Diagnostic and prognostic significance of Crohn's disease-like pathology in surgically diverted recta of patients with ulcerative colitis.

Aims: Diversion colitis (DC), commonly seen in surgically diverted bowel, can exhibit features resembling Crohn's disease (CD) even in patients with an established ulcerative colitis (UC). The superposition of DC on inflammatory bowel disease (IBD) complicates pathological assessment and potentially alters the diagnosis from UC to CD. We investigated the diagnostic and prognostic significance of CD-like histological features in DC.

Methods and results: We examined diverted recta from 202 patients (84 females, 118 males; median age = 37, range = 7-79) who underwent post-diversion proctectomy from 2018 to 2023. Pre-operative diagnoses included UC (n = 162), CD (n = 20), indeterminate IBD (IIBD, n = 11) and non-IBD (n = 9). We evaluated granulomas and deep mucosal ulcers and scored transmural chronic inflammation (TCI) on a four-tier scale. Patients were followed for 8-73 months for development of CD-like complications, e.g. small bowel enteritis, strictures or fistulas.

Conclusions: TCI was present in all groups but was less frequent in non-IBD (P = 0.015), with median scores similar for UC and CD (median = 1), higher in the IIBD (median = 2) and lower in the non-IBD (median = 0, P = 0.084). TCI scores did not correlate with the development of CD-like complications (CDLC) and therefore did not have prognostic significance. Conversely, granulomas and fissuring ulcers were significantly more common in CD than UC and IIBD and absent in non-IBD (P < 0.0001 and P = 0.0009, respectively). These features correlated with higher TCI scores (P = 0.023 and P = 0.009, respectively). In summary, granulomas and fissuring mucosal ulcers in diverted recta favours a diagnosis of CD, while TCI alone does not justify altering a diagnosis of UC.