BACKGROUND Perianal fistulae are either primary(idiopathic)or secondary[commonly associated with Crohn’s disease,(CD)].It is assumed,although not proven,that the pathophysiology differs.AIM To systematically compare the clinical phenotypes,cytokine and phosphoprotein profiles of idiopathic and CD-related perianal fistulae.METHODS Sixty-one patients undergoing surgery for perianal fistula were prospectively recruited(48 idiopathic,13 CD)into a cohort study.Clinical data,including the Perineal Disease Activity Index(PDAI)and EQ-5D-5L were collected.Biopsies of the fistula tract,granulation tissue,internal opening mucosa and rectal mucosa were obtained at surgery.Concentrations of 30 cytokines and 39 phosphoproteins were measured in each biopsy using a magnetic bead multiplexing instrument and a chemiluminescent antibody array respectively.Over 12000 clinical and 23500 laboratory measurements were made.RESULTS The PDAI was significantly higher(indicating more active disease)in the CD group with a mean difference of 2.40(95%CI:0.52-4.28,P=0.01).Complex pathoanatomy was more prevalent in the CD group,namely more multiple fistulae,supralevator extensions,collections and rectal thickening.The IL-12p70 concentration at the internal opening specimen site was significantly higher(median difference 19.7 pg/mL,99%CI:0.2-40.4,P=0.008)and the IL-1RA/IL-1βratio was significantly lower in the CD group at the internal opening specimen site(median difference 15.0,99%CI=0.4-50.5,P=0.008).However in the remaining 27 cytokines and all 39 of the phosphoproteins across the four biopsy sites,no significant differences were found between the groups.CONCLUSION CD-related perianal fistulae are more clinically severe and anatomically complex than idiopathic perianal fistulae.However,overall there are no major differences in cytokine and phosphoprotein profiles.
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