Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand Correspondence: Yaovalux Chamgramol, Ph.D.
Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, 40002, Thailand.
Tel. +66-043-363691, Fax. +66-043-348388,
Background: Tuberculosis is a treatable disease, but remains a major cause of mortality. Culture for Mycobacterium is needed to make a definitive diagnosis; thus, loop-mediated isothermal amplification (LAMP) was attempted for its detection in formalin-fixed, paraffin-embedded (FFPE) samples. Materials and method: Archival FFPE blocks were used from 64 patients with a clinical diagnosis of tuberculous lymphadenitis from Srinagarind Hospital, Khon Kaen University, between 2007 and 2011. The
clinical data, routine surgical pathologic examination, AFB stain, culture of Mycobacterium were researched retrospectively. Six primers were used to target the M. tuberculosis 16S rRNA gene for specific amplification and hydroxy naphthol blue (HNB) to detect the LAMP products.
Results: Seven of 23 (30%) samples of tuberculous lymphadenitis (culture positive for M. tuberculosis) were LAMP positive while all respective 23 and 21 cases of reactive hyperplasia lymph node (culture negative for Mycobacterium) and non-tuberculous lymphadenitis (culture positive for others Mycobacterium, excluding M. tuberculosis) were LAMP negative. Compared to culture, the sensitivity of LAMP in detecting M.tuberculosis in FFPE lymph node was 30.4%, specificity 100%, positive predictive value 100%, and negative predictive value 71.9%.
Conclusion: LAMP for diagnosis of tuberculous lymphadenitis in FFPE lymph nodes has limitations because of the degradation of M. tuberculosis DNA in paraffin-embedded samples. Its simplicity, quick-application, high specificity and low cost make it an alternative in fresh clinical samples. Further studies on fresh lymph nodes are warranted.