Muscle MRI in Becker Muscular Dystrophy and in Limb-girdle Muscular Dystrophy Type 2I

The purpose of this study is to investigate the paradoxical muscle enlargement seen in patients affected by Becker muscular dystrophy and Limb-girdle muscular dystrophy type 2I.

Becker and limb-girdle muscular dystrophies are both hereditary muscular disorders. Both diseases appear clinically with shrinkage and muscle weakness of the muscles around the shoulder girdle and pelvis, while muscle hypertrophy of the calves and tongue is seen.

The quality of the enlarged calves has to the investigators knowledge not previously been described, and their hypothesis is that the normal correlation between muscle strength and muscle cross-section is absent in the calf muscles. Thus the investigators hypothesis suggests that there is no actual hypertrophy of the calf muscles, but rather a pseudohypertrofy with reduced force per cross-sectional area. With a picture of increased fat infiltration and disorganized muscle fibers.

The enlarged calves' muscle quality will be assessed primarily on the basis of the muscle structure on MRI (assessed on both T1 imaging, 3-point Dixon scans, and diffusion tension imaging), and based on a calculation of muscle strength per cross-sectional area. Isokinetic muscle dynamometry (Biodex-4) will be used to measure muscle strength. The findings will be compared with results from non-affected controls.

Additionally the investigators want to describe the tongue muscle appearance on T1-weighted MRI.

Inclusion criteria

• Danish patients genetically verified with either becker muscular dystrophy or limb-girdle muscular dystrophy type 2I
• calves enlargement

Exclusion criteria

• Patients who have metal implants in the body, for instance surgical clips, cochlear implants, pacemaker etc.
• pregnant or breast-feeding patients
• patients who are claustrophobic
• atrophic calves