleration signal was significantly (p<0.02) higher in the PD group compared to the control group. Many acceleration-parameters were also significantly different (p<0.05) between groups; most were not correlated with TUG duration. CONCLUSIONS Accelerometer-derived parameters are sensitive to group differences, indicating that PD patients have poorer mobility during specific aspects of the TUG. In addition to test duration, these measures may serve as complementary and objective bio-markers of PD to augment the evaluation of disease progression and the response to therapeutic interventions.

Bilateral coordination of walking and freezing of gait in Parkinson’s disease

Freezing of gait (FOG) in Parkinsons disease (PD) occurs most frequently during turns or step initiation, two tasks that likely demand a high degree of bilateral coordination between the legs. Our objective was to test the hypothesis that impairments in bilateral coordination of stepping are associated with FOG in PD. We compared locomotion features while walking on level ground between patients with PD that experience FOG (PD + FOG; n = 21) and patients with PD that do not (PD − FOG; n = 13). To study bilateral stepping coordination, we defined the stride duration of one foot as a gait cycle or 360°, determined the relative timing of contralateral heel‐strikes and defined this as the phase, ϕ (ideally, ϕ = 180°). The sum of the coefficient of variation of ϕ and the mean absolute difference between ϕ and 180° was defined as the phase coordination index (PCI), representing variability and inaccuracy, respectively, in phase generation. During the ‘Off’ state (= 12 h off anti‐parkinsonian medication), PCI values were higher (poorer coordination) in PD + FOG compared with PD − FOG (P < 0.024). Stride‐to‐stride phase adjustments, Δϕ, were also studied. Both groups scaled their ‘converging’ adjustments (towards 180°) to the same extent, but when generating diverging Δϕ (away from 180°), PD + FOG patients exhibited larger errors compared with PD − FOG patients (P < 0.006). This study demonstrates that patients with PD who experience FOG have distinctive impairments in the bilateral coordination of locomotion. Poor bilateral coordination of walking may predispose to FOG, especially during challenging tasks that demand a high degree of left–right coordination.

Bilateral coordination of gait and Parkinson’s disease: the effects of dual tasking

The aetiology of gait disturbances in Parkinson’s disease (PD) is not fully understood. Recently, it was shown that in patients with PD, bilateral coordination of gait is impaired and that walking while being simultaneously engaged in a cognitive task is detrimental to their gait. To assess whether cognitive function influences the bilateral coordination of gait in PD, this study quantified left–right stepping coordination using a phase coordination index (PCI) that evaluates both the variability and inaccuracy of the left–right stepping phase (φ) generation (where the ideal φ value between left and right stepping is 180°). This report calculated PCI values from data obtained from force sensitive insoles embedded in subjects’ shoes during 2 min of walking in a group of patients with PD (n = 21) and in an age matched control group (n = 13). All subjects walked under two walking conditions: usual walking and dual tasking (DT) (ie, cognitive loading) condition. For patients with PD, PCI values were significantly higher (ie, poorer coordination) during the DT walking condition compared with usual walking (p<0.001). In contrast, DT did not significantly affect the PCI of the healthy controls (p = 0.29). PCI changes caused by DT were significantly correlated with changes in gait variability but not with changes in gait asymmetry that resulted from the DT condition. These changes were also associated with performance on a test of executive function. The present findings suggest that in patients with PD, cognitive resources are used in order to maintain consistent and accurate alternations in left–right stepping.

The role of gait rhythmicity and bilateral coordination of stepping in the pathophysiology of freezing of gait in Parkinson's disease†

Freezing of gait (FOG) is a disabling episodic gait disturbance that is common among patients with Parkinsons disease (PD). In this review, we describe a new approach for understanding the mechanisms underlying this puzzling phenomenon. We propose that impairments in the ongoing regulation of gait, even during periods in which freezing is not present, set the stage for the occurrence of a FOG episode. More specifically, three “interictal” walking attributes are associated with FOG: gait rhythmicity, gait asymmetry, and bilateral dyscoordination of left–right stepping. Gait is less rhythmic, more asymmetric, and less coordinated among PD patients with FOG, when compared with PD patients without FOG. We describe the relationship between these changes and other features of patients with FOG and discuss whether these gait changes may predispose to FOG or if they also cause FOG, perhaps, when they are altered beyond a certain threshold or exacerbated by another trigger.

An instrumented timed up and go: the added value of an accelerometer for identifying fall risk in idiopathic fallers

The Timed Up and Go (TUG) test is a widely used measure of mobility and fall risk among older adults that is typically scored using a stopwatch. We tested the hypothesis that a body-fixed accelerometer can enhance the ability of the TUG to identify community-living older adults with a relatively high fall risk of unknown origin. Twenty-three community-living elderly fallers (76.0 ± 3.9 years) and 18 healthy controls (68.3 ± 9.1 years) performed the TUG while wearing a 3D-accelerometer on the lower back. Acceleration-derived parameters included Sit-to-Stand and Stand-to-Sit times, amplitude range (Range), and slopes (Jerk). Average step duration, number of steps, average step length, gait speed, acceleration-median, and standard-deviation were also calculated. While the stopwatch-based TUG duration was not significantly different between the groups, acceleration-derived TUG duration was significantly higher (p = 0.007) among the fallers. Fallers generally exhibited lower Range and Jerk (p < 0.01). While TUG stopwatch duration successfully identified 63% of the subjects, an accelerometer-derived three-measure-combination correctly classified 87% of the subjects. Accelerometer-derived measures were generally not correlated with TUG duration. These findings demonstrate that fallers have difficulty with specific TUG aspects that can be quantified using an accelerometer. Without compromising simplicity of testing, an accelerometer can apparently be combined with TUG duration to provide complementary, objective measures that allow for a more complete, sensitive TUG-based fall risk assessment.

Toward Automated, At-Home Assessment of Mobility Among Patients With Parkinson Disease, Using a Body-Worn Accelerometer

Objective. To develop an automated and objective method to assess mobility in Parkinson disease (PD) patients in daily-life settings and to investigate whether accelerometer-derived measures discriminate between PD and healthy controls as they walk and simulate activities of daily living (ADL). Methods. Healthy older adults (17) and patients with PD (22) wore a triaxial accelerometer on their lower back during short walks (validation study) and during a walk around the medical center to simulate daily activities (ADL simulation). The variability (consistency and rhythmicity) of stepping was assessed. The patients completed the walks before and after taking their anti-Parkinsonian medications. Frequency-based acceleration measures included dominant frequency, amplitude (strength of signal frequency), width (frequency dispersion), and slope (a combination reflecting amplitude and width) of the main frequency of the power spectral density in the 0.5- to 3.0-Hz band. A subset of the Unified Parkinson-Disease Rating Scale provided a clinical measure of gait impairment (UPDRS-Gait5). A PD patient and control wore the sensors for 3 days at home. Results. The width was larger, and the amplitude and slope were smaller in the PD patients compared to the controls in the validation study and ADL simulation (P < .02). The width decreased, and the amplitude and slope increased when patients took anti-Parkinsonian medications (P < .007). Significant correlations were observed between acceleration-derived measures and UPDRS-Gait5. The data obtained at home was similar to the clinic data. Conclusions. Frequency-derived measures are valid and sensitive estimates of stride-to-stride variability that can be used to assess the quality and consistency of walking in patients with PD in real-life settings.

Is freezing of gait in Parkinson's disease a result of multiple gait impairments? Implications for treatment.

Several gait impairments have been associated with freezing of gait (FOG) in patients with Parkinsons disease (PD). These include deteriorations in rhythm control, gait symmetry, bilateral coordination of gait, dynamic postural control and step scaling. We suggest that these seemingly independent gait features may have mutual interactions which, during certain circumstances, jointly drive the predisposed locomotion system into a FOG episode. This new theoretical framework is illustrated by the evaluation of the potential relationships between the so-called “sequence effect”, that is, impairments in step scaling, and gait asymmetry just prior to FOG. We further discuss what factors influence gait control to maintain functional gait. “Triggers”, for example, such as attention shifts or trajectory transitions, may precede FOG. We propose distinct categories of interventions and describe examples of existing work that support this idea: (a) interventions which aim to maintain a good level of locomotion control especially with respect to aspects related to FOG; (b) those that aim at avoiding FOG “triggers”; and (c) those that merely aim to escape from FOG once it occurs. The proposed theoretical framework sets the stage for testable hypotheses regarding the mechanisms that lead to FOG and may also lead to new treatment ideas.

The neurobiology of falls

Falling is a major clinical problem; especially, in elderly population as it often leads to fractures, immobilization, poor quality of life and life-span reduction. Given the growing body of evidences on the physiopathology of balance disorders in humans, in recent years the approach of research on falls has completely changed and new instruments and new definitions have been formulated. Among them, the definition of “idiopathic faller” (i.e. no overt cause for falling in a given subject) represented a milestone in building the “science of falling”. This review deals with the new determinants of the neurobiology of falling: (1) the role of motor impairment and particularly of those “mild parkinsonian signs” frequently detectable in elderly subjects, (2) the role of executive and attentive resources when coping with obstacles, (3) the role of vascular lesions in “highest level gait disorder” (a condition tightly connected with senile gait, cautious gait and frailty), (4) the role of the failure of automaticity or inter-limbs coordination/symmetry during walking and such approach would definitely help the development of screening instrument for subjects at risk (still lacking in present days). This translational approach will lead to the development of specific therapeutic interventions.

Evidence for a relationship between bilateral coordination during complex gait tasks and freezing of gait in Parkinson’s disease

BACKGROUND Freezing of gait is a debilitating and common gait disturbance observed in individuals with Parkinsons disease (PD). Although the underlying mechanisms of freezing remain unclear, bilateral coordination of steps, measured as a phase coordination index, has been suggested to be related to freezing. Phase coordination index has not, however, been measured during tasks associated with freezing such as turning and backward walking. Understanding how bilateral coordination changes during tasks associated with freezing may improve our understanding of the causes of freezing. METHODS Twelve individuals with PD who freeze (freezers), 19 individuals with PD who do not freeze (non-freezers), and 10 healthy, age-matched older adults participated. General motor disease severity and freezing severity were assessed. Phase coordination index was calculated for all subjects during forward walking, backward walking, continuous turning in small radius circles, and turning in large radius circles. RESULTS Freezers and non-freezers had similar disease duration and general motor severity. Stepping coordination (measured as phase coordination index) was significantly worse in freezers compared to non-freezers and controls. Turning and backward walking, tasks related to freezing, resulted in worse coordination with respect to forward walking. Coordination was associated with severity of freezing scores such that worse coordination was correlated with more severe freezing. CONCLUSIONS These results provide evidence that stepping coordination is related to freezing in people with PD. Identifying variables associated with freezing may provide insights into factors underlying this symptom, and may inform rehabilitative interventions to reduce its occurrence in PD.