Background: Crohn's disease (CD) is a progressive disease that over time can lead to the development of complications such as strictures or internal penetrating disease that will ultimately lead to surgery. Only few population-based studies have investigated the risk factors for disease progression in CD including the effect of smoking. We therefore sought to identify the risk factors associated with complicated CD in a Danish population-based inception cohort from the biological era.
Methods: All incident patients diagnosed with CD or UC in a well-defined Copenhagen area 1.1.2003–31.12.2004 were registered and followed prospectively until 31.12.2011. Clinical data including medical and surgical treatment and disease phenotype according to the Montreal classification were registered. Disease progression in CD was defined as the first occurrence of a bowel stricture (B2) or internal penetrating disease (B3), defined by endoscopy, cross-sectional imaging or surgery, or the need for non-perianal surgery. Possible associations between disease progression and multiple covariates (age, gender, disease location, type of medical treatment, diagnostic delay and smoking status) were analysed by Cox regression analyses using the proportional hazard assumption.
Results: The cohort consisted of 213 incident CD patients that were followed prospectively. Of those, a total of 165 (77%) patients had non-penetrating, non-stricturing disease behaviour (B1) at diagnosis and were included in the analysis. Of those with B1, 44 (27%) patients experienced progression of disease during the seven year follow-up: 21 (48%) B2, 5 (11%) B3, and 18 (41%) had surgery. Patients with ileal disease location (L1 or L3) had increased risk of disease progression (HR =2.1 CI95%: 1.1–4.0) as was also seen in patients who did not receive medical treatment during follow-up compared to those who did (HR =9.0 CI95%: 3.3–25.0). Other covariates including active smoking at the time of diagnosis were not associated with the risk for a disease progression.
Conclusions: In this population-based inception cohort of unselected CD patients one out of four patients with B1 behaviour at diagnosis experienced disease progression during follow-up. Clinical variables associated with the risk of progression were ileal disease location and not receiving medical treatment for CD. Smoking was not associated with the risk of disease progression in CD.