Inflammatory bowel disease (Proceedings)

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Inflammatory bowel disease (Proceedings)

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Aug 01, 2008

Inflammatory bowel disease (IBD) in dogs and cats is the name used for many disorders of the small and large bowel of the gastrointestinal tract. IBD is a term that is an umbrella that covers many mechanisms of disease, many of which have not been discovered and others that have been suspected but not proven. Response to treatment of IBD can often lead to an initiating cause by eliminating other causes with failure of treatment. However, sometimes response to treatment is due to secondary effects of a primary cause such as bacterial overgrowth and inflammation of the gut that can occur secondary to a food allergy with response to antibiotics and immunosuppressive drugs. Diagnosis of IBD in mild cases can be a clinical diagnosis with trial and error of treatments that are not harmful. Definitive diagnosis requires a tissue biopsy of the small and large bowel by endoscopic exam or celiotomy. Differentiating other diseases that look like IBD is critical due to the possibility of neoplasia. Treatment modalities differ based on whether the patient is a dog or cat and whether the clinical signs are primarily small or large bowel or both. Prognosis in mild to moderate IBD patients is very good with proper treatment and owner compliance. Severe cases can also be responsive with more intensive therapy and good owner compliance and good communication and between the clinician and owner. Side-effects of some of the more potent drugs in these cases can be a limiting factor but usually not. Some cases have a poorer prognosis due to the presence of certain cytological inflammatory cells on histopathology.

Etiology of Inflammatory Bowel Disease

The most common causes of IBD as we understand them at this point in time in veterinary medicine are food allergies, hypersensitivity to gut bacteria, overgrowth of bacteria in the gut and a primary immune-mediated disease . There may also be a genetic component as certain breeds are over-represented for IBD. Bacterial overgrowth is hard to prove as this can occur secondary to any inflammation of the intestine. It is hypothesized that any inflammation of the gut causes a more porous mucosa breaking down the gut barrier from ingesta allowing the intestine to absorb or be exposed to antigens that are foreign. This may create a hypersensitivity to the foreign particles in the ingesta and start the inflammatory process. Even eliminating the inciting cause such as a food protein may sometimes not be enough as the immune process may continue inspite of omitting the food protein. It has been hypothesized that in puppies that have had a history of intestinal parasites that are untreated such as in a shelter or stray environment may have had a leaky barrier for a long time and are exposed to many foreign antigens. Later in life when they see that antigen again, even with a healthy intestinal barrier, their immune sytstem may react causing the inflammation to recur.

Clinical Signs of Inflammatory Bowel Disease

The signalment in dogs and cats is usually an adult with most dogs being middle aged at presentation. However, there has been patients as young as 4 months old diagnosed with IBD. Usually there is also a history of the dog or cat having periodic episodes of vomiting and diarrhea that resolved on their own. Many times these patients are presented when the disease has progressed and is not resolving as it did in the past. There are also certain breeds that are predisposed to IBD. The German Shepherd, Shar Pei, basenji, soft-coated wheaten terrier dogs and the Siamese cat. In dogs, there is usually small bowel or large bowel diarrhea or a combination of the two. Vomiting may also occur. Weight loss, depressed appetite, anorexia, hematochezia, melena and sometimes hemetemesis can be present. Other signs that the owner may notice are postprandial pain, borborygamis, abdominal pain and the patient eating grass. Cats may present with the same clinical signs as dogs but one distinguishing feature that is different is that cats may only vomit and have no diarrhea. The majority of dogs have both vomiting and diarrhea. When a dog presents for vomiting only the patient should be tested for more common causes of vomiting with IBD lower on the differential diagnoses list. Cats are also a bit different in that IBD can be a part of what is called "triaditis". Triadiditis includes IBD, cholangitis and chronic pancreatitis. Usually their clinical signs are identical to IBD. It is important to know this when a cat is diagnosed on intestinal biopsy as having IBD but is not responding to traditional treatment for IBD. Further evaluation of the liver and pancreas may be needed to give more specific treatment for all three problems.

Differential Diagnoses of IBD

Intestinal parasites should always be ruled out prior to extensive diagnostics and treatment. A patient presenting for the first time with vomiting, diarrhea and even hematochezia may have been exposed to table food, garbage or a toxin with improvement of clinical signs seen within 1-2 days of supportive care. Cholangiohepatitis, other liver diseases and pancreatitis can also cause these same clinical signs and have a waxing/waning history. Gastrointestinal neoplasia such as lymphoma and adenocarcinoma can start with the identical clinical signs. There are also fungal diseases such as histoplasmosis and pythium that can look like IBD. A patient presenting with ascites and severe hypoproteinemia , hypocholesterolemia, and lymphopenia may have a primary condition called Lymphangiectasia. Lymphangiectasia is caused by inflammation of the lacteals in the mucosa and leakage of its contents such as protein, lymphocytes and cholesterol into the gut. However, this can also occur secondary to any of the above differentials and IBD if severe enough. An intestinal biopsy is needed to distinguish this condition since treatment is to give immunosuppressive therapy as a primary treatment.