F032 Towards digital-motor outcomes for limb movements in spastic ataxia: a comparative validation of Q-motor in ataxia and hereditary spastic paraplegia – lessons learnt for HD

<h3>Background</h3> Q-Motor assessments, widely used in HD, capture upper-limb ataxia with digital-motor outcomes that are patient-meaningful and sensitive to change. Whether Q-Motor also captures damage to the pyramidal tract – an ideal prerequisite for trial outcomes in spastic ataxias –, and how this interferes with digital measures for cerebellar ataxia is unknown. <h3>Methods</h3> This cross-sectional single-center study validated digital upper-limb measures of finger-tapping, diadochokinesia, grip-lift, spiral-drawing and target-reaching, together with lower limb measures of foot-tapping, in 41 patients with hereditary spastic paraplegia (HSP; age: 48±14 ; Spastic Paraplegia Rating Scale [SPRS]: 19±9) as compared to 46 cross-genotype ataxia patients (age: 50±18; SARA: 12±6). Validation criteria comprised discrimination from 48 matched controls, and significant correlations to each disease severity (SPRS or SARA), activities of daily living (FARS-ADL), and the 9-hole-peg-test (9HPT). <h3>Results</h3> Speed measures of finger-tapping and diadochokinesia, but no other movement feature or task, captured HSP motor impairment in the upper-limbs. These measures better reflected impaired fine motor function in HSP than in ataxia (|rho9HPT|=0.7–0.8 vs. 0.5–0.6), comparable to smoothness of target-reaching as most sensitive measure for upper-limb ataxia (|rho9HPT|=0.8). Correlations of finger-tapping to disease severity were limited to the dominant hand in HSP ((|rhoSPRS|=0.3–0.4), while upper-limb ataxia was better captured in the non-dominant hand. In In the lower-limb, speed of foot-tapping captured both ataxia (|rhoSARA|=0.4–0.7) and spastic paraplegia (|rhoSPRS|= 0.4–0-6), with strong discrimination of HSP from controls (AUC=0.96), while variability measures of tap duration were specific for ataxia. Discussion: Digital tapping speed measures capture cerebellar ataxia and pyramidal tract involvement, while variability measures appear specific for ataxia. Sensitivity for the interaction of both systems in spastic ataxias is being validated in ARSACS and SPG7. <h3>Conclusion</h3> Q-Motor presents a promising digital-motor outcome for spastic ataxias. This study demonstrates that Q-Motor can be applied in other movement disorders beyond HD.