Abstract :
Background & Objectives: Tuberculous meningitis is a common infection of the CNS, posing significant
diagnostic and management challenges. Death in TBM patients is strongly associated with delay in
diagnosis and treatment. Since, any single conventional or automated method for diagnosis of TBM has
limited sensitivity; the main objectives of this study was – 1. Detect TBM by a combination of Direct
Microscopy by ZN Staining, Culture by solid (LJ) and liquid media (BacT/Alert), besides GeneXpert (RTPCR)
in clinically suspected cases.; 2. Evaluate the role of GeneXpert for detection of Mycobacterium
tuberculosis in CSF and demonstrate the sensitivity, specificity, PPV and NPV of GeneXpert in comparison
with a set composite reference standard.
Materials and Methods: This was a prospective cross-sectional study carried out by the Department of
Microbiology, GMC, Srinagar, from August ’17 to September ’19 CSF samples of 450 patients suspected
of TBM were included in the study. CSF volume
was devised which comprised of culture, ZN staining and empirical diagnosis. The samples were tested by
ZN staining, solid culture, liquid culture and GeneXpert MTB/RIF using proper protocols. Patient details
were obtained on a preformed proforma.
Results: Of the 450 suspected patients, 10% had Definitive TBM. The median age was 35 years with an
almost equal male to female ratio. The sensitivities of ZN staining, Solid culture, liquid culture and Gene
Xpert were 3%, 38%, 76% and 63% respectively. The specificity was 100% for all these tests, 95% CI being,
99-100%. The NPV was 84.02%, 100%, 91% and 93.6% whereas, the PPV was 84.89%, 100%, 100% and
99.1% respectively. Rifampicin resistance was positive in 2%. 95% cases had a very low bacillary load and
2.2% patients showed low and medium bacillary load. 12% patients had concomitant pulmonary TB and
10% with other forms of extrapulmonary TB.
Conclusion: Gene/Xpert as a frontline diagnostic tool, is a game changer. It abridges presumptive
prescribing of tuberculosis treatment. Speedy detection of TBM especially in smear negative cases and
detection of drug resistance in the paucibacillary CSF improves outcome for patients with TBM /MDR
TBM. However, additional tests, with better sensitivity are required and we must make the best use of the
tests we have by testing adequate volumes (5 -10ml) of CSF.
Keyword :
Acid fast bacilli, CB-NAAT, GeneXpert, Tuberculous meningitis.