Feline Inflammatory Bowel  Disease

Douglas C. Bronstad, DVM,
Diplomate, American College of Veterinary Internal Medicine (Internal Medicine)

Feline inflammatory bowel disease (IBD) is a newly recognized disease and has been cited in several recent papers in the veterinary literature.  The increased recognition of this unique disease has stimulated clinicians to include it in the differential diagnosis when a cat presents with signs of vomiting, diarrhea, or weight loss. In my experience, it is the most common chronic primary gastrointestinal (GI) disorder of cats.

Etiology

The cause of (IBD) is unknown, although numerous theories have been proposed. One favored by most academicians is that this disease is an immune-mediated hypersensitivity reaction to indiscriminate antigens, including enteric bacteria and dietary components. Response to corticosteroids in the majority of the cases supports assertions of immune-mediated disease. There is no evidence that this disease is heritable.

Pathophysiology and Histopathology

Inflammatory bowel disease is characterized by an infiltration of inflammatory cells in the mucosal lining of the bowel (ie., stomach, intestines, or colon). Depending on the degree of inflammation and their location within the bowel, these infiltrates can affect the secretions, motility, and absorptive capacity of the bowel, creating an environment in which vomiting and diarrhea may develop.

The inflammatory infiltrates can be quite variable, in terms of severity and cell type. The most common cell types are lymphocytes and plasma cells. When both are present, the infiltrate is termed lymphoplasmacytic.  Eosinophilic infiltrates may be seen as the primary infiltrating cell (i.e., eosinophilic gastroenteritis); however, this cell line is more commonly seen as a component in a mixed population of cells that includes lymphocytes and plasma cells. Neutrophils can also be part of a mixed inflammatory response and have been suggested by one author to result from a microbial component of the disorder.

Terms often used by pathologists to describe this disease process include lymphocytic, plasmacytic, lymphoplasmacytic, eosinophilic, suppurative (i.e., predominantly neutrophilic), and commonly, a mixed inflammatory infiltrate. This disease is often segmental, and the degree of infiltrate may vary considerable, depending on the biopsy site.  In order to make a definitive diagnosis of IBD multiple biopsies of the GI tract may be required. The degree of mucosal infiltrate reported may not be a true reflection of the severity of the disease process.

History, Clinical Signs, and Physical Examination

Historical background and clinical signs of IBD can be quite variable and often are vague. The most common clinical signs noted in chronic or refractory cases are vomiting, diarrhea, or both, but anorexia and weight loss may be the sole presenting complaints in some cases.  Vomiting is the most common clinical sign on presentation. The character of the vomitus can be variable, and hematemesis is occasionally seen. Weight loss is also a variable component of the disease. Many cats have not lost weight at the time of presentation; however others may be severely emaciated owing to the chronicity of the condition and the area of bowel involved, leading to a malabsorption syndrome. Diarrhea is usually present when there is intestinal or colonic involvement, and the character of the diarrhea depends on what area of the bowel is predominantly affected (i.e., small bowel versus large bowel diarrhea). If the mucosal infiltrate is predominantly gastric or duodenal, vomiting is the primary presenting clinical sign and stools may be normal.

An IBD cat can have variable physical findings, depending on a number of factors including chronicity of the disease process and location of the disease in the bowel. The physical findings may be unremarkable in some cases, whereas other affected cats present with more severe changes, such as a thin to emaciated body condition, varying degrees of abdominal tenseness, palpably thickened intestinal loops, mesenteric lymphadenopathy, and various degrees of dehydration. It is very important for the veterinarian to do a complete organ system review during the physical examination, to rule out concurrent disease processes.


Diagnosis

A minimum data base for all IBD cases should include a fecal examination, complete blood count (CBC, biochemical profile including baseline thyroxine (T4), urinalysis, and survey abdominal radiographs. It is important to screen for other disease processes that may be causing the clinical signs.

Laboratory findings in cases of IBD can be variable; however, the majority of cases have minimal laboratory changes. The complete blood count often is normal, although mild to moderate leukocytosis may be seen. Eosinophilia is a nonspecific indicator of eosinophilic gastroenteritis.   Occasionally, mild elevations in alanine aminotransferase, alkaline phosphatase, amylase, and lipase may be associated with IBD. Urinalysis usually is normal. Survey abdominal radiography is often unremarkable, and barium GI contrast studies may demonstrate normal to irregular mucosal lining abnormalities and thickened intestinal walls. In most cases radiography is unrewarding.

