IBS is thought to be caused by abnormal motility or movement of the intestinal tract. It generally causes chronic and intermittent signs, but the affected animals do not lose weight and otherwise appear healthy. Certain patterns of illness may appear following a stressful event in the animal's life. The most common signs are bouts of diarrhea and abdominal cramping, bloating or discomfort. There is no specific test to diagnose IBS, so it is therefore a diagnosis of exclusion. This means that all other known causes of gastrointestinal disease that produce similar clinical signs must be ruled out prior to making an appropriate diagnosis of this disease process. Other diseases that may cause similar clinical signs include: Diseases involving other body systems that have gastrointestinal side effects. These might include diseases affecting the kidneys and/or urinary tract, liver, immune system and endocrine system (hormone producing glands).
Bacterial infection of the GI tract. Campylobacter, Salmonella and Clostridium are types of bacteria that can infect the GI tract and cause diarrhea and vomiting.
Parasitism. Intestinal worms or Giardia (a protozoal organism) can also cause vomiting and diarrhea.
Food allergy or intolerance. Animals that have allergies or an intolerance to certain foods may manifest their allergies via diarrhea and/or vomiting.
Overgrowth of GI bacteria. The GI tract normally contains many normal bacteria; however, excessive growth of the bacteria may lead to an overabundance, which impedes normal GI function.
Inflammatory bowel disease (IBD). IBD is a common cause of diarrhea and vomiting in both dogs and cats. The clinical signs may be very similar to IBS, but it is a different disease. IBD is characterized by the presence of inflammatory cells in the lining of the intestinal wall, as noted by intestinal biopsy.
Fungal disease of the GI tract. Histoplasmosis and Pythiosis are fungal infections that can involve the GI tract and cause vomiting and diarrhea. These infections are specific to certain geographical areas.
Neoplasia. Cancers affecting the GI tract, most notably lymphosarcoma, can cause similar clinical signs as IBS. Lymhposarcoma is a cancer of the lymphoid tissues, of which there is an abundant supply in the GI tract.