Tuberculous Meningitis (TBM)

Definition

Tuberculous meningitis (TBM) is the most severe form of central nervous system tuberculosis, caused by dissemination of Mycobacterium tuberculosis to the meninges and brain parenchyma

Pathogenesis 

 Key Steps:

  1. Primary infection → hematogenous spread → formation of Rich foci (subpial/subependymal granulomas)
  2. Rupture of Rich focus into subarachnoid space
  3. → Thick gelatinous exudate accumulates at brain base (interpeduncular fossa)
  4. → Complications cascade:
    • Cranial nerve palsies (III, VI)
    • Obliterative vasculitis → infarcts (MCA territory common)
    • CSF flow obstruction → hydrocephalus

 Pathology

  • Dense basal meningeal exudates
  • Granulomas with caseation
  • Endarteritis obliterans → ischemic strokes
  • Ependymitis → hydrocephalus

Clinical Features (Subacute Course — Hallmark)

Typical progression (2–6 weeks)

 CLASSICAL STAGING (MRC Staging – VERY HIGH-YIELD)

Stage

Clinical Features

Stage I (Early / Prodromal)

Mild fever, malaise, headache, personality changes; no focal deficits

Stage II (Meningitic phase)

Meningeal signs + altered sensorium + cranial nerve palsies

Stage III (Advanced)

Coma, severe neurologic deficits, decerebrate rigidity, poor prognosis

1. PRODROMAL PHASE (1–3 WEEKS)

  • Insidious onset
  • Low-grade fever (often evening rise)
  • Persistent headache (progressively worsening)
  • Malaise, fatigue, anorexia, weight loss
  • Behavioral/personality changes (early clue)
  • Irritability (common in children)

 2. MENINGEAL PHASE

A. MENINGEAL IRRITATION SIGNS

  • Neck stiffness
  • Positive Kernig’s sign
  • Positive Brudzinski’s sign
  • Photophobia, vomiting

 May be less prominent than in pyogenic meningitis

B. ALTERED MENTAL STATUS

  • Confusion → drowsiness → stupor → coma
  • Memory impairment
  • Disorientation

 Due to:

  • Cerebral edema
  • Hydrocephalus
  • Vasculitic infarcts

C. CRANIAL NERVE PALSY 

 Mechanism: Basal exudates compress nerves

Nerve

Clinical Feature

II

Visual loss (optic neuritis / papilledema)

III

Ptosis, diplopia

IV

Vertical diplopia

VI (most common)

Lateral rectus palsy → diplopia

VII

Facial weakness

 6th nerve palsy = most common cranial nerve involvement

 3. FOCAL NEUROLOGICAL DEFICITS

 Mechanism: TB vasculitis → infarction (especially basal ganglia,Internal capsule)

  • Hemiparesis / hemiplegia
  • Aphasia
  • Movement disorders (rare)

 4. SIGNS OF RAISED ICP

  • Persistent vomiting
  • Headache (worse in morning)
  • Papilledema
  • Altered consciousness
  • 6th nerve palsy (false localizing sign)

 Causes:

  • Communicating hydrocephalus
  • Exudate obstruction
  • Cerebral edema

 5. HYDROCEPHALUS FEATURES

Very common in TBM (especially children)

  • Increasing head size (infants)
  • Bradycardia, hypertension (late)
  • Declining GCS


 6. SEIZURES

  • Focal or generalized
  • More common in children

 Causes:

  • Cortical irritation
  • Tuberculomas
  • Infarcts

7. SYSTEMIC FEATURES 

  • Weight loss
  • Night sweats
  • Chronic cough (pulmonary TB)
  • Lymphadenopathy

 Always look for extra-CNS TB focus


 8. SPECIAL PRESENTATIONS

A. TBM in Children

  • Irritability, refusal to feed
  • Bulging fontanelle
  • Seizures more common

B. TBM in HIV (VERY IMPORTANT)

  • Atypical presentation
  • Less meningeal signs
  • More rapid progression
  • Higher risk of:
    • Tuberculomas
    • Stroke

 9. COMPLICATION-RELATED FEATURES

A. Vasculitis → Stroke

  • Sudden focal deficit
  • Common in lenticulostriate territory

B. Tuberculoma

  • Focal seizures
  • Mass effect

C. Spinal Arachnoiditis

  • Paraparesis
  • Bladder involvement

 10. RED FLAG CLINICAL TRIAD 

 Subacute fever + headache + altered sensorium ± cranial nerve palsy

 11. DIFFERENTIATING FROM PYOGENIC MENINGITIS

Feature

TB Meningitis

Pyogenic Meningitis

Onset

Subacute (weeks)

Acute (hours–days)

Fever

Low-grade

High-grade

Cranial nerve palsy

Common

Rare

Focal deficits

Common

Less common early

Course

Progressive

Rapid

Diagnosis

1️⃣ CSF Analysis (first check contraindication of lumbar puncture)

Parameter

Typical TBM Finding

Opening pressure

↑

Cells

50–500 cells/mm³ (lymphocytic)

Protein

↑↑ (100–500 mg/dL)

Glucose

↓ (<40 mg/dL or CSF:serum <0.5)

Chloride

↓ (classical but not reliable)


 2. MICROBIOLOGICAL CONFIRMATION 

 AFB SMEAR (Ziehl-Neelsen stain)

  • Sensitivity: 10–20% (very low)
  • Requires large CSF volume (≥10 mL)

 Negative smear does NOT rule out TBM


 CSF CULTURE (MGIT / Lowenstein-Jensen)

