Simple SummaryPatients with microscopic colitis have chronic watery diarrhea. The cause of this disorder is uncertain. Some patients appear to have a genetic predisposition, some patients have changes in the bacterial flora in their colon, and some patients have increased amounts of bile acid in their colon. These patients often have autoimmune disorders, such as celiac disease. No laboratory tests can establish this diagnosis. These patients must undergo colonoscopy with biopsy. The pathologist usually classifies these patients as lymphocytic colitis with increased numbers of lymphocytes in the mucosa or collagenous colitis with an increase in collagen deposition in the submucosa. Budesonide is the recommended initial treatment, which is a poorly absorbed oral corticosteroid medication. Some patients improve when treated with medications that bind bile acids.AbstractMicroscopic colitis is a type of inflammatory bowel disease and is classified as either collagenous colitis or lymphocytic colitis. The typical presentation is chronic watery diarrhea. The disease occurs more frequently in women aged 60–65 years and is increasing in incidence. The pathophysiology of microscopic colitis remains poorly understood and has not been well-described with possible several pathogeneses. To date, the diagnosis of microscopic colitis depends on histological tissue obtained during colonoscopy. Other non-invasive biomarkers, such as inflammatory markers and fecal biomarkers, have been studied in microscopic colitis, but the results remains inconclusive. The approach to chronic diarrhea is important and being able to differentiate chronic diarrhea in patients with microscopic colitis from other diseases, such as inflammatory bowel disease, functional diarrhea, and malignancy, by using non-invasive biomarkers would facilitate patient management. The management of microscopic colitis should be based on each individual’s underlying pathogenesis and involves budesonide, bile acid sequestrants, or immunosuppressive drugs in refractory cases. Cigarette smoking and certain medications, especially proton pump inhibitors, should be eliminated, when possible, after the diagnosis is made.