Right Dorsal Colitis
Right dorsal colitis (RDC) is a disease that is complicated and the pathophysiology poorly understood, but there is a relationship between RDC and the use of non-steroidal anti-inflammatory drugs (NSAIDs), including phenylbutazone (Bute) and flunixin meglumine (Banamine). Most NSAIDs are not specific and therefore inhibit both good and bad prostaglandins. The good prostaglandins protect the mucosal lining of the gastrointestinal tract. Right dorsal colitis occurs when ulcerations develop in the specific area of the large intestine (right dorsal colon) which causes a decrease in nutrient absorption and an increase in protein loss. Although inadvertent overdose of or prolonged therapy with these drugs is a definite cause of RDC, many horses are sensitive to NSAIDs and develop signs of RDC with appropriate dosing. The unique blood supply to the right dorsal colon is one thought as to why horses develop this disease associated with NSAIDs.
Right dorsal colitis can be associated with high doses of or prolonged therapy with NSAIDS, but other predisposing factors include stress, immune-mediated response, infection and genetics. Ponies and younger horses that are showing are at a higher risk of developing this disease. Clinical signs include complete loss of or decreased appetite, lethargy, mild colic, diarrhea and weight loss. On bloodwork specific abnormalities include anemia, low protein levels, low albumin levels and low calcium levels and occasionally elevated kidney levels.
Diagnosis is made based on clinical signs, history of NSAID use, laboratory blood tests indicating low protein and low albumin, and ruling out other diseases that cause low protein including maldigestion/malabsorption, kidney disease, peritonitis, and inflammatory/infiltrative bowel disease. Diagnostic tests such as abdominal ultrasound, abdominal tap with fluid analysis, urinalysis, and intestinal absorption tests help to rule out other causes of protein loss. In some cases of RDC, thickening and edema of the large intestine wall can be imaged with ultrasound on the right side of the abdomen. A definitive diagnosis can be made on histopathology by right dorsal colon biopsy during an exploratory surgery.
Initial treatment consists of medical therapy and dietary management. In most cases changing the diet to an easily digestible, low bulk, pelleted, complete feed decreases the workload on the ulcerated large intestine and helps manage the signs of colic and diarrhea. Misoprostol is a synthetic prostaglandin that is used in cases of RDC to promote colonic mucosal ulcer healing. It is thought to stimulate increased secretion of mucus that lines the GI tract and increase mucosal blood flow thereby providing some mucosal protection in the large intestine. All other gastroprotectants (omeprazole, sucralfate, ranitidine) have not been proven to work outside of the stomach, however they are commonly used in treatment of RDC as NSAIDs can also cause gastric ulceration. Other treatments include the use of psyllium to possibly increase the amount of omega 3 fatty acids, a natural anti-inflammatory, within the colon.
Horses with severe clinical signs and very low protein levels may need supportive therapy including IV fluids, plasma, and other types of pain management to treat RDC. In the most severe cases, exploratory surgery and right dorsal colon resection may be considered.
One of the most important aspects in prevention of RDC is the judicious use of NSAIDs. Consulting with your veterinarian when NSAIDs are needed to treat your horse’s illness or injury, being accurate about dosing on body weight when your equine friend is a pony or a miniature horse, and following your veterinarian’s recommendations for the length of time needed for NSAID therapy, are ways to be sure NSAIDs are being administered judiciously. Using more specific NSAID drugs such as firocoxib, (Equioxx) if your horse is sensitive to NSAIDs, also helps to decrease the chances for adverse reactions. In some horses, the concurrent use of ulcer prevention therapy during NSAID therapy can decrease the possibilities of adverse reactions. Most importantly, talk to your veterinarian and ask questions!
If you have any questions regarding RDC or any other equine health issues, please discuss them with your veterinarian or contact the veterinarians at NEEMSC.
Kimberly Brothwell, DVM
Jacqueline Bartol, DVM, DACVIM