Assessing muscle function is a key step in measuring changes and evaluating the outcomes of therapeutic interventions in Duchenne Muscular Dystrophy (DMD). Regarding the large use of corticosteroids (CS) in this population to delay the loss of function, our goal was to monitor the evolution of motor function in patients with DMD treated by corticosteroids (CS) and to study the responsiveness of Motor Function Measure (MFM) in this population in order to provide an estimation of the number of subject needed for a clinical trial.

A total of 76 patients with DMD, aged 5.9 to 11.8 years, with at least 6 months of follow-up and 2 MFM were enrolled, 30 in the CS treated group (8±1.62 y) and 46 in the untreated group (7.91±1.50 y).

The relationship between MFM scores and age was studied in CS treated patients and untreated patients. The evolution of these scores was compared between groups, on a 6-, 12- and 24-month period by calculating slopes of change and standardized response mean. At 6, 12 and 24 months, significant differences in the mean score change were found, for all MFM scores, between CS treated patients and untreated patients. For D1 subscore specifically, at 6 months, the increase is significant in the treated group (11.3±14%/y; SRM 0.8) while a decrease is observed in the untreated group (–17.8±17.7%/y; SRM 1). At 12 and 24 months, D1 subscore stabilized for treated patients but declined significantly for untreated boys (–15.5±15.1%/y; SRM 1 at 12 mo and–18.8±7.1%/y; SRM 2.6 at 24 mo). 21 patients lost the ability to walk during the study: 6 in the CS treated group (25% at 24 months, mean age: 10.74±1.28 y) and 15 in the untreated group (64.71% at 24 months, mean age: 9.20±1.78 y).

Patients with DMD treated by CS present a different course of the disease described in this paper using the MFM. Based on these results, an estimation of the number of patients needed for clinical trial could be done.