Background: Perianal complications in patients with Crohn's disease are common and have a negative impact on the patients' quality of life. Data about the long-term disease course of perianal Crohn's disease in the era of biological treatment are limited. In this population-based cohort study, we sought to investigate the occurrence, clinical risk factors, and disease course of perianal disease.

Methods: A total of 213 Crohn's disease patients were included in a prospective population-based inception cohort. Data were retrieved from medical records and national health administrative databases. Perianal disease was defined as a perianal fistula and/or abscess. Associations between outcomes and covariates were analyzed by Cox regression analysis.

Results: A total of 48 (22.5%) patients developed perianal disease after 10 years. Colonic disease location (hazard ratio [HR], 1.99; 95% confidence interval [CI], 1.01-3.92) and penetrating behavior (HR, 5.65; 95% CI, 2.65-12.03) were associated with the development of perianal disease. The cumulative risk of undergoing abdominal surgery was 51% after 10 years. Patients with perianal disease had a higher rate of resection (HR, 3.92; 95% CI, 1.86-8.67) and hospitalization (HR, 1.01; 95% CI, 1.00-1.01). There was no significant difference in the rate of sick leave, unemployment, or disability pension between patients with and without perianal disease.

Conclusions: Patients with perianal disease carry a higher risk of surgery and hospitalization, and this suggests a more severe disease course and poorer prognosis among these patients, even in the era of biological treatment. These findings underline the importance of optimizing treatment strategies for patients with perianal disease.