S119 Diagnostic Transition from Ulcerative Colitis to Crohn’s Disease: A Single-Center Retrospective Study

Background: Differentiating between ulcerative colitis (UC) and Crohn’s disease (CD) can be clinically challenging. Established diagnostic criteria for inflammatory bowel disease (IBD) are based on clinical, endoscopic, radiographic, and histological findings. However, some patients initially diagnosed with UC may later present characteristics typical of CD, necessitating a diagnostic revision. Population studies from Scandinavia have reported diagnostic transition rates from UC to CD ranging from 3% to 14% over a 5-year follow-up period. Despite the overlap in the management of UC and CD, an accurate diagnosis is essential for optimizing treatment strategies, surgical interventions, and eligibility for clinical trials. The aim of this study is to determine the frequency of diagnostic migration from UC to CD and to describe the clinical and demographic characteristics of patients who experienced this transition. Methods: This retrospective study was conducted at the IBD of the General Hospital of Mexico “Dr. Eduardo Liceaga.” Medical records of 164 patients diagnosed with UC were reviewed. Patients who experienced a diagnostic transition to CD, confirmed through clinical, endoscopic, radiological, and histological findings consistent with CD, between April 2023 and April 2024, were identified. Data collected included demographic and clinical information such as age, gender, Montreal classification, treatments received, and surgical history. Statistical analysis was performed using SPSS software version 19, applying descriptive statistics to calculate frequencies and means with standard deviation for the clinical and demographic characteristics. Results: Of the 164 UC patients, 5 (3.05%) experienced a diagnostic transition to CD during the follow-up period. The mean duration from UC diagnosis to diagnostic transition was 2.2±1.6 years. The gender distribution was 3 males (60%) and 2 females (40%). The mean age at initial UC diagnosis was 42.46 ± 14.13 years, and at the time of re-evaluation and transition to CD was 44.4 ± 14.13 years. Prior to the transition, all patients had UC classified as E3 according to the Montreal classification. Three patients (60%) had not undergone prior surgery, while 1 had a 2-stage total proctocolectomy with ileal pouch-anal anastomosis and another had a total colectomy with ileostomy. The mean number of hospitalizations before the diagnostic transition was 1.5 ± 0.5. Prior to the transition, 3 patients were on biological therapy, and 2 were on conventional therapy. Following the diagnosis of CD, most patients were classified as A2 (80%), L3 (60%), and B2 (60%) according to the Montreal classification. One patient (20%) required ileal resection with ileostomy. Conclusions: In this study, 3.05% of patients initially diagnosed with UC were reclassified to CD within an average of 2.2±1.6 years. These findings underscore the importance of thorough follow-up with periodic re-evaluations to enhance management and outcomes for IBD patients.