Inflammatory Bowel Disease (IBD) in Cats
Diagnosis In-depth A history and physical exam are necessary to guide the diagnostic work-up. Careful history taking should help determine if the clinical signs are primarily consistent with upper or lower GI signs, or both. Physical exam findings of animals with IBD may include thickened intestinal loops and evidence of malnutrition due to intestinal disease. Complete blood count. The CBC evaluates the red and white blood cells as well as the platelets. Occasionally animals with IBD will have elevated white blood cell counts, but this is a non-specific finding. Animals with the eosinophilic form of IBD may have an elevated eosinophil count. Eosinophils are a specific type of white blood cell. The CBC is helpful to rule out other disease processes that may cause signs similar to IBD. Biochemical profile. The biochemical profile helps to evaluate liver and kidney function as well as assessing blood sugar, protein and electrolyte levels (sodium and potassium are examples of electrolytes). This is imperative in ruling out diseases of other body systems such as liver and kidney disease. In severe cases of IBD the blood proteins may be low due to protein loss into the GI tract and decreased absorption of protein. Other biochemical parameters are usually within normal limits. Urinalysis. Evaluation of the urine together with the biochemical profile is necessary to assess kidney function, as well as to rule out protein loss through the kidneys in animals with low blood proteins. Fecal tests. Fecal analysis is necessary to diagnose bacterial and parasitic infections. A fecal float looks for worm eggs. A fecal culture is necessary to rule out the bacterial causes of infection, and there is a specific fecal test to look for Giardia. Trypsin-like immunoreactivity (TLI). The TLI assesses production of digestive enzymes by the pancreas and rules out pancreatic insufficiency. This would be more commonly run in dogs, as pancreatic insufficiency is rare in cats. Additionally, pancreatic insufficiency causes signs consistent with upper GI disease, so testing would be limited to animals with the appropriate clinical signs. Bacterial overgrowth can be assessed in several ways. One method involves getting samples of intestinal juice and culturing it to evaluate the total number of bacteria present. Bacterial overgrowth can also be implied by measuring blood levels of cobalamin (Vitamin B12) and folate. Cobalamin is often consumed by bacteria and folate is a substance produced by bacteria. Therefore, alterations in the levels of these two substances can be suggestive of bacterial overgrowth. Thoracic radiographs. Chest X-rays are useful to rule out evidence of spread of cancer to the lungs. Since cancer has to be considered in animals presenting with chronic GI illness, chest X-rays are a good idea prior to any invasive diagnostic procedures. Abdominal ultrasound. Ultrasound exam of the abdomen may help pinpoint the site of the problem. Animals with IBD may have completely normal exams, or they may show evidence of intestinal wall thickening, loss of normal intestinal detail and enlarged abdominal lymph nodes. Ultrasound exam may also be useful in identifying solitary intestinal tumors or abnormalities associated with other abdominal organs such as the liver and kidneys. Food trial. Switching the animal’s food to a new diet or a hypoallergenic diet may indicate an allergy to a specific food if the signs resolve following cessation of the previous diet. Intestinal biopsy. Biopsy of the intestine is the only way to obtain a diagnosis of IBD. The microscopic evaluation of tissue from the intestine is required to confirm a suspected diagnosis. However, it is important to rule out other causes of GI disease prior to obtaining a biopsy, as different disease processes can cause a similar appearance on microscopic exam. Intestinal biopsy may be obtained either via endoscopy, which is a scope placed into the GI tract either via the mouth or the rectum, laparoscopy, in which a scope is paced into the abdominal cavity through a small incision made in the body wall, or surgery. The largest biopsies may be obtained via surgery but this is also the most invasive method to obtain a biopsy. Endoscopic biopsies only sample the innermost layer of the intestinal wall.
Treatment principles for IBD involve manipulating the diet to try to dampen any hypersensitivity of the immune system to certain foods. Most animals with IBD require treatment with drugs as well. Drug therapy is aimed at decreasing the inflammation associated with the infiltrate of white cells in the gut as well as decreasing the ability of the immune system to cause inflammation. Dietary therapy consists of introducing a diet that the animal has never eaten. The protein source in the diet is usually thought to cause the greatest response on the part of the immune system, thus a highly digestible protein that the animal has not been previously exposed to is recommended. Available protein sources include rabbit, venison, whitefish, duck and others. To keep the diet as hypoallergenic as possible, additives and preservatives should be avoided. A number of prescription pet foods are available through veterinarians. Home-cooked diets are only recommended if appropriate vitamin and mineral supplementation is provided through the help of a veterinary nutritionist. The alternative to feeding this type of diet is to feed a hydrolyzed protein diet. Hydrolyzed proteins are partially degraded (broken down) such that they are less likely to cause an adverse immune response. Common protein sources such as chicken can be used, but the immune system does not recognize the protein as chicken because it is not in its complete form. Addition of soluble fiber to the diet is sometimes recommended for cases of lower GI IBD, as it can normalize fecal consistency, improve the motility of the colon and improve general colonic function. Antibiotics. Metronidazole is a widely used antibiotic for IBD. It has many mechanisms of activity including killing some GI bacteria, which may contribute to clinical signs, killing protozoal organisms, and dampening the immune response. Its effects on the immune system make it a good anti-inflammatory drug to use in management of IBD. Tylosin is another antibiotic that may be useful for treating cats. The drug is highly concentrated so it is not convenient for dosing cats and small dogs. The mechanism by which it acts is unclear, but it is effective for some cats with lower GI signs. Other types of antibiotics may be used as well. Corticosteroids. Corticosteroids such as prednisone are both anti-inflammatory and immunosuppressive, depending upon the dose at which they are given. They are an important component of treatment for IBD. By inhibiting the immune system, they help control the influx of white cells and the resultant inflammation in the wall of the gastrointestinal tract. Initial doses are generally quite high. Depending on response to therapy, the dose is gradually tapered over weeks to months. Sulfasalazine. This is an anti-inflammatory drug that works primarily in the colon, and is therefore used for cases of lower GI IBD. Other immunosuppressive drugs. There are a multitude of other drugs that also suppress the immune system. Multi-drug therapy with immunosuppressive drugs is sometimes needed in severe cases, or to enable a reduction in the corticosteroid dose. Reducing corticosteroid doses may be indicated if side effects are severe.