Objective

To assess the applicability and the responsiveness of the motor function measure 1 (MFM) in the myotonic dystrophy type 1 (DM1) population.

Materials/patients and methods

We conducted an observational, retrospective, multicenter cohort study using data from the MFM database ( http://www.motor-function-measure.org/data-bank.aspx ). Only DM1 patients with at least one MFM-32 score were included. The distributions of the MFM scores (total score and 3 subscores) were analyzed by age. MFM responsiveness was estimated in patients with at least two MFMs (at least six months between the two evaluations). Hypothetical sample sizes for specific effect sizes in clinical trial scenarios are given.

Results

The descriptive study includes 618 patients from 29 physical medicine and rehabilitation or neurology department aged 6.2–80.4 years. 1038 MFM-32 for DM1 patients are registered in the MFM database and 228 patients have a least two evaluations. 930 MFM were realized in adults’ patients (> 18 years old). Mean age at the MFM execution was:

MFM D1 subscore (standing and transfers) is the more sensitive score to show deterioration (–2.32 points/year). MFM D2 (proximal and axial motricity) and D3 (distal motricity) subscores showed less changes over time (–1.43 + –4.25 points/year for D2, –0.53 + –4.18 points/year for D3). Significant responsiveness was obtained with the D1 subscore (standardized response mean [SRM] =. 550).

Discussion/Conclusion

MFM scale and particularly the D1 subscore is a reliable and valid outcome measure applicable in longitudinal follow-up and clinical trials in the DM1 population.