Microscopic colitis: epidemiology and treatment.

Microscopic colitis, a chronic diarrheal condition, is characterized by colonic intraepithelial lymphocytosis, expansion of the lamina propria with acute and chronic inflammatory cells, and preserved crypt architecture. These changes, in association with a thickened subepithelial collagen band, are termed collagenous colitis, whereas changes occurring without a thickened collagen band are classified as lymphocytic colitis. Population-based epidemiologic studies confirm that microscopic colitis is most frequently diagnosed in middle-aged or elderly women and that its incidence is rising. Although these disorders diminish patients' quality of life, they are not associated with an increased risk of colorectal cancer, and survival is not diminished. Clinical and histologic improvement after therapy have been noted in one randomized trial of bismuth subsalicylate and three randomized clinical trials of oral delayed-release budesonide. A treatment algorithm for microscopic colitis is proposed.