MRI in the assessment of muscular pathology: a comparison between limb-girdle muscular dystrophies, hyaline body myopathies and myotonic dystrophies.

PURPOSE:
The continuous discovery of new subtypes of neuromuscular disorders demands more accurate imaging analyses. We set out to establish the specific patterns of muscular involution using magnetic resonance imaging (MRI).
MATERIALS AND METHODS:
A systematic clinical evaluation based on the Medical Research Council scale and MRI was completed in ten patients with calpainopathy [limb-girdle muscular dystrophy (LGMD)-2A], 16 with dysferlinopathy (LGMD-2B), ten with hyaline body myopathy (HBM), six with myotonic dystrophy (MD) types 1 and 5 with MD type 2. Severity of fibroadipose degeneration was specifically staged using T1-weighted sequences. Turbo inversion recovery magnitude (TIRM) sequences were used to assess oedema-like changes.
RESULTS:
T1 scans showed recurrent patterns of fibroadipose replacement, whereas TIRM images revealed differences in oedema-like changes between the various diseases. In LGMD, the posterior compartments are more vulnerable to degeneration. In HBM, fatty muscle degeneration and oedema are allocated to muscles of the posterior compartments of the leg. In MD, fatty muscle degeneration and oedematous changes are allocated to muscles of the anterior thigh and posterior lower leg.
CONCLUSIONS:
Imaging examination suggests a characteristic pattern of muscle involvement. MRI represents an important diagnostic technique useful in differential diagnosis, thanks to the distinctive patterns observed in the distribution of muscular changes between the different muscular diseases.