M. tuberculosis bacilli in oral biopsies containing granulomatous inflammation with caseous necrosis

<title>Abstract</title> <bold>Objectives</bold> This study aimed to investigate the presence of the <italic>Mycobacterium tuberculosis</italic> bacillus in formalin-fixed paraffin-embedded (FFPE) oral samples that contained granulomas with caseous necrosis. <bold>Materials and Methods </bold>FFPE biopsies that showed granulomas with caseous necrosis, suggestive of the diagnosis of tuberculosis, were selected. <italic>M. tuberculosis</italic> was searched by Ziehl-Neelsen staining (ZN), immunohistochemistry (IHC), nested-PCR, and GeneXpert® MTB/RIF assays. <bold>Results</bold> Nine samples showing granulomas with caseous necrosis were selected. There was a predominance of males (2.5:1), with a mean age of 50 (19-89) years, and the tongue was the most affected anatomical site (n=4). The bacillus was not identified by the ZN technique in any sample, and IHC staining showed a coarse granular pattern staining, suggestive of <italic>M. tuberculosis</italic>, in three of them. Nested-PCR and the GeneXpert® MTB/RIF assays were positive in two and three of the samples, respectively. <bold>Conclusions</bold> Molecular tests and IHC may be useful auxiliary methods for suspected cases of tuberculosis. <bold>Clinical Relevance </bold>This study provides information on the utilization and efficacy of diagnostic methods necessary to aid pathologists in accurately diagnosing oral TB lesions.