A Comparative Evaluation of Different Histopathological Indices of Mucosal Healing in Ulcerative Colitis, and Their Correlation With Clinical Follow-up Data

Ulcerative colitis (UC) is a chronic inflammatory disease of idiopathic origin affecting the rectum and colon. Patients classically manifest with rectal bleeding, diarrhea, tenesmus, urgency, abdominal pain, weight loss, fever, and malaise. Pathologically, it is defined by a continuous mucosal inflammation of the rectum and a variable extent of the colon, without granulomas on mucosal biopsies. The course of UC is characterized by periods of remission and relapsing. In patients with extensive or severe inflammation, acute complications such as severe bleeding and toxic megacolon, which can lead to perforation, may occur. Patients newly diagnosed with UC have a 5-year risk of colectomy of 10-35%, and ultimately, persistent and extensive inflammatory activity increases the long-term risk of dysplasia and colorectal cancer.

While treatment of patients with UC is primarily aiming to achieve clinical remission (CR) and endoscopic remission (ER), there is now interest in targeting histological healing (HH) in addition to CR, as symptoms may not reliably correlate with histological activity. Moreover, ER is not always an accurate indicator of histological healing. Furthermore, histological changes tend to lag behind CR after treatment. Accordingly, histological remission may be considered as an independent predictor of clinical relapse better than endoscopic appearances.

The Selecting Therapeutic Targets in Inflammatory Bowel Disease (STRIDE) II committee introduced a treat-to-target approach and proposed that the therapeutic target in UC should include clinical and patient-reported outcome remission, alongside endoscopic remission, with Mayo endoscopic subscore of 0. Histologic remission is not a formal target of medical therapy, but it is considered an "adjunct to endoscopic remission to represent a deeper level of healing.

However, Various studies have elucidated that histologic remission serves as a distinct treatment objective from endoscopic remission, offering a superior prediction of clinical remission. In few studies, histological remission seems to correlate with long-term clinical remission, better clinical outcomes, and a lower risk of intestinal dysplasia, even though significant data are still lacking.

Currently, about 30 histologic scoring systems in UC have been described and used for quantitative assessment, but 3 have recently undergone scientific validation namely the Gobeos score (GS), Nancy Index (NI) and Robarts Histopathologic Index (RHI). For histologic measurements of disease activity to affect clinical decision making, pathologists should agree upon which standardized features to report and the definitions of these parameters.