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

Author(s): Karthik Sundar1 , Nayyar Iqbal2 , Sudhagar Mookkappan3 , Sheela Devi4 , Aneesh Basheer

BACKGROUND One of the most common forms of central nervous tuberculosis is tubercular meningitis 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 diagnosis of tuberculosis is based on clinical presentation and cerebrospinal fluid analysis. GeneXpert is a reliable and rapid diagnostic modality for diagnosing pulmonary tuberculosis. Various studies have shown various sensitivity patterns of GeneXpert in TBM. This study aims to find the utility of GeneXpert in TBM. METHODS All adult patients who presented with signs and symptoms of meningitis were included in the study. Detailed history was recorded and physical examination done. All patients were subjected to routine blood investigations, chest X ray, brain imaging along with lumbar puncture for cerebrospinal fluid (CSF) analysis. Apart from routine CSF analysis for cell type, cell count, and biochemical analysis, 3-5 ml of CSF was sent for GeneXpert to intermediate reference laboratory at Government Hospital for Chest Diseases, Pondicherry. On the basis of clinical history, examination, and investigations, composite gold standard for the diagnosis of TBM was defined. The composite gold standard included definite case of TBM, highly probable case of TBM, probable case of TBM and definitely not TBM. Sensitivity and specificity were calculated for GeneXpert for the composite gold standard. RESULTS 100 patients were included in the study. 64 were males and 36 were females. TBM was detected in 22 cases. Mean age for TBM was 42 ± 19.2 years. Among 22 cases of TBM, only one case was categorized as definite TBM, and the rest 21 were either highly probable TBM (7) or probable TBM cases (14). Common clinical signs and symptoms on presentation were headache (87%), fever (78%), neck rigidity (69%), seizure (52%) and altered sensorium (74%). GeneXpert and CSF culture was positive in only one case with sensitivity of 14% and specificity of 100%. Adenosine deaminase (ADA) was high in 13 cases with sensitivity of 60% and specificity of 100%. CONCLUSIONS The utility of GeneXpert in diagnosing tubercular meningitis is very insignificant. Negative GeneXpert in CSF analysis does not rule out TBM as sensitivity is 14% but positive GeneXpert has 100% specificity. In the absence of reliable diagnostic test, clinician should look for specific signs and symptoms of meningitis along with routine CSF analysis and CSF ADA level.