Immunohistochemistry using a Mycobacterium tuberculosis complex specific antibody for improved diagnosis of tuberculous lymphadenitis

The clinical and histological criteria used to diagnose lymphadenitis caused by Mycobacterium tuberculosis complex organisms have poor specificity. Acid-fast staining and culture has low sensitivity and specificity. We report a novel method for diagnosis of tuberculosis that uses immunohistochemistry to detect the secreted mycobacterial antigen MPT64 on formalin-fixed tissue biopsies. This antigen has not been detected in non-tuberculous mycobacteria. Polymerase chain reaction (PCR) for amplification of IS6110 from DNA obtained from the biopsies was used as a gold standard. Fifty-five cases of granulomatous lymphadenitis with histologically suspected tuberculosis obtained from Norway and Tanzania were evaluated. Four known tuberculosis cases were used as positive controls, and 16 biopsies (12 foreign body granulomas and four other non-granulomatous cases) as negative controls. With immunohistochemistry, 64% (35/55) and with PCR, 60% (33/55) of granulomatous lymphadenitis cases were positive. Using PCR as the gold standard, the classical tuberculosis histology had sensitivity, specificity, positive and negative predictive values of 92, 37, 60, and 81%, respectively, and immunohistochemistry had sensitivity, specificity, positive and negative predictive values of 90, 83, 86, and 88%, respectively. The observed agreement between PCR and immunohistochemistry was 87% (kappa = 0.73). Immunohistochemistry with anti-MPT64 antiserum is a rapid, sensitive, and specific method for establishing an etiological diagnosis of tuberculosis in histologic specimens. Immunohistochemistry has the advantages over PCR of being robust and cheap, and it can easily be used in a routine laboratory.