Occurrence of inflammatory bowel disease in patients with chronic inflammatory skin diseases: a cohort study

BACKGROUND: Several studies linked various chronic inflammatory skin diseases (CISDs) with inflammatory bowel disease (IBD) in a range of data sources with mixed conclusions. OBJECTIVE: We compared the incidence of IBD-ulcerative colitis (UC) and Crohn\u27s disease (CD)- in patients with a CISD versus similar persons without a CISD. METHODS: In this cohort study using nationwide, longitudinal, commercial insurance claims data from the US, we identified adults and children who were seen by a dermatologist between 2004-2020, and diagnosed with either psoriasis, atopic dermatitis, alopecia areata, vitiligo, or hidradenitis suppurativa. Comparator patients were identified through risk-set sampling; they were eligible if they were seen by a dermatologist at least twice and not diagnosed with a CISD. Patient follow-up lasted until either IBD diagnosis, death, disenrollment, or end of data stream, whichever came first. IBD events, ulcerative colitis (UC) or Crohn\u27s (CD), were identified via validated algorithms-hospitalization or diagnosis with endoscopic confirmation. Incidence rates were computed before and after adjustment via propensity-score (PS) decile stratification to account for IBD risk factors. Hazard ratios (HR) and 95% confidence intervals were estimated to compare the incidence of IBD in CISD versus non-CISD. RESULTS: We identified patients with atopic dermatitis (n=123,614), psoriasis (n=83,049), alopecia areata (n=18,135), vitiligo (n=9,003) or hidradenitis suppurativa (n=6,806), and comparator patients without a CISD (n=2,376,120). During a median follow-up time of 718 days, and after applying PS adjustment for IBD risk factors, we observed increased risk of both UC (HR =2.30; 1.61-3.28) and CD (HR =2.70; 1.69-4.32) in patients with hidradenitis suppurativa, an increased risk of CD (HR =1.23; 1.03-1.46) but not UC (HR =1.01; 0.89-1.14) in psoriasis, and no increased risk of IBD in atopic dermatitis (HR =1.02; 0.92-1.12, HR =1.08; 0.94-1.23), alopecia areata (HR =1.18; 0.89-1.56, HR =1.26; 0.86-1.86) or vitiligo (HR =1.14; 0.77-1.68, HR =1.45; 0.87-2.41). CONCLUSIONS: IBD was increased in patients with hidradenitis suppurativa. Crohn\u27s disease alone was increased in patients with psoriasis. Neither ulcerative colitis nor Crohn\u27s disease was increased in patients with atopic dermatitis, alopecia areata or vitiligo