P276 Predictive value of changes in 3D volumetry in perianal fistulas in patients with Crohn’s disease under biologic therapy. A pilot study

Abstract

Abstract Background Changes in the 3D volumetry of perianal fistulas measured by magnetic resonance (MR) could be an imaging biomarker of interest. The objective of the study is to determine the value of volumetric changes in perianal fistulas in patients with Crohn's disease (CD) after biological treatment to predict subsequent clinical outcomes. Methods Retrospective single-center pilot study. We have included CD patients with perianal fistulas who started biological therapy between 2012-2020 and have 1) both pre- and post-treatment (3-18 months) pelvic MR and 2) follow-up after post-treatment MR of at least 2 to 5 years. According to the last visit, patients were categorized as clinically active (perianal discharge) or in remission (absence of draining). Using an specific software (vEUA, Motilent, London), we calculated the 3D volumetry of the fistulas, the active component (hypersignal on T2) and the fibrotic component (hyposignal on T2). We compared MR volumetric changes between both pre and post treatment MRs and calculated the value of MR volumetric changes in predicting clinical remission using a multivariate stepwise logistic regression analysis. Results Among the 24 patients included, 13 were in perianal clinical remission in the last follow-up. The percentage (%) of volumetric changes in the active component was significantly higher in patients achieving perianal clinical remission compared to non-responder patients (82.5% vs 38.7%, p=0.007). The % of change of the fibrotic component was also significantly higher in patients achieving perianal remission (120% vs 34%, p=0.03). The % of change of the active component was identified as predictor of clinical remission (OR 1.06 [1.02-1.11] P=0.008). A reduction of ≥16% of the active MR component has a sensitivity of 85% and specificity of 82% to predict clinical perianal remission on the long-term. Conclusion Changes in the 3D volumetry on MR of perianal fistulas have value in predicting clinical response. The decrease in the active component could be therefore a good biomarker to define therapeutic targets in fistulizing perianal CD.