Right Dorsal Ulcerative Colitis

CHAPTER 95 Right Dorsal Ulcerative Colitis



Many horses with right dorsal ulcerative colitis (RDUC) are performance animals with a history of treatment with one or more nonsteroidal anti-inflammatory drugs (NSAIDs). No predilections associated with age, sex, or breed have been identified. The prevalence of RDUC in horses is unknown, but it appears to be low.


Right dorsal ulcerative colitis primarily affects the right dorsal segment of the colon, but it can affect other segments. It is characterized by mucosal ulceration of variable severity with thickening, inflammation, and edema of the underlying submucosa and lamina propria. Depending on the duration of disease, fibrosis may be evident and may be accompanied by development of intestinal strictures. Right dorsal ulcerative colitis has been associated with NSAID administration at higher than recommended doses but may also be seen in horses treated with appropriate doses of NSAIDs. Other factors that may increase the risk of RDUC in horses treated with NSAIDs include underlying inflammation of the colon, dehydration, and sepsis-endotoxemia. Individual variation in NSAID sensitivity may also affect the risk of developing RDUC. Although treatment with any NSAID may cause RDUC, most reported cases have been associated with phenylbutazone treatment. It is unclear whether this reflects a propensity for phenylbutazone to cause RDUC or the relatively common and often chronic use of this drug for musculoskeletal conditions in the horse.


The mechanism by which NSAIDs cause mucosal ulceration is via inhibition of cyclo-oxygenase (COX) activity and suppression of intestinal prostaglandin production. Nonselective NSAIDS such as phenylbutazone and flunixin that inhibit both COX-1 and COX-2 are more damaging to the gastrointestinal tract in general and likely to be a causative factor in RDUC than are selective COX-2 inhibitors such as firocoxib that spare the homeostatic and reparative prostaglandins produced by COX-1–dependent pathways. Prostaglandins are critical for maintaining epithelial integrity and repair following damage. Treatment with NSAIDs disrupts epithelial barrier function in both healthy and healing colon, resulting in increased permeability to microbial products, such as endotoxin. Absorption of microbial molecules potentiates an inflammatory reaction that worsens mucosal injury. Administration of NSAIDs may cause ulceration throughout the alimentary tract, and it is not clear why the right dorsal colon is a particularly susceptible site.



May 28, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Right Dorsal Ulcerative Colitis

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