Evaluation of polymerase chain reaction for rapid diagnosis of clinically suspected tuberculous meningitis

Setting: Since conventional bacteriological methods rarely detect Mycobacterium tuberculosis in cerebrospinal fluid (CSF) and are of limited use in the diagnosis of tuberculous meningitis (TBM), clinical features suggestive of TBM supported by indirect evidence such as CSF examination and computerized tomography (CT) of the head have been used for the early diagnosis of TBM. Objective: We evaluated the efficacy of polymerase chain reaction (PCR) in the diagnosis of TBM. Methods: Coded CSF samples from 40 patients with TBM and from 49 patients with other neurological disorders were processed. In the absence of a reliable sensitive and specific test for M. tuberculosis in CSF, we used a set of established clinical criteria as the gold standard. Accordingly, the patients were divided into definite, highly probable, probable and possible TBM. The samples were decoded only after completion of the laboratory tests. Results: PCR was positive in 2/4, 19/20, 13/16 patients with highly probable, probable and possible TBM respectively. None of the samples were positive by conventional bacteriological methods. However, 3/49 CSF samples from non-TBM patients were also found positive by PCR. PCR detected M tuberculosis genomic DNA in the CSF of 85% of clinically suspected TBM cases and 6.1% of non-tuberculous controls. Conclusion: PCR, along with the suggested clinical criteria, offers a rapid and fairly accurate diagnosis of TBM.