Molecular detection of Mycobacterium tuberculosis in tissues showing granulomatous inflammation without demonstrable acid-fast bacilli.

Early diagnosis of tuberculosis (TB) is important for early medical intervention and prevention of spread of the bacteria. It is not uncommon to observe granulomatous inflammation but without demonstrable acid-fast bacilli (AFB) on Ziehl-Neelsen (ZN) staining in tissues sent for histologic examination, and the definitive diagnosis of TB cannot be made because no concurrent tissue is sent for TB culture. In this study, the authors explored the feasibility of using polymerase chain reaction (PCR) for early detection of Mycobacterium tuberculosis (Mtb) in formalin-fixed, paraffin-embedded tissues where a definite diagnosis of TB cannot be made. One hundred fifteen patients (131 paraffin blocks of biopsy specimens) with granulomatous inflammation but ZN-negative for AFB were studied. DNA was extracted from paraffin sections and amplified by PCR with the IS6110 primers (specific for the Mtb complex) and the specific 122-base pairs (bp) PCR product was detected by agarose gel electrophoresis. Sixty-eight of the 115 (59%) patients were TB-PCR positive, thus enabling definite diagnosis of TB in significant numbers of these patients in 3 days. The authors conclude that molecular diagnosis by PCR is useful for early detection of TB in histologic material where morphologic features are suggestive but not confirmatory because of negative staining for AFB.