Relation of Postural Instability to Gait Dynamics in Patients with Parkinson’s Disease

Rhythm as typified by stride interval is an important factor in walking. The stride interval of patients with Parkinson’s disease (PD) randomly fluctuates, and the stride interval variability is large. However, the relationship between gait rhythm dynamics and motor symptoms in PD patients has not been determined. The purpose of this study is to examine the relationship between one of the motor symptoms— postural instability—and the gait dynamics in PD patients. The stride interval variability was quantified using the coefficient of variation (CV) and the fluctuation property of stride interval is quantified as the scaling exponent α using detrended fluctuation analysis. We used multiple test and receiver operator characteristic (ROC) analysis to examine the relationship between severity of postural instability and gait dynamics. We divided PD patients into 3 groups: no postural instability, mild postural instability and obvious postural instability group. We compared the distribution of CV and α among the groups. Then, we compared the performance of the classification by CV with that by α. Forty-five patients with PD and 17 healthy elderly people walked around 200m without any support. The severity of postural instability was determined using the modified HoehnYahr scale (mH-Y). Patients with mH-Y 2.5 have mild postural instability, and patients with mH-Y 3 and more than 3 have obvious postural instability. As a result, the classification by CV has a high performance when we differentiate between the presence and absence of postural instability. Also, the classification by α has a high performance when we differentiate between mild postural instability and obvious postural instability. These results suggest that CV and α can be used to differentiate severity of motor symptoms in patients with PD. Index Terms – Gait rhythm, Postural instability, Coefficient of variation, Detrended fluctuation analysis.