What is Inflammatory Bowel Disease?
Inflammatory Bowel Disease (IBD) is a disorder in which one or more sections of the gastrointestinal tract have become invaded with inflammatory cells. Over time, this inflammation causes the intestine to become less efficient at absorbing nutrients from digested food and weight loss, vomiting or diarrhea often result. Early signs are often subtle which allows IBD to go undiagnosed for months to years until the dog begins to develop more serious symptoms.
IBD is not a specific diagnosis as there are several types of IBD recognized. The different types of IBD are characterized by the type of cell that is causing the inflammation (see Table 1) and the specific section of the gastrointestinal tract that is affected. There are many causes of gastrointestinal inflammation that are not "true IBD" and your veterinarian must investigate these possibilities before confirming a diagnosis of IBD.
How Does a Dog Develop IBD?
The cause of IBD is poorly understood. It appears that genetics, diet, intestinal infection and abnormalities of a dog's immune system all play a role. The intestine is responsible for processing large amounts of food and bacterial particles called antigens. Antigens can be recognized by a dog's body as "foreign" and cause an abnormal allergic (immune-type) response. The end result is that the lining of the intestine is invaded with inflammatory cells and this inflammation interferes with the ability to digest and absorb nutrients.
Common antigens in the intestine include proteins and preservatives from the food, parasites, viruses or bacteria, and ingested foreign material (toys, garbage, etc). Any of these antigens can start an abnormal immune response but eventually the inflammation continues even when the antigen is no longer present. In most instances, an exact underlying cause cannot be identified and this is called idiopathic (or true) IBD.
What are the symptoms of IBD?
Occasional vomiting and diarrhea that occur over weeks to years are the most common signs of IBD in dogs. These symptoms may be responsive to brief changes in diet or short courses of antibiotics, but eventually return. The signs are usually slowly progressive but can be severe and sudden in onset in advanced stages of the disease. A combination of symptoms is most common in dogs with IBD as the stomach, small intestine and colon may be involved.
Stomach inflammation (called gastritis) typically causes loss of appetite and vomiting. Vomit may contain undigested food, partially digested food, clear or brownish liquid or even a small amount of blood.
Inflammation of the small intestine (called enteritis) often causes vomiting, diarrhea and weight loss. Vomit may be clear liquid, yellow or green bile, foam or food. Diarrhea is usually soft to watery, large volume and occurs one to three times daily. The small intestine is the main area of nutrient absorption and with chronic inflammation nutrient malabsorption often results. Affected dogs will frequently exhibit weight loss, lethargy and general unthriftiness.
Colon inflammation (called colitis) most often causes diarrhea. The diarrhea is usually of small volume and very frequent (up to ten or more times per day). Dogs with colitis often strain to defecate and have blood or mucus in the stool. These dogs usually remain active, have a healthy appetite and do not lose weight.
How is IBD diagnosed?
There are many causes of vomiting and diarrhea in dogs and the most difficult part of diagnosing IBD is eliminating other possibilities. A complete blood count, chemistry panel, urinalysis, fecal examination and culture, x-rays of the chest and abdomen and sometimes abdominal ultrasound are used to screen for metabolic disorders (such as liver, kidney, pancreas or thyroid disease); intestinal parasites (including Giardia and Cryptosporidia); bacterial, fungal or viral infections; dietary allergies; foreign bodies and cancer. Specialized blood tests such as cobalamine and folate are often recommended to determine the severity of intestinal malabsorption.
If all screening tests fail to reveal an underlying cause for the recurrent gastrointestinal signs, IBD is suspected and biopsy of the intestines is required to make a definitive diagnosis. Obtaining biopsies involves anesthesia and either surgery or endoscopy. Surgery allows adequate viewing of all sections of the intestine and deeper biopsies can be obtained for the most accurate diagnosis. Endoscopy allows your veterinarian to look at the inside of the stomach and intestines without surgery by using a fiber-optic scope with a built-in biopsy instrument. Endoscopy has the advantage of being much less invasive; however, it is not appropriate for all patients as it cannot reach some portions of the small intestine.
Intestinal biopsies must be sent to a laboratory for microscopic examination. A pathologist will report the changes as mild, moderate or severe IBD and describe the inflammatory cell that is present (see Table 1). This confirms the type and severity of IBD present and helps your veterinarian determine the best treatment plan for your dog.
How is IBD treated?
Most dogs with true IBD require medication in addition to dietary management to have complete resolution of symptoms. If dietary management alone results in complete improvement a diagnosis of IBD caused by an adverse reaction to food is made.
Highly digestible diets are usually recommended for dogs with IBD because nutrients from these diets are more completely absorbed and the amount of diarrhea will be minimized. Diets that contain a single protein source never previously eaten and a carbohydrate source that is unlikely to be antigenic (such as potato) may also be recommended. Commercial products are available or your veterinarian can advise you on a homemade dog food recipe. An appropriate diet must be fed for eight to twelve weeks before a positive affect may be seen.
Fiber supplementation is recommended for IBD that affects the colon. Dietary fiber improves stool consistency and produces fatty acids that nourish the colon and discourage the growth of harmful bacteria.
Corticosteroids (aka steroids, cortisone, prednisone) are the mainstay of therapy for IBD. Corticosteroids inhibit the inflammatory process and reduce the inflammation within the intestine. As steroids have potentially severe side effects, the goal of therapy is to gradually adjust the dose to the lowest possible amount that controls symptoms. Over time, many dogs can be weaned off steroids completely and be maintained on diet alone.
There are several other anti-inflammatory medications available and you should ask your veterinarian if any of them are right for your dog. Metronidazole is an antibiotic that helps restore the normal balance of intestinal bacteria and also has anti-inflammatory properties. The beneficial effects of metronidazole can sometimes reduce the dosage of steroids that are needed. Dogs with severe cases of IBD often need more aggressive anti-inflammatory therapy. Azathioprine, chlorambucil and cyclosporine are examples of drugs that reduce inflammation by suppressing the immune system.
Some dogs benefit from antacid, anti-nausea or anti-diarrheal therapy. Your veterinarian can advise if any of these are right for your dog.
Studies in humans suggest that supplementation of omega-3 fatty acids helps decrease inflammation within the gastrointestinal tract. Although more research needs to be done to fully determine their benefit in dogs with IBD, it is a reasonable treatment option.
What is the long term prognosis for dogs with IBD?
IBD can be controlled, but not cured. All patients with IBD will require a strict diet and possibly anti-inflammatory medication to manage their disease. Most dogs with IBD do well for many years while others require alterations in therapy every few months to treat flare-ups and recurrent symptoms. Unfortunately, a few dogs will fail to respond to treatment and some severe forms of IBD can progress to intestinal cancer.
Keep your dog with IBD on the right track—have your veterinarian examine him or her several times each year to ensure no problems arise because of disease or medication.