Direction specific preserved limits of stability in early progressive supranuclear palsy: a dynamic posturographic study.

OBJECTIVES: To quantitatively detect the nature of balance impairment in patients with progressive supranuclear palsy (PSP) using dynamic posturography.
METHODS: Twenty clinically diagnosed PSP patients (8 women, 12 men; age: 62.1 ± 7.7 years; duration: 2.6 ± 1.3 years) and 20 healthy controls were studied. All subjects were right side dominant. They were evaluated by dynamic posturography (Biodex, USA). The measurements included (i) balance indices: ability to control balance in all directions (overall balance index, OBI), front to back (anterior-posterior index, API) and side-to-side (medio-lateral index, MLI), and (ii) the limits of stability (LOS) in 8 directions: forward (FW), backward (BW), right (RT), left (LT), forward-right (FW-RT), forward-left (FW-LT), backward-right (BW-RT) and backward-left (BW-LT).
RESULTS: Compared to controls, patients showed significantly higher OBI (p<0.001), API (p=0.003) and MLI (p<0.001), implying impaired balance. The total LOS score was significantly lower (implying poor stability) in PSP than in controls (18.3 ± 7.3 vs. 28.4 ± 8.5, p<0.001). Patients took significantly longer time to complete LOS test (262.7 ± 33.0 s vs. 135.4 ± 20.6 s, p<0.001). Direction-wise analysis showed that PSP patients had significantly lower LOS scores in FW, BW, RT, FW-RT, BW-RT and BW-LT directions compared to controls. However the scores in LT and FW-LT did not differ significantly.
CONCLUSIONS: PSP patients showed impaired balance indices and decreased overall LOS compared to controls. Though LOS is affected in PSP, the scores in the left (non-dominant side) and forward-left (non-dominant forward diagonal) directions were preserved.