Background: It is unknown if the clinical manifestations and phenotype of disease are comparable between early- and elderly-onset inflammatory bowel disease (IBD). We aimed to seek differences in disease phenotype, course, complications, and treatment between early- and elderly-onset IBD patients.

Methods: This retrospective cohort study on registered IBD patients in the Iranian Registry of Crohn's and Colitis (IRCC) compared demographics, disease phenotype, disease activity, IBD-related surgery and medications between early- and elderly-onset IBD. A generalized linear regression model was used to investigate the relative risk of age at diagnosis adjusted for gender and disease duration for the outcomes.

Results: From 10048 IBD patients, 749 with early-onset (7.5%), and 472 (4.7%) elderly-onset IBD were enrolled: 855 (63.1%) ulcerative colitis (UC) and 366 (26.9%) Crohn's disease (CD). Left-sided colitis was more frequent among elderly-onset UC patients (P<0.001). Ileum and ileocolonic locations were the most common types in elderly-onset and early-onset CD patients, respectively. In comparison with elderly-onset UC, early-onset cases more often used prednisolone (22.1% vs. 11.4%, P=0.001), immunomodulators (44.9% vs 25.2%, P<0.001) and anti-tumor necrosis factors (TNF) (20.1% vs 11.9%, P=0.002). Elderly-onset UC patients had 0.7 times lower risk of aggressive phenotype (95%CI:0.6‒0.9, P=0.005). Early-onset CD was associated with higher use of prednisolone (27.7% vs 8.1%, P<0.001), immunomodulators (58.7% vs 41.8%, P=0.005) and anti-TNF (49.6% vs 35.4%, P=0.006).

Conclusions: Early-onset IBD was associated with a more aggressive phenotype and higher prednisolone, immunomodulators, and anti-TNF use.