Definition and Clinical Features Top
Microscopic colitis is the overarching term for two diseases: lymphocytic colitis and collagenous colitis; they are diseases of unknown etiology characterized by the presence of distinctive microscopic lesions without macroscopic (endoscopic) or radiologic changes.
Signs and symptoms: Watery diarrhea (high-volume bowel movements, which nevertheless rarely cause dehydration), often not associated with abdominal pain but with abdominal cramps; flatulence; weight loss. The endoscopic appearance of the colon is usually normal, although occasionally it may reveal minor mucosal edema, areas of hyperemia, and petechiae. When performing colonoscopy, it is mandatory to obtain biopsy specimens from the ascending colon and terminal ileum in patients with unexplained watery diarrhea. The results of routine laboratory tests and radiography of the small intestine and colon are normal.
Diagnosis is based on the results of histologic examination of biopsy specimens. An increase in the number of intraepithelial lymphocytes (≥20/100 surface epithelial cells) is the cardinal histologic feature of lymphocytic colitis. There is no associated crypt distortion, and the crypt architecture is preserved. The increase in the number of intraepithelial lymphocytes can be maximal on the right side of the colon; therefore, the diagnosis of microscopic colitis can sometimes be missed if the patient only has a flexible sigmoidoscopy as the investigation.
Collagenous colitis has similar histologic features to lymphocytic colitis except that in addition there is thickening of the collagen layer at the base of epithelial cells (defined as thickness ≥10 microm) accompanied by an increase in the number of lamina propria inflammatory cells.
Differential diagnosis should include irritable bowel syndrome, celiac disease, Crohn disease, ulcerative colitis, lactose intolerance, abuse of laxatives, amyloidosis, hormone-producing tumors, and disturbances of the bile acid circulation.
The management of microscopic colitis should include a workup for celiac disease (see Celiac Disease), because there is an association between the two disorders and both can manifest with diarrhea.
Microscopic colitis is also associated with nonsteroidal anti-inflammatory drugs (NSAIDs), proton pump inhibitors (PPIs), statins, and selective serotonin reuptake inhibitors (SSRIs). The benefits of these drugs may outweigh the risks, as microscopic colitis has a benign course, but if the disease is dramatically reducing quality of life and is difficult to treat or there is not a strong indication for these drugs, they should be discontinued. Smoking cessation should also be advised.
Patients with mild diarrhea symptoms should be prescribed antidiarrheal drugs, such as loperamide. Other alternatives for mild symptoms include cholestyramine, mesalamine (INN mesalazine), or bismuth salts. Patients with moderate to severe diarrhea should be prescribed budesonide (initially 9 mg/d orally for 6-8 weeks; maintenance treatment with low doses of 3-6 mg/d orally); this therapy is very effective, with a number needed to treat of 2 for collagenous colitis and a number needed to treat of 3 for lymphocytic colitis.Evidence 1Strong recommendation (benefits clearly outweigh downsides; right action for all or almost all patients). Moderate Quality of Evidence (moderate confidence that we know true effects of the intervention). Quality of Evidence lowered due to the small number of patients studied. Chande N, McDonald JW, Macdonald JK. Interventions for treating lymphocytic colitis. Cochrane Database Syst Rev. 2008 Apr 16;(2):CD006096. doi: 10.1002/14651858.CD006096.pub3. Review. PubMed PMID: 18425936. Chande N, McDonald JW, Macdonald JK. Interventions for treating collagenous colitis. Cochrane Database Syst Rev. 2008 Apr 16;(2):CD003575. doi: 10.1002/14651858.CD003575.pub5. Review. PubMed PMID: 18425892. Miehlke S, Madisch A, Kupcinskas L, et al; BUC-60/COC Study Group. >Budesonide is more effective than mesalamine or placebo in short-term treatment of collagenous colitis. Gastroenterology. 2014 May;146(5):1222-30.e1-2. doi: 10.1053/j.gastro.2014.01.019. Epub 2014 Jan 15. PubMed PMID: 24440672. In patients not responding to budesonide or other treatment alternatives, immunosuppressive therapy such as azathioprine, methotrexate, or anti–tumor necrosis factor agents may be considered with caution. Surgical treatment (split ileostomy and subtotal colectomy) is limited only to patients with severe disease not responding to other treatment modalities.