The importance of molecular diagnosis in extrapulmonary tuberculosis

Introduction: Extrapulmonary tuberculosis (EPTB) is a serious diagnostic problem, due to the fact that Ziehl-Neelsen (ZN) staining and culture are useful but cannot detect a large number of cases due to a paucity of bacilli on smears (paucibacillary). Objective: To determine the usefulness of the nested polymerase chain reaction (PCR) in diagnosing the disease. Material and methods: From September 2002 to February 2008, 469 patients with suspected EPTB were studied. The clinical profile of the patients was evaluated and the corresponding biological samples were obtained. After ZN staining and Lowenstein-Jensen (LJ) cultures were processed, mycobacterial DNA was isolated from specimens and the nested PCR was performed. Results of ZN, culture and PCR were compared. Results: There were 183 confirmed EPTB patients, based on laboratory parameters (either culture isolation of Mycobacterium tuberculosis and ZN or any two, positive PCR), imaging studies and clinical response to therapy. Conclusion: PCR can be considered a valuable adjunct to ZN, culture techniques, imaging studies and response to therapy in the diagnosis of EPTB.