By Arnold Plotnick, MS, DVM, ACVIM
Inflammatory Bowel Disease
Tom K., a lawyer in New York City, came home from work to what had become a familiar sight: two or three small puddles of vomit, in various rooms of his apartment. Previous visits to the veterinarian had shown Tom’s cat, Boo, to be in relatively good health. Blood tests and x-rays had revealed no abnormalities. Boo was deemed “a vomiter” by the veterinarian, and Tom had learned to live with Boo’s multiple messes. In the past few months, however, Boo’s problem had gradually grown more severe, and his thrice weekly episodes had now become thrice daily. “I guess I had grown used to it”, said Tom, “but now it’s really gotten out of hand.”
On physical examination, Boo, a 10 ½ pound 8 year-old orange tabby, was bright and alert, and no abnormalities were detected. Blood tests and urinalysis were performed and were normal, indicating that a systemic illness, such as hyperthyroidism or chronic renal failure, was not responsible for Boo’s clinical signs, and that a primary gastrointestinal disorder was the likely cause. “Tom”, I said, “I have a sneaking suspicion that Boo has inflammatory bowel disease.”
Inflammatory Bowel Disease (IBD) is an uncontrolled or excessive gastrointestinal inflammatory response, resulting in the infiltration of inflammatory cells into various segments of the gastrointestinal tract. There is no age, gender, or breed predisposition for feline IBD, however, most cats tend to be middle aged or older. Inflammatory Bowel Disease is often mistakenly called Irritable Bowel Syndrome.
The most common symptom of feline IBD is weight loss. This may or may not be accompanied by a decreased appetite, vomiting, or diarrhea. In Boo’s case, vomiting was his only clinical sign. He still had a good appetite, had no diarrhea, and had managed to maintain his weight.
In most cats, physical examination tends to be normal. The most common finding on examination is weight loss. Occasionally, thickened or fluid-filled intestines are evident when the abdomen is examined.
Feline IBD is a diagnosis of exclusion. In other words, there are many disorders that can cause gastrointestinal inflammation, and these should be ruled out before honing in on a diagnosis of IBD. Examples of other disorders to consider include intestinal parasites, viral infections such as feline leukemia or feline immunodeficiency virus, food intolerance, food allergy, gastrointestinal cancer, and metabolic disorders such as hyperthyroidism.
In cases of IBD, routine laboratory tests tend to be normal. Protein levels in the bloodstream may be either high or low. Increased liver enzymes are occasionally reported in cases of feline IBD and may be important given the recent studies that reveal that many cats with IBD have concurrent inflammation of the liver and bile ducts (cholangiohepatitis) and/or pancreatitis. In one published case series, a low cholesterol level was the most common biochemical abnormality reported.
In any workup for gastrointestinal disease, x-rays and ultrasound are important diagnostic tools to rule out a GI obstruction or an abdominal mass. Radiographs, however, are ineffective for diagnosing IBD. Increased intestinal wall thickness and enlarged intestinal lymph nodes may be visible on ultrasound in suspected cases of IBD, however, these finding are suggestive, not diagnostic, of IBD. Ultimately, a definitive diagnosis requires obtaining biopsy specimens from the GI tract.
Biopsies of the GI tract can be obtained either via endoscopy or exploratory surgery. Endoscopy is a procedure in which a long, flexible snake-like probe (the endoscope) enters the GI tract through the cat’s mouth (“upper GI endoscopy”) or anus (“lower GI endoscopy”), in order to visualize the internal lining of the GI tract and obtain biopsy specimens.
Endoscopy is a relatively non-invasive method of obtaining biopsies. However, if concurrent abnormalities are present such as markedly increased liver enzymes on the chemistry profile, enlarged lymph nodes, or an abnormal liver or pancreas is seen on ultrasound, abdominal exploratory surgery may be warranted so that biopsy specimens of these organs can be obtained in addition to the biopsies of the gastrointestinal tract. Endoscopy offers advantages over surgery in that it is less invasive, allows for direct examination of the mucosal surfaces (innermost lining) of the GI tract, and may guide the endoscopist to a good location for obtaining biopsy specimens if irregularities or ulcerations of the mucosal surface are detected. The limitations of endoscopy are that the biopsy specimens that are obtained by this method consist only of the mucosal lining rather than a full-thickness biopsy of the intestinal tract, occasionally resulting in a misdiagnosis if the disease process primarily involves a deeper layer of the intestinal wall. Another limitation is that during upper GI endoscopy, the endoscope can only reach the stomach and the duodenum (the first part of the small intestine). The jejunum (the next part) and the ileum (the final part) cannot be reached with an endoscope. Both procedures – endoscopy and abdominal exploratory surgery – require general anesthesia.
The typical finding on biopsy specimens of the GI tract is an increased number of inflammatory cells, as well as an altered structure of the intestinal lining. Depending on the predominant cell type seen in the biopsy specimens and the section of the GI tract that is affected, the condition is given a name. For example, if lymphocytes and plasma cells are the primary inflammatory cell detected, the inflammation is called “lymphoplasmacytic”. If eosinophils (a type of white blood cell often indicating allergic or parasitic disease) are the predominant cell type, the term “eosinophilic” is used. The part of the gastrointestinal tract that is affected is also included in the naming. For example, if the small intestine is affected, the term “enteritis” is used; if the stomach is involved, the term “gastritis” is used (see “Glossary, Sidebar 1). Finally, the pathologist is likely to subjectively describe the degree of severity of the inflammatory change. For example, a pathology report might read: “lymphoplasmacytic gastritis, mild; lymphoplasmacytic enteritis, severe”, indicating that both the stomach and small intestine are infiltrated with lymphocytes and plasma cells, with the small intestine being the more severely affected site. Lymphoplasmacytic is the most prevalent form of feline IBD. Eosinophilic is the second most common form. Other forms (suppurative, granulomatous) have been described, but are much less common. Boo’s endoscopy did yield a diagnosis of IBD, specifically, severe lymphoplasmacytic enteritis.
A dilemma for pathologists is distinguishing severe lymphoplasmacytic inflammation from early stage lymphosarcoma, a type of cancer. In fact, it has been speculated that severe forms of IBD can transform into lymphosarcoma over time.
Treatment of feline IBD can be challenging. The goal of treatment is to identify and remove the cause of the inflammation if possible, and to suppress the immune response. This is usually accomplished through the use of special diets and immunosuppressive drugs.
No one diet is suitable for cats with IBD. Some cats respond to a particular diet while others may show a lesser response, or no response at all. Highly digestible diets may be beneficial. A hypoallergenic diet may produce significant improvement in some cats with IBD. A hypoallergenic diet is a diet that contains a protein source that the cat has never been exposed to before. There are numerous commercially manufactured hypoallergenic diets available through most veterinarians that contain novel protein sources such as rabbit, venison, and duck. A few prescription diet manufacturers have marketed hypoallergenic diets in which the protein has been hydrolyzed into fragments that are too small to be detected by the immune system, obviating the need to specifically identify a suitable novel protein. Hypoallergenic diets alone, however, are inadequate at inducing long-lasting remission in cats with IBD. If a cat responds completely to a novel protein diet alone, the likely diagnosis is food sensitivity or allergic reaction to food rather than IBD.
Corticosteroids are the most commonly prescribed immunosuppressive drugs for the treatment of IBD. Typically, oral prednisone is given for at least 2 to 4 weeks. If clinical signs resolve, the dosage of prednisone is slowly tapered until the lowest effective dose is reached. In cases of severe inflammation in which a dietary change and prednisone are ineffective, other immunosuppressive drugs can be added. If cats with severe IBD do not respond to treatment, the veterinarian may need to reassess the diagnosis and consider that the severe IBD may in fact be lymphosarcoma.
Although IBD isn’t curable, the prognosis is good for adequate control of the disease. In one case series, 79% of cats with IBD showed a positive response to treatment with diet and prednisone. Fortunately for Tom, Boo responded dramatically to prednisone and a change in diet, with his vomiting episodes decreasing to approximately one episode a month. “I certainly don’t miss the sound of Boo vomiting in the middle of the night”, says Tom, “and Boo has never looked and felt so good.”
Gastritis – inflammation of the stomach
Enteritis – inflammation of the small intestine
Colitis – inflammation of the colon (large intestine)
The above terms can be combined to describe situations in which concurrent inflammation of different parts of the GI system are present, for example:
Gastroenteritis – inflammation of the stomach and small intestine
Enterocolitis – inflammation of the small intestine and colon
Gastroenterocolitis – inflammation of the stomach, small intestine, and colon