Objective: To test if perturbations that induce backward or forward steps are better for distinguishing reactive stepping impairment between people with mild-to-moderate early PD and matched controls.

Background: Postural instability in Parkinson’s disease is tested clinically by applying an unexpected backward pull that requires reactive backward steps to maintain balance. It is unclear if a backward fall is the most appropriate direction for distinguishing between those with and without postural instability.

Method: Sixty-two individuals (40 PD) were tested. Rapid forward (backward fall) or backward (forward fall) translations of the support surface were applied to induce postural reactions requiring at least 1 step to restore balance. Principle component analysis was applied to the center of pressure time series data. The number of steps taken and the first principle component (PC1) were entered in linear repeated-measures mixed effect models separately.

Results: Fewer steps were required to recover from a forward fall than from a backward fall in both the PD and control subjects. The group difference between PD and control was significantly greater in the forward than in the backward direction in both number of steps (p < 0.01) and PC1 (p = 0.03).

Conclusion: These findings demonstrate that differences in reactive stepping between people with PD and healthy adults are most evident when the applied perturbation requires a forward step rather than a backward step.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/an-objective-comparison-of-forward-and-backward-postural-instability-in-early-parkinsons-disease/