Background: Pyoderma gangrenosum (PG) and erythema nodosum (EN) are the most common cutaneous manifestations of inflammatory bowel disease (IBD) but little is known regarding their etiopathogenesis.
Methods: We performed a case–control study comparing characteristics between IBD patients with a documented episode of PG (PG+) and/or EN (EN+) with those without PG (PG−) and EN (EN−). Data on clinical features were obtained by chart review. IBD-related serology was determined using enzyme-linked immunosorbent assay and genome-wide data generated using Illumina technology. Standard statistical tests for association were used.
Results: We identified a total of 92 cases of PG and 103 cases of EN with genetic and clinical characteristics, of which 64 PG and 55 EN cases were available for serological analyses. Fewer male subjects were identified in the PG(+) (odds ratio 0.6, P = 0.009) and EN(+) groups (odds ratio 0.31, P = 0 < 0.0001). Colonic disease, previous IBD-related surgery, and noncutaneous extra-intestinal manifestations were more common among both PG(+) and EN(+) patients compared with controls. PG(+) was associated with anti-nuclear cytoplasmic antibody seropositivity (P = 0.03) and higher anti-nuclear cytoplasmic antibody level (P = 0.02) in Crohn's disease. Genetic associations with PG included known IBD loci (IL8RA [P = 0.00003] and PRDM1 [0.03]) as well as with USP15 (4.8 × 10−6) and TIMP3 (5.6 ×10−7). Genetic associations with EN included known IBD susceptibility genes (PTGER4 [P = 8.8 × 10−4], ITGAL [0.03]) as well as SOCS5 (9.64 × 10−6), CD207 (3.14 × 10−6), ITGB3 (7.56 × 10−6), and rs6828740 (4q26) (P < 5.0 × 10−8). Multivariable models using clinical, serologic, and genetic parameters predicted PG (area under the curve = 0.8) and EN (area under the curve = 0.97).
Conclusion: Cutaneous manifestations in IBD are associated with distinctive genetic characteristics and with the similar clinical characteristics, including the development of other extra-intestinal manifestations suggesting shared and distinct etiologies.