Diagnosis



The diagnostic challenge is to determine whether a patient who presents with diarrhea, ab­dominal pain, rectal bleeding, fever, or any of the other manifestations listed above has IBD or not and, if so, whether the disease represents UC or Crohn’s disease. The list of disorders that must beconsidered varies with the clinical presentations and may be a long one: acute bacillary dysentery, amebiasis, pseudomembranous colitis, ischemic colitis, colonic neoplasms, angiodysplasia, and many others. Laboratory studies are generally not helpful in the diagnosis of IBD except to exclude other possibilities. The diagnosis rests on (1) di­rect visualization of the colonic mucosa by sig­moidoscopy or colonoscopy, with biopsy of an ab­normal area if indicated; (2) a radiological study of the colon, and of the ileum if indicated, pref­erably using an air-contrast barium enema tech­nique; (3) exclusion of other possibilities by ap­propriate studies (bacterial cultures, or the search for trophozoites of Entamoeba histolytica, for ex­ample).

The characteristic endoscopic findings in acute UC are those described under “Pathology” above: a friable, granular, diffuse uniform lesion of the mucosa that may exhibit superficial ulcerations or that bleeds easily when rubbed with a cotton swab. With more chronic disease, deeper ulcers and pseudopolyps may be found. In Crohn’s.dis­ease the mucosa is often patchily involved and may even appear normal except for a “cobble­stone appearance” due to distortions caused by submucosal inflammation and linear ulcerations. When present, ulcers may be shallow and super­ficial or deep and longitudinal and may be found in areas of mucosa that look otherwise normal, A biopsy confirms submucosal inflammation and may demonstrate granulomas in up to 50 per cent of patients.

Radiographic studies are of particular impor­tance in the diagnosis of IBD and in demonstrating the extent of its involvement. An aircontrast bar­ium enema usually demonstrates the diffuse le­sions of UC and may show the presence of small or large pseudopolyps (Fig. 40-1). The study may be normal in early disease, however, and is less sensitive than direct visualization of the mucosa by endoscopy. Late in the disease a smooth “lead-pipe” foreshortened colon with loss of haustral markings may be noted. Radiographic studies of Crohn’s colitis most typically show skip areas, rectal sparing, longitudinal ulcers, and segmental narrowing of the bowel. Fistulas may be present. In the small bowel, especially the terminal ileum, there is usually loss of the normal mucosal pattern and reduction in the size of the lumen to produce the characteristic “siring sign.”

Although the classic differences between UC and Crohn’s disease of the colon as described above usually allow this distinction to be made, these two entities are sometimes difficult to dis­tinguish at the time that IBD is diagnosed.