Body sway and movement strategies for control of postural stability in people with spinocerebellar ataxia type 3: A cross-sectional study

Background: Postural instability with an excessive body sway is a disabling manifestation in spinocerebellar ataxia type 3. Whether the larger body sway reflects distinct movement strategies for postural control remains uncertain. This study compared the control of postural stability of people with spinocerebellar ataxia type 3 with healthy subjects using body sway and movement strategy analyses derived from bi- and three-dimensional posturography.

Methods: Twenty-three patients (7 men, 16 women, 47 ± 11 years) and 102 healthy participants (34 men, 68 women; 44 ± 22 years) underwent posturography while standing with eyes open/closed tasks. Postural stability was assessed using elliptical area and average velocity of body sway. Spatial patterns (single-, double-, or multi-centered) were derived from the number of high-density regions in the three-dimensional statokinesigram.

Findings: Repeated measures two-way analysis-of-variance showed a vision-by-group interaction effect for area (F_1,122 = 28.831, P < 0.001, η² = 0.037) and velocity (F_1,123 = 59.367, P < 0.001, η² = 0.073); sway area and velocity were higher in spinocerebellar ataxia type 3 and increased under eyes-closed condition, with a higher increase in the spinocerebellar ataxia type 3. A main effect for group (F_1,123 = 11.702, P < 0.001, η² = 0.061) but not vision (F_1,123 = 2.257, P = 0.136, η² = 0.005) was found for the number of high-density regions. Spatial patterns were different between groups under trials with eyes closed (χ²_2,125 = 7.46, P = 0.023) but not open (χ²_2,125 = 2.026, P = 0.363), with a shift from single- to double- or multi-centered spatial patterns.

Interpretation: Compared to healthy subjects, a larger body displacement and velocity in spinocerebellar ataxia type 3, mainly under visual constraints, are not related to the predominance of either ankle or hip movement strategies.