Magnetic Resonance Imaging in a large cohort of facioscapulohumeral muscular dystrophy patients: pattern refinement and implications for clinical trials

OBJECTIVE: therapeutic perspectives raised attention on the development of instruments to accurately evaluate the degree of pathology in patients with facioscapulohumeral muscular dystrophy. We aimed to analyze the type and extent of muscle involvement on MRI in a large cohort of patients representative of the broad clinical spectrum of this disease. METHODS: pelvic and lower limb muscle MRI scans of 269 symptomatic individuals and 19 non-penetrant gene carriers were assessed. Comparative analysis of the upper girdle scan in 181 of these subjects was also performed. RESULTS: we found a peculiar susceptibility and resistance of particular muscles. Combined involvement of abdominal and hamstring muscles with iliopsoas sparing is common in facioscapulohumeral muscular dystrophy (67% of the patients). Adductor longus and/or rectus femoris, whose involvement can go clinically undetected, are often typically affected in early disease (69% of patients below age 45). The extent of lesions on lower limb MRI showed a high correlation with overall clinical severity. One-fourth of the non-penetrant gene carriers showed abnormalities on MRI. Hyperintensities on short-tau inversion recovery sequences, markers of active disease, were found in muscles without signs of fatty replacement in 35% of patients, representing early lesions. INTERPRETATION: Our large-scale cross-sectional data provides preliminary evidence for the usefulness of MRI in clinical trials, and sets the baseline for longitudinal studies. Muscle MRI can be also used for distinguishing facioscapulohumeral muscular dystrophy from other myopathies in selected cases. Finally, our results are consistent with a model that configures facioscapulohumeral muscular dystrophy as a "muscle-by-muscle" disease