Rethinking EDSS-based ambulation assessment in multiple sclerosis using continuous variable monitoring

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by relapses and progressive disability. The Expanded Disability Status Scale (EDSS), used to quantify disability, is based on single, discretely assessed and potentially inaccurate patient-estimated walking ability, whereas digital health technologies (DHTs) enable continuous activity monitoring and more objective assessment of real-world functional performance.

In this prospective observational study conducted at two German centers, patients with relapsing-remitting MS (RRMS) underwent clinical assessments at baseline (V1) and study completion (V2). Walking distance and step counts were measured using a measuring wheel and pedometer, while continuous physical activity was assessed via smartwatch-derived metrics.

Sixteen patients with RRMS were included (median age 57.5 years [interquartile range (IQR) 49.25-63.25]; median EDSS 4.5 [IQR 3.5-6]). Patient-estimated walking distance at V1 showed moderate correlation with clinically measured distance (Spearman's ρ = 0.60, p = 0.013), with 12 of 16 patients misjudging distances relative to EDSS thresholds. Walking distance showed intra-individual variability between V1 and V2 (median absolute difference: 113.6 m). Median daily walking distance (ρ = -0.61, p = 0.0123), step count (ρ = -0.64, p = 0.0082), and peak steps (ρ = -0.69, p = 0.0032) correlated negatively with EDSS.

Patient-estimated maximum walking distance demonstrated moderate agreement with clinical performance and frequently crossed EDSS thresholds, while clinical assessments varied substantially within individuals over the short study duration, underscoring the limitations of single evaluations. In contrast, smartwatch-derived metrics aligned with clinical measures, reflected EDSS scores, and captured real-world mobility.