Crohn's Disease & Ulcerative Colitis

Like Crohn's disease, ulcerative colitis is a chronic inflammatory disease of the GI tract. Though these disorders share certain pathogenic and clinical similarities, there are distinct differences.

The inflammatory process in ulcerative colitis is restricted to the colon and is usually limited to the mucosal and submucosal regions of the bowel wall. Ulcerative colitis may involve varying portions of the colon: universal in 50 percent, left-sided in 30 percent, and restricted to the rectum and sigmoid in 20 percent.

Infrequently, ulcerative colitis may involve the terminal ileum, a condition known as "backwash ileitis." In contrast, the inflammatory process in Crohn's disease involves the entire bowel wall, extending to the serosa, and may involve associated mesentery and lymph nodes.

Surgical resection (proctocolectomy) is curative in ulcerative colitis, but not so for Crohn's disease, in which recurrence proximal to the site of anastomosis or ileostomy is common.

There are several distinct differences in the clinical presentation of these two disorders. Rectal bleeding is more common and more severe in ulcerative colitis. Patients with ulcerative colitis do not suffer from perianal disease, have less frequent and less severe abdominal pain, and uncommonly develop abdominal masses compared with those who have Crohn's disease.

Malnutrition may occur in ulcerative colitis, but it tends to be less frequent and less severe than in Crohn's disease. The incidence of ulcerative colitis is low in smokers in contrast to the increased incidence in Crohn's disease.

Several diagnostic differences may be useful in distinguishing these disorders. Pathohistologic features of ulcerative colitis include a continuous diffuse tissue-inflammatory reaction that involves the rectum in nearly all circumstances. In addition, patients with chronic long-standing ulcerative colitis frequently develop a tubular, fibrosed, shortened colon.

Prominent lymphoid hyperplasia and granulomas in Crohn's disease are frequently used to distinguish these disorders. Patients with ulcerative colitis do not develop abdominal fistulae and rarely develop intestinal obstruction but sometimes do develop strictures.

Patients with severe acute ulcerative colitis may develop dilatation of the colon that can progress to toxic megacolon. In contrast, toxic dilatation of the colon occurs infrequently in Crohn's disease.

Note: In 10 to 15 percent of patients, a clear distinction cannot be made between ulcerative colitis and Crohn's disease. The term "colitis of indeterminate origin" is used to classify these patients.

Last updated Jan 4/07