title: 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 (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.
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, USA. modlesky@udel.edu
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Modlesky
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Cavaiola
authors.forename: Jarvis J
authors.initials: JJ
authors.lastname: Smith
authors.forename: David A
authors.initials: DA
authors.lastname: Rowe
authors.forename: David L
authors.initials: DL
authors.lastname: Johnson
authors.forename: Freeman
authors.initials: F
authors.lastname: Miller
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D016022:Case-Control Studies; D002547:Cerebral Palsy / Q000473:pathology*; D002648:Child; D006801:Humans; D008962:Models, Theoretical; D018482:Muscle, Skeletal / Q000033:anatomy & histology*