BACKGROUND: The relationship between clinical and histological parameters in collagenous colitis (CC) is poorly understood. Smoking is a risk factor for CC, whereas its impact on clinical activity and outcome is not well known.

METHODS: In a post hoc analysis of pooled data from two randomized controlled trials we assessed the association between demographic data (gender, age, smoking habits, family history of inflammatory bowel disease), clinical variables (duration of symptoms, mean number of stools/watery stools per day, abdominal pain, clinical remission) and histological data (thickness of the collagen band, inflammation of the lamina propria, total numbers of intraepithelial lymphocytes, degeneration). Moreover, we analysed the predictive value of baseline parameters for clinical outcome in a logistic regression model.

RESULTS: Pooled data were available from 202 patients with active CC, of whom 36% were current smokers, 29% former smokers and 35% non-smokers. Smoking status was associated with decreased ability to achieve clinical remission (current smokers vs non-smokers: odds ratio [OR] 0.31, 95% confidence interval [CI] 0.10-0.98, p = 0.045; former smokers vs non-smokers: OR 0.19, 95% CI 0.05-0.73, p = 0.016). Current smokers had an increased mean number of watery stools at baseline compared with non-smokers (p = 0.051) and increased mean number of watery stools per se was associated with decreased likelihood of obtaining clinical remission (OR 0.63, 95% CI 0.47-0.86, p = 0.003). Patient characteristics and histology at baseline had no association with clinical parameters and no predictive value for clinical outcome.

CONCLUSION: Smoking worsens clinical symptoms in CC and is associated with an increased number of watery stools and decreased likelihood of achieving clinical remission. There is no significant association between histology and clinical data.