Five‐Year Outcomes and Disease Trajectories in Moderate‐to‐Severe Ulcerative Colitis: A Korean Multicenter Inception Cohort

BACKGROUND AND AIM: The incidence of ulcerative colitis (UC) has been increasing in Asia. Comprehensive data on the long-term course of moderate-to-severe UC remain scarce. This study investigated the clinical outcomes and factors associated with a disabling disease course in Korean patients with moderate-to-severe UC. METHODS: The moderate-to-severe ulcerative colitis in Korea study was a prospective, multicenter, hospital-based inception cohort study that enrolled patients with newly diagnosed moderate-to-severe UC between August 2014 and February 2017. Clinical outcomes and factors associated with a disabling disease course were evaluated over 5 years. RESULTS: Among 353 patients included, the median follow-up duration was 4.9 (interquartile range, 2.1-5.0) years, and 214 patients (60.6%) completed the 5-year follow-up. At 5 years, the cumulative rates of outcomes were clinical relapses, 62.9%; proximal disease extension, 29.5%; and UC-related hospitalization, 22.4%. Colectomy was required in two patients (0.6%), without mortality. A disabling disease course occurred in 171 patients (48.4%), with cumulative probabilities of 41.0%, 51.1%, and 53.9% at 12, 36, and 60 months, respectively. Elevated baseline white blood cell count was independently associated with a disabling disease course (adjusted hazard ratio: 1.06; 95% confidence interval: 1.00-1.12; p = 0.035). Five distinct partial Mayo score-based disease trajectory clusters were identified, demonstrating clear prognostic separation. CONCLUSIONS: While Korean patients with moderate-to-severe UC showed a benign structural disease course with minimal colectomy rates, approximately half experienced a disabling disease course. The identified disease trajectories provide a novel framework for risk stratification and personalized management.