Cytomorphological patterns of M. bovis BCG and M. tuberculosis on fine needle aspiration biopsies: does HIV make a difference?

To determine if fine needle aspiration (FNAB) of mycobacterial lymphadenopathy can differentiate infection with M. bovis BCG (BCG) from M. tuberculosis (TB) and whether HIV status affects discriminatory cytological features. A retrospective study of culture positive, fine needle aspiration biopsies of lymph nodes in children (<13 years) between 2003 and 2008. A total of 77 aspirates were available for evaluation with 67 (87%) patients having known HIV status. BCG occurred at a younger age (6 months), predominantly axillary lymph nodes (90%) compared with TB (5 years and 20% axillary lymph nodes). Amorphous necrosis was only seen in aspirates from TB lymph nodes, while in HIV negative children with TB, foamy macrophages were absent. On ZN staining there were more organisms in the BCG group and in HIV positive patients the organisms were present in both extra- and intracellular locations, whereas in the HIV negative patients the organisms were predominantly extracellular in location. Demographic and cytomorphologic features that can assist in distinguishing between the two mycobacterial species include: age of patient, location of the lymph node, and presence/absence of amorphous necrosis and foamy macrophages on FNAB. However the only reliable method to identify the mycobacterial species is by mycobacterial culture and/or PCR.