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 interve ntion and prevention of spread of the bacteria. Tt is not uncommon to obser ve granulomatous inflammation but without demonstrable acid-fast bacilli (A FB) on Ziehl-Neelsen (ZN) staining in tissues sent for histologic examinati on, and the definitive diagnosis of TB cannot be made because no concurrent tissue is sent for TB culture. Tn this study, the authors explored the fea sibility of using polymerase chain reaction (PCR) for early detection of My cobacterium tuberculosis (Mtb) in formalin-fixed, paraffin-en;bedded tissue s where a definite diagnosis of TB cannot be made. One hundred fifteen pati ents (131 paraffin blocks of biopsy specimens) with granulomatous inflammat ion but ZN-negative for AFB were studied. DNA was extracted from paraffin s ections 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 a garose gel electrophoresis. Sixty-eight of the 115 (59%) patients were TB-P CR 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 mor phologic features are suggestive but not confirmatory because of negative s taining for AFB.