Abstract
Introduction: With the advent of emerging molecular therapies for muscular dystrophies, the need for knowledge about natural history course of such diseases is of utmost importance in the preparation for future trials. However, for Becker muscular dystrophy such knowledge is scarce.Objective: In this 1-year follow-up study, we examined disease progression in Becker muscular dystrophy by monitoring changes in MRI-assessed muscle fat fraction (FF) in axial and lower limb muscles and quantitative muscle strength of axial muscles.Methods and Materials: Sixteen patients with Becker muscular dystrophy were investigated by (1) muscle strength of the trunk using a Biodex dynamometer and (2) Dixon muscle MRI of paraspinal and lower limb muscles. Quantitative MRI data was analyzed in two parts: The first part consisted of all participants (N = 16). The second analysis assessed two separate groups comprising lesser affected participants (N = 5) and more severely affected patients (n = 11).Results: Trunk extension and flexion strength remained stable from baseline to follow-up. MRI did not show any significant increase in muscle FF % from baseline to follow-up in all patients, except for multifidus at the spinal level T12 (p = 0.01). However, when we analyzed the two subgroups, according to disease severity, FF% increased in the lesser severely affected group at L4/L5 erector spinae (p = 0.047), sartorius (p = 0.028), gracilis (p = 0.009), tibialis anterior (p = 0.047), peroneals (p = 0.028), and gastrocnemius medialis (p = 0.009), while the severely affected group only increased significantly at T12 multifidus (p = 0.028) and T12 erector spinae (p = 0.011). No difference in muscle strength was observed in the two subgroups.Conclusion: Our results add to the existing knowledge about the natural rate of disease progression in BMD. As quantitative MRI was able to identify changes where strength assessment was not, MRI could be a strong biomarker for change in BMD. However, our findings show that it is important to stratify patients with BMD according to phenotype for future clinical trials.
Highlights
With the advent of emerging molecular therapies for muscular dystrophies, the need for knowledge about natural history course of such diseases is of utmost importance in the preparation for future trials
Mean trunk muscle strength did not differ from baseline to follow-up in the whole cohort (Figure 2) or the two subgroups
The first analysis showed no significant change in muscle FF% of the measured muscles of the back, thighs, and lower legs from baseline to follow-up, except for multifidus at spinal level T12 (Figures 3A–C), but all muscles showed a nominal increase in fat fraction from baseline to follow-up (3A–C)
Summary
With the advent of emerging molecular therapies for muscular dystrophies, the need for knowledge about natural history course of such diseases is of utmost importance in the preparation for future trials. With the advent of emerging molecular therapies for muscular dystrophies, there is a need to know how the natural history of these diseases is, but for Becker muscular dystrophy such knowledge is scarce, especially with regard to axial muscles. Quantitative strength assessment of the lower limb muscles and the muscles of the trunk using Biodex has been established to be a reliable method in previous studies [5, 6]. With this 1-year follow-up study, we wish to gain knowledge on how axial muscle involvement progresses over time in BMD using quantitative muscle MRI
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