Incidence, disease course, therapeutic strategies and outcomes of inflammatory bowel disease-unclassified patients in Western Hungary: A population-based cohort

BACKGROUND The number of population-based studies on unclassified inflammatory bowel disease (IBD-U) is very limited. AIM To evaluate the long-term incidence, disease course and surgery rates of IBD-U in a prospective population-based cohort. METHODS The present study is a continuation of the well-established Veszprem IBD cohort with patient inclusion between 1977 and 2018. Both in-hospital and outpatient records were collected. The source of age- and gender-specific demographic data was derived from the Hungarian Central Statistical Office. Medical therapy, surgery and change in disease phenotype were analyzed. RESULTS Data of 119 incident IBD-U patients were analyzed [male/female: 55/64; median age at diagnosis: 34 years (interquartile range: 24-47.5)]. Adjusted mean incidence rate was 0.76 (95%CI: 0.63-0.9)/105 person-years in the total study period. Disease extent at diagnosis was extensive (pancolitis) in 56.3%. Twenty-two of 119 (18.5%) patients were reclassified to Crohn’s disease during follow up, the probability of developing terminal ileum involvement was 6.8%, while perianal disease developed in 5% (n = 6). The probability of receiving biological therapy in patients diagnosed after the year 2000 (n = 62), was 15.5% (SD: 4.8) at 5 years. The overall resective surgery rate was 16.8%. Segment resection was performed in 5.0% of the patients, and 11.8% underwent subtotal or total colectomy. The cumulative probability of resective surgery was 7.6% (SD: 2.4) at 1 year, 9.3% (SD: 2.7) at 5 years, 13.5% (SD: 3.3) at 10 years, and 18.5% (SD: 3.9) at 20 years. CONCLUSION These data extend our knowledge on the overall burden of IBD-U. Colonic involvement was extensive in a high proportion of IBD-U. Disease reclassification to Crohn’s disease was relatively high. High rates of biological therapy and surgery rates support a relatively severe disease course of IBD-U.