The Spectrum of Perianal Crohn's Disease in a Population-Based Cohort

BACKGROUND: Perianal Crohn's disease represents a phenotype distinct from luminal Crohn's disease and may follow a different course. To date, the only detailed classifications of perianal Crohn's disease arise from referral center cohorts that do not reflect the spectrum of disease in the population as a whole. OBJECTIVES: The aim of this study was to document the rate, classification, and time course of symptomatic perianal Crohn's disease in a population-based cohort. DESIGN: This is a population-based cohort study. SETTING: This study was conducted in the Canterbury region of New Zealand. PATIENTS: All patients with IBD in Canterbury, New Zealand, were eligible for recruitment over a 3-year period. MAIN OUTCOME MEASURES: The clinical records of all patients with Crohn's disease were reviewed, and all symptomatic perianal disease was classified according to the American Gastroenterological Society position statement. The rate of perianal involvement and timing of onset relative to Crohn's diagnosis was determined. RESULTS: Ninety-one percent of IBD patients in the region were recruited. Seven hundred fifteen patients had Crohn's disease, of which 190 (26.6%) patients had symptomatic perianal disease. The median age of patients with perianal disease was 37 years (range, 4-82 years) and 58.4% were female. Median follow-up was 9 years (range, 2 months to 45 years) from Crohn's disease diagnosis. Onset of perianal disease ranged from 18 years pre-Crohn's diagnosis to 33 years post-Crohn's diagnosis. Fistulas were the most common lesion (50% of patients), followed by perianal abscesses (42.1%), fissures (32.6%), skin tags (11.1%), strictures (7.4%), and hemorrhoids (1.6%). The cumulative probability at 20 years of any perianal Crohn's disease was 42.7% and of a perianal fistula 28.3%. LIMITATIONS: This study assumed all noted perianal lesions were related to Crohn's disease and the retrospective classification may have been inaccurate in some cases. CONCLUSIONS: This study provides the first detailed classification of perianal Crohn's disease in a population-based cohort.