T_2 mapping provides multiple approaches for the characterization of muscle involvement in neuromuscular diseases: a cross-sectional study of lower leg muscles in 5–15-year-old boys with Duchenne muscular dystrophy

摘要

Skeletal muscles of children with Duchenne muscular dystrophy (DMD) show enhanced susceptibility to damage and progressive lipid infiltration, which contribute to an increase in the MR proton transverse relaxation time (T_2). Therefore, the examination of T_2 changes in individual muscles may be useful for the monitoring of disease progression in DMD. In this study, we used themean T_2, percentage of elevated pixels and T_2 heterogeneity to assess changes in the composition of dystrophic muscles. In addition, we used fat saturation to distinguish T_2 changes caused by edema and inflammation from fat infiltration in muscles. Thirty subjects with DMD and 15 age-matched controls underwent T_2-weighted imaging of their lower leg using a 3-TMR system. T_2 maps were developed and four lower leg musclesweremanually traced (soleus, medial gastrocnemius, peroneal and tibialis anterior). The mean T_2 of the traced regions of interest, width of the T_2 histograms and percentage of elevated pixels were calculated. We found that, even in young children with DMD, lower leg muscles showed elevated mean T_2, were more heterogeneous and had a greater percentage of elevated pixels than in controls. T_2 measures decreased with fat saturation, but were still higher (P{L-End} <0.05) in dystrophic muscles than in controls. Further, T_2 measures showed positive correlations with timed functional tests (r=0.23–0.79). The elevated T_2 measures with and without fat saturation at all ages of DMD examined (5–15 years) compared with unaffected controls indicate that the dystrophic muscles have increased regions of damage, edema and fat infiltration. This study shows that T_2 mapping provides multiple approaches that can be used effectively to characterize muscle tissue in children with DMD, even in the early stages of the disease. Therefore, T_2 mapping may prove to be clinically useful in themonitoring ofmuscle changes caused by the disease process or by therapeutic interventions in DMD.