Colonic or Rectal Inflammation in Dogs

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Colitis and Proctitis in Dogs

Histiocytic ulcerative colitis is a bowel disease that causes the lining of a dog's colon to thicken, with varying degress of loss to the superficial lining (known as ulceration). The thickening is due to the infiltration of various cells in the layers under the lining. And when the colon becomes inflamed, there is a reduction in the colon's ability to absorb water and store feces, leading to frequent diarrhea, often with mucus and/or blood. Proctitis, conversely, is the inflammation of the dog's anus and the lining of the rectum.

Although inflammation of the colon and rectum can occur in any breed of dog, Boxers seem to be particularly susceptible to this condition, and will usually show clinical signs by two years of age.

The condition or disease described in this medical article can affect both dogs and cats. If you would like to learn more about how this disease affects cats, please visit this page in the PetMD health library.

Symptoms and Types

Some of the symptoms that may indicate inflammation of the colon or rectum are frequent bowel movements with a only a small amount of stool, and prolonged straining after a bowl movement. Inflammation can also cause the stool to vary in consistency from semi-formed to fluid (or become diarrhea). Evacuating stool can further irritate the inflamed tissue of the colon and rectum, and cause it to tear. As a result, chronic diarrhea will often have mucus and/or blood in it.

The irritation and ulceration of the colon can also lead to responsive vomiting and weight loss because of the dog's decreased appetite.


There are a variety of possible causes for this condition. The source can be from intestinal or rectal parasites; bacterial infection; fungal infection; or an algae infection (water based). It may also be the result of a foreign object or abrasive material being swallowed by the a dog, causing trauma to the intestines.

An otherwise healthy system can occasionally react to infection or disorder by retreating into itself, in some cases, urine or waste products will reverse into the body system instead of leaving it, resulting in abnormal amounts of waste products in the bloodstream. Urea, a waste product in urine, is one of the potentially harmful products that can enter the bloodstream. This can cause other problems for the animal's body, as well, but one of the possible indicators of waste back-up is inflammation of the intestinal tract.

An inflammed intestinal tract can also be a good indicator of an inflammation of other organs. For example, long-term inflammation of the pancreas (pancreatitis) will irritate the intestines. Inflammatory or immune disorders, diet, and the swallowing of foreign objects can also affect the dog's entire system (systemic), leading to inflammation of the colon and rectum.

Perhaps less worrisome than an immune disorder, but a critical consideration nonetheless, is the possibility that the condition is the result of allergies. If an allergy is presenting itself through inflammation of any organ or system, it will be important to pinpoint the source of the allergy, since reactions to allergens tend to intensify with further contact, sometimes with fatal results.

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