Focal lymphocytic colitis and collagenous colitis: patterns of Crohn's colitis?

The morphologic findings in mildly active colonic Crohn's disease (CD) include crypt disarray, patchy edema, and small lymphoid aggregates with neutrophils, sometimes associated with aphthous ulcers. We describe four patients with CD whose colonic biopsies focally showed a lymphocytic colitis morphology, and one patient with CD whose biopsies showed a collagenous colitis morphology. The lymphocytic and collagenous colitis patterns of injury preceded the eventual clinical pathologic diagnosis of CD in four patients. Colonoscopic abnormalities were found in four patients. The lymphocytic colitis pattern was focal, involving some biopsy fragments, whereas other biopsy fragments were normal or had minimal nonspecific inflammation. In one patient, moderate numbers of neutrophils were admixed with the lymphoplasmacytic infiltrates. The presence of colonoscopic abnormalities, focal changes, and moderate admixed neutrophils could assist in the distinction from lymphocytic or collagenous colitis, both of which are colonoscopically normal, usually diffuse, and devoid of, or contain only a sparse number of, neutrophils. A limited number of biopsy fragments may be incorrectly interpreted as lymphocytic or collagenous colitis. The temporal relationships suggest that these morphologic patterns precede typical active CD.