Are collagenous colitis and lymphocytic colitis distinct syndromes?

The term microscopic colitis has largely evolved to be an umbrella term which includes the histopathological entities of lymphocytic colitis and collagenous colitis. The purpose of this review is to compare these two syndromes. Lymphocytic colitis and collagenous colitis are characterized by chronic watery diarrhea, normal radiographic and endoscopic findings, and abnormal colonic mucosa on biopsy with lymphocytic infiltration of the lamina propria but minimal crypt distortion. Collagenous colitis is further characterized by a thickened subepithelial collagen band. Lymphocytic colitis has an equal sex distribution, while collagenous colitis has a marked female predominance. Histocompatibility phenotypes are also dissimilar. These findings suggest that lymphocytic colitis and collagenous colitis may be related but distinct syndromes.