DETECTION OF MYCOBACTERIA WITH USE OF IMMUNOHISTOCHEMISTRY IN GRANULOMATOUS LESIONS STAINING NEGATIVE WITH ROUTINE ACID-FAST STAINS

Mycobacterial infections carry considerable morbidity and mortality in both immunocompetent and immunodeficient patients, making it extremel y important to detect mycobacteria in tissue sections whenever possibl e. This study sought to determine whether immunoperoxidase techniques could detect mycobacteria missed by routine acid-fast stains. Formalin -fixed paraffin-embedded histology sections with granulomatous lesions from 42 patients, staining negative with acid-fast stains, were immun ostained with bacille Calmette-Guerin (BCG) antibody by using immunope roxidase technique. Sixteen of the 42 cases were classified as typical mycobacterial epithelioid granulomas with caseous necrosis, and the r emaining 26 as atypical. Six (14.3%) of the 42 had positive immunoreac tivity for mycobacterial cells, cell fragments, and debris with anti-B CG. Of these five cases, three had culture-proven mycobacterial infect ion. Only two of the six were considered to be typical granulomas, wit h no significant correlation between the immunoperoxidase stain and mo rphologically typical granulomas. Anti-BCG immunoperoxidase is an impo rtant complementary test to standard acid-fast stains, which occasiona lly miss the organisms not suspected morphologically. Immunoperoxidase stains detect organisms faster than cultures, are easier to read, and detect mycobacterial cell fragments with damaged capsular integrity m issed by routine acid-fast stains.