Crohn's disease or intestinal tuberculosis.|
Tuberculosis has been resurrected as a major public health problem world-wide in recent years. It continues to be a major cause of morbidity and mortality in developing countries.
However, its incidence is also increasing in developed countries, mainly in the immigrant population and in patients with AIDS. It has been estimated that some 7 to 8 million new cases and 2 to 3 million deaths are occurring annually .
Meanwhile, the incidence of Crohn's disease has risen gradually in Far East, including China, in recent decades [2-4]. Therefore, in geographical regions where both Crohn's colitis and tuberculosis are prevalent, the differential diagnosis of Crohn's disease and intestinal tuberculosis poses a challenge for clinicians.
Clinically and radiologically, the 2 diseases are sometimes similar; however, the ultimate natural history is different.
A trial of anti-tuberculosis therapy may often be prescribed before Crohn's disease is definitely diagnosed.
The diagnostic procedure of choice is colonoscopy and biopsy . Colonoscopic differentiation between intestinal tuberculosis and Crohn's diseases can be difficult, taking into account that both entities may present themselves with mucosal ulcerations and nodularity, apthous ulcers, odematous mucosal folds, strictures and pseudopolyps, and luminal narrowing .
Theoretically, biopsies under colonoscopy are important, since several histological parameters considered characteristics of either Crohn's disease (discontinuous chronic inflammation, focal lesions, microgranulomas) or intestinal tuberculosis (caseating granulomas and acid fast bacilli) [7-9]. Nevertheless, biopsy is usually of limit diagnostic value in the differential diagnosis between intestinal tuberculosis and Crohn's disease, since some parameters such as granulomas and acid fast bacilli present only in a small proportion of patients [10, 11].
Molecular biology techniques, such as polymerase chain reaction (PCR), are useful methods for the differentiation of Crohn's disease from intestinal tuberculosis because they allow the amplification and identification of very small quantities of mycobacterium DNA. This is further confirmed by a recent study, in which a positivity rate of 64.1% by PCR for detection of acid fast bacilli had been achieved in intestinal tuberculosis specimens, whilst 0 in Crohn's disease specimens .
Recently in our department the diagnosis of Crohn's disease was made by capsule endoscopy in a patient complaining recurrent intestinal bleeding with unknown origin. The main finding of capsule endoscopy was a narrowing ring with ulcerations in the distal ileum (see Figure 1).
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- Gan HT, Chen YQ, Ouyang Q, Bu H, Yang XY. Differentiation between intestinal tuberculosis and Crohn's disease in endoscopic biopsy specimens by polymerase chain reaction. Am J Gastroenterol 2002; 97: 1446-51.
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In Western Europe it is easier to differentiate tuberculosis of the digestive tract from Crohn's disease, not least because the former is rare.
Tuberculosis of the digestive tract is more often associated with active pulmonary tuberculosis, and florid granulomas with caseous necrosis are more often found in biopsies performed in ulcerated regions of the bowel. Finally, the tuberculin reaction is usually positive.
Granulomas are less common in Crohn's disease, and they may be found in areas of the bowel that appear normal at endocsopy.