Objective: To characterize spatiotemporal biomarkers derived from a quantitatively assessed pull test in patients with early Parkinson’s disease (PD).

Background: The pull test is a standard clinical tool for evaluating postural instability in PD and has established validity and reliability. However, the five-point ordinal scoring system used to score it has limited sensitivity to subtle postural control deficits, particularly in early-stage PD (Hoehn and Yahr stage < 3). To address this limitation, we previously developed a method to extract objective biomechanical biomarkers from pull test performances with scores of 0–2 using inertial sensors [1].

Method: Twenty-seven patients with early PD (modified Hoehn and Yahr stage 2–2.5; mean age 71.5 ± 7.7 years) were enrolled. During the pull test, inertial sensors (MicroStone, MVP-RF8-HC; sampling frequency 200 Hz) were attached to the examiner’s right hand and the participant’s lower trunk. Acceleration data and derived displacement measures were used to calculate posterior center-of-gravity displacement (COG-P), weight-shift time (WST), and weight-shift velocity (WSV), defined as quantitative biomarkers of postural stability. Biomarkers were compared across pull test scores using the Kruskal–Wallis test, with a significance threshold of 5%.

Results: Pull test scores were 0 (n = 13), 1 (n = 9), and 2 (n = 5). Associations between pull test scores and all biomarkers were found. Significant differences in COG-P and WST were found between patients with pull test scores of 0 and 1 (P = 0.002, P < 0.001), 0 and 2 (P < 0.001, P < 0.001), and 1 and 2 (P = 0.022, P < 0.001). Both biomarkers demonstrated progressive deterioration across increasing scores, indicating stepwise impairment of postural control with disease progression. Significant differences in WSV were found between scores 0 and 1 (P < 0.001) and scores 0 and 2 (P < 0.001), but not between scores 1 and 2. These findings indicate that WSV decreases once the pull test score exceeds 0, suggesting early vulnerability to disease-related postural dysfunction.

Conclusion: Quantitative biomarkers derived from the pull test exhibit distinct spatiotemporal characteristics and may provide clinically meaningful, objective measures of postural instability for early-stage assessment and management of PD.

References: [1] Taniuchi R, Kanai S, Hara A, et al. Extraction of the pull force from inertial sensors during the pull test for Parkinson’s disease: A reliability study. J Mov Disord. 2024;17(2):150-157.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spatiotemporal-biomarkers-of-early-postural-instability-in-parkinsons-disease-implications-for-early-intervention/