Differentiating Crohn’s from Intestinal TB: Searching for the Holy Grail !

In a large by study Yao He et al including 310 patients, a normogram consisting of various clinical, laboratory, endoscopic, imaging and histologic findings, was established in a derivation cohort and further validated in 98 consecutive patients. Two separate normograms containing information about age, transverse ulcer, rectal involvement, skip lesions of the small bowel, target sign, comb sign, and interferon-gamma release assays (for model 1) or purified protein derivative (for model 2) were seen to have a high degree of specificity and sensitivity.

Unfortunately, this is not the first paper to derive such a normogram and unlikely to be last. Prediction is a risky buisness and the validity of the findings can only be established by testing in other prospective cohorts. Differentiating ITB from CD is easy in some of the cases where the typical findings like presence of ascites, fever, pulmonary lesions, demonstration of AFB or caseating granulomas may help in achieveing a secure diagnosis. However, in a difficult case these normograms can help quantify the likelihood of one diagnosis over the other. Another similar normogram was reported by Limsrivilai J et al and suggested a multiparameter model which helped identify the probability of the underlying diagnosis based on the frequency of the underlying condition.

The problem with these normograms is that they may not function as well once used in real life situations. In countries like India where ITB may be as likely or more likely prevalence wise, subjecting a patient with ITB to steroids on basis of normograms may not be helpful. Clinicians and gastroenterologists in India prefer starting ATT and look for mucosal healing to be sure of what the underrlying diagnosis is. Normograms are possibly helpful but certainly not a holy grail.

References

He Y, Zhu Z, Chen Y, et al. Development and Validation of a Novel Diagnostic Nomogram to Differentiate Between Intestinal Tuberculosis and Crohn’s Disease: A 6-year Prospective Multicenter Study. Am J Gastroenterol. 2019 Feb 7. doi: 10.14309/ajg.0000000000000064.

Limsrivilai J, Shreiner AB, Pongpaibul A, et al. Meta-Analytic Bayesian Model For Differentiating Intestinal Tuberculosis from Crohn’s Disease. Am J Gastroenterol. 2017 Mar;112(3):415-427. doi:10.1038/ajg.2016.529.

Pratap Mouli V, Munot K, Ananthakrishnan A, et al. Endoscopic and clinical responses to anti-tubercular therapy can differentiate intestinal tuberculosis from Crohn’s disease. Aliment Pharmacol Ther. 2017;45:27-36 Jan;45(1):27-36.

Sharma V, Mandavdhare HS, Dutta U. Letter: mucosal response in discriminating intestinal tuberculosis from Crohn’s disease-when to look for it? Aliment Pharmacol Ther. 2018 Mar;47(6):859-860.