Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), used to be common in the West. However, the number of patients with IBD is increasing in newly industrialized countries, including Korea. The incidence and prevalence of UC have been steadily rising in the country since the late 1980s.

Data from the Health Insurance Review and Assessment Service (HIRA) indicates that about 46,600 UC patients were in Korea in 2019, with UC growing by 7 percent on average a year between 2015 and 2019.

Despite the continuous rise in the number of patients with IBD in Korea, the nation lacked epidemiologic and clinical research, especially long-term population-based studies, unlike in the Western countries.

A research team, led by Professor Yang Suk-kyun of Asan Medical Center, conducted a 30-year study on UC's natural course in the two southeastern districts of Seoul, Songpa-gu and Kangdong-gu, which the researchers call SK.

Korea Biomedical Review met Professor Ye Byong-duk of the Department of Gastroenterology at Asan Medical Center, a principal researcher, to better understand the long-term study on 1,013 patients diagnosed with UC between 1986 and 2015.

Question: Could you give an overview of UC in Korea, such as its trends, age groups affected, and clinical characteristics?

Answer: According to our 30-year longitudinal SK population-based epidemiologic study published in 2020, UC's mean annual incidence rate in Korea soared almost 20 times from 0.33 to 6.58 per 100,000 people from 1986 to 2015.

The HIRA data showed that 59 percent of patients were male, and 40 percent of patients were between the age of 40 and 59. Also, among the patients, 29 percent were in their 20s and 30s, and 28 percent were older than 60. The clinical presentation of UC patients was similar to that of Western patients except that proctitis was more common in Korean patients' diagnoses.

Q: What made you decide to conduct the study?

A: UC's clinical characteristics in diagnosing Korean patients are not significantly different from those of Western patients. However, there have been no studies on the long-term prognosis of UC at a population level, although there have been several domestic researches on the disease. An unbiased, population-based cohort study with a long-term follow-up duration was necessary to get a clear picture of the epidemiological characteristics and the long-term prognosis of UC in the nation.

Q: What are the epidemiologic differences between UC in Korea and the West?

A: Recently conducted studies in the West found that UC's incidence has been stabilized or declining. However, the number of patients diagnosed with UC is rising in Korea. The healthcare experts in this field expect the increasing trend of UC incidence to continue here.

Q: Why do you think research on UC has not been actively conducted in non-Western countries?

A: Awareness of the disease among Koreans, including doctors, has been low as UC was uncommon in countries outside the West. This situation made it difficult for physicians to accurately diagnose UC and to carry out related studies in earnest. Although long-term cohort studies require a considerable number of patients, the disease's low incidence caused difficulty in recruiting enough people diagnosed with UC.

Q: What is the significance of the study considering the current situation of UC in Korea?

A: Our study involved more than 1,000 patients with UC over 30 years in the Songpa-Kangdong districts of Seoul. We have come up with long-term outcomes by following up on them for more than 100 months on average, which allowed us to apply the study result to therapeutic decision-making and patient education in daily clinical practice.

Q: What are the key findings of this 30-year longitudinal cohort?

A: In our cohort, the cumulative colectomy rate was significantly lower than in Western studies. Only 28 out of 1,013 patients, or 2.8 percent, removed all or part of their colon, demonstrating cumulative risks of colectomy at one, five, 10, 20, and 30 years after diagnosis of 1.0, 1.9, 2.2, 5.1 and 6.4 percent, respectively.

Q: Why did Korean UC patients show lower colectomy rates?

A: The reason for the low colectomy rate is unclear. In our cohort, the proportion of patients with proctitis was relatively higher than in Western studies. However, the colectomy rate among patients with extensive colitis was still lower than that of Western patients.

While there is a cultural preference for not receiving colectomy in Korea, this does not fully explain the difference because avoiding the surgery could raise mortality. However, Korean UC patients' death rate in our study was similar to that of healthy individuals. Also, the therapeutic strategy and the quality of UC treatment were close to the West. The reason for a lower colectomy rate in our cohort is unclear. Still, we believe unknown genetic and environmental factors may play a role.

Q: Were there challenges or concerns you faced with this longitudinal study?

A: Identifying all UC cases diagnosed between 1986 and 2015 was a tough job. Also, we had difficulties in tracking patients because they could easily visit multiple medical institutes.

Q: Which areas need improvement related to IBD research?

A: Data from tracing IBD patients are critical for evaluating the long-term prognosis more accurately. However, stringent laws that protect personal information make epidemiological studies in humans much more difficult. Non-commercial scientific research is needed to take an approach based on a less strict standard to promote such kinds of research with scientific value.

Q: How do you think the situation involving IBD in Korea will change in the future?

A: The steady rise of IBD patients is likely to continue in the future. Although the awareness of IBD among doctors and the public has grown, the overall level still appears inadequate.

Many IBD patients are still receiving a delayed diagnosis and inappropriate treatment, and these issues will not be easily resolved. Demand for healthcare resources to care for IBD patients continues to grow. So, we need a strategy to solve these issues from medical specialists, healthcare authorities, and the general population's perspective.

Q: Are there any other ongoing studies based on this cohort?

A: Studies on patients with CD and specific groups of IBD patients, such as those who developed the disease at an advanced age, are in progress. Also, we are planning to conduct more extended follow-up studies of the SK-IBD cohort.