What is inflammatory bowel disease?
Inflammatory bowel disease is the leading cause of chronic vomiting and diarrhea in cats. It is not a disease in itself but is the name given to a group of disorders caused by to the infiltration of inflammatory cells (white blood cells) in the mucosa of the gastrointestinal tract. Cats of any age can be affected although middle-aged and older cats are more susceptible than young ones.
Both the upper and lower intestinal tract can be affected and in some cases both.
IBF's are classified according to the type of inflammatory cell infiltrating the gastrointestinal wall. Lymphocytic-plasmacytic enterocolitis is the most common form of IBD. Lymphocytes (a type of white blood cell) and plasma cells (antibody producing cells) are the predominant types of inflammatory cells present in the mucosa of the small and large intestine. Eosinophilic Enterocolitis is the second most common form of IBD, eosinophils may be found in the stomach, small intestine or colon, Granulomatous (Regional) Enteritis in which macrophages are found in the lower small intestine and colon.
If the inflammation is restricted to the large intestine it is referred to as colitis, if the small intestine is involved it is referred to as enteritis and if both the large and small intestine are involved it is referred to enterocolitis, if the stomach is involved it is referred to as gastritis. 
Persistent inflammation results in fibrosis (formation of scar-like 'fibrous' tissue), poor digestion and absorption may also result.
What causes IBD in cats?
The cause of IBD is still unknown although evidence suggests that it could be the result of certain bacteria, dietary allergy or intolerance, genetic influence and parasites causing cats to produce antibodies that attack their own digestive tract. It has also been suggested that there is an inappropriate immune response to the natural flora in the intestine.
What are the symptoms of IBD in cats?
Clinical signs vary depending on the region affected and may include:
- Diarrhea (possibly outside the litter tray)
- Loss of appetite (anorexia) or increase in appetite (polyphagia)
- Weight loss
How is IBD diagnosed?
Your veterinarian will perform a physical examination of your cat upon which may show weight loss, dehydration, thickened intestinal loops upon palpitation. He will also obtain a medical history from you. There are many other conditions which may produce similar symptoms to IBD so your veterinarian will wish to rule these out. Other conditions include various parasites, neoplasia, hyperthyroidism, diabetes, salmonellosis, campylobacteriosis, chronic renal failure, liver disease, chronic pancreatitis.
Tests performed may be:
- Complete blood count. Most cases will reveal a normal CBC but some cats may have become anemic. Higher numbers of white blood cells may be observed.
- A biochemical profile to evaluate for diabetes mellitus, liver disease, renal disease.
- Total T4 (TT4) to evaluate for hyperthyroidism.
- A fecal examination should be performed to evaluate for worms and Giardia.
- FIV and FeLV tests may suggest if a secondary disease is present.
- X-Rays/Ultrasound don't help diagnose IBD but are useful to rule out other medical conditions such as cancer.
- The only definitive way to diagnose IBD is via biopsy/histopathology of the intestinal tract. Increased numbers of plasma cells, lymphocytes, eosinophils, and neutrophils are seen in the intestinal wall. The types of cells present will provide a diagnosis of which type of IBD the cat has.
As pancreatitis can run concurrently with IBD, your veterinarian may also wish to run one (or more) of the following tests;
- fTLI (feline Trypsin-Like Immunoreactivity) - This test measures the concentrations of trypsin-like proteins in serum.
- TAP (trypsin activation peptide)
- fPLI (feline Pancreatic Lipase Immunoreactivity) - This test measures feline pancreatic lipase (an enzyme secreted by the pancreas which breaks down fat) immunoreactivity in serum
Once a diagnosis has been made the IBD will be graded into mild, moderate or severe.
How is IBD treated?
If a cause can be identified then elimination of the cause.
- A highly digestible, low-fat diet containing a novel protein should be instituted.
- If the colon is affected, a high fibre diet should also be provided.
- Corticosteroids - Prednisone is the drug of choice (as well as dietary therapy) for all types of IBD. These drugs have anti-inflammatory and immunosuppressive properties.
- Antibiotics such as metronidazole sometimes used in conjunction with dietary therapy to help manage IBD.
- Other immunosuppressive drugs which may be useful in some cases of IBD. Azathioprine is one such drug but may have side effects and is therefore only used in refractive (unresponsive to diet and corticosteroids) IBD. Cats on this drug should have a CBC every week for the first month and every 2-3 weeks while the cat is on the drug.
- Sulfasalazine is the drug of choice for lymphatic-plasmacytic colitis.
 The Cornell Book of Cats