Isolated perianal fistulizing Crohn's disease in contemporary clinical practice: a multicenter ECCO-CONFER cohort...

Isolated perianal fistulizing Crohn's disease (IPFCD) is an uncommon presentation of Crohn's disease with an uncertain natural history. We aimed to characterize contemporary diagnostic strategies, management approaches, and long-term outcomes, including progression to luminal Crohn's disease.

We conducted a retrospective multicenter cohort study across 25 centers within the ECCO-CONFER network. Adult patients with IPFCD and no evidence of luminal Crohn's disease at baseline were included. The primary outcome was progression to luminal Crohn's disease. Secondary outcomes included clinical and radiological fistula response and patterns of medical and surgical management. Time-to-event analyses were performed using Kaplan-Meier methods.

A total of 121 patients were included with a median follow-up of 76 months (IQR 46-118). Diagnostic pathways were heterogeneous, with most patients undergoing colonoscopy (91.7%) and pelvic magnetic resonance imaging (63.6%), alongside variable use of additional modalities. Management was intensive, with 76.9% receiving biologic therapies and 85.1% undergoing combined medical-surgical treatment. Complete clinical remission was achieved in 57% of patients, while radiological healing was observed in 46.4%. During follow-up, 42 (34.7%) patients developed luminal Crohn's disease. Median progression-free survival was 145.6 months, with a median time to luminal diagnosis of 110 months (IQR 40-152). No consistent predictors of progression were identified.

Approximately one-third of patients with IPFCD developed luminal Crohn's disease over long-term follow-up, typically after several years. However, many patients remain free of intestinal involvement, reflecting a heterogenous disease course and highlighting the need for standardized evaluation and improved risk stratification.