D.P.19 Progression of muscle damage in dystrophinopathy

Abstract The progression of muscle damage was studied in the patients with dystrophinopathy (Duchenne and Becker muscular dystrophy) using CT in order to describe natural history and investigate genotype–phenotype correlations. Muscle volume index (MVI) is the estimated muscle volume contained within a given CT slice and calculated using the CT histogram-based procedure after correcting for a partial volume effect. %MVI is calculated by dividing the MVI by the entire volume of the region of interest. We applied this method to CT scans of skeletal muscles retrospectively selected from 44 patients with DMD and 22 patients with BMD in our hospital. Diagnosis was based on clinical aspects, muscle biopsy and gene analysis. In DMD, %MVI declined exponentially with age. We subdivided DMD patients according to the mutation sites (proximal/distal to exon 45). DMD patients carrying proximal mutations showed a higher degree of muscular impairment than DMD with distal mutations. In BMD, there was a correlation between disease duration and ln (%MVI). BMD patients carrying deletion of exon 45–47 showed more rapid progression of muscle damage than BMD with deletion of exon 45–48. This study provided novel data on genotype–phenotype correlations in dystrophinopathy and suggested that location of the mutation might influence motor outcome. Those findings may be useful in the clinical management of patients and clinical trials.