Introduction
While acute pouchitis develops in up to 80% of patients with ulcerative colitis (UC) after ileal pouch-anal anastomosis (IPAA), little is known about the clinical and microbial features of normal pouches that remain durable over time.
Aims & Methods
This study aims to decipher the biology of durable normal pouch phenotype by comparing clinical, endoscopic, and microbial features across pouch phenotypes. Patients undergoing IPAA for UC or familial adenomatous polyposis (FAP) were prospectively followed at a comprehensive pouch clinic. Follow-up included clinical visits; blood and stool sampling; pouch endoscopies with biopsies. The normal spectrum was divided into FAP; ultra normal (UN, ≥10 years from ileostomy closure without pouchitis); and normal with later progression to pouchitis (NLP, normal at sampling with later pouchitis during follow-up), and compared to pouchitis flare sampling. Stool samples underwent shotgun metagenomic sequencing. Analyses included overall comparisons across all four phenotypes and pairwise comparisons between phenotype pairs, using Kruskal-Wallis and Fisher’s exact tests, and mixed linear regression models with patient identity as a random effect. Multiple testing was corrected using false discovery rate (q<0.2).
Results
Sixty patients were included: FAP (n=16), UN (n=20), NLP (n=14), and pouchitis (n=10) (baseline median age 46.7y; pouch age 10.1y; 55% female). Median follow-up was 17.7y; UN was durable for a median of 20.8y. Among patients with UC, pre-IPAA disease extent and IPAA indication were comparable (p>0.9 and p=0.27); UN patients had lower pre-IPAA exposure to immunomodulatory/advanced therapy (p=0.08). Clinical, endoscopic and histologic Pouchitis Disease Activity Index subscores gradually increased across FAP, UN, NLP, and pouchitis; median fecal calprotectin was 51.5, 130, 317.7, and 831 mg/g, respectively. Shannon diversity was comparable, whereas Microbial Dysbiosis Index (MDI) gradually increased across phenotypes (FAP -2.76, UN -1.74, NLP -0.91, pouchitis -0.78). Principal coordinates analysis (Jaccard dissimilarities) showed significant differences in overall microbial community composition across phenotypes (p=0.026). Pairwise differential abundance analysis supported gradual taxonomic shift, from comparable taxa between FAP and UN, to maximal separation (53 taxa) between FAP and pouchitis. Taxa with significant pairwise differences showed a graded distribution across phenotypes: Prevotella copri, Blautia wexlerae and Faecalibacterium prausnitzii were more abundant in FAP and UN; Ruminococcus gnavus was higher in NLP and pouchitis. UN and NLP significantly differed by 9 taxa, including Clostridium perfringens, Veillonella parvula and Fusobacterium animalis. In longitudinal analysis of patients with NLP (27 samples), over a follow-up period from 3,496 to 27 days prior to first pouchitis, MDI gradually increased over serial pre-flare samples before pouchitis onset (p=0.032).
Conclusion
The normal pouch phenotype encompasses a heterogeneous spectrum characterized by distinct clinical, endoscopic and microbial features. Patients with UC post-IPAA who sustain UN pouch for over a decade uniquely demonstrate hybrid phenotype, with clinically intermediate features but taxonomic similarity to FAP and microbial separation from those who later progress to pouchitis, the latter harboring dysbiotic taxa and showing progressive MDI increase towards flare. This restratification of normal pouch phenotype trajectory has mechanistic and clinical implications, potentially guiding intervention and prevention, thus modifying disease course.