Posturographic abnormalities in ambulatory atypical parkinsonian disorders: Differentiating characteristics

Background: Postural instability is a common complaint in patients with Parkinson's disease (PD), multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). However, objective evaluation to identify posturographic characteristics to enable clinical differentiation is limited. Method: Postural sway abnormalities in 35 atypical parkinsonian patients (19 PSP, 16 MSA), 35 matched PD patients, and healthy subjects were assessed under static posturography with eyes-open (EO) and eyes-closed (EC). Results: With EO, MSA patients showed a significantly greater mean ML sway than PD patients (p = 0.03), but with EC even more parameters were significantly different, including mean sway in both ML (p = 0.02) and AP directions (p = 0.01), sway area (p = 0.001), and sway path length (p = 0.003). While differences between MSA and PD were seen in both ML and AP directions, significant differences between PD and PSP were limited to greater mean ML sway (p = 0.01) with EO, greater mean (p = 0.002) and maximal AP sway (p = 0.02) amongst PSP patient with EC. Moderate and significant correlation was demonstrated between HY stage and mean AP sway amongst APD patients (r = 0.56, p < 0.01) and in PSP patients (r = 0.62, p < 0.01). Conclusion: Our study identifies a number of objective sway measures assessed with EC that are potentially useful for clinical differentiation between APDs and PD. In comparison to PD, MSA showed greater sway area and a mean sway distance in both AP and ML directions, while the difference was limited to AP in PSP. Significant correlation between HY stage and sway parameters further supports postural sway as a potential disease progression marker in APDs.