Prevalence and incidence of microscopic colitis in patients with diarrhoea of unknown aetiology in a region in central Spain.

Background: Often previously overlooked, microscopic colitis, including collagenous colitis and lymphocytic colitis, has now emerged as a common cause of chronic diarrhoea.

Aims: To evaluate the prevalence and incidence of microscopic colitis in patients with diarrhoea of unknown aetiology.

Methods: 271 consecutive patients who were referred to the General Hospital of Tomelloso from April 2008 to December 2010 for diarrhoea of unknown aetiology underwent a full colonoscopy to obtain biopsy samples to diagnose microscopic colitis on the basis of commonly accepted histological criteria. All patients were classified according to the Roma III criteria for diarrhoea-dominant irritable bowel syndrome.

Results: In 234/271 consecutive patients with normal endoscopic appearance we observed 32/234 patients with microscopic colitis (30 lymphocytic colitis and 2 collagenous colitis) with a prevalence of microscopic colitis of 48 cases/100,000 inhabitants (95%CI: 30-65) and mean annual standardised incidence of 18 cases/100,000 inhabitants (95%CI: 16.0-20.0). Analysing only the patients that met the Roma III criteria (84/271), we observed 10.7% microscopic colitis diagnosis, with higher risk in the presence of autoimmune disease, seronegative celiac disease and intake of non-steroidal anti-inflammatory drugs.

Conclusions: Microscopic colitis was found in 13.7% of patients with chronic diarrhoea. Microscopic colitis is present in a relevant proportion of symptomatic patients meeting diagnostic criteria for irritable bowel syndrome (10.7%).