Laboratory studies
A complete blood count, urinalysis, and serum chemistry tests are appropriate during the initial evaluation of a patient with suspected Inflammatory bowel disease.
Examination of the stool
Stool from patients suspected of having ulcerative colitis should be examined for leukocytes and ova and parasites, cultured for bacterial pathogens including Escherichia coli 0 57:47 and Yersinia and tested for C. difficile titer.
Fecal leukocytes are common to most inflammatory conditions of the colon but are not common in irritable bowel syndrome or noncolonic diarrhea with exacerbation of hemorrhoidal bleeding.
Examination for ova and parasites may establish the diagnosis of amebiasis, although the sensitivity of stool examination for amebae is lower than 40%. The serum indirect hemagglutination and gel diffusion precipitant tests are more than 90% sensitive for amebic infection. It is particularly important to obtain several stool samples for examination of ova and parasites before barium contrast studies are performed, because the presence of barium in the gastrointestinal tract can obscure ova and parasites for a week or more.
Bacterial pathogens may be identified by stool culture. Of particular interest is Campylobacter jejuni ileocolitis, which may present with acute, colicky lower abdominal pain, fever, bloody diarrhea with mucus, and many of the endoscopic, radiologic, and histologic features of ulcerative colitis. The disease typically subsides within several days but may run a protracted course, in which case treatment with erythromycin may provide relief of symptoms.
Another pathogen that may complicate the diagnosis of ulcerative colitis is C. difficile, the bacterial agent that has been implicated in antibiotic-associated pseudomembranous colitis. C. difficile may be relevant to ulcerative colitis in two ways. First, antibiotic-associated colitis may be confused with ulcerative colitis. Second, C. difficile may be responsible for exacerbations of preexisting ulcerative colitis. When chronic ulcerative colitis is in remission, the demonstration of C. difficile toxin in the stool is probably related to recent treatment with sulfasalazine or antibiotics. Colonic infection with enteroinvasive E. coli, especially E. coli 0157:H7, may resemble ulcerative colitis and present with similar findings.
Flexible sigmoidoscopy or colonoscopy
is indicated in the evaluation of rectal bleeding of any cause. The normal rectal and colonic mucosa appears pink and glistening. When the bowel is distended by insufflated air, the submucosal vessels can be seen. Normally, there is no bleeding when the mucosa is stroked with a cotton swab or touched gently with the tip of the sigmoidoscope.
In ulcerative colitis, the mucosal surface becomes irregular and granular. The mucosa is friable, meaning that it bleeds easily when touched. With more severe inflammation, bleeding may be spontaneous. These findings are nonspecific and may be seen in most of the conditions listed in Table 36-3. In some patients with chronic ulcerative colitis, pseudopolyps develop. The rectal mucosa is normal in patients who have Crohn’s disease without rectal involvement.
If the disease does affect the rectum, the appearance may be similar to that of ulcerative colitis or may include linear ulcerations and fissures.
Mucosal biopsy
Sigmoidoscopic or colonoscopic mucosal biopsies in patients with Inflammatory bowel disease generally are safe; however, they should not be performed if toxic megacolon is suspected. In ulcerative colitis, the histopathology of the rectal mucosa may show a range of abnormal findings. These include infiltration of the mucosa with inflammatory cells, flattening of the surface epithelial cells, a decrease in goblet cells, thinning of the mucosa, branching of crypts, and crypt abscesses.
All of these findings, including crypt abscesses, are nonspecific and may be seen in other colitides, including Crohn’s disease, bacterial colitis, and amebiasis. Because endoscopic biopsies include mucosa and a variable proportion of submucosa, the transmural nature of Crohn’s disease cannot be appreciated. However, substantial submucosal inflammation or fissuring of the mucosa may suggest Crohn’s disease. The finding of noncaseating granulomas also strongly favors a diagnosis of Crohn’s disease, but granulomas are identified infrequently in mucosal biopsies from patients with established Crohn’s disease and may accompany other conditions, such as tuberculosis and lymphogranuloma venereum. The identification of amebic trophozoites by biopsy confirms that diagnosis. Large numbers of mucosal eosinophils are typical of eosinophilic colitis.
Radiography
The plain film of the abdomen usually is normal in patients with mild-to-moderate Inflammatory bowel disease. Air in the colon may provide sufficient contrast to indicate loss of haustral markings and shortening of the bowel in ulcerative colitis or narrowing of the bowel lumen in Crohn’s disease.
In severe colitis of any cause, the transverse colon may become dilated. When this finding is accompanied by fever, elevated white cell count, and abdominal tenderness, toxic megacolon is likely. The plain film of the abdomen should be repeated once or twice a day in patients with toxic megacolon to follow the course of colonic dilatation.
Computed tomography of the abdomen and pelvis may be very informative in patients presenting with chronic or recurrent abdominal pain and suspicion of Inflammatory bowel disease. Abdominal masses and abscesses, fistulas, and, most commonly, inflammatory thickening of the involved bowel wall may facilitate the diagnosis of Inflammatory bowel disease.
Barium enema should not be performed in patients who are acutely ill with colitis because of the possibility that the preparation for barium enema or the procedure itself may precipitate toxic megacolon. Even in patients with mild-to-moderate colitis, vigorous cathartic preparation for barium enema should be avoided. Rather, oral electrolyte solutions such as GoLYTELY are preferable to prepare patients for barium enema or colonoscopy.
Some patients with early ulcerative colitis have normal findings on barium enema examination. Double-contrast studies, however, usually reveal a diffuse granular appearance of the mucosa. Loss of haustration, ulcerations, pseudopolyps, and shortening of the bowel are later developments. Sometimes an area of narrowing requires differentiating between a benign stricture and carcinoma. Reflux of barium into the terminal ileum may show dilatation and mild mucosal irregularity for several centimeters, the so-called backwash ileitis associated with ulcerative colitis.
The diagnosis of Crohn’s disease can be inferred on the basis of several radiologic findings. Narrowing of the bowel from fibrosis or edema and formation of fistulas reflect the transmural nature of the disease. Involvement of the terminal ileum and presence of skip areas in either the large or the small bowel strongly favor a diagnosis of Crohn’s disease rather than ulcerative colitis. Finally, mucosal changes of deep ulcers and linear fissures are characteristic of Crohn’s disease.
An upper gastrointestinal and small-bowel series may be of diagnostic help in the evaluation of Crohn’s disease. Whether one performs an upper gastrointestinal and small-bowel x-ray series or a barium enema first or as the only barium contrast study is a matter of clinical judgment that depends on the patient’s signs and symptoms. For example, consider a patient who complains of weight loss, right lower abdominal pain, and diarrhea and has a right lower abdominal mass by physical examination; flexible sigmoidoscopy to 50 cm is normal, but an upper gastrointestinal and small-bowel x-ray series shows typical findings of Crohn’s disease in the terminal ileum. In this instance, a barium enema, at least in the initial evaluation of the patient, is not necessary because treatment is likely to be the same regardless of whether Crohn’s disease affects the colon.
It is important to remember that, in the radiologic evaluation of a patient with chronic or recurrent abdominal pain, a routine upper gastrointestinal series is not sufficient. It should be accompanied by a small-bowel series to evaluate the small intestine for Crohn’s disease, tumors, and strictures.
As indicated previously, Crohn’s disease can affect any portion of the digestive tract. However, about 75% of patients with Crohn’s disease have, at a minimum, involvement of the terminal ileum. In about 5%, Crohn’s disease involves the duodenum. Sometimes these patients clinically resemble patients with peptic ulcer disease. Although they may improve with a peptic ulcer regimen, symptoms typically recur. Nodularity and narrowing of the proximal duodenum and sometimes involvement of the adjacent antrum are evident by barium contrast studies. The diagnosis is confirmed by endoscopy and biopsy.
Colonoscopy and upper gastrointestinal endoscopy.
Colonoscopy is useful in diagnosis and in assessing progression of proctitis or colitis over time. Periodic colonoscopy also is recommended for screening patients who have colitis for longer than 7 years for cancer and precancerous changes. Although the diagnosis of Crohn’s disease often is made on the basis of clinical and radiologic findings, colonoscopy is useful in obtaining biopsy material from the proximal colon or terminal ileum to help confirm the diagnosis.
As with barium enema examination, colonoscopy may precipitate toxic megacolon in patients with severe colitis, thus should be performed when clinically indicated. The preceding comments regarding preparation for barium enema apply also to colonoscopy. Upper gastrointestinal endoscopy may be useful in differentiating Crohn’s disease of the duodenum from peptic ulcer disease.
Jennifer is a clinical pharmacologist. She helps doctors of all medical specialties choose medications. Jennifer consults about drug dosage, interactions, and side effects.