Efficacy of an in-house polymerase chain reaction assay for rapid diagnosis of Mycobacterium tuberculosis in patients with tubercular lymphadenitis: Comparison with fine needle aspiration cytology and conventional techniques

Abstract

Tubercular lymphadenitis (TB-L) is the most common manifestation of extrapulmonary tuberculosis. Excisional biopsy with histopathological examination, Ziehl-Neelsen staining (ZNS) and culture and fine needle aspiration (FNA) cytology, although useful in the diagnosis of TB-L, cannot diagnose a substantial proportion of cases. We investigated the role of an in-house polymerase chain reaction (PCR) assay targeting the IS6110 gene from the FNA material in the diagnosis of the disease. The clinical profile of 150 patients with lymphadenopathy was noted and the fine needle aspirate was collected. After cytological processing, ZNS and culture on Lowenstein-Jensen media, mycobacterial DNA was isolated from the residual aspirate material and IS6110 gene PCR was performed. Results of cytology, ZNS, culture and IS6110 gene PCR were compared. There were 49 confirmed patients of TB-L based on laboratory parameters (either culture isolation of Mycobacterium tuberculosis or any two of cytology, ZNS, PCR positive) and clinical response to therapy. Sensitivity and specificity of FNA was 89.8% and 96%, of ZNS was 40.8% and 99%, of culture was 40.8% and 100% and of IS6110 gene PCR test was 100% and 92.1%. IS6110 PCR can be considered a valuable adjunct to cytology, ZNS and culture techniques in the diagnosis of TB-L.