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

Area of Science:

• Neurology
• Musculoskeletal Disorders
• Medical Imaging

Background:

• Calf hypertrophy is a hallmark of Becker muscular dystrophy (BMD).
• The underlying cause of this hypertrophy—whether true muscle growth or fatty infiltration—remains unclear.
• Understanding the composition of calf hypertrophy is crucial for assessing disease progression.

Purpose of the Study:

• To differentiate between fatty degeneration and true muscle hypertrophy in BMD calf muscles.
• To evaluate the correlation between muscle size, fatty replacement, and disease severity.
• To explore the utility of a novel imaging analysis approach.

Main Methods:

• Magnetic resonance imaging (MRI) scans of calf muscles from 29 BMD patients were analyzed.
• A semiquantitative visual score (calf MRI score, CMS) was used to assess fatty replacement.
• Cross-sectional area (CSA) of lower leg posterior compartment muscles was measured and correlated with CMS and clinical data.

Main Results:

• No significant correlation was found between muscle cross-sectional area (CSA) and fatty replacement (CMS).
• The calf MRI score (CMS) showed a significant correlation with disease severity (p<0.001).
• Muscle cross-sectional area (CSA) did not correlate with disease severity (p=0.969).

Conclusions:

• True muscle hypertrophy, rather than fatty degeneration, significantly contributes to calf hypertrophy in Becker muscular dystrophy.
• The calf MRI score (CMS) shows promise as a surrogate marker for assessing BMD disease severity.
• Simple image analysis can effectively distinguish between muscle growth and fatty infiltration in BMD.