Abstract
Valid methods for assessing regional muscle mass in children are needed. The aim of this study was to determine whether dual-energy X-ray absorptiometry (DXA) can accurately estimate midthigh muscle mass from MRI (muscle(MRI)) in typically developing children and children with quadriplegic cerebral palsy (CP). A mathematical model predicting muscle(MRI) from midthigh, fat-free soft tissue mass from DXA (FFST(DXA)) was developed using 48 typically developing children (6-13 y) and was validated using the leave-one-out method. The model was also tested in children with quadriplegic CP (n = 10). The model produced valid estimates of midthigh muscle mass (muscle(DXA)) in typically developing children, as indicated by a very strong relationship between muscle(DXA) and muscle(MRI) (r(2) = 0.95; SEE = 68 g; P < 0.001), no difference in muscle(DXA) and muscle(MRI) (P = 0.951), and visual examination using a Bland-Altman plot. Muscle(DXA) was very strongly related to muscle(MRI) in children with CP (r(2) = 0.96; SEE = 54 g; P < 0.001); however, muscle(DXA) overestimated muscle(MRI) by 15% (P = 0.006). The overestimation of muscle(MRI) by muscle(DXA) was strongly related to the lower ratio of muscle(MRI) to FFST(DXA) (muscle(MRI)/FFST(DXA)) in children with CP (r(2) = 0.75; P = 0.001). The findings suggest that the DXA-based mathematical model developed in the current study can accurately estimate midthigh muscle mass in typically developing children. However, a population-specific model that takes into account the lower muscle(MRI)/FFST(DXA) is needed to estimate midthigh muscle mass in children with quadriplegic CP.