Age and sex but not disease activity or duration are associated with muscle mass in paediatric Crohn's disease.

Background: There is evidence of low muscle mass in adults with active Crohn's disease (CD) compared to patients in remission, but this has not been explored in paediatric CD.

Aim: To assess the psoas muscle cross sectional area (PCSA) measured using magnetic resonance enterography (MRE) in paediatric CD patients and compare this between those with active or inactive disease.

Design: Paediatric CD patients who underwent MRE during 2016 to 2023 were included. Muscle mass was measured as PCSA at the right and left area of psoas muscle at the upper level of Lumbar 3 (L3) vertebra. Disease activity was defined by a clinical radiologist based on MRE images. Bivariable regression was used to explore unadjusted relationships, whereas a multiple linear regression model was constructed to adjust for potential confounders (disease activity, sex, age at MRE, disease duration, and current biologic use).

Results: 107 patients with CD (57.9% males) aged 13.0 (11.0, 15.0) [median (interquartile range)] were included. Most patients (64.5%) had active disease and the median disease duration for the whole cohort was 0.97 (0.49, 3.07) years. There was no difference in PCSA between patients with active or inactive disease [25.06 (19.51, 33.99) and 26.51 (20.62, 36.99) cm², respectively]. After adjusting for all covariates, the multivariable model identified sex and age at MRE as significant predictors of PCSA. Males had a 6.72 cm² (-11.19, -2.25cm²; p=0.004) higher PCSA compared to females. For every 1-year increase in age, PCSA increased by 2.92 cm² (2.04, 3.81; p<0.001), adjusting for other covariates. Disease activity (p= 0.22), disease duration (p= 0.49) and current biologic use (p= 0.94) did not show significant associations with PCSA.

Conclusion: Age and sex but not disease activity or duration are significantly associated with muscle mass as measured by PCSA in paediatric CD.