ABSTRACT
In 1976, Linstrom introduced the term of collagenous colitis while describing a 48-year-old woman with watery diarrhea, normal rectal mucosa on proctoscopy, and a thickened subepithelial collagenous deposit on rectal biopsy (1). The term ‘‘microscopic colitis’’ was subsequently introduced by Read et al. in 1980 while reporting on eight patients with chronic diarrhea, normal endoscopic exam, and increased number of inflammatory cells on colonic biopsy (2). Lazenby et al. proposed replacing the term microscopic colitis with the less ambiguous term of lymphocytic colitis for patients with watery diarrhea and an increased number of intraepithelial lymphocytes on colonic biopsy, but without a thickened subepithelial collagen layer (3). Collagenous and lymphocytic colitis share many clinical and pathologic features. Whether they represent separate diseases or are just different pathologic manifestations of the same disease process is currently not known. For the purpose of this chapter, they will, when considered collectively, be referred to as microscopic colitis.
