184 Gut and Liver, Vol. 5, No. 2, June 2011 mune disease (p<0.05). 5. Relation to irritable bowel syndrome There was only one patient showing symptoms of irritable bowel syndrome (ROME III) of 22 patients diagnosed as micro- scopic colitis. 6. Treatment of microscopic colitis The improvement of diarrhea after probiotics shown in 4 cases (18.2%), loperamide was medicated in 8 cases (36.4%), budesonide was in one case (4.5%), mesalazine was in one case (4.5%). Other 3 cases show relief after quitting suspicious drug and there were 5 cases were following by conservative treat- ment. DISCUSSION Chronic diarrhea is a common symptom in the division of gastroenterology and, microscopic colitis may be one of the im- portant causes of chronic diarrhea.5 The terminology, microscopic colitis, first mentioned in the case of a patient with chronic diarrhea whose colon shows no visible abnormality but infiltration in lymphocyte on tis- sue biopsy in 1980.6 Collagenous colitis was first described by Lindström5 in 1976 and lymphocytic colitis by Lazenby et al.6 in 1989. In Western countries, the incidence rate of collagenous colitis is 0.6-2.3/100,000, while the prevalence rate is 10-15.7/100,000. The incidence rate of lymphocytic colitis is 3.1/100,000, while the prevalence rate is 14.4/100,000.7,8 According to the cur- rent report from Olesen et al.,2 in Western, an incidence rate of collagenous colitis increases from 3.7/100,000 to 6.1/100,000, and that of lymphocytic colitis increase from 3.1/100,000 to 5.7/100,000 every year. In Western countries, the male to fe- male ratio is 1:3 in collagenous colitis and 1:2.5 in lymphocytic colitis. The average age is 63.8 for female and 60.7 for male.9 There are no available data in Korea and Asia about the inci- dence and prevalence of microscopic colitis. However, previous single center study on 2008 reported that the domestic frequen- cy was 15%.8 According to this multicenter study, the diagnostic frequency of microscopic colitis among chronic diarrhea is 22%. It means that microscopic colitis is not a rare disease entity any more and shows increasing frequency in Korea as well as in Western countries. This study also shows that there is difference in sex ratio and average age in Korea compared to Western. Especially, lymphocytic colitis was diagnosed among much younger patient, 20s-40s, compared to previous research.1,2,5,7-9 It could mean that the young patients with chronic diarrhea might have been misdiagnosed as irritable bowel syndrome without tissue biopsy.10 The cause of microscopic colitis is not yet clear, bile acids, toxin, infection,11-13 and especially drugs such as NSAIDs, H2 blocker, PPI14 seems to play an important role in microscopic colitis. These factors increase bowel permeability and cause an influx of antigens into lamina propria. And then theses induce inflammation, epithelial cell may be involved in immune system additionally.15,16 This hypothesis is supported to, in contrast to when exposed to fecal materials, not reaction of inflammation when it was not exposed to fecal materials such as ileostomy. But we could not find accumulation of immune complex, com- plement, immunoglobulin. Microscopic colitis patients presented with autoimmune dis- ease such as thyroid disease, type I diabetes and rheumatic ar- thritis and its rate is 40% to 50%.17 There is a higher prevalence rate of hypercholesterolemia and thyroid disease among patient with microscopic colitis.9 From this study, 18.2% of patient showed an association with autoimmune disease (p<0.05). How- ever, its correlation with each of the autoimmune disease has not been proved so far. Collagenous colitis occurring group take NSAIDs 5 times more than the control group, and taking NSAIDs worsens the diarrhea and stopping them relieves the symptom. It is sug- gested that NSAIDs caused the inflammation during the initia- tive phase of the disease.18,19 Two cases of collagenous colitis patient taking NSAIDs in this study also resolved diarrhea after discontinuing the drug. It was reported that other drugs also may cause microscopic colitis. Aacarbose, aspirin, lansoprazole, ranitidine, sertraline, and ticlopidine have higher chance of causing the disease. Also, carbamazepine, flutamide, lisinopril, levodopa, benserazide, oxetorone, paroxetine, simvastatin, tar- dyferon, vinburnine are categorized as the causing drugs.3,4 There is a theory that bacterial infection is one of the causes of microscopic colitis, based on the facts that biopsy specimen of microscopic colitis shows concomitant acute inflammation, collagenous colitis like a pathology after C. difficile20 or Y. en- terocolitica21 infection and relieve of symptom after antibiotics treatment in some patient, but the suspicious bacteria is not found yet. Also, an increase of nitric oxide production by inducible ni- tric oxide synthase (iNOS) in colonic epithelium of microscopic colitis patient was observed and budesonide decreases iNOS mRNA, which shows clinical and histological improvement.1 The cause of collagen deposit in collagenous colitis is not known yet. Basement membrane of epithelium in normal colon is composed of type III collagen and produced by fibroblast between crypts of colon mucosa, then it moves to superior por- tion of the organ along with the crypts and develop 5 to 7 μm of collagen layer in subepithelium. However, the collagen layer consists of type I, III and VI and thickens from 7 to 80 μm in collagenous colitis. A decrease of sodium absorption in lympho- cytic colitis and a increase of chloride secretion in collagenous colitis induce diarrhea as a common symptom in both disease.22 Microscopic colitis has a significant relation with irritable bowel syndrome. Although this study shows only one case fits