Cross-sectional comparison of in vivo Viscoelastic Response (VisR) ultrasound in lower limb muscles of boys with and without duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a genetic disorder that causes progressive muscle degeneration involving necrosis and inflammation, with subsequent replacement of muscle fibers by fibrosis and fatty tissue. These compositional changes underlie mechanical property alterations in affected muscles, which may be assessed using Viscoelastic Response (VisR) ultrasound. We hypothesize that VisR will delineate differences in the viscoelastic properties of lower limb skeletal muscles in boys with versus without DMD. VisR imaging was performed in the vastus intermedius (VI), rectus femoris (RF), sartorius (SM) and gastrocnemius (GM) muscles of seven boys (4 DMD, 3 control) aged 7.9 – 10.4 years. Parametric images of relative elasticity (RE) and relative viscosity (RV) were rendered. From the parametric images, percent muscle area with relatively high RE or RV value was calculated and compared (Wilcoxon rank-sum) between DMD and control on a per-muscle basis. In the VI, RF and SM, percent muscle with relatively high RV was larger (VI: 17.7% v. 13.1% RF: 98.9% v. 93.7%, SM: 43.2% v. 40.6% p < 0.05) in DMD than control muscles. In the VI, percent muscle with relatively high RE was larger (32.8% v. 29.5%, p < 0.05) in DMD muscles. No significant differences were observed in the GM between DMD and control. VisR results were consistent with temporally-matched functional testing using a hand-held dynamometer, which showed 40.5% to 70.0% lower force output in DMD RF, VL and SM - and only 21.8% lower force output in DMD GM - relative to the corresponding control muscles. These results suggest that VisR imaging is relevant to delineating viscoelastic property alterations that are associated with dystrophic muscle degeneration in boys with DMD, in vivo.