Diagnostic value of different PCR assays for the detection of mycobacterial DNA in granulomatous lymphadenopathy.

Diagnosis of mycobacterial infection is made by assessment of characteristic histological features, staining of acid-fast bacilli, or agar culture. Recent advances in molecular biology have provided alternative approaches for the detection of mycobacteria, but only limited data are available dealing with the comparative evaluation of these methods. In order to determine the diagnostic applicability of polymerase chain reaction (PCR)-based assays, 20 formalin-fixed and paraffin-embedded lymph nodes with bacille Calmette-Guérin (BCG) lymphadenitis were investigated which in Löwenstein Jensen agar culture were either positive or negative (ten cases each); ten lymph nodes with non-specific lymphadenitis served as negative controls. Ziehl-Neelsen staining as well as three different PCR assays (including nested PCR), amplifying a specific sequence of the Mycobacterium tuberculosis complex or sequences of the 65 kD antigen gene, were performed. Positive culture was only obtained from lymph nodes which had been surgically removed within 20 weeks after vaccination (P < 0.001). In contrast to microscopic examination, which yielded no more information than agar culture, PCR detection of mycobacterial DNA was unrelated to culture findings. Combined use of different assays, as well as DNA extraction from at least three paraffin sections from each specimen, resulted in the detection of mycobacterial DNA in all lymph nodes with amplifiable DNA (18 out of 20 cases). Controls remained consistently negative. Thus, the combined use of different PCR assays is proposed as a rapid and sensitive technique for the detection of mycobacterial DNA in formalin-fixed and paraffin-embedded tissue.