Relative Value of Immunohistochemistry in Detection of Mycobacterial Antigen in Suspected Cases of Tuberculosis in Tissue Section.

OBJECTIVE: Due to its infectious nature, complex immunological response, chronic progression, and the necessity for long-term treatment, tuberculosis has always been a major health burden. Immunohistochemistry (IHC) has the capacity to highlight the occurrence of mycobacterial antigens for tissue diagnosis. This study was conducted to understand the advantage of immunostaining over culture of Mycobacterium tuberculosis.

MATERIAL AND METHODS: A cross-sectional study was conducted on 30 samples of suspected cases of tuberculosis. Specimens received were fixed in 10% formalin and processed; 3-5 µm thick sections were made from paraffin block, stained with hematoxylin and eosin, Ziehl-Neelsen stain, and immunohistochemistry. Culture was done using Lowenstein-Jensen medium. Immunohistochemistry was interpreted as fine granular brownish cytoplasmic, coarse granular brownish cytoplasmic, and bacillus staining.

RESULTS: Out of the 30 samples studied, 12 (40.0%) were culture positive while 20 (66.7%) of them were IHC positive. Immunohistochemistry showed 17 granulomatous lesions of which 11 (55.0%) were well-formed granulomas. The sensitivity and negative predictive value were found to be high with immunohistochemistry, while specificity and positive predictive value were found to be on the lower side. Among the 20 positive IHC cases, the degree of staining was fine granular cytoplasmic staining in 13 cases (65.0%) and coarse granular staining in 7 cases (35.0%).

CONCLUSION: Immunohistochemistry is a reliable test with high sensitivity as well as high negative predictive value which can be done rapidly for establishing an etiological diagnosis of tuberculosis in histologic specimens.