VALUE OF THE POLYMERASE-CHAIN-REACTION (P CR) FOR DIAGNOSING TUBERCULOUS MENINGITIS

The prognosis of tuberculous meningitis (TBM) depends on early therapy based on rapid diagnosis.To study the clinical value of PCR in diagno sis of TBM, we investigated CSF specimens from 49 patients. After cell lysis and DMA preparation following a standard protocol,we performed a half-nested PCR with primers able to detect mycobacterial DNA. PCR r esults were evaluated according to clinical features, histopathologica l data, and bacteriological results. PCR detected four of five cases o f confirmed TBM, corresponding to a sensitivity of 80%. Positive PCRs were also obtained in 25% CSF samples of non-TBM patients. Most of the se false positive results were due to amplification of Mycobacteria fo rtuitum (M. fortuitum) as determined by direct sequencing analysis.ro enhance specificity of our half nested protocol,the oligonucleotide pr imers that were specific for several mycobacterial subspecies were sub stituted by a primerpair,which allows selective amplification of DNA f rom Mycobacteria tuberculosis (M.tuberculosis).By using the altered PC R protocol, the screening of CSF samples revealed a much higher specif icity (97%) and constant sensitivity (80%) in diagnosis of TBM.These f indings indicate, that Nl.fortuitum,as an ubiquitous mycobacterial sub type of low pathogenicity, can potentially contaminate clinical specim ens and account for false positive PCR results.Therefore, the clinical value of PCR in diagnosis of TBM strongly depends on appropriate olig onucleotide primers, that allow to differentiate between mycobacterial subtypes.