Postural sway approaches center of mass stability limits in Parkinson's disease.

BACKGROUND: Although Parkinson's disease (PD) is a well recognised risk factor for falls, how this disease and its therapy affect postural stability and leaning balance remains unclear. The aim of this study was to examine the effects of PD and levodopa on postural sway and leaning balance.
METHODS: Performances of 28 PD participants {median [inter-quartile range (IQR)] duration of PD: 10 (6-13) years, median (IQR) UPDRS motor score "off": 22 (14-31) "on" and "off" levodopa were compared with 28 age- and gender-matched healthy controls on two measures of controlled leaning balance [ratio of anterior-posterior (AP) sway to maximal balance range (MBR) and coordinated stability].
RESULTS: PD participants had greater ratio of AP sway to MBR than controls (P < 0.001), indicating that they swayed more as a proportion of their limits of stability, both "off" and "on" levodopa (P < 0.001). They also performed poorer in the coordinated stability test both "off" and "on" levodopa compared to controls (P < 0.001, for both), suggesting greater difficulty in controlling the center of mass at or near the limits of stability. Levodopa improved PD "participants" leaning balance (P < 0.001) and reduced the AP sway to MBR ratio (P < 0.001), although not to the level of controls.
CONCLUSIONS: PD participants perform poorer than controls in leaning balance tests but significantly improve when "on" levodopa. Regardless of medication state, PD participants sway markedly more as a percentage of their limits of stability than controls suggesting a higher risk of falling.