The diagnostic plan for a cat with chronic diarrhea should include food trials, multiple fecal examinations or therapeutic deworming, assessment of thyroid and FeLV/FIV status, and determination of intestinal vitamin (cobalamin) status. In adult cats, the potential causes of intestinal inflammation include infection, food sensitivity/intolerance, endocrinopathies, neoplasia, protozoal infestation, and parasitic triggers. Radiography and ultrasonography are important in assessing presence of infiltrative diseases, such as histoplasmosis, feline infectious peritonitis, granulomas, and lymphosarcoma. Intestinal biopsies are essential, for both diagnosis of inflammatory bowel disease (IBD) and to rule out other specific causes of clinical signs. The most effective therapies for IBD involve steroids or other drugs that interrupt the proinflammatory pathways active in the gut. Antibiotic therapy with metronidazole has been used effectively for a number of years and continues to be recommended for initial therapy of IBD. The major difference between food allergy and intolerance is the length of time on a dietary elimination trial required to achieve a response. The key is to select a diet that has a novel protein source and is balanced and nutritionally adequate. Tritrichomonas foetus infects the large intestine in cats, causing chronic large-bowel diarrhea characterized by hematochezia, increased frequency of defecation, increased mucus, and tenesmus. Infections are most common in young cats in crowded conditions. Ronidazole reduces diarrhea in cats with trichomonosis and can clear the infection; however, some cats continue to shed the organism for life. This drug is not approved for use in cats and is potentially hepatotoxic and neurotoxic. Cryptosporidium parvum is a coccidian parasite that infects the microvilli of the intestinal epithelium of kittens and immunosuppressed cats. Azithromycin is effective in humans, and although its effectiveness in cats for this infection is unknown, its use in these cases should be considered. Giardia infections are subclinical or transient, but in kittens infection is typically associated with acute onset of malodorous, pale, mucoid diarrhea. Treatment of giardiasis in cats and kittens includes specific antiprotozoal therapy combined with environmental control. Metronidazole is highly effective.

This article addresses a common and often frustrating problem in practice and contains informative, topical information particularly on Tritrichomonas, Giardia, Cryptosporidium, and food sensitivity. However, it does not address the many other causes of chronic diarrhea, both infectious and noninfectious, so the clinician should beware of "spot diagnosing" cases on the basis of these descriptions without considering other common differential diagnoses and performing further investigations as indicated. The author differentiates dietary allergy from IBD, whereas in practice these disorders may be impossible to distinguish without a carefully performed diet trial, because food allergy can also lead to inflammatory changes in the gut-so hypoallergenic dietary therapy is perhaps even more important than the author suggests. Treatment, apart from diet, is discussed only briefly. The use of sulfasalazine is mentioned, but this drug is potentially dangerous and of limited utility in cats.

Diagnosis and management of chronic diarrhea in kittens and cats. Zoran DL. Navc Proc 2009, p 518.