Ambulatory capacity and disease progression as measured by the 6-minute-walk-distance in Duchenne muscular dystrophy subjects on daily corticosteroids

In order to understand contemporary natural history of Duchenne muscular dystrophy (DMD), we report 6-minute walk distance (6MWD) and its change over time from a large single centre population of corticosteroid treated DMD boys. Sixty-five boys on daily corticosteroid treatment were identified with a mean (SD) age of 9.5 (2.3) years at first observation. 6MWD was described for 1 year age groupings. In addition, changes in 6MWD at 1, 1.5 and 2 years (±12 weeks) of follow-up were evaluated. The same evaluations were applied to 6MWD data converted to percent predicted values based on the Geiger equation. 6MWD showed an increase from age group 4.5-5.5 years to age group 6.5-7.5 years, followed by a decline, which became precipitous from 12.5 years onwards. From 15.5 years, all boys were unable to perform the 6-min test. Changes in 6MWD demonstrated a mean (median, SD) decline of −43 (−14, 90) m at 1 year (N = 25, mean baseline age 9.5 years), −64 (−56, 99) m at 1.5 years (N = 18, mean baseline age 9.6 years), −125 (−106, 139) m at 2 years (N = 14, mean baseline age 10.0 years). Conversion to percent predicted values showed the same pattern of evolution.This study provides data on the ambulatory capacity and its changes over time in a homogenous cohort of 65 DMD boys on daily corticosteroids. The variability, the age-related aspects and the slope of decline of the 6MWD should be considered in the design and interpretation of therapeutic trials in ambulant DMD patients.