Muscle Magnetic Resonance Imaging versus Clinical Function in Duchenne Muscular Dystrophy

Background: Impairment in patients with Duchenne muscular dystrophy (DMD) has been evaluated primarily by muscle fiber microscopy examination. Pathologic examination is limited by the choice of muscle and the invasiveness of muscle biopsy. Magnetic resonance imaging (MRI) of the muscle is a noninvasive method of evaluating muscle preservation. Objective: To compare muscle MRI and clinical function in patients at different stages (from early to terminal stage) of DMD, and to evaluate the correlation between fatty infiltration grade on MRI and clinical functional scale. Materials and methods: Thirty-one boys with DMD, of mean age 7.76 ± 4.99 years, underwent evaluation of clinical functional score grades (scores 1-4) while undergoing muscle MRI of the lower leg, thigh and pelvis. Fatty infiltration grade of 31 muscles was assessed by T1WI MRI using the Mercuri scale (from 0 to 4). Spearman correlation analysis was performed to assess the correlation between T1WI fatty infiltration grade and clinical functional grade. Results: Seventeen muscles showed positive correlations between fatty infiltration grade on T1WI MRI and clinical function. The gluteus maximus, adductor magnus, and gastrocnemius muscles were the most representative, because they were involved during early stages of DMD and their shapes were easier to distinguish on MRI. The obturator internus, gracilis and sartorius muscles were rarely involved until the terminal stage of disease. Damage to these three muscles could be used to predict terminal stage. Fatty infiltration grade on muscle MRI corresponded to microscopic parameters, including a reduced number of muscle cells, arrangement disorder, and fatty and connective tissue infiltration. Conclusion: The results of muscle MRI showed good correlation with clinical function in patients with DMD. Because muscle MRI is a reliable and non-invasive method of assessing muscle damage, MRI is useful in the diagnosis and follow-up of patients with DMD. The Mercuri scale, which measures fatty infiltration on T1WI MRI, is a convenient method of evaluating disease severity and progression.