From the Guidelines
To diagnose TB meningitis, you should perform a lumbar puncture to collect cerebrospinal fluid (CSF) for analysis, which is the gold standard diagnostic approach, as recommended by recent guidelines 1. The CSF typically shows lymphocytic pleocytosis (100-500 cells/μL), elevated protein (100-500 mg/dL), and low glucose (usually less than 45 mg/dL or CSF:serum glucose ratio <0.5) 1. Some key points to consider when diagnosing TB meningitis include:
- Request specific TB testing on the CSF including acid-fast bacilli (AFB) smear, TB culture, and nucleic acid amplification tests like GeneXpert MTB/RIF.
- Supporting tests include tuberculin skin test or interferon-gamma release assays (IGRAs) like QuantiFERON-TB Gold, though these only indicate TB exposure, not necessarily active disease.
- Brain imaging with MRI is preferred over CT and may show basal meningeal enhancement, hydrocephalus, tuberculomas, or infarcts.
- A thorough history focusing on TB exposure, risk factors, and symptoms like persistent headache, fever, neck stiffness, and altered mental status is essential.
- The diagnosis is often presumptive based on clinical presentation, CSF findings, and epidemiological factors, as microbiological confirmation can take weeks or have low sensitivity.
- Treatment should not be delayed if TB meningitis is strongly suspected, as early intervention significantly improves outcomes in this potentially fatal condition, and high-dose corticosteroids and tuberculosis treatment should be initiated immediately at diagnosis, with ART initiation recommended when tuberculous meningitis is under control, based on clinical improvement and changes toward normal in CSF parameters, within 2 to 4 weeks thereafter 1.
From the Research
Diagnostic Approaches for TB Meningitis
To diagnose TB meningitis, several approaches can be considered, including:
- Cerebrospinal fluid (CSF) analysis, which is the basis for diagnosis and follow-up of tuberculous meningitis 2
- CSF cell counts, glucose, and protein assays 3
- Staining and culturing of CSF for Mycobacterium tuberculosis 3
- Polymerase chain reaction (PCR) assays for M. tuberculosis DNA sequences in CSF 3, 4, 5
- Interferon-gamma release assays and biomarkers in CSF 6
Laboratory Parameters
Laboratory parameters that can aid in the diagnosis of TB meningitis include:
- High protein content in CSF 2, 3
- Low glucose level in CSF 2, 3
- Elevated CSF cell count with a high percentage of lymphocytes 2, 3
- Presence of M. tuberculosis in CSF, confirmed by culture or PCR 2, 3, 4, 5
Diagnostic Challenges
Despite these approaches, diagnosing TB meningitis remains challenging due to: