There are many potential causes of acute diarrhea in cats, but a smaller number of etiologies are associated with the development
of feline chronic diarrhea. Primary intestinal diseases (malignancy, inflammatory bowel disease, food sensitivity, and infection)
account for most of the causes of feline chronic diarrhea, but chronic diarrhea may also develop with extra-intestinal disease
(hepatobiliary disease, exocrine pancreatic insufficiency, and hyperthyroidism). The syndrome of small intestinal bacterial
overgrowth is an important cause of chronic diarrhea in the dog, but cats may be refractory to the development of this syndrome.
Inflammatory Bowel Disease (IBD)
Chronic inflammation of the gastrointestinal tract (inflammatory bowel disease; IBD) is the most important cause of chronic
diarrhea (and vomiting) in cats. Inflammatory bowel disease is not a single disease entity per se, but simply the culmination of chronic, sustained inflammation of the gut. A complete medical investigation should always
be performed to consider all of the known causes of chronic diarrhea in the cat. A diagnosis of IBD is considered only after
known causes (e.g., infection, toxicity, neoplasia, metabolic disorders, allergy/sensitivity reactions, maldigestion of exocrine
pancreatic insufficiency) of chronic diarrhea have been carefully excluded.
Clinical findings in feline IBD may include reduced body mass, thickened bowel loops, fever, abdominal pain, mesenteric lymphadenopathy,
and, hepato/splenomegaly in cats with eosinophilic enteritis and hypereosinophilic syndrome. Hematologic and serum biochemical
abnormalities are occasionally observed but are fairly non-specific. Abdominal radiographic and ultrasonographic studies
are also usually non-diagnostic with occasional findings of fluid or gas-filled loops of bowel, intestinal wall abnormalities,
and mesenteric lymphadenopathy.4 Intestinal biopsy (endoscopy or laparotomy) may help differentiate this spectrum of disorders from other known causes
of enteritis.4 Dietary manipulation alone or in combination with drug therapies are the basis of therapy in this disorder. The prognosis
is good for control in most cases, but not always curative.
Lymphosarcoma, adenocarcinoma, and mast cell tumors are the most common tumors of the gastrointestinal tract in cats. Lymphosarcoma
quite often involves diffuse segments of the bowel, whereas adenocarcinomas and mast cell tumors are usually more focal.
Weight loss, anorexia, and diarrhea are the most important clinical signs.
Intestinal lymphoma may develop over many months, and affected animals usually present with clinical signs of weight loss
and diarrhea. Histologically, lymphosarcoma is usually characterized by diffuse mucosal and submucsoal infiltration of neoplastic
lymphocytes. Malabsorption results from progressively reduced absorptive area in intestinal villi. Diffuse thickening of
the small intestine and mesenteric lymphadenopathy are frequent physical examination findings, although these same findings
can be observed in cats with moderate to severe inflammatory bowel disease. Ultrasonography is useful in evaluating intestinal
thickness and mesenteric lymph nodes, but definitive diagnosis requires endoscopic or full thickness biopsies.