LAUSR

The world’s largest number of tuberculosis patients reside in India. Extrapulmonary tuberculosis (EPTB) comprises 19% of the total caseload of tuberculosis, the latest Indian report accounting for 28% of all notified cases. Cutaneous tuberculosis (CT) is seen in 1.5% of EPTB and presents in a variety of morphological forms which have been traditionally accommodated in a working classification, that is, primary inoculation occurring in those unexposed to the bacilli and secondary in sensitized individuals which can be endogenous, exogenous, or hematogenous in origin, and tuberculids. They mimic other dermatoses, recognition of which is largely based on clinical experience followed by investigations. Being essentially paucibacillary, tests needed to confirm CT seldom yield conclusive results. Histopathology shows varying patterns of granulomatous inflammation, and acid-fast bacilli are rarely demonstrable; cultural isolation of mycobacteria is difficult and depending on the medium, solid or liquid, it can be improved. The result of polymerase chain reaction (PCR) is also not dependable, leading one to consider a therapeutic response as essential but not proof of diagnosis, in a patient strongly suspected to have CT. Later attempts to develop PCR assays targeting different gene stretches of M. tuberculosis have improved the diagnostic sensitivity, where a positive test in an appropriate clinical setting confirms CT even when the histopathology at times fails to reveal granulomatous inflammation, but when negative the decision cannot be based solely on PCR results. Though specificity can reach up to nearly 100%, the sensitivity of PCR depending on the method exhibits a wide range from 16% up to 80%. The most commonly targeted gene is IS-6110 followed by 16 s r DNA, MPB64, and rpoB. Evaluating Xpert MTB/RIF diagnostic assay in extrapulmonary specimens against a composite reference standard in which treatment response was included, it was found useful only in lymph node tuberculosis; the poor sensitivity in others and CT