Relative value of immunohistochemistry in detection of mycobacterial antigen in suspected cases of tuberculosis in tissue sections.

Abstract

The diagnosis of tuberculosis (TB) depends on identification of the infecting organism. The diagnosis presents as a challenge due to its diverse clinical presentation and low yield of acid-fast bacilli (AFB) in tissue sections. The aim of the present study is immunohistochemical localization of tubercle bacilli or their components that persist in the granulomas, but have lost the property of staining with acid-fast stain, assess the advantage of immunostaining over conventional Ziehl-Neelsen (ZN) staining and further to study the staining pattern on immunohistochemistry (IHC). The study population comprised 100 suspected cases of TB. Tissue sections from these were subjected to hematoxylin and eosin, ZN and IHC staining using polyclonal antibody to Mycobacterium tuberculosis followed by a comparative analysis of the results. Cases of lepromatous leprosy were used as a positive control. Acid-fast bacilli were identified by ZN stain in 23% of cases. IHC identified 72% cases. In the present study, IHC had higher sensitivity (95.56%) and negative predictive value (96.43%), but lower specificity (35.06%) and positive predictive value (30.56%) than ZN stain which had the sensitivity, specificity, positive predictive value and negative predictive values of 30.56%, 96.43%, 95.65% and 41.56% respectively. Immunohistochemistry is a simple and sensitive technique for localization of tubercle bacilli and their components on tissue sections. It can be easily incorporated in routine histopathology laboratory and serve as an efficient diagnostic adjunct to conventional ZN staining. This will help reduce the practice of prescribing empirical antitubercular treatment based on clinical suspicion alone.