Diagnosis of Tuberculous Cervical Lymphadenitis with Fine Needle Aspiration Cytology and Nested Polymerase Chain Reaction

Kim, Kyung Rae; Lee, Ki Seog; Cho, Young Up

Abstract

BACKGROUND: Molecular methods have rapidly replaced the classic diagnostic procedures of tuberculosis. Especially, the nested polymerase chain reaction (nPCR) is widely used for the diagnosis of tuberculosis in various specimens. In our previous publication, we suggested the availability of nPCR in specimens of solid tissues and in fine needle aspirates for the diagnosis of tuberculous cervical lymphadenitis (TCL), but nPCR has the possibility of false positive due to its repetitive amplification and contamination. Also, nPCR shows variable sensitivity and specificity, depending on the kind of target sequence and the probe used. We intended to improve the diagnostic efficacy of nPCR by the means of combination with the result of fine needle aspiration cytology (FNAC). And we applied restriction fragment length polymorphism (RFLP) to the amplicon of nPCR to rule out false positives.
METHODS
Thirty five specimens of aspirates from enlarged cervical lymph nodes of suspected TCL cases were examined by cytological examination and nPCR. Fifteen amplicons from nPCR were analyzed by RFLP. The sensitivity and the specificity were calculated in each nPCR and FNAC. The sensitivity and the specificity based on the result from combining nPCR and FNAC were also calculated. The results of RFLP were compared with the results of the corresponding nPCR.
RESULTS
Twenty patients were definitely diagnosed as having tuberculosis based on the result of FNAC, nPCR, and tissue pathology. The sensitivity of FNAC was calculated to be 0.8, and the specificity was 0.92. The sensitivity of nPCR was calculated to be 0.76 and the specificity was 1.0. When we analyzed the patients infected with tuberculosis who had had positive results in FNAC or nPCR, the results showed a sensitivity of 0.95 and a specificity of 0.92. There were no different RFLP fragmentation patterns between the individual amplicons of the same nPCR results.
CONCLUSIONS
The result of combining FNAC and nPCR offered good sensitivity and specificity in the diagnosis of TCL. It is suggested that anti-tuberculosis medication be immediately started when the result of FNAC or nPCR reveals a positive reaction. RFLP did not show any diagnostic value in our series, but it could be a great help in differential diagnosis of another strain of M. tuberculosis or atypical mycobacterium in treatment-resistant cases of TCL.