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Digital Motor Outcomes Capture Upper Limb and Mild Stage Impairment in Hereditary Spastic Paraplegia
Malin Schulze1, Dominik Hermle1, Robin Schubert2
1Division Translational Genomics of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research and Center of Neurology, University of Tübingen, Tübingen, Germany.
Introduction:
Digital motor outcomes may surpass the sensitivity of clinician-reported outcomes in hereditary spastic paraplegia (HSP), particularly in cases of mild upper limb impairment and early disease stages. We thus validated a trial-ready quantitative motor (Q-Motor) assessment of rapid alternating limb movement tasks against clinician-reported, patient-focused, and performance outcomes in HSP.
Methods:
Exploratory single-center cross-sectional assessment in 41 patients with different HSP genotypes (age: 48 ± 14 years), with speeded foot tapping, diadochokinesia, and finger tapping measured by a high-resolution force transducer. Validation comprised discrimination from 48 age- and sex-matched controls; correlations to the Spastic Paraplegia Rating Scale (SPRS; mean: 18.6 ± 9.1), Friedreich Ataxia Rating Scale- Activities of Daily Living (FARS-ADL), and Nine-Hole Peg Test (9HPT); and stratification by functional stage (FARS stage: mild/moderate/severe = ambulatory/walking aid/wheelchair).
Results:
Foot tapping best discriminated patients with HSP from controls (e.g., frequency: area under the curve [AUC] = 0.94-0.96), and particularly captured HSP severity and functional impairment by measures of foot elevation and cumulative tap force (across all measures: |rhoSPRS|= 0.33-0.59; |rhoADL|= 0.35-0.56). Speed measures of diadochokinesia and finger tapping captured functional impairment (|rhoADL|= 0.32-0.60) and impaired dexterity (|rho9HPT |= 0.53-0.77) in the upper limbs of patients with HSP-even in the mild stage, and with slowed finger tapping even in patients without upper limb pyramidal signs. Foot tapping measures were most sensitive in discriminating mild-stage impairment (AUC = 0.72-0.95) and predominantly changed between mild and moderate HSP, while upper limb measures of diadochokinesia and finger tapping predominantly changed from moderate to severe HSP.
Conclusion:
Q-Motor captures motor impairment in HSP, even in the upper limbs and mild disease stages, and should be further evaluated as a possible trial outcome by longitudinal validation in genotypically stratified cohorts and mapping to patient experience.
