The Incidence and Disease Course of Perianal Crohn's Disease: A Danish Nationwide Cohort Study, 1997-2015

Perianal Crohn's disease [CD] places a considerable burden on patients' quality of life and is complex to treat. Despite its impact and high frequency, few studies have investigated the incidence and disease course of perianal CD. The aim of this study was to assess the incidence and disease course of perianal CD in adult patients throughout a 19-year period.

The cohort comprised all individuals aged 18 years or older who were diagnosed with CD in Denmark between January 1, 1997, and December 31, 2015, according to the National Patient Registry [NPR].

A total of 1812 [19%] out of 9739 patients with CD were found to have perianal CD. Perianal fistulas were the most common manifestation, accounting for 943 [52%] cases. The incidence of perianal CD remained stable over time. Patients with perianal CD were found to have an increased risk of undergoing major abdominal surgery compared with patients without perianal CD (hazard ratio: 1.51, 95% confidence interval [CI]: 1.40 to 1.64, p <0.001) in a multivariate Cox regression analysis. The incidence rate ratios of anal and rectal cancer in perianal CD patients were 11.45 [95% CI: 4.70 to 27.91, p <0.001] and 2.29 [95% CI: 1.25 to 4.20, p = 0.006], respectively, as compared with non-IBD matched controls.

In this nationwide study, 19% of CD patients developed perianal disease. Patients with perianal CD were at increased risk of undergoing major surgery compared with non-perianal CD patients. The risk of anal and rectal cancer was increased in patients with perianal CD compared with non-IBD matched controls.

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