Does stool form and frequency correlate with colonic transit in adults with fecal incontinence?

Background: Stool form correlates with colonic transit time (CTT) in adults with constipation, but data do not exist for adults with fecal incontinence (FI). Our aim was to assess the correlation between bowel diary data (form and frequency) and CTT among adults with FI. Methods: Using baseline data from a randomized controlled trial to treat FI with psyllium and loperamide to improve stool consistency, data from 7-day bowel diaries were abstracted for bowel movements, FI episodes, percentage of incontinent bowel movements (PIBMs), and average stool consistency with the validated Bristol Stool Form Scale for bowel movements and FI episodes. FI severity was measured with the Fecal Incontinence Severity Index (FISI scores, range 0-54). CTT (hours) was completed using Modified Metcalf methodology with radio-opaque markers. Bowel movements, FI episodes, PIBMs, stool form, and FISI scores were correlated with CTT using Spearman's rank correlation. Results: From the 78 participants with FI and baseline CTT data, mean age was 60.7 (±10.1) years and 67% were men. At baseline, participants had 17.3 (±12.0) bowel movements per week, 7.6 (±6.8), 31.4% PIBMs, mean stool form of 4.9 (±1.1) for bowel movements and 6.1 (±0.9) for FI episodes. FISI scores averaged 30.2 (±12.2) at baseline. The mean CTT was 30.9 (±17.3) hours. We found negative correlations for bowel movements and CTT (Spearman's rho =-0.35, p= 0.002), but not for FI episodes and CTT. We also found negative correlations for bowel movement stool form and CTT (Spearman's rho =-0.26, p=0.02), but not for FI episode stool form and CTT. PIBMs and CTT were also correlated (Spearman's rho = 0.38, p<0.001); whereas, FI severity on the FISI was not, p>0.05. Conclusions: From the baseline data from 7-day bowel diaries among participants in a clinical trial, the frequency of bowel movements, percentage of FI episodes, and stool form of bowel movements, moderately correlated with colonic transit time among adults with at least weekly FI. Given these findings, clinical trials for the treatment FI should consider including stool form and frequency as bowel diary outcome measures.