Whole Body BMC in Pediatric Crohn Disease: Independent Effects of Altered Growth, Maturation, and Body Composition

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Abstract
Whole body BMC was assessed in 104 children and young adults with CD and 233 healthy controls. CD was associated with significant deficits in BMC and lean mass, relative to height. Adjustment for lean mass eliminated the bone deficit in CD. Steroid exposure was associated with short stature but not bone deficits relative to height. Introduction: Children with Crohn disease (CD) have multiple risk factors for impaired bone accrual. The confounding effects of poor growth and delayed maturation limit the interpretation of prior studies of bone health in CD. The objective of this study was to assess BMC relative to growth, body composition, and maturation in CD compared with controls. Materials and Methods: Whole body BMC and lean mass were assessed by DXA in 104 CD subjects and 233 healthy controls, 4–26 years of age. Multivariable linear regression models were developed to sequentially adjust for differences in skeletal size, pubertal maturation, and muscle mass. BMC-for-height z scores were derived to determine CD-specific covariates associated with bone deficits. Results: Subjects with CD had significantly lower height z score, body mass index z score, and lean mass relative to height compared with controls (all p < 0.0001). After adjustment for group differences in age, height, and race, the ratio of BMC in CD relative to controls was significantly reduced in males (0.86; 95% CI, 0.83, 0.94) and females (0.91; 95% CI, 0.85, 0.98) with CD. Adjustment for pubertal maturation did not alter the estimate; however, addition of lean mass to the model eliminated the bone deficit. Steroid exposure was associated with short stature but not bone deficits. Conclusion: This study shows the importance of considering differences in body size and composition when interpreting DXA data in children with chronic inflammatory conditions and shows an association between deficits in muscle mass and bone in pediatric CD.