Introduction
The collective term Inflammatory Bowel Disease (IBD) is used in canine and feline gastroenterology to describe patients affected by persistent or recurrent GI signs that have histological evidence of inflammatory infiltration of the GI mu- cosa.1 However, the indiscriminate use of the term “IBD” in small animal gastroenterology is problematic.
The condition can only be termed “idiopathic IBD” if no underlying cause for the inflammation can be found. A number of other diseases are recognized as being associated with chronic intestinal inflammation (Table 9.3). It is the duty of the clinician to rule out these known causes through systematic investigation before reaching a diagnosis of idiopathic IBD, which is, by definition, of unknown cause.It seems likely that idiopathic IBD is actually a group of disorders and not a single disease entity, as variations of the histological appearance do exist. The histological nomenclature for IBD reports the predominant cell type present and forms the basis for its traditional classification (Table 9.4). Lympho- plasmacytic enteritis (LPE) is the most common form of idiopathic IBD reported in both dogs and cats and yet, even within this group, variations do exist in its distribution within the GI tract, its severity, its pattern within the lamina propria (i.e., villus, upper crypt, or lower crypt), and in the ratio of lymphocytes to plasma cells. A severe form has been reported in Basenjis. Isolated lymphoplasmacytic colitis (LPC) has been reported quite frequently by some authors, whereas others believe it usually occurs in concert with more diffuse intestinal inflammation (i.e., LPE).2
Eosinophilic (gastro-)enteritis (EGE) is less common than LPE, but is the second most frequently diagnosed variant of IBD. Granulomatous enteritis is considered rare, although a report of a condition called “regional enteritis” bears a strong resemblance to granulomatous enteritis in humans.
Histiocytic ulcerative colitis is a rare condition seen almost exclusively in Boxers (see 6.4.2.1).Neutrophilic infiltration is the hallmark of the variants of IBD occurring in humans, namely Crohn's disease (CD) and ulcerative colitis (UC). Yet predominantly neutrophilic infiltration is uncommon in idiopathic IBD in cats and rare in dogs.
Table 9.3: Causes of chronic intestinal inflammation
Chronic infection
Giardia
Histoplasma
Toxoplasma
Mycobacterium
Prototheca
Pythium and other zygomycetes
Pathogenic bacteria
Campylobacter spp., Salmonella spp., pathogenic E. coll
Food allergy
Associated with other primary GI diseases
Lymphoma
Lymphangiectasia
Idiopathic
CD is characterized by periods of remission, with relapses where initial neutrophilic inflammation is followed by granuloma formation. This disease can affect any part of the intestine but is typically localized to the terminal jejunum and ileum. It is further characterized by fistulous tract formation and intestinal obstruction due to granuloma formation, often necessitating surgical resection of affected tissue. In comparison, UC is restricted to the colon and differs histologically from CD as the neutrophilic inflammation is associated with ulceration and crypt abscessation. Thus, canine and feline IBD bear little resemblance histologically or clinically to IBD (i.e., CD and UC) in humans, but they may still share a common etiology.
9.2.5