Calf muscle involvement in Becker muscular dystrophy: When size does not matter

Introduction Calf hypertrophy is a common feature in Becker muscular dystrophy (BMD), and it is still debated to which extent fatty degeneration or true muscle hypertrophy account for it. We wanted to investigate the relative contribution of these two components using a simple image analysis approach and their possible correlation with disease severity.

Methods Twenty-nine BMD patients' MRI scans were analyzed. A semiquantitative visual score assessing fatty replacement of calf muscles (calf MRI score, CMS) was calculated and correlated with the cross sectional area (CSA) of lower leg posterior compartment muscles, digitally measured on acquired images.

Results The correlation between CSA and CMS was not significant. CMS in contrast correlated with disease severity (p <0.001) while CSA did not (p = 0.969).

Conclusions In BMD, a major contribution to calf hypertrophy is provided by real muscle hypertrophy rather than by fatty degeneration. CMS appears to be a potential surrogate marker of disease severity.