Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) can involve either or both the small and large bowel. Crohn disease and ulcerative colitis are the best known forms of IBD, and both fall into the category of "idiopathic" inflammatory bowel disease because the etiology for them is unknown. The underlying mechanisms for their development may be based upon abnormal immune responses.

The bowel normally contains a large number of bacteria, all producing a variety of antigenic substances that are normally tolerated and do not elicit an immune response. However, persons with IBD may have defects in mucosal immunity that trigger inappropriate inflammatory reactions to gut organisms.

Pathologic findings are generally not specific, although they may suggest a particular form of IBD.

• "Active" IBD is characterized by acute inflammation with epithelial injury characterized by mucosal erosion, ulceration, cryptitis and crypt abscess formation.

• "Chronic" IBD is characterized by architectural changes:

  • Crypt distortion or crypt branching

  • Basal lymphoplasmacytosis separating the base of the crypts from the mucosa

  • Presence of Paneth cells in the mucosa distal to the colonic splenic flexure

  • Presence of pyloric-type mucus glands / pyloric gland metaplasia in ileum or colon

Crypt abscesses (active IBD consisting of neutrophils in crypt lumens) can occur in many forms of IBD, not just ulcerative colitis.

In up to 1/6 of idiopathic IBD cases, it is not possible to distinguish ulcerative colitis and Crohn disease, and these are termed "indeterminate colitis."