Assessment of perianal fistulizing Crohn's disease activity with endoanal ultrasound: A retrospective cohort study.

Background: Perianal fistulas pose dual challenges to Crohn's disease (CD) patients. Low patient compliance due to the complexity of existing examination methods plagues the treatment and follow-up management of perianal CD.

Aim: To determine the accuracy of endoanal ultrasound (EUS) and shear wave elastography (SWE) for evaluating perianal fistulizing CD (PFCD) activity.

Methods: This was a retrospective cohort study. A total of 67 patients from August 2022 to December 2023 diagnosed with CD were divided into three groups: Non-anal fistula group (n = 23), low-activity perianal fistulas [n = 19, perianal disease activity index (PDAI) ≤ 4], high-activity perianal fistulas (n = 25, PDAI > 4) based on the PDAI. All patients underwent assessments including EUS + SWE, pelvic magnetic resonance [pelvic magnetic resonance imaging (MRI)], C-reactive protein, fecal calprotectin, CD activity index, PDAI.

Results: The percentage of fistulas indicated by pelvic MRI and EUS was consistent at 82%, and there was good consistency in the classification of perianal fistulas (Kappa = 0.752, P < 0.001). Significant differences were observed in the blood flow Limberg score (χ ² = 8.903, P < 0.05) and shear wave velocity (t = 2.467, P < 0.05) between group 2 and 3. Shear wave velocity showed a strong negative correlation with magnetic resonance novel index for fistula imaging in CD (Magnifi-CD) score (r = -0.676, P < 0.001), a weak negative correlation with the PDAI score (r = -0.386, P < 0.05), and a weak correlation between the Limberg score and the PDAI score (r = 0.368, P < 0.05).

Conclusion: EUS combined with SWE offers a superior method for detecting and quantitating the activity of perianal fistulas in CD patients. It may be the ideal tool to assess PFCD activity objectively for management strategies.