Long-Term Development of Bone Geometry and Muscle in Pediatric Inflammatory Bowel Disease

OBJECTIVES: The muscle-bone unit is crucial for normal bone development. As muscle mass is frequently reduced in pediatric patients with inflammatory bowel disease (pIBD), we investigated the impact of muscles on the bone development over time. METHODS: Bone and muscle parameters were measured repeatedly in 102 pIBD patients (67 boys; 82 Crohn's disease; 30 newly diagnosed) by peripheral quantitative computed tomography (pQCT) at the forearm. The first and last measurements were included in the evaluation. Results were expressed as sex- and age-specific and partly height-corrected Z-scores for a healthy reference population. RESULTS: At baseline, patients showed reduced Z-scores for height (median ―0.7; range ―3.7 to 1.6), trabecular bone mineral density (TrbBMD; ―0.6; 3.0-2.8), and for height-corrected cortical cross-sectional area (CSA height ; ―0.4; ―3.0 to 2.2), cortical thickness (CrtTh height ; ―0.7; ―3.0 to 1.2), and MuscleCSA height (―1.0; ―4.9 to 2.0; all P<0.01). Cortical bone mineral density (CrtBMD) and height-corrected TotalCSA height Z-scores were elevated (0.57; -4.55 to 2.8, both P<0.01). Over time, TotalCSA height (+0.36; ―1.5 to 4.5) further increased, CorticalCSA height (+0.21; ―2.1 to 3.0) and MuscleCSA height (+0.64; ―2.0 to 3.9, all P<0.01) improved, whereas CrtBMD decreased toward normalization (―0.36; ―5.1 to 3.6, P<0.05). The change in MuscleCSA height significantly correlated with the changes in TrbBMD (r=0 .42 ), TotalCSA height (r=0.35), CorticalCSA height (r=0 . 38), and CrtTh height (r=0.24; all P<0.02). The relations became even stronger after adjustment for several confounders. CONCLUSIONS: Bone metabolism and geometry are altered in pIBD patients expressed by low trabecular mineral density, low cortical thickness, and high cortical mineral density. The increased height-corrected cortical CSA might reflect a compensatory effect. In our cohort, treatment increased height-corrected muscle CSA and its changes were closely associated with bone parameters. Therefore, physical activity to enhance muscle mass and bone health should be promoted in pIBD patients.