Background/Aims: The incidence of ulcerative colitis (UC) in Thailand (crude incidence rate of 0.28 per 100,000 persons) is much lower than in the West. The burden of UC varies in different populations. The aim of this study was to evaluate the natural history of UC over the two decades in Bangkok, Thailand. Methods: This retrospective study included patients who were diagnosed with UC between 2000 and 2018 in 2 university hospitals. To evaluate changes in the disease course, we stratified patients into 2000–2009 cohort and 2010–2018 cohort. The cumulative probability of endoscopic healing, UC-related hospitalization and colectomy was estimated using the Kaplan-Meier method. Results: A total of 291 UC patients were followed for total of 2,228 person-years. Comparison between 2 cohorts, there were no differences in disease pattern and severity whereas an increase in the combination use of oral and topical mesalamine and the early use of thiopurine was observed. Only 1% of patients for each cohort required biologic agent at 5 years. The rate of achieving mucosal healing increased from 15% to 46% at 3 years (P< 0.01). The rate of UC-related hospitalization decreased from 30% to 21% at 5 years (P< 0.05). The rate of colectomy decreased from 6% to 2% at 5 years (P< 0.05). Conclusions The natural history of UC in a low incidence country was less aggressive than the West. Over the past two decades, the rates of UC-related hospitalization and colectomy have been decreasing which were similar to the West.

Background/Aims: The incidence of ulcerative colitis (UC) in Thailand (crude incidence rate of 0.28 per 100,000 persons) is much lower than in the West. The burden of UC varies in different populations. The aim of this study was to evaluate the natural history of UC over the two decades in Bangkok, Thailand. Methods: This retrospective study included patients who were diagnosed with UC between 2000 and 2018 in 2 university hospitals. To evaluate changes in the disease course, we stratified patients into 2000–2009 cohort and 2010–2018 cohort. The cumulative probability of endoscopic healing, UC-related hospitalization and colectomy was estimated using the Kaplan-Meier method. Results: A total of 291 UC patients were followed for total of 2,228 person-years. Comparison between 2 cohorts, there were no differences in disease pattern and severity whereas an increase in the combination use of oral and topical mesalamine and the early use of thiopurine was observed. Only 1% of patients for each cohort required biologic agent at 5 years. The rate of achieving mucosal healing increased from 15% to 46% at 3 years (P< 0.01). The rate of UC-related hospitalization decreased from 30% to 21% at 5 years (P< 0.05). The rate of colectomy decreased from 6% to 2% at 5 years (P< 0.05). Conclusions The natural history of UC in a low incidence country was less aggressive than the West. Over the past two decades, the rates of UC-related hospitalization and colectomy have been decreasing which were similar to the West.