Atypical "overlapping" variants of inflammatory bowel diseases

Objective: to analyze the challenges associated with the morphological interpretation of histological specimens that simultaneously exhibit characteristic histological features of both ulcerative colitis (UC) with features of Crohn's disease (CD), and CD with features resembling UC (so-called " overlapping " forms).Object and methods. Between 2019 and 2024, UC was diagnosed in 180 patients and CD in 120 patients. The average age of the patients was 48 ± 6 years. Diagnoses were established based on a combination of clinical-laboratory, endoscopic, and morphological data. A search was conducted for cases that posed diagnostic difficulties and whose characteristics were ambiguous and contained features of both UC and CD, resulting in 60 cases identified over a more than 5-year observation period. UC with features of CD was established in 58 cases (32.2%), and CD with features of UC in 2 cases (1.6%).Results. 24 patients with UC had focal and segmental inflammation in colon. Among 13 patients with left-sided colitis, focal lesions in the form of chronic active inflammation were found in the periappendicular and cecal regions, and in 2 patients with UC, granulomas termed "cryptolytic" were found, associated with the destruction of crypts, which can be difficult to distinguish from granulomas in CD. In patients with UC, ileitis was detected in 18 patients, with the inflammatory process predominantly confined to the distal 1-2 cm of the ileum in most cases. Five patients exhibited ileitis without involvement of the cecum, and the inflammatory process was not related to a retrograde mechanism. In 2 patients with CD, the inflammatory process was isolated to the distal sections of the colon, and the diagnosis was established based on the presence of typical CD changes in the upper gastrointestinal tract and the development of severe anal-perianal complications and sacroiliitis.Conclusion. Features typical for CD, such as relative or absolute integrity of the rectum, the presence of unaffected segments, and involvement of the ileum in the pathological process, can also be found in UC, especially in patients who have undergone treatment. The role of the pathologist is to determine the extent and severity of the disease, and to identify dysplasia or malignant transformation.