Background: Accurate measurement of functional disease progression in Duchenne Muscular Dystrophy (DMD) requires sensitive and objective outcomes. One such outcome, SV95C (Stride Velocity at the 95th centile) captured at the ankle using a magneto-inertial wearable sensor, has been qualified by EMA for regulatory decision making in pivotal trials in DMD. These ankle-worn sensors also allow the detection and measurement of various other ambulation-relevant endpoints during normal daily living, including stair climbing . The aim of this study was to evaluate the real-world stair climbing velocity as a potential novel outcome measure in DMD.
Methods: Analytical validation of the stair climbing algorithm relied on sensor data acquired from the ankle worn device in the clinic in 5 DMD patients. Clinical validation relied on functional tests performed in clinic with 46 ambulant DMD patients including the 6 Minute Walk Test (6MWT), North Star Ambulatory Assessment scale (NSAA) and 4 Stair Climb Test (4SCT), as well as during normal daily living.
Results: We explored the utility of the algorithm to detect stair climbing variables in 46 ambulant DMD patients (age: 4.8 to 14.5 years; Mean (SD): 6MWT: 349 meters (53); NSAA: 23.4 (5.4); 4SCT: 4.51 seconds (2.25)).
The stair reconstruction algorithm showed good accuracy at detecting stairs and stair height (median error approximately 1cm). SCV50C (median Stair Climbing Velocity) is correlated with 4SCT (Spearman=(-)0.79 [95% CI (-)0.88 – (-)0.62]). Strong internal reliability was found for SCV50C (ICC=0.93 [95% CI 0.87-0.96]). SCV50C presented a low MDC of 0.04.
Conclusions: These results validate the accurate performance of Stair Climbing reconstruction algorithm computed from data acquired by an ankle-worn sensor in DMD patients during normal daily living. The SCV50C variable shows excellent internal reliability and transversal correlation with the gold standard 4-stair climb test. Longitudinal data will further define the optimal stair-related variable in DMD.