Association between body mass index and age of disease onset with clinical outcomes in paediatric-onset Crohn's Disease (CD): a UK nation-wide analyses using the NIHR-IBD BioResource.

Background: The evidence on the relationship between adiposity and disease outcomes in paediatric Crohn's disease (CD) is limited and lacks consensus.

Aim: To investigate the relationship between (a) body mass index (BMI) and clinical CD outcomes (hospitalisation, surgery, disease behaviour, biologic use, extra-intestinal manifestations (EIMs)) and (b) the age of CD onset with clinical outcomes.

Design: Clinical outcomes were examined in CD patients diagnosed at age <17 years and enroled in the National Institute for Health Research IBD-UK BioResource at a median age of 24 years. All outcomes and BMI were recorded at the time of enrolment. Participants were categorised into normal (<25 kg/m) and high (≥25 kg/m) BMI. Age at disease diagnosis was categorised into pre-puberty/early puberty (<11 years), puberty (11-14 years) and post-puberty (15-17 years). Spearman rank correlation was used to test the associations between continuous variables and chi-square test to compare categorical variables.

Results: 848 participants with CD were included (51.8% males) and median age at diagnosis was 14 years. Participants with high BMI experienced a greater frequency of EIMs (P = 0.05) than those with low BMI (1 type of EIM: 18.5% vs. 13.2%, respectively; ≥2 types of EIMs: 7.8% vs. 5.6%, respectively). Age at diagnosis and BMI showed weak correlations with corticosteroid use (ρ = 0.08, P = 0.03 and ρ = -0.09, P = 0.01; respectively). An early diagnosis (<11 years) was associated with higher occurrence of stenosing and penetrating disease behaviour (P = 0.01) and hospitalisations (P < 0.001).

Conclusions: A higher BMI and an earlier age of disease onset are associated with worse CD clinical presentation.