Objective: The objective of the study was to investigate which postural sway condition and which measures are most sensitive to prodromal and manifest spinocerebellar ataxia (SCA).

Background: Large postural sway while standing reflects poor neural control of balance and is related to high fall risk in people with SCA. Wearable technology has the potential to quantify postural sway during various balance conditions (e,g., standing feet apart versus feet together) in clinical settings. However, there is no consensus about which postural sway condition is more sensitive to SCA and which sway measures (from different sensor placements) best reflect postural control impairments in SCA.

Method: One hundred one people with SCA (SCA1 (n=13); SCA2 (n=25); SCA3 (n=21); SCA6 (n=42) with SARA scores 9.4 ± 4.0), 40 people with prodromal SCA (SARA<3) and 99 age-matched healthy control (HC) subjects participated in this study. All subjects wore two synchronous, inertial sensors (by APDM Wearable Technology-Clario, Int.) attached to the sternum and the lumbar L5 region. Subjects stood quietly for 30 s with eyes open in two different conditions: fee-apart using a template and with feet-together. We derived the same 30 sway measures from the sternum and lumbar areas, including sway area, velocity, frequency, area, angle, jerkiness, etc. The Area Under Curves (AUC) was calculated for each sway measure in both postural sway conditions and body locations to determine the objective sway measures that best separated the prodromal and manifest SCA groups from the HC cohort.

Results: The top 10 AUCs discriminating sway in the prodromal and manifest SCA groups from the HC group were from the sternum location during the feet-together condition. Further, the same top two sway measures best discriminated prodromal and manifest SCA from HC. Specifically, sway ellipse area (AUC for prodromal SCA vs. HC=0.76, and manifest SCA vs. HC= 0.95) and average velocity (AUC for prodromal SCA v. HC=0.75, and manifest SCA vs. HC = 0.94).

Conclusion: Sway measures from the sternum sensors during the standing, feet-together condition are most sensitive to prodromal and manifest SCA. The best sway measures reflecting the balance control characteristics of SCA are ellipse area and average velocity. We are now examining the relationship to clinical- and patient-reported outcomes, and sensitivity to the progression of postural sway measures for use in clinical trials and clinical practice.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/digital-sway-measures-for-spinocerebellar-ataxia/