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.