Microscopic colitis: a common and an easily overlooked cause of chronic diarrhoea.

Microscopic colitis, comprising collagenous colitis and lymphocytic colitis, is characterised clinically by chronic watery diarrhoea, a macroscopically normal colonic mucosa where diagnostic histopathological features are seen on microscopic examination. The annual incidence of each disorder is 4-6/100,000 inhabitants, with a peak incidence in 60-70 year old individuals and a noticeable female predominance in collagenous colitis. The aetiology is unknown. Abdominal pain, weight loss, fatigue, and faecal incontinence are common symptoms in addition to chronic diarrhoea that impair the health-related quality of life of the patient. There is an association to other autoimmune disorders such as celiac disease, diabetes mellitus, thyroid disorders and arthritis. Budesonide is the best-documented short-term treatment, but the optimal long-term strategy needs further study. The long-term prognosis is good and the risk of complications including colonic cancer is low.