Preliminary Report on the Muscle Imaging Assessment of Viltolarsen Efficacy for Treating Duchenne Muscular Dystrophy

ABSTRACT Background We propose the muscle volume index (MVI) and MVI‐percentage (%MVI) as indicators for quantitatively evaluating residual muscle tissue using computed tomography (CT) in patients with muscular dystrophy. Aim We evaluated two patients with Duchenne muscular dystrophy (DMD) who underwent Viltolarsen therapy, using CT data. Methods CT scans from two patients with DMD who were treated with Viltolarsen were compared retrospectively with untreated patients with DMD as controls. Case 1 had been taking Viltolarsen since the age of 9 years and had muscle CT data from ages 5, 10, 12, and 13 years. Case 2 recieved Viltolarsen since the age of 15 years and had muscle CT data from ages 16 to 18 years. The %MVIs of these scans were calculated for the middle part of the thigh and lower leg. We evaluated the efficacy of the two treatments by comparing their values with the 95% confidence interval (CI) of the approximate exponential regression curve for the controls. Results The %MVI value for Case 1 prior to Viltolarsen initiation was below the 95% CI, and the %MVI value remained above the upper limit of the 95% CI. In Case 2, the %MVI value remained within the 95% CI. The stratified analysis based on corticosteroid use yielded similar results. The efficacy in Case 1 was supported by functional test assessments. The results of the %MVI assessment were consistent with those of the functional tests. Conclusions The efficacy of Viltolarsen in the treatment of DMD can potentially be evaluated using CT data.