Background: Extra pulmonary tuberculosis (EPTB) constitutes 18% of all tuberculosis (TB) cases and tuberculous lymphadenitis (TBL) constitutes 20-40% of EPTB. Diagnosis of TBL is challenging because of the paucibacillary nature of the disease.
Objective: To investigate the diagnostic potential of a new antigen detection test based on the detection of M. tuberculosis complex specific antigen MPT64 from fine needle aspirate (FNA) cytology smears and biopsies obtained from patients with clinically suspected TBL using immunohistochemistry (IHC).
Materials and methods: This study was conducted at Khyber Teaching Hospital and Rehman Medical Institute, Peshawar, Pakistan, from January 2018 to April 2019. Samples, including FNA (n = 100) and biopsies (n = 8), were collected from 100 patients with presumptive TBL. Direct smears and cell blocks were prepared from the FNA samples. All samples were subjected to hematoxylin-eosin (H&E) staining, Ziehl-Neelsen (ZN) staining, and immunostaining with polyclonal anti-MPT64 antibody. The culture was performed only for biopsy specimens. All patients were followed until the completion of anti-TB treatment. The response to treatment was included in the composite reference standard (CRS) and used as the gold standard to validate the diagnostic tests.
Results: The sensitivity, specificity, positive and negative predictive values for ZN staining were 4.4%,100%,100%,56%, for culture were 66%,100%,100%,50%, for cytomorphology were 100%,90.91%,90%,100%, and for immunostaining with anti-MPT64 were all 100%,respectively. The morphology and performance of immunohistochemistry were better with cell blocks than with smears.
Conclusion: MPT64 antigen detection test performed better than ZN and cytomorphology in diagnosing TBL. This test applied to cell blocks from FNA is robust, simple, and relatively rapid, and improves the diagnosis of TBL.