Differences in phenotype and disease course in adult and paediatric inflammatory bowel disease

Jacobsen et al. compared the phenotype and disease course in paediatric-onset inflammatory bowel disease (PIBD; diagnosed <15 years) and adult-onset IBD (AO-IBD; diagnosed ≥18 years) in Copenhagen.1 This population-based study concluded that paediatric-onset ulcerative colitis (PO-UC) patients had more extensive disease and a higher disease burden than adult-onset (AO-UC), with no difference between paediatric-onset Crohn's disease (PO-CD) and adult-onset (AO-CD). The strengths of this study included prospective collection of both cohorts, and rigorous validation of PIBD case accrual. Benchimol et al. in their excellent, extensive systematic review of the incidence of PIBD,2 concluded that PIBD continues to rise; new data from Northern Europe have confirmed this, both in Scotland3 and Finland.4 In contrast, with the quoted annual Danish PIBD incidence of 7/100 000,1 approximately 84 patients should have been diagnosed during the 6 years studied, and not the 51 children reported. The authors have not discussed this apparent epidemiological anomaly, a marked decrease in incidence over recent years, following the previous increase presented by Vind et al.5 Comparisons of phenotype and disease course of PIBD vs. AO-IBD have been published from Scotland (416 PIBD and 1297 AO-IBD),6 Northern France (206 PO-CD, 412 AO-CD),7 and Italy (133 PIBD, 179 AO-IBD);8 Jakobsen et al. report only 49 PIBD and 173 AO-IBD cases. Although the UC outcome data are consistent with our previous observations6 (i.e. more severe disease within the first 2 years from diagnosis), we are concerned about the validity of the predominantly negative conclusions drawn from the small Danish PO-CD cohort (n = 29). Other than sample size, other key issues include the fact that isolated L3 Montreal classification9 location phenotype was classed as 'extensive disease' (most current literature supports this being L3 + L4 disease), and data pertaining to 5-year surgery risk in a cohort were presented without complete 5-year follow-up. We believe that these factors limit the validity of the conclusions drawn on the phenotype, treatment and disease course of PO-CD vs. AO-CD. Declaration of personal interests: None. Declaration of funding interests: PH is funded by a Medical Research Council project grant for PICTS (G0800675).