A Study on the Utility of GeneXpert in Cerebrospinal Fluid in the Diagnosis of Tuberculous Meningitis

BACKGROUND
\nOne of the most common forms of central nervous tuberculosis is tubercular
\nmeningitis and has high morbidity and mortality. The natural course of TBM is subacute in nature; hence, the symptoms may persist for weeks before diagnosis. The
\ndiagnosis of tuberculosis is based on clinical presentation and cerebrospinal fluid
\nanalysis. GeneXpert is a reliable and rapid diagnostic modality for diagnosing
\npulmonary tuberculosis. Various studies have shown various sensitivity patterns of
\nGeneXpert in TBM. This study aims to find the utility of GeneXpert in TBM.
\nMETHODS
\nAll adult patients who presented with signs and symptoms of meningitis were
\nincluded in the study. Detailed history was recorded and physical examination
\ndone. All patients were subjected to routine blood investigations, chest X ray, brain
\nimaging along with lumbar puncture for cerebrospinal fluid (CSF) analysis. Apart
\nfrom routine CSF analysis for cell type, cell count, and biochemical analysis, 3-5
\nml of CSF was sent for GeneXpert to intermediate reference laboratory at
\nGovernment Hospital for Chest Diseases, Pondicherry. On the basis of clinical
\nhistory, examination, and investigations, composite gold standard for the diagnosis
\nof TBM was defined. The composite gold standard included definite case of TBM,
\nhighly probable case of TBM, probable case of TBM and definitely not TBM.
\nSensitivity and specificity were calculated for GeneXpert for the composite gold
\nstandard.
\nRESULTS
\n100 patients were included in the study. 64 were males and 36 were females. TBM
\nwas detected in 22 cases. Mean age for TBM was 42 ± 19.2 years. Among 22
\ncases of TBM, only one case was categorized as definite TBM, and the rest 21
\nwere either highly probable TBM (7) or probable TBM cases (14). Common clinical
\nsigns and symptoms on presentation were headache (87%), fever (78%), neck
\nrigidity (69%), seizure (52%) and altered sensorium (74%). GeneXpert and CSF
\nculture was positive in only one case with sensitivity of 14% and specificity of
\n100%. Adenosine deaminase (ADA) was high in 13 cases with sensitivity of 60%
\nand specificity of 100%.
\nCONCLUSIONS
\nThe utility of GeneXpert in diagnosing tubercular meningitis is very insignificant.
\nNegative GeneXpert in CSF analysis does not rule out TBM as sensitivity is 14%
\nbut positive GeneXpert has 100% specificity. In the absence of reliable diagnostic
\ntest, clinician should look for specific signs and symptoms of meningitis along with
\nroutine CSF analysis and CSF ADA level.
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