Postural sway as a marker of progression in Parkinson's disease: a pilot longitudinal study

Abstract

Objective measures of postural control that are sensitive to Parkinson's disease (PD) progression would improve patient care and accelerate clinical trials. Although measures of postural sway during quiet stance in untreated PD have been shown to differ from age-matched control subjects, it is not known if sway measures change with disease progression in early PD. In this pilot study, we asked whether accelerometer-based metrics of sway could provide a practical tool for monitoring progression of postural dyscontrol in people with untreated or newly treated PD. We examined 13 subjects with PD and 12 healthy, age-matched control subjects. The PD subjects had been recently diagnosed and had not started any antiparkinsonian medications at the baseline session. All subjects were tested 3-6 months and 12 months after the baseline session. Subjects were asked to stand quietly for two minutes while wearing an inertial sensor on their posterior trunk that measured trunk linear acceleration. Our results suggested that objective sway measures deteriorated over one year despite minimal changes in UPDRS motor scores. Medio-lateral (ML) sway measures were more sensitive than antero-posterior sway measures in detecting progression. The ML JERK was larger in the PD group than the control group across all three testing sessions. The ML sway dispersion and ML sway velocity were also significantly higher in PD compared to control subjects by the 12-month evaluation. It is feasible to measure progression of PD prior to onset of treatment using accelerometer-based measures of quiet standing.

Figure 1

Lower trunk acceleration trajectories in the horizontal plane for representative control and PD (P13) subjects across time.

Figure 2

Comparison of group mean sway measures in PD treated (PD Med), non-treated (PD noMed), and control subjects across time. Note that the PD Med subjects were tested OFF medication.

Figure 3

Left panel: Mean clinical measures in PD subjects across time. Right panel: Comparison of group mean clinical measures in PD treated (PD Med) and non-treated (PD noMed) across time.