P0696Isolated vs Crohn’s Disease-Related Complex Perianal Fistulas: Similar Profiles but Challenging Fistula Phenotype with Delayed Radiological Healing in Isolated Disease

Background Because of very limited comparative data, there is still doubt whether complex perianal fistula (cPAF), in isolated form (I-cPAF) and in association with Crohn’s disease (CD-cPAF), are different phenotypes of CD and how different is their treatment responses. Methods We retrospectively compared patients with I-cPAF and CD-cPAF in terms of clinical characteristics and clinical and radiologic remission rates. Among 72 patients who presented with symptoms of cPAF, 29 had I-cPAF, while the remaining patients either had concomitant luminal Crohn’s disease at baseline or developed it during follow-up. I-cPAF was confirmed with no gastrointestinal involvement in cross sectional imaging, gastroscopy and colonoscopy both initially and finally in follow-up. Clinical remission (CR) was defined as the absence of fistula drainage with gentle compression for ³ 3 months, and radiologic remission (RR) as complete fibrotic closure of fistula tracts on MRI. Results Data from 72 patients were analysed, of whom 40.3% (n:29) had I-cPAF. The median follow-up for the entire cohort was 95.5 (98) months and was comparable between I-cPAF and CD-cPAF (p:0.167; 82 (97) vs 100 (96.5) months). Table 1a summarizes demographic, clinical, and laboratory features of the overall cohort and of I-cPAF versus CD-cPAF. In the CD-cPAF group, ileal and ileocolonic disease locations were present in 34.1% and 41.5% of patients, respectively, with rectal involvement in 34.1%; penetrating and stricturing phenotypes were observed in 20.5% and 10.3%. In both groups, nearly half of patients had more than one fistula tract, whereas trans-sphincteric fistulas were more frequent in I-cPAF (67.9% vs 43.2%). Rates of abscess, drainage, and seton placement were similar (Table 1a). Initial albumin and haemoglobin levels were lower and CRP higher in CD-cPAF than in I-cPAF. Infliximab (IFX) was the most commonly used anti-TNF, with overall IFX treatment persistence of 80.3%, without group differences (p:0.94). CR occurred in approximately 70% of patients and was similar between I-cPAF and CD-cPAF (p:0.86). However RR was significantly less frequent in I-cPAF (Table 1b, Figure 1) with comparable MRI interval patterns in both groups. The CR–RR interval was comparable between groups (p:0.559), with a median of 28 (32.5) months in the entire cohort. Conclusion Despite its lower inflammatory burden and more challenging trans-sphincteric PAF profile with a lengthy radiological healing, largely shared fistula characteristics and clinical remission rates between I-cPAF and CD-cPAF, strongly support that I-cPAF is a different phenotype of CD. Conflict of interest: Bickes, Emre: No conflict of interest Mr. Bakkaloglu, Oguz Kagan: No conflict of interest Bayar, Melikşah: No conflict of interest Akpınar, Atilla: No conflict of interest Eskazan, Tugçe: No conflict of interest Sirolu, Sabri: No conflict of interest Simsek, Osman: No conflict of interest Tutar, Onur: No conflict of interest Erzin, Yusuf Ziya: No conflict of interest Hatemi, Ali Ibrahim: No conflict of interest Çelik, Aykut Ferhat: No conflict of interest