Lessons for future clinical trials in adults with Becker muscular dystrophy: Disease progression detected by muscle magnetic resonance imaging, clinical and patient‐reported outcome measures

Background and purpose Because Becker muscular dystrophy (BMD) is a heterogeneous disease and only few studies have evaluated adult patients, it is currently still unclear which outcome measures should be used in future clinical trials. Methods Muscle magnetic resonance imaging, patient‐reported outcome measures and a wide range of clinical outcome measures, including motor function, muscle strength and timed‐function tests, were evaluated in 21 adults with BMD at baseline and at 9 and 18 months of follow‐up. Results Proton density fat fraction increased significantly in 10/17 thigh muscles after 9 months, and in all thigh and lower leg muscles after 18 months. The 32‐item Motor Function Measurement (MFM‐32) scale (−1.3%, p = 0.017), North Star Ambulatory Assessment (−1.3 points, p = 0.010) and patient‐reported activity limitations scale (−0.3 logits, p = 0.018) deteriorated significantly after 9 months. The 6‐min walk distance (−28.7 m, p = 0.042), 10‐m walking test (−0.1 m/s, p = 0.032), time to climb four stairs test (−0.03 m/s, p = 0.028) and Biodex peak torque measurements of quadriceps (−4.6 N m, p = 0.014) and hamstrings (−5.0 N m, p = 0.019) additionally deteriorated significantly after 18 months. At this timepoint, domain 1 of the MFM‐32 was the only clinical outcome measure with a large sensitivity to change (standardized response mean 1.15). Discussion It is concluded that proton density fat fraction imaging of entire thigh muscles is a sensitive outcome measure to track progressive muscle fat replacement in patients with BMD, already after 9 months of follow‐up. Finally, significant changes are reported in a wide range of clinical and patient‐reported outcome measures, of which the MFM‐32 appeared to be the most sensitive to change in adults with BMD.