, Volume 22, Issue 6, pp 485-496

Canine histiocytic ulcerative colitis

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Canine histiocytic ulcerative colitis (CHUC) is a chronic debilitating disease of boxer dogs. Study of this disorder may provide information essential to the understanding of pathogenic mechanisms that result in progressive large bowel ulceration. In this study, large intestinal mucosal biopsy specimens from seven affected boxers and four normal dogs were examined by light and electron microscopy. The earliest morphologic change discernible was focal, acute inflammation and epithelial cell degeneration at the luminal surface of the large bowel. These latter changes were nonspecific in nature. The basement membrane of affected epithelium consistently was effaced and intercellular spaces were dilated. Neutrophils were found between intact, degenerating epithelial cells and within the subjacent lamina propria. Convincing evidence for an infectious cause of CHUC was not found. Observed microorganisms probably were secondary invaders since they were present only in lesions exhibiting actual epithelial disruption. The PAS-positive macrophages, which are pathognomonic for the disease, were engorged with numerous digestive vacuoles that mainly contained phospholipid membranes. A developmental sequence was observed which suggested that these PAS-positive cells arose from the actively phagocytic, normal-appearing macrophages found in the surface-oriented mucosal lesions.