Ulcerative Colitis (UC) is a chronic, non-specific intestinal inflammatory disease of unknown cause, featuring abdominal pain, diarrhea, and bloody stools. Endoscopy shows diffuse, continuous lesions with erosion and shallow ulcers, worst in the rectum and diminishing proximally. Current treatments (aminosalicylates, corticosteroids, immunosuppressants, biologics, small molecule drugs) are not curative. Endoscopic mucosal healing is a key treatment goal, improving steroid-free remission, reducing colectomy rates, recurrence, hospitalization, and colorectal cancer risk.

Common endoscopic scoring systems: Baron score (poor consistency), Mayo Endoscopic Score (MES, simple but lacks prognostic info), and Ulcerative Colitis Endoscopic Severity Index (UCEIS, more detailed and consistent but cumbersome). Disease extent is important for severity, as proximal extension increases relapse, treatment escalation, and cancer risk. However, MES and UCEIS assess only the worst segment, underestimating total disease burden.

Other scores (UCCIS, MMES, DUBLIN) attempt to incorporate lesion extent but have limitations (small samples, lack of validation, unclear severity cutoffs). Data on short-/medium-term endoscopic changes and long-term outcomes are scarce.

We therefore propose a new endoscopic scoring system, the CAT-DESIRE score, aiming to evaluate its reliability, validity, and predictive role in medium-/long-term prognosis and treatment response, providing a simple, accurate tool for assessing disease burden and guiding clinical decisions.

Ulcerative Colitis (UC) is a chronic, non-specific inflammatory disease of the intestine with unknown causes and mechanisms. Its main clinical manifestations include abdominal pain, diarrhea, and bloody stools. The typical endoscopic appearance of UC is diffuse and continuous lesions, accompanied by erosion and shallow ulcers. The lesions are most severe in the rectum and gradually become less severe towards the proximal part. Currently, the main therapeutic drugs for UC include aminosalicylic acid preparations, corticosteroids, immunosuppressants, biologics, and small molecule drugs, but there is no cure. The choice of treatment plan is based on a comprehensive assessment of the disease. Endoscopic examination can objectively determine the lesion range and assess the disease activity, which is of great significance for monitoring treatment response and providing individualized optimal treatment plans. Endoscopic mucosal healing has become an important goal in the treatment of UC, and it has been proven to achieve better long-term efficacy, including increasing the rate of steroid-free remission, reducing the need for colectomy, and lowering the risks of recurrence, hospitalization, and colorectal cancer.

There are several endoscopic scoring systems currently applied in clinical and research assessment of UC. Different endoscopic scoring tools have different advantages and limitations. The initial endoscopic classification of UC was the Baron score, which, due to not measuring the consistency indicators among researchers, had a 40% disagreement in classifying normal, mild, moderate, or severe activity, and there was little supporting data. The Mayo endoscopic score (MES) and the Ulcerative Colitis Endoscopic Severity Index (UCEIS) are currently the two main endoscopic scoring systems for evaluating mucosal inflammation symptoms and disease activity. MES is easy to use but lacks information on disease prognosis. UCEIS distinguishes mucosal inflammation and disease activity more detailedly through a greater number of layers (0-8) than MES (0-3), and shows higher internal and inter-rater consistency, but is more computationally cumbersome.

The disease range is potentially important in evaluating the severity of UC. The IBSEN study showed that disease expansion is an important independent factor for colectomy in UC patients. Qiu and his colleagues further proved that proximal disease expansion would increase the risk of recurrence and treatment intensification. Additionally, Ekbom et al. and Lutgens MW et al. also reported a close relationship between colorectal cancer and disease expansion. Therefore, quantifying the inflammatory load is crucial for individualized treatment of UC patients. However, the MES and UCEIS scoring systems only consider the most severely affected intestinal segment, thereby underestimating the actual disease range and burden. For example, for a patient with total colitis, multiple large ulcers, and a baseline Mayo endoscopic score of 3, if there is improvement after treatment but still has a single ulcer in the sigmoid colon, the Mayo endoscopic score remains 3 and belongs to endoscopic non-response.

The Ulcerative Colitis Colon Severity Index (UCCIS) takes into account four different variables (granularity, vascular pattern, ulcers, and bleeding-fragility) for all colon segments and shows correlation with clinical indicators and laboratory parameters of disease activity. However, due to the small sample size, its feasibility and simplicity need to be proven in clinical practice. The Modified Mayo Endoscopic Score (MMES) is based on the Mayo endoscopic score and combines the degree of mucosal inflammation and lesion distribution in different intestinal segments, better reflecting endoscopic response and improvement numerically. However, this score does not have a clear boundary for disease severity and lacks inter-rater and inter-observer consistency validation, which may change the proportion of patients defined as remission and affect treatment or regulatory decisions. The DUBLIN scoring method for the degree of luminal inflammation burden in ulcerative colitis, published by Rowan et al. in 2019, is the product of MES (0-3) and the disease lesion range (E1-E3). This scoring method shows a good correlation with MES, UCEIS, fecal calcium protein, and other inflammatory markers, as well as histological activity. However, due to the single-center study and the small sample size, the inter-observer and intra-observer consistency has not yet been verified.

At present, there are few data on how endoscopic changes in the short and medium term affect long-term clinical outcomes. By combining the advantages and limitations of different UC endoscopic scoring systems published previously, we propose a new endoscopic scoring system - the CAT-DESIRE score. We hope to evaluate the reliability and validity of the CAT-DESIRE score, verify its predictive role in medium- and long-term prognosis, therapeutic efficacy and adjustment, and provide a reliable and simple tool for comprehensive and accurate assessment of the disease burden and treatment effect of UC patients, in order to better guide clinical treatment decisions.

Inclusion Criteria:

• 1. Adult patients (aged 18 - 75 years);
• 2. Diagnosed with ulcerative colitis for at least 3 months;
• 3. Have had endoscopic examination results for at least 2 times, with clear endoscopic images (including endoscopic pictures of the terminal ileum, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum at least one picture for each of these 7 areas);
• 4. Complete clinical data.

Exclusion Criteria:

• 1. Crohn's disease, intestinal Behcet's disease, intestinal tuberculosis, toxic megacolon and unclassified inflammatory bowel disease.
• 2. The length of the colon lesion could not be evaluated.

A total of 235 UC patients were recruited from 9 specialized IBD diagnosis and therapy centers across China, with all patients undergoing paired endoscopic evaluations. Nine specialized IBD diagnosis and therapy centers are the Air Force Military Medical University First Affiliated Hospital, the Beijing Peking Union Medical College Hospital, the Xi'an Jiaotong University Affiliated Second Hospital, the Shanghai Ruijin Hospital, the Xinjiang Urumqi Affiliated First Hospital, the Sichuan Huaxi Hospital, the Wuhan Xiehe Hospital, the Shanghai Jiao Tong Renji Hospital, and the Seventh Medical Center of PLA General Hospital.