Static Posture Instability as a Sensitive Biomarker for Motor Abnormalities in Pre‐ataxic Spinocerebellar Ataxia Type 3 Patients

Abstract Background Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder, with balance instability as a feature of the disease. Balance instability often manifests before the onset of obvious ataxic symptoms in patients. However, current clinical scales exhibit limited sensitivity in characterizing changes in pre‐ataxic patients. Objectives Our research aims to identify appropriate postural characteristics for tracking motor changes in pre‐ataxic patients with SCA3 over time. Methods The posturographic platform assessed 102 participants (34 pre‐ataxic SCA3 patients, 34 ataxic patients with SCA3, and 34 healthy controls) to measure their postural balance. Multivariate comparative analyses assessed the differential postural characteristics across the three groups. The Taiwanese formula was employed to estimate the age of onset for pre‐ataxic patients. A Spearman's rho test was employed to assess correlations between postural characteristics and the time manifestation for pre‐ataxic patients. Results Compared to the healthy control group, we observed significant abnormalities in the static posture of pre‐ataxic patients ( P < 0.01). Compared to the pre‐ataxic group, ataxic patients have significant abnormalities in all variables ( P < 0.05). The sway range standard deviation (SD), total sway area, and limits of stability were positively correlated with the estimated time to onset. The total sway area is more closely associated with time to manifestation, whereas the sway range SD in the medial–lateral direction of the center of foot pressure is the most sensitive indicator of postural instability in pre‐ataxic patients. Conclusion Static posture instability is a sensitive diagnostic parameter that may assist in capturing disease progression in the pre‐ataxic stage of SCA3. © 2025 International Parkinson and Movement Disorder Society.