Inflammatory bowel disease (IBD) is an important and relatively common medical problem of dogs seen at the Animal Clinic at Thorndale. It is not a specific disease; rather, the term IBD represents several processes that are manifested as inflammation of the bowel. It may involve only the small intestine, large intestine, or stomach; in some cases, all parts of the gastrointestinal tract are affected.
Prevalence
IBD most often occurs in middle-aged dogs, although it may occur in any age dog. Males and females are equally affected. It may be more common in Rottweilers and German Shepherd Dogs as compared to other breeds.
Causes/Transmission
In most dogs, the cause (or causes) of IBD are not found. When a cause is not identified, it is called “idiopathic IBD.” Some of the identified causes include infection with certain types of bacteria or other parasites, toxins, dietary or food intolerance, or immune reactions. Regardless of the cause, the lining of the intestine (mucosa) becomes damaged by the inflammatory process and allows leakage of proteins across the normally intact barrier into the deeper layers of the bowel wall. These proteins are intended to remain confined to the inside of the intestine and are therefore recognized as foreign invaders by the immune system. The immune system tries to process these foreign proteins, many immune reactive cells rush into the deeper layers of the bowel trying to help, and it leads to yet further damage of the intestinal lining. The resulting increase in thickness of the intestinal wall means nutrients cannot be properly absorbed and diarrhea and vomiting result.
Clinical Signs
Three general presentations have been identified for IBD: (1) dogs with primarily vomiting, (2), dogs with primarily diarrhea, and (3) dogs with both vomiting and diarrhea. It often begins as an intermittent event but, over months to years, progresses to the point that medical care is sought.
Diagnosis
Chronic inflammation stimulates immune cells, primarily lymphocytes and plasma cells, to invade the stomach and/or intestinal wall. Occasionally, eosinophils and neutrophils will be found. Thus, the disease is diagnosed when these cells are identified microscopically in abnormal numbers in the tissue. A pathologist is responsible for this part of the diagnosis; his or her report usually calls the disease lymphoplasmacytic gastritis (stomach), lymphoplamsamcytic enteritis (intestine), or lymphoplasmacytic colitis (colon).
In order to obtain these cells, a biopsy is required. In most cases, an endoscope is passed into the dog’s stomach, small intestine or colon (with the dog under anesthesia). A tiny biopsy instrument is passed through the endoscope and used to take small samples of the lining (mucosa) of the affected organ. These biopsies, while fairly superficial, are extremely helpful in determining the type of cells present. Biopsies can also be obtained during an exploratory surgery, certainly a much more invasive procedure.
While the presence of an inflammatory process is determined with a biopsy, isolating the cause of the inflammation will usually require other tests. Tests or treatments should be performed to rule out stomach and intestinal parasites, cancer, and infections. In addition, diseases of the kidney, liver, and pancreas should also be ruled out. In many cases, the cause cannot be determined.
Without a biopsy, the diagnosis of IBD may be presumptive based on other findings. There are often clues such as a thickened bowel or stomach wall on ultrasound, response to certain medications (steroids) and hypoallergenic diets. It is important to know that many of the changes seen could also signify lymphoma, a common cancer. Thus the biopsy can be very helpful, especially if there is limited response to treatment.
Treatment
When possible, an underlying cause is identified and treated. Sometimes the above mentioned tests will do that, and sometimes a cause cannot be found. Unfortunately, many cases of IBD are considered idiopathic.
Some dogs with IBD respond to a change in diet. This is done in two ways. First, a food is chosen that contains a protein source that the dog has not eaten in the past. Alternatively, hydrolyzed protein diets which are designed specifically to be hypoallergenic may be tried. If changing protein sources is not helpful, a high-fiber diet is tried. Unfortunately, a true food trial requires that the test diet be fed exclusively for 6-10 weeks.
If dietary therapy is not successful or feasible, drugs are used to suppress the inflammatory reaction. Corticosteroids are the most effective so they are used first. Prednisolone is the most effective of the corticosteroids and has the least side effects. However, it is not effective in all dogs. Sometimes a stronger drug is used initially to gain control of the disease. Then, prednisolone is tried again as a maintenance drug. Other drugs can be tried if corticosteroids are not successful.
Corticosteroids are renowned for causing a variety of side effects in humans. This is not a much a problem in dogs as humans; however, to minimize any possible adverse effects, our goal is to use the lowest possible dose that is effective and to eventually administer it on an “every other day” schedule. By giving prednisolone every other day, the last dose is out of the body for about 12 hours before the next dose is given. During this 12 hour period, the adrenal glands are stimulated to function and the body does not forget how to manufacture its own corticosteroids.
It will be necessary to begin therapy with a rather high dose, but once response occurs, the dose is gradually tapered to the point that the signs are controlled. Long-term therapy is required for many dogs. Generally, a dog is treated for a few months then prednisolone is tapered to a lower dose to see if it is still needed. If the signs of vomiting or diarrhea recur, prednisolone therapy is resumed.
Prognosis
In most cases, it is reasonable to hope for control of the disease. However, unless a specific cause can be identified, a cure is not expected. Also, the intestinal biopsies taken with the endoscope can be helpful in determining the severity of the IBD, which helps in considering prognosis. In some cases of severe lymphoplasmacytic IBD, the dog will progress to a malignant process, called intestinal lymphoma. This has a grave prognosis.
Transmission to Humans
IBD is not transmitted to humans. Potentially, some of the parasitic causes of IBD could be infectious to humans but, in most cases, a cause is not identified