A DXA-Based Mathematical Model Predicts Midthigh Muscle Mass from Magnetic Resonance Imaging in Typically Developing Children but Not in Those with Quadriplegic Cerebral Palsy ,

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 (muscleMRI) in typically developing children and children with quadriplegic cerebral palsy (CP). A mathematical model predicting muscleMRI from midthigh, fat-free soft tissue mass from DXA (FFSTDXA) 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 (muscleDXA) in typically developing children, as indicated by a very strong relationship between muscleDXA and muscleMRI (r2 = 0.95; SEE = 68 g; P < 0.001), no difference in muscleDXA and muscleMRI (P = 0.951), and visual examination using a Bland-Altman plot. MuscleDXA was very strongly related to muscleMRI in children with CP (r2 = 0.96; SEE = 54 g; P < 0.001); however, muscleDXA overestimated muscleMRI by 15% (P = 0.006). The overestimation of muscleMRI by muscleDXA was strongly related to the lower ratio of muscleMRI to FFSTDXA (muscleMRI/FFSTDXA) in children with CP (r2 = 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 muscleMRI/FFSTDXA is needed to estimate midthigh muscle mass in children with quadriplegic CP.