There is increasing awareness and diagnosis of inflammatory bowel disease (IBD) in dogs and cats. Idiopathic inflammatory bowel diseases are defined as a group of disorders characterized by persistent clinical signs of gastrointestinal (GI) disease, and histological evidence of inflammation of undetermined cause in the lamina propria of small and/or large intestines.

In order to diagnose IBD correctly, certain criteria should be met. These include: 1) primary or secondary signs of GI disease observed by the clinician or owner; 2) persistent clinical signs (weeks rather than days); 3) clinical signs associated with chronic inflammation in the lamina propria of the small and/or large intestines (endoscopic or surgical biopsies); and 4) GI inflammation of no demonstrable cause (clinically or pathologically).

The proposed pathophysiology of IBD questions whether the disease is due either to an appropriate or excessive response to a foreign antigen or an inappropriate response to a normal antigen. Possible antigens include bacterial, dietary and/or parasitic antigens. Increased GI tract permeability, which enables larger peptides to access and stimulate the immune system, may also play a role. It is unclear whether the increased GI tract permeability is a cause or an effect of IBD, or possibly both. Presently the role of cytokines and immune modulation is being investigated, as well as possible roles of genetic predisposition via the major histocompatibility complex and IgA deficiency (failure to bind antigens in the GI lumen).

Any dog breed may be affected. However, breeds that have a higher prevalence of IBD include the German Shepherd, Shar Pei, and Yorkshire Terrier, however, many other breeds such as the Rottweiler, Basenji (immunoproliferative enteropathy), Irish Setter (gluten-sensitive enteropathy) and Soft-coated Wheaten Terrier (protein-losing enteropathy plus protein-losing nephropathy) have their own variant of IBD. There is no apparent breed predisposition in cats, and no sex predilection in either species.

History and clinical signs depend upon the segment of bowel that is affected. Vomiting, diarrhea (small and/or large bowel), anorexia, borborygmi, flatulence, weight loss, melena, and perhaps regurgitation (secondary to gastroesophageal reflux) may be observed. These can be persistent or cyclic. Vocalization during defecation (especially in cats) may also occur with severe colitis. In dogs, IBD typically affects young to middle-aged patients. In older dogs, neoplasia would be highly suspected. In cats, IBD most commonly is seen in middle-aged to older cats, although it has been reported in kittens as young as 5 months of age. The physical examination can be normal. Abnormal findings may include weight loss, cachexia, "gassy" or thickened bowel loops (the latter primarily in cats), and generalized poor condition.