Static balance impairment and its change after pallidotomy in Parkinson's disease

Minimal detectable change of the timed "up & go" test and the dynamic gait index in people with Parkinson disease

BACKGROUND

The minimal detectable change (MDC) is the smallest amount of difference in individual scores that represents true change (beyond random measurement error). The MDCs of the Timed "Up & Go" Test (TUG) and the Dynamic Gait Index (DGI) in people with Parkinson disease (PD) are largely unknown, limiting the interpretability of the change scores of both measures.

OBJECTIVE

The purpose of this study was to estimate the MDCs of the TUG and the DGI in people with PD.

DESIGN

This investigation was a prospective cohort study.

METHODS

Seventy-two participants were recruited from special clinics for movement disorders at a university hospital. Their mean age was 67.5 years, and 61% were men. All participants completed the TUG and the DGI assessments twice, about 14 days apart. The MDC was calculated from the standard error of measurement. The percentage MDC (MDC%) was calculated as the MDC divided by the mean of all scores for the sample. Furthermore, the intraclass correlation coefficient was used to examine the reproducibility between testing sessions (test-retest reliability).

RESULTS

The respective MDC and MDC% of the TUG were 3.5 seconds and 29.8, and those of the DGI were 2.9 points and 13.3. The test-retest reliability values for the TUG and the DGI were high; the intraclass correlation coefficients were .80 and .84, respectively.

LIMITATIONS

The study sample was a convenience sample, and the participants had mild to moderately severe PD.

CONCLUSIONS

The results showed that the TUG and the DGI have generally acceptable random measurement error and test-retest reliability. These findings should help clinicians and researchers determine whether a change in an individual patient with PD is a true change.

Dyskinesia-induced postural instability in Parkinson's disease

Parkinson's disease (PD) patients may complain of unsteadiness and impaired balance not only when OFF, but also while being ON with levodopa-induced dyskinesia (LID), yet influence of LID upon postural stability has not been specifically examined. In this study, we addressed this issue using static and dynamic posturography in patients with advanced PD and typical LID. Relevant postural stability parameters were measured on force platforms when patients were OFF and ON, either in quiet standing or when performing leaning tasks designed to stress postural stability. Simultaneously, LID was assessed clinically using a dyskinesia rating scale of severity and subjective unsteadiness was computed. Displacement of the net center of pressure (COPnet), range of COPnet in the mediolateral and antero-posterior directions and 95% confidence ellipse area for both feet were measured as indicators of postural stability and used for comparison analyses. We found a significant increase of COPnet displacement in all tasks up to 556% (mean: 125+/-165%) when patients were ON with dyskinesia compared to the OFF state. In about half of the patients, this increase was marked and correlated with subjective unsteadiness while ON. There was a good correlation between the clinical scores of dyskinesia severity and most COPnet values. Patients demonstrated a tendency to sustain their weight on the foot less affected by dyskinesia, probably as a compensatory mechanism. Our results suggest that LID may compromise balance and independently contribute to postural instability in advanced PD.

Postural control of the trunk during unstable sitting in Parkinson's disease

Postural instability and falls, both common in Parkinson's disease (PD), have been related to altered trunk control. In this study, we investigated dynamic trunk control with subjects balancing on a seat mounted on a hemisphere, for up to 15s in five trials. We compared eight PD patients with a fall-history, eight without a fall-history, and eight matched healthy subjects. The number of trials completed without balance loss and the time to balance loss were significantly lower in PD patients as compared to healthy controls, whereas the PD patients with a fall-history did not perform significantly less than the patients without a fall-history. Multivariate analysis of variance showed significant effects of group on movements of the center of pressure (CoP) under the seat with the largest amplitudes among the PD fallers and the smallest amplitudes among the healthy controls. Univariate analyses revealed that this effect was mainly based on a significantly larger root mean square CoP displacement in the medio-lateral direction, with significant post hoc differences between all three groups. Trunk angular deviations were significantly smaller among PD patients than controls. Finally, both CoP movements and trunk movements had a significantly lower frequency content and were thus slower in PD patients than in controls, except for anterior-posterior CoP movements. The results show that trunk control is affected in PD and suggest that these changes may be related to postural instability and fall risk.

Gait Initiation and Dynamic Balance Control in Parkinson’s Disease

OBJECTIVE

To determine whether the magnitude of the separation between the center of pressure (COP) and the whole-body center of mass (COM) during gait initiation can differentiate patients with varying severity of Parkinson's disease (PD) disability.

DESIGN

Cross-sectional, intact groups research design.

SETTING

Biomechanics research laboratory.

PARTICIPANTS

Forty-three patients were stratified into 2 groups based on the Hoehn and Yahr (H&Y) disability score, which heavily favors balance in determining disability. The 2 groups were: H&Y score of 2.0 or less (n=23; age, 61+/-10y) or H&Y score of 2.5 or higher (n=20; age, 70+/-9y).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The peak COP-COM distance represents the maximum separation between the location of the whole-body COM and the ground reaction force's COP, and thus is an indicator of dynamic balance control. The peak COP-COM was evaluated during 3 phases of the COP trajectory during a gait initiation task.

RESULTS

The peak magnitude of the COP-COM distance was significantly greater during the end of the single-support phase in the less disabled patients (H&Y score <or=2.0) than in more balance disabled patients (H&Y score >or=2.5) (P=.004).

CONCLUSIONS

The differences in COP-COM distances between these H&Y groups suggest that patients with PD who have impaired postural control produce shorter COM-COP distances than do persons without clinically detectable balance impairment. This method of evaluation could prove a useful quantitative index to examine the impact of interventions designed to improve ambulation and balance in PD.

Falls in Parkinson's disease

PURPOSE OF REVIEW

To summarize the latest insights into the clinical significance, assessment, pathophysiology and treatment of falls in Parkinson's disease.

RECENT FINDINGS

Recent studies have shown that falls are common in Parkinson's disease, even when compared with other fall-prone populations. The clinical impact of falls is considerable, often leading to an incapacitating fear of renewed falls. The associated costs for society are substantial. Clinical assessment often includes the retropulsion test, and recent studies have offered practical recommendations regarding the execution and scoring of this test. Insights into the pathophysiology underlying falls are growing and point to an important role for the loss of inter-segmental flexibility ('stiffness'), which predisposes patients to falls in a backward or medial-lateral direction. New evidence has clarified why Parkinson's disease patients commonly fall during transfers and under 'dual tasking' circumstances. The absence of adequately directed arm movements may explain the relatively high proportion of hip fractures in Parkinson's disease. The importance of freezing of gait as a cause of falls is recognized, and we are beginning to understand the different manifestations of gait freezing. Recent work has defined the contributions of pharmacotherapy, stereotactic neurosurgery, physiotherapy and multidisciplinary interventions in the treatment of postural instability to prevent falls in Parkinson's disease.

SUMMARY

No dramatic breakthroughs have occurred during the review period, but new information in various areas may be useful for practising clinicians. Interesting new questions have been raised that should fuel studies of pathophysiological mechanisms, which could help in the development of improved treatment strategies to reduce falls in Parkinson's disease.