Corticosteroids in Duchenne muscular dystrophy: impact on the motor function measure sensitivity to change and implications for clinical trials

Aim To monitor the evolution of the motor function of ambulatory patients with Duchenne muscular dystrophy (DMD) treated by corticosteroids for 2 years in comparison with untreated patients. Method This observational, multicentre cohort study explores the evolution of the motor function measure (MFM) over a 24‐month period for 29 ambulant corticosteroids‐treated and 45 ambulant untreated patients with DMD. Results Significant differences were found between mean MFM scores in corticosteroids‐treated and untreated groups for domain 1 of the MFM (standing position and transfers; D1), domain 2 of the MFM (axial and proximal motor function; D2), and domain 3 of the MFM (distal motor function; D3). Subscores were between 0 months and 6 months, and 0 months and 24 months. For the D1 subscore specifically, there was a significant increase in the corticosteroids‐treated group (mean±standard deviation [SD] slope of change=12.6±15.5%/y), while a decrease was observed in the untreated group (−17.8±17.7%/y) between 0 months and 6 months (p