P1222 The macroscopic and microscopic distribution of IBD in patients with PSC: a polytomous latent class analysis on 3177 endoscopies
Authors: Sneek D , van der Meer A , Mol B , Ponsioen C , Inderson A , Weersma R , Hansen B , de Vries A ,   EpiPSC2
Published: January 2025

Abstract

Background
Inflammatory bowel disease (IBD) in patients with primary sclerosing cholangitis (PSC) is a distinct disease entity requiring specific management1. Data on characterisation of the phenotype of PSC-IBD are limited and subclassification is lacking. Therefore, this study aims to describe the macroscopic and microscopic distribution of IBD in patients with PSC.

Methods
A retrospective analysis was conducted on data from PSC-IBD patients included in the EpiPSC2 registry, comprising patients from 46 hospitals across the Netherlands. Data on inflammation at macro- and microscopic level in the ileum and 6 colonic segments were collected on every available endoscopy. Data after (hemi)colectomy were excluded.
Polytomous latent class analysis was used to identify subgroups of IBD distribution2. First, latent class models (LCM) were fitted on all endoscopic and histologic data and Akaike and Bayesian information criteria were used to determine the optimal number of classes. After random sampling with replacement the LCM with the ideal number of groups was fitted on 20 samples of one endoscopy with inflammation per subject, and the pooled class probability was calculated per subgroup.

Results
A total of 3177 endoscopies from 522 PSC-IBD patients (median of 5 [IQR 2-9] endoscopies per patient) were included. The maximum depth of insertion was the terminal ileum in 62% and caecum in 27% of endoscopies. Macroscopic inflammation was observed in 1521 (48%) endoscopies from 428 patients. Segmental colon biopsies were obtained during 650 (20%) endoscopies in 237 subjects, and ileum biopsies in 144 (22%) endoscopies in 100 subjects. Microscopic inflammation in any segment was observed in 265 (41%) endoscopies.
An LCM with four classes was the best fit to the macro- and microscopic data: no inflammation, right-sided colitis (pooled class probability 36%), left-sided colitis (30%), and pancolitis (34%). In right-sided colitis and pancolitis the probability of ileal involvement was 16% and 22%, whereas left-sided colitis most often displayed an absence of ileal involvement (probability of 4%) [fig.1]. For microscopic inflammation no pooled class probabilities could be calculated due to low sample size. In 139 (21%) endoscopies, LCM showed more extensive inflammation at microscopic assessment as compared to macroscopic assessment.

Conclusion
Macroscopic and microscopic inflammation in PSC-IBD may be classified into right sided colitis, left sided colitis, and pancolitis. The microscopic extent exceeds macroscopic inflammation in over 20% of endoscopies with segmental biopsies. Future research into the prognostic implication of this subclassification on PSC- and IBD-related outcomes is required.

References
1.van Munster KN, Bergquist A, Ponsioen CY. Inflammatory bowel disease and primary sclerosing cholangitis: One disease or two? J Hepatol. 2024;80(1):155-68.2.
2.Lewis J, Linzer D. poLCA: An R Package for Polytomous Variable Latent Class Analysis. Journal of Statistical Software. 2011;42