Microscopic colitis includes both collagenous and lymphocytic colitis – so named because of their normal macroscopic appearance at colonoscopy. Both are characterised histologically by the presence of an increased number of intra-epithelial lymphocytes. Collagenous colitis is also distinct from other forms of colitis due to the presence of a thickened collagen band in the subepithelium [1,2,3].
The cause of Microscopic Colitis is unknown, although and immune mechanism is likely. There have been multiple associations, and these include:
- Medications – Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) – such as asprin, are much more commonly ingested in individuals with microscopic colitis, with some improvement typical with cessation of NSAIDS [1,4]. Antidepressants including selective serotonin re-uptake inhibitors (SSRIs) cholesterol lowering statin drugs, and acid lowering proton pump inhibitors (PPIs) all have an association with microscopic colitis [1,4].
- Infection – It has been proposed that bacterial toxins from previous infection may be a factor.
- Bile acid malabsorption – this is based on an observed improvement in colitis with the use of bile-binders such as cholestyramine [1,4].
- Autoimmune disorders – microscopic colitis is more common in patients with other auto-immune disorders such as eczema and celiac disease .
Microscopic colitis is more common in females. This is particularly the case with collagenous colitis, with a 4:1 female to male ratio. The incidence of these conditions is rare ranging from 0.5 to 5% per 100,000
for Collagenous colitis and 3 to 5% per 100,000 Lymphocytic colitis [1,5]. It occurs more commonly in late adulthood, with a peak age of onset in the 6th and 7th decade.
Typically, microscopic colitis presents with the passage of frequent non-bloodied watery stools per day.
Blood tests that may be elevated include ESR/CRP. Auto-antibodies such as ANCA, anti-nuclear and anti-mitochondrial anti-bodies are elevated in approximately 50% of patients . Faecal calprotectin levels are elevated in patients with active microscopic colitis .
The diagnosis of microscopic colitis is based upon performing colonoscopy which allows biopsy of the often normal appearing colon. This allows for microscopic (histopathological) examination. Histological changes are more pronounced in the proximal colon and so biopsies should be taken from the right colon.
Microcytic colitis typically is associated with a predominance of intra-epithelial lymphocytes (≥20 intraepithelial lymphocytes per 100 epithelial cells). Collagenous colitis also has a thickened subepithelial collagen band (≥10μm) .
Microscopic colitis is often self-limiting, with many cases resolving spontaneously. However, relapse is reported in 30-60%. There has been no documented increased risk of colorectal cancer or inflammatory bowel disease in patients with microscopic colitis.
Medications such as those listed above, should be ceased to determine if they are causative factors. Once infection has been excluded, troublesome diarrhoea can be treated with loperamide. Budesonide (9mg daily for 6 weeks) causes cure in almost 90% of patients compared with 50% without treatment .
- Dietrich C. Lymphocytic and collagenous colitis. Up to Date. Sep 2010.
- Jaskiewicz MD. Microscopic colitis in routine colonoscopies. Digestive diseases and sciences. 2006;51(2):241-244.
- Liszka L. Histopathological diagnosis of microscopic colitis. Journal of Gastroenterology and Hepatology. 2006;21:792-797.
- Datta I. Microscopic colitis:a review for the surgical endoscopist. Canadian Journal of Surgery. 2009;52(5):167-72.
- Chande N. Interventions for treating lymphocytic colitis. The Cochrane Database of Systematic Reviews. Vol 3 2008.