Background: The etiology of lymphocytic colitis, a microscopic colitis syndrome, has remained elusive. Because 1) many infectious enteritides exhibit seasonal variability in incidence and 2) a few investigators have proposed some infectious mechanism in lymphocytic colitis, our aim was to determine if any variability in symptom onset existed among lymphocytic colitis patients diagnosed at our in stitution. Study: We identified 71 nonduplicated, consecutive patients with lymp hocytic colitis over a 4-year period using rigorous clinicopathologic inclusion criteria: 1) chronic watery diarrhea, 2) endoscopically normal colon, 3) no evi dence for celiac sprue or drug-induced colitis, 4) diffuse colitis with increas ed intraepithelial lymphocytes of at least 10 lymphocytes per 100 epithelial cel ls, 5) evidence of surface epithelial damage, and 6) no significant neutrophilic infiltrates, architectural distortion of the mucosa, or subepithelial collagen deposits. The date of diagnosis was corrected for month of onset of symptoms. Re sults: The distribution of month of onset of symptoms showed a statistically sig nificant (χ2 test of homogeneity, P = 0.0008) temporal variability and seasonal incidence pattern with excess cases during summer and fall and a paucity of cases during colder months. Conclusions: To our knowledge, this is the first study to examine systematically and report a significant seasonal inci dence pattern of lymphocytic colitis. Our observations may support a potential l ink to an infectious source in lymphocytic colitis.
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