Rethinking Low Anterior Resection Syndrome: Higher Than Expected Pre-Surgical Incidence and the Role of Gut Microbes

BACKGROUND: Low anterior resection syndrome, characterized by a constellation of defecatory dysfunction symptoms, is a frequent complication after low anterior resection surgery. However, the mechanisms underlying low anterior resection syndrome, including potential associations with intestinal microbiota, remain poorly defined. OBJECTIVE: To characterize the onset and progression of low anterior resection syndrome across the rectal cancer treatment pathway and to examine microbial community shifts in relation to low anterior resection syndrome development. DESIGN: Prospective cohort study with a nested subgroup undergoing repeated clinical and microbial assessments. SETTING: St Paul's Hospital, Vancouver, Canada. PATIENTS: Rectal adenocarcinoma patients undergoing curative-intent resection with restoration of bowel continuity. INTERVENTIONS: Prospectively collected cohort without intervention. MAIN OUTCOME MEASURES: The primary outcome was presence of low anterior resection syndrome (score ≥ 21). Secondary outcomes included microbial diversity and composition changes. RESULTS: Pretreatment bowel dysfunction meeting low anterior resection syndrome-score criteria was present in 42% (30/71) of patients, without significant association with demographic or clinical variables. By the end of follow-up, 64% exhibited low anterior resection syndrome. New-onset low anterior resection syndrome correlated with lower tumor height (p = 0.04). Microbial beta diversity differed between no pretreatment bowel dysfunction and pretreatment bowel dysfunction meeting low anterior resection syndrome criteria at baseline (p < 0.001), but alpha diversity did not, and no microbial features predicted subsequent new-onset low anterior resection syndrome. LIMITATIONS: Single-center design with small sample size. CONCLUSIONS: Bowel dysfunction meeting low anterior resection syndrome criteria is common before rectal cancer treatment and increased postoperatively. Although baseline microbial profiles differed, no association between bacterial diversity and low anterior resection syndrome development could be demonstrated. Routine pretreatment bowel dysfunction assessment may guide patient counseling and quality of life. See Video Abstract.