Signatures of Parkinson's disease in complexity of low-frequency fluctuations of postural sway velocity

TL;DR

This study investigates how low-frequency sway velocity complexity differs between Parkinson's patients, older controls, and young controls, revealing potential diagnostic markers for postural instability in Parkinson's disease.

Contribution

It introduces the use of Lempel-Ziv complexity of sway velocity as a novel biomarker to differentiate Parkinson's disease from healthy aging.

Findings

Mediolateral LZC is lower in Parkinson's patients compared to age-matched controls.

Aging increases LZC, while Parkinson's decreases it, showing opposite effects.

LZC of sway velocity can distinguish Parkinson's patients with 92% sensitivity and 87% specificity.

Abstract

Posturography is routinely used to qualitatively assess one of the cardinal symptoms of Parkinson's disease -- postural instability. While most measures of balance control are derived from displacement of the center of pressure there is evidence that such control is more likely to be velocity-based. We performed static posturographic tests (eyes open and eyes closed) during quiet standing in narrow stance for n=30 patients with Parkinson's disease (PDP) in the ON state and compared the results with those of n=30 age-matched senior controls (HSC) and n=60 young controls (HYC). We used differentiator filters to generate time series of low-frequency fluctuations of sway velocity and calculated their Lempel-Ziv complexity (LZC). With eyes closed, the mediolateral LZC of HSC 0.21 (0.02) was significantly higher than those of HYC 0.19 (0.02) and PDP 0.18 (002). Thus aging and PD have opposite effects on mediolateral LZC which strongly differentiates between HSC and PDP (92% sensitivity and 87% specificity).