Routine diagnosis of the histopathological activity of ulcerative colitis (UC) requires multiple biopsy samples, and an endocytoscopy system (ECS) provides real-time ultra-magnifying microscopic imaging in vivo. We have established an ECS score (ECSS) to determine a histopathological activity index of UC. Fifty-five UC patients (mean age 40.7 years; 67% men) were enrolled. A super-magnifying ECS with magnification 450× was used, and sample biopsies were obtained. Matts' histopathological grade was determined, to evaluate disease severity, by two pathologists, with consensus. The ECSS of UC was independently determined by at least two investigators, with consensus. In total, 76 pairs of ECSS and Matts' histopathological grades were independently acquired. To validate the ECSS, inter-observer agreement between three endoscopists, with consensus, and another endoscopist, was calculated as the kappa value. We also evaluated the correlation between the ECSS and Matts' histopathological grade, and between the conventional Matts' endoscopic grade and Matts' histopathological grade. The ECSS of UC intestinal mucosa, i.e., the sum of the indices for shape (0-3) and distance between crypts (0-2), and the visibility of superficial microvessels (0-1), showed a strong correlation with Matts' histopathological grades (ρ = 0.713, P < 0.001); as well, there was a strong correlation between the conventional Matts' endoscopic grade and Matts' histopathological grade (ρ = 0.694, P < 0.001). Furthermore, the ECSS showed high reproducibility (κ = 0.79, 95% confidence interval [CI] 0.71-0.87). Our novel ECSS has good predictive value for the histopathological activity of UC.
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