Long-term changes in disease extent and severity in ulcerative colitis: a population-based cohort from the Norwegian...

The long-term disease course of Ulcerative Colitis (UC) remains incompletely understood. This study aimed to characterize the longitudinal changes of disease extent and severity in UC in a population-based cohort.

Incident UC cases were identified among adult participants (≥20 years) in the Trøndelag Health Study (HUNT) and validated thorough hospital records. Participation in a HUNT survey enabled access to hospital records, allowing verification of the diagnosis and detailed assessment of the disease course. Cases were followed from diagnosis, until the end of follow-up on 1 April 2024. Longitudinal changes in disease extent and severity were assessed using the validated Montreal Classification.Kaplan-Meier methods and Cox proportional hazard regression were used to estimate progression rates and hazard ratios (HRs) with 95% Confidence Intervals (CIs).

The study included 736 UC cases with a median follow-up of 5.3 years (interquartile range 1.5-11.8). Progression in disease extent occurred most frequently during the first three years after diagnosis. Cases presenting with proctitis had the highest annual risk of progressing in extent (7.5%), compared to those with left-sided colitis (3%). After 10 years, the proportion with proctitis declined from 43% to 24%, whereas the proportion of left-sided colitis and extensive colitis increased from 36% to 44% and 21% to 32%, respectively. Male sex was associated with a significantly lower risk of progression in extent compared to females (HR 0.56 95%CI 0.36-0.88). Men also showed a tendency towards a lower risk of developing more severe disease, although this did not reach statistical significance (HR 0.71, 95% CI 0.78-1.04). After 10 years, the proportion of patients experiencing severe disease increased from 24% to 45%. Patients diagnosed in the most recent time-period (2010-2023) had a significantly higher hazard of developing more severe disease during follow-up compared with those diagnosed before 2002 (HR 2.13 95% CI 1.13-4.03). Age at diagnosis and smoking status were not associated with changes in disease extent or severity.

Cases with UC demonstrated progression in disease extent over time. Disease severity followed a relapsing-remitting course, but with an increasing proportion of cases developing more severe disease during follow-up. Cases diagnosed after 2010 also showed a tendency towards a more severe disease course. Female sex was associated with a higher risk of progression in extent and having episodes of severe disease during follow-up.