Crohn's Disease:     Diagnosis    



Table 1. Overview

Physical Exam
The intestinal nature of the disease may be difficult to assess. A patient may have a completely normal physical examination of the right lower quadrant. For months, the only objective evidence of disease may be unexplained low-grade fever, polyarthralgia, iron deficiency anemia, hypoalbuminemia, guaiac-positive stools, elevated C-reactive protein, or an elevated erythrocyte sedimentation rate. Children and teenagers who present with fever and arthralgia may be given a misdiagnosis of rheumatic fever or juvenile rheumatoid arthritis. Prepubescent patients may have a slowing of growth 1–2 years before weight gain slows or gastrointestinal symptoms begin. This is because inflammatory mediators impair bone growth and mineralization before the intestinal lesions are extensive enough to cause cramping or diarrhea.

The diagnosis of Crohn's disease is established by a combination of clinical, radiographic, endoscopic and pathological findings. The physician gains confidence in the diagnosis by observing the patient's course. Laboratory evidence of inflammation, such as an elevated C-reactive protein, an elevated erythrocyte sedimentation rate or hypoalbuminemia, can support a diagnosis of Crohn's disease, but its absence does not exclude the illness. In addition, multiple investigations have confirmed the association between serum anti-Saccharomyces cerevisiae antibodies and Crohn’s disease in about two-thirds of patients, although the reasons are poorly understood.


Radiographic Diagnosis
The availability of excellent imaging techniques such as barium contrast x-rays (Figure 13) and computed tomography (CT) should make it unusual for Crohn's disease to be diagnosed unexpectedly at exploratory laparotomy. A double-contrast barium enema x-ray can show the right colon and the terminal part of the ileum, the areas most often involved in Crohn's disease. The examiner looks for aphthous ulcers (seen as small filling defects with an opaque center), loss of mucosal detail, cobblestone filling defects, segmental areas of involvement, fistula, and an asymmetric appearance. Spasm or scarring, producing the classic string sign, may narrow the ileal lumen. Abdominal CT is the preferred technique for suspected intra-abdominal abscesses.  

Figure 13. Patient positioning and room set-up for barium contrast study.

Small Bowel Series
This is a fast, safe procedure for visualization of the small bowel. The patient drinks a barium suspension and overhead abdominal radiographs are taken at 20–30 minute intervals. When the barium reaches the right colon, fluoroscopy is performed while moving the patient in various positions to unwind superimposed bowel loops. Compression spot radiographs are obtained with attention to the terminal ileum. Small-bowel x-rays reveal the proximal extent of disease, skip areas, and stenosis and dilation, indicating partial obstruction.

Enteroclysis is more sensitive for focal lesions (such as adhesions), but has a higher rate of complications and technical difficulty. With the patient mildly sedated, a tube is passed through the nose and advanced into the jejunum. Under constant fluoroscopic imaging, barium is infused through the tube with a methylcellulose solution, resulting in distension and coating of small-bowel loops. The appearance is similar to a double-contrast enema. 


Endoscopic Diagnosis
Flexible sigmoidoscopy or colonoscopy with colorectal biopsies can reveal focal inflammation granulomas even when the patient has no gross findings. However, the preparation for colonoscopy or barium enema x-rays can be risky for acutely ill patients with fulminant colitis. For these patients, flexible sigmoidoscopy and a small bowel series with colon follow-through may give the clinician enough information to make diagnostic and therapeutic decisions.

Flexible Sigmoidoscopy
The flexible sigmoidoscopy is an examination of the rectum and the lower colon. It is performed with a lighted, flexible, hollow tube. The sigmoidoscope is inserted into the anus through the rectum and into the sigmoid colon (Figure 14). Before sigmoidoscopy, the colon must be clear of stool to ensure good visibility. The patient must undergo a preparation that may include a liquid diet, enema, and laxatives to clear stool from the colon.       

Figure 14. A, Sigmoidoscope position in the colon; B, tip of sigmoidoscope; C, endoscopic image.

The physician is able to visualize the lower part of the colon. Biopsy forceps may be inserted through a channel of the scope to remove a small sample of tissue for microscopic examination. Sometimes it is necessary for the doctor to introduce air into the colon to improve visibility. Most patients feel a little cramping or discomfort when having a flexible sigmoidoscopy (Figure 15). 

Figure 15. Patient positioning for sigmoidoscopy and colonoscopy.

A colonoscopy involves the examination of the rectum and the entire colon. It is performed with a lighted, flexible, hollow tube. Colonoscopy permits the physician to visualize the entire colon. The colonoscope allows the doctor to assess the disease progress and to ascertain the effectiveness of therapy (Figures 15 and 16).          
Figure 16. A, Position of the colonoscope in the colon; B, endoscopic view; C, colonoscope tip.

Biopsy forceps may be inserted through the colonoscope to remove a small sample of tissue for microscopic examination (Figure 17). Before having a colonoscopy, the colon must be clear to ensure good visibility. The patient must undergo a preparation that may include a liquid diet, enema, and laxatives to clear stool from the colon.          

Figure 17. Biopsy of colonic mucosa.

The patient is sedated before the colonoscopy begins. Many people sleep through the entire procedure and feel little or no discomfort. The insertion of air during the procedure may cause some discomfort.


Differential Diagnosis
Other diseases that have the same distribution as Crohn's disease are ileal or ileocecal tuberculosis, yersiniosis, lymphoma, carcinoid tumors, amyloidosis, actinomycosis, histoplasmosis (usually in immunocompromised hosts), carcinoma of the cecum, and amebic involvement of the cecum. Tuberculosis deserves special mention. About 50% of patients with intestinal tuberculosis have evidence of pulmonary tuberculosis. The cecum is usually fibrotic and narrowed, and a few patients have typical calcified abdominal nodes. Culture and histological studies should be done on colonoscopic biopsy specimens and material from fistulae to rule out tuberculosis and actinomycosis. When a positive tuberculin skin test and other clinical features make tuberculosis a possibility, the physician may want to initiate anti-tuberculous drugs, especially if corticosteroid or immunomodulator drugs are being considered as treatment for presumed Crohn's disease. In a small minority of cases, laparotomy is required to distinguish Crohn's disease from tuberculosis, or most importantly, lymphoma before therapy can be started.

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