Here is a complete clinical guide to suspected TBM.
Tuberculous Meningitis (TBM) - Complete Clinical Guide
1. Clinical Presentation
TBM characteristically has a subacute onset over 1-2 weeks - slower than typical bacterial meningitis. Key features:
Classical symptoms:
- Headache (>50% of cases), low-grade fever, malaise, anorexia for days to weeks
- Neck rigidity / meningism (75% of cases), Kernig's and Brudzinski's signs
- Lethargy, confusion, altered sensorium
Features that point specifically toward TBM:
- Cranial nerve palsies - especially ocular (CN III, IV, VI) due to basal exudate (20% of cases)
- Symptoms >5 days before presentation
- History of TB exposure or contact, prior TB, or immunocompromise (HIV)
- Evidence of TB elsewhere - pulmonary TB on CXR in ~2/3 of cases
- Systemic TB features: weight loss, night sweats, prolonged cough >2 weeks
Risk factors: HIV, malnutrition, diabetes, steroid use, young children, immigrants from high-burden countries.
2. Diagnosis
Uniform Case Scoring System (Marais Criteria)
Use this scoring system to classify TBM before confirmatory results:
| Category | Feature | Points |
|---|
| Clinical (max 6) | Symptom duration >5 days | 4 |
| Systemic TB symptoms (weight loss, night sweats, cough >2 wk) | 2 |
| TB contact / positive TST/IGRA (child <10 yr) | 2 |
| Focal neurological deficit (excluding CN palsy) | 1 |
| Cranial nerve palsy | 1 |
| Altered consciousness | 1 |
| CSF (max 4) | Clear appearance | 1 |
| Cells 10-500/μL | 1 |
| Lymphocyte predominance >50% | 1 |
| Protein >1 g/L | 1 |
| CSF:plasma glucose <50% or CSF glucose <2.2 mmol/L | 1 |
| Neuroimaging (max 6) | Hydrocephalus | 1 |
| Basal meningeal enhancement | 2 |
| Tuberculoma | 2 |
| Infarct | 1 |
| Pre-contrast basal hyperdensity (CT) | 2 |
| TB elsewhere (max 4) | CXR - active TB (non-miliary) | 2 |
| CXR - miliary TB | 4 |
| CT/MRI/US evidence of extracranial TB | 2 |
Classification:
- Definite TBM: AFB on CSF smear, positive CSF culture, or positive Xpert MTB/RIF + suggestive clinical features
- Probable TBM: Score ≥12 (if neuroimaging available) or ≥10 (if no neuroimaging). At least 2 points must come from CSF or imaging criteria
- Possible TBM: Score 6-11 (imaging available) or 6-9 (no imaging); alternative diagnosis not confirmed
CSF Analysis (Lumbar Puncture - cornerstone of diagnosis)
| Parameter | Typical TBM Finding |
|---|
| Opening pressure | Raised (often >200 mm H₂O) |
| Appearance | Clear / slightly turbid / xanthochromic |
| White cells | 10-1000/μL, lymphocyte predominance (early = neutrophils) |
| Protein | Elevated: 1-8 g/L (100-800 mg/dL) |
| Glucose | Low (<45 mg/dL); CSF:blood glucose <50% |
| AFB smear | Positive in only 10-40% (low sensitivity); do at least 3 samples |
| Culture | Gold standard - positive in up to 80%; takes 4-8 weeks |
| Xpert MTB/RIF | Sensitivity ~80%, specificity high - preferred first test |
| ADA (adenosine deaminase) | Elevated (>10 U/L supportive) |
Harrison's 22e: "AFBs are infrequently seen on direct smear of CSF sediment, but repeated lumbar punctures increase the yield. Culture is diagnostic in up to 80% and remains the gold standard. Xpert MTB/RIF has sensitivity up to 80% and is the preferred initial option. A negative result does NOT exclude TBM."
Important: Do NOT delay ATT for culture results. Treat empirically if clinical suspicion is high.
Neuroimaging
MRI with gadolinium is preferred over CT. Classic findings:
MRI in TBM: Gadolinium enhancement of the basal meninges (bright white areas at the base of brain), multiple abscesses, and hydrocephalus - from Adams & Victor's Principles of Neurology
- Basal meningeal enhancement (most characteristic)
- Hydrocephalus (communicating, due to obstruction of basal cisterns)
- Infarcts (from vasculitis of perforating arteries)
- Tuberculomas (ring-enhancing lesions)
Other Investigations
- CXR - look for pulmonary TB, miliary pattern
- Mantoux / TST - helpful if positive, but negative in immunocompromised
- IGRA (Interferon-gamma release assay) - QuantiFERON
- Sputum AFB / GeneXpert if pulmonary involvement suspected
- HIV serology - mandatory in all TBM cases
- Blood: CBC, LFT, RFT, electrolytes (hyponatremia from SIADH is common)
- Fundoscopy - papilledema, choroidal tubercles
3. Treatment
ATT Regimen
| Phase | Duration | Drugs | Notes |
|---|
| Intensive | 2 months | HRZE (INH + Rifampicin + Pyrazinamide + Ethambutol) | Four-drug regimen |
| Continuation | 7-10 months | HR (INH + Rifampicin) | Total duration 9-12 months for TBM |
Total duration: 9-12 months (longer than pulmonary TB due to CNS penetration issues)
Drug doses (adults):
- Isoniazid (H/INH): 5 mg/kg/day (max 300 mg) - best CNS penetration
- Rifampicin (R/RIF): 10 mg/kg/day (max 600 mg)
- Pyrazinamide (Z/PZA): 20-35 mg/kg/day
- Ethambutol (E/EMB): 15 mg/kg/day
Note: Ethambutol and ethionamide have poor CSF penetration once inflammation resolves. Fluoroquinolones (levofloxacin/moxifloxacin) have excellent CNS penetration and are useful in MDR-TBM as fourth drugs.
Add pyridoxine 50 mg/day with INH to prevent peripheral neuropathy.
Adjunctive Corticosteroids (MANDATORY)
Corticosteroids reduce mortality and should be given in all TBM patients (except special circumstances).
Dexamethasone regimen (WHO/guidelines):
| Weeks | Route | Dose |
|---|
| Week 1 | IV | 0.4 mg/kg/day |
| Week 2 | IV | 0.3 mg/kg/day |
| Week 3 | IV | 0.2 mg/kg/day |
| Week 4 | IV | 0.1 mg/kg/day |
| Weeks 5-6 | Oral | 4 mg/day, then taper by 1 mg/week |
Total steroid duration: 6-8 weeks with tapering.
Harrison's 22e: "Clinical trials demonstrated that patients given adjunctive glucocorticoids experience faster resolution of CSF abnormalities and elevated CSF pressure, resulting in lower rates of death or severe disability and relapse. Dexamethasone significantly enhanced survival among persons >14 years."
Note on HIV patients: A recent placebo-controlled trial showed no benefit from adjunctive dexamethasone in TBM patients with HIV - individualise this decision.
Alternatively, prednisolone 60 mg/day orally, tapered over 6-8 weeks, is acceptable.
4. Complications and Monitoring
Common Complications
| Complication | Mechanism | Management |
|---|
| Hydrocephalus | Basal exudate blocking CSF flow | Serial LPs; VP shunt or EVD if progressive |
| Stroke / Infarct | Vasculitis of perforating arteries | Supportive; optimise ATT |
| Hyponatremia | SIADH (very common) | Fluid restriction, hypertonic saline if severe |
| Seizures | Cortical irritation, infarct, TB | AEDs; levetiracetam or phenytoin |
| Cranial nerve palsies | Basal exudate | Usually improve with treatment |
| Raised ICP | Hydrocephalus | Mannitol, dexamethasone, LP, shunt |
| Arachnoiditis | Chronic inflammation | Steroids, hyaluronidase intrathecally in some cases |
Note on VP shunting: Required in up to 25% of cases with obstructive hydrocephalus. Shunt complications (infection, malfunction) occur in 20-40% of cases.
Monitoring During Treatment
- Serial LPs - monitor CSF cell count, protein, glucose response
- Serial neuroimaging (especially if tuberculoma present - may initially enlarge before resolving)
- LFTs monthly - INH and RIF are hepatotoxic; stop ATT if symptomatic hepatitis or ALT >3x ULN with symptoms
- Visual acuity and color vision - Ethambutol can cause optic neuropathy (check monthly)
- Serum sodium - watch for SIADH
- GCS / neurological status - daily in acute phase
- Uric acid - Pyrazinamide causes hyperuricemia
5. Prognosis
- Overall mortality: ~10-20% in treated cases; up to ~50% when treatment is delayed to the coma stage
- Neurological sequelae in 20-30% of survivors: cognitive impairment, seizures, hemiparesis, visual defects, deafness
- HIV co-infection worsens prognosis significantly (mortality ~21% or higher)
- Key message: Early diagnosis and immediate ATT initiation is the single most important determinant of outcome
Summary - Immediate Action in Suspected TBM
Suspected TBM
↓
1. Urgent CT/MRI head (rule out mass lesion before LP)
2. Lumbar puncture → CSF for: cells, protein, glucose, AFB smear, culture, Xpert MTB/RIF, ADA
3. CXR, HIV test, LFT, RFT, electrolytes, CBC
4. Start ATT IMMEDIATELY (do not wait for culture)
→ 2HRZE / 7-10HR
5. Add Dexamethasone (taper over 6-8 weeks)
6. Pyridoxine 50mg/day with INH
7. Monitor for hyponatremia, raised ICP, seizures
8. Neurosurgery consult if hydrocephalus develops
(Sources: Harrison's Principles of Internal Medicine 22e, Adams & Victor's Principles of Neurology 12e, Marais Uniform Case Definition Criteria, Index-TB Guidelines India, Medscape TBM Guidelines)