A definitive diagnosis of IBD can be made only by mucosal or full-thickness intestinal biopsy. Gastric, duodenal, or colonic mucosal biopsy can be easily obtained by fiberoptic endoscopic techniques. However, many general practices cannot justify the expense of this equipment and must rely on other techniques to acquire a biopsy or utilize a referral center that has endoscopic capability. Full-thickness intestinal biopsy specimens can be obtained via an exploratory celiotomy. Multiple areas of the bowel (i.e., gastric, duodenal, jejunal, ileal) can be biopsied with this approach. At least two or three specimens should be taken from various areas of the bowel at the time of surgery.   Since IBD is predominantly a mucosal disease, the gross appearance of the serosal side of the bowel may be normal. Do not assume that the cat does not have IBD because the gross appearance of the bowel is normal. Full-thickness biopsy specimens have the advantage of histopathologically evaluating both the submucosal and serosal region. Endoscopic biopsy is less invasive but limited to the mucosal side of the bowel and by the inability to reach certain areas of the small intestine (i.e., jejunum).

Treatment

The treatment of choice for most cases of IBD is prednisone or prednisolone. The dosage should he individualized, depending on the severity of clinical signs and the chronicity of the problem. initially 1.0 to 2.0 mg/lb per day divided in two doses is recommended.   Reduction of the dose should he slow and gradual, especially in chronic cases.  For an average 10-lb cat 5 mg of prednisolone b.i.d. for 2 weeks, 5 mg s.i.d. for 2 weeks, then 5 mg q.o.d. for 4 weeks or as needed for maintenance therapy is usually recommended. The larger dose (2 mg/lb/day) can be used for severe or reftactory cases. The most common mistakes made during treatment of IBD are starting with an insufficient dose of prednisolone and not giving the drug long enough. Parenteral administration (i.e., intramuscular [IM] or subcutaneous [SQ] may he necessary for the initial 24 to 48 hours if vomiting precludes absorption of orally administered medication. For fractious animals or ones whose owners have difficulty administering oral medications, methylprednisolone acetate (Depo-Medrol) may be tried. however, response to this varies.

Prophylactic antibiotic therapy may be indicated in cases of IBD. Criteria that determine antibiotic use include the presence of peripheral leukocytosis, elevated hepatic or pancreatic enzymes on the biochemical profile, bleeding from the GI tract, suspected bacterial overgrowth or stagnant loop syndrome, and severe mucosal inflammatory changes with a neutrophilic component. Two antibiotics that are often used in combination with prednisolone therapy are amoxicillin (Amoxi-tabs) and metronidazole (Flagyl). Amoxicillin has both aerobic and anaerobic bactericidal effects and is dosed at 5 to 10 mg/lb b.i.d. for 10 to 14 days or as long as deemed necessary by the veterinarian.  Metronidazole is primarily an anaerobic bactericidal antibiotic and often shows dramatic clinical response in combination with prednisolone therapy in refractory IBD cases. Metroniclazole also has an antiprotozoan effect and aids in inhibiting cell-mediated immune responses in the intestinal tract. For IBD therapy metronidazole is typically dosed at 5 to 10 mg/ lb twice or thrice daily for 2 to 4 weeks, or as deemed necessary by the veterinarian. An average cat would receive approximately a quarter to a half of a 250-mg tablet two or three times a day.

Additional immunosuppression may be necessary in cases that are refractory to prednisolone. Azathioprine (Imuran), may be added to the therapeutic regime at 0.14 mg/ lb every other day in combination with prednisolone.  Azathioprine is available only in a 50-mg tablet; to achieve a small dose the tablet can be crushed and mixed in a palatable liquid. Some vets use a dose of a quarter tablet (12.5 mg) every other day in an average 10-lb cat without severe complications, although this is about ten times the recommended dose. Bone marrow suppression is a potential side effect of azathioprine therapy, and a CBC should be monitored every 2 weeks during the first month, then monthly thereafter. Most cats tolerate the drug well.

If colitis is a predominant part of the IBD, sulfasalazine (Azulfidine) can be added to the regimen. The typical dose is 7 to 10 mg/lb b.i.d. or t.i.d. or approximately a quarter of a 500-mg tablet at each dose for an average 10-lb cat. Potential side effects in cats include anorexia and anemia. This drug must be administered more cautiously to cats than it is to dogs.

If dietary allergens are a possible cause of IBD, a hypoallergenic diet is indicated. Hypoallergenic diets (e.g., lamb and rice) may be indicated. Long-term dietary management may be necessary in chronic IBD cases. Low-gluten diets that have been suggested include Science Diet Feline Maintenance. Other recommended diets are Nature's Receipe Rabbit and Prescription Diet Feline c/d.  Bran supplementation has also been suggested for colitis.   Novel and single-protein diets have also been used with success.   You and your veterinarian must use clinical judgment and gauge response to dietary changes via trial and error.

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