By Dr. Gail Mason, DVM, MA, DACVIM Staff Internist, Portland Veterinary Emergency & Specialty Care
Granulomatous colitis (GC) is a rare, breed-specific type of inflammatory bowel disease (IBD) that attacks the large intestine or colon. The disease occurs in boxer dogs as well as French Bulldogs and other different breeds. Dogs are typically younger than 4 years of age. Affected dogs will demonstrate signs of diarrhea and severe colitis. These include frequent, small-volume bowel movements often containing blood (hematochezia) and straining to defecate (dyschezia). The surface of the colon becomes very inflamed and often ulcerated which is painful. In advanced cases, there may be weight loss and a decreased appetite. From a comparative aspect, GC also occurs in people, predominantly as Crohn's disease. It appears to involve a defect in the dog’s own immune system.
The colon is the term for the large or lower intestine, and it is the last segment of the digestive tract. It has 3 main functions which include absorbing water, storing stool, and further digesting on absorbing nutrients. The bacterial population in the colon is about 10 times denser than that of the small intestine. Bacteria, often referred to as beneficial bacteria, transform fibers that are undigestible in the small intestine and process them into chemicals that provide nourishment to the colonic cells. Bacteria that live in the colon not only nourish the cells of the colon but also control the pH of the colonic environment. This is important as excreted toxins are trapped in the stool and will be eliminated rather than reabsorbed into the body.
Colitis is a general term for inflammation of the colon which can result from stress, dietary indiscretion, parasites, adverse food reactions, malignancy, certain medications, and the genetic granulomatous syndrome.
Dogs that have sudden symptoms of colitis are generally treated symptomatically. The episodes may look dramatic but are often resolved quickly with medications such as metronidazole, tylosin or sulfasalazine as well as dietary therapy. A fecal exam should be performed to check for parasites, especially Giardia and whipworm infections. You may choose to deworm your dog empirically even if the fecal tests are negative. Remember, no test is perfect.
If the symptoms of colitis have been recurrent or chronic or the dog is a Boxer, French bulldog, or mastiff-type breed, then a further workup is advised. A routine blood panel and urinalysis are in order, as they are with any chronic disease to assess the patient's general health.
In a young dog with chronic or repetitive episodes of colitis, a further diagnostic workup is recommended. Abdominal ultrasound can provide useful information as to the general health of the intestinal tract. While it does not result in a specific diagnosis, measurements of the intestinal wall thickness are very helpful. Ultimately, the diagnosis of colitis, and specifically of granulomatous colitis is achieved by performing colonoscopy, biopsy, and bacterial culture. A visual exam performed by a specialist will generally show that the lining of the colon is reddened, has a cobblestone appearance, and is very ulcerated. The biopsy will demonstrate mucosal (surface) ulceration and what is termed “histiocytic inflammation.” It is important that tissue from the lining of the colon be submitted for bacterial culture. The hallmark of GC is a positive bacterial culture for an organism called invasive E. coli.
One of the hallmarks of GC is that patients do not tend to respond well to the typical treatments for colitis, including metronidazole, sulfasalazine, Tylosin powder, high-fiber diets, immunosuppressive drugs, and pre + probiotic therapy. Instead, patients may show an excellent and durable response to an antibiotic known as enrofloxacin. Antibiotics, when given twice daily for approximately 8 weeks, result in a reasonably high cure rate for this specific form of colitis. Future research is aimed at genetic testing to eliminate the disease, vaccination against the E. coli bacteria, or development of new antibiotics against resistant E. coli strength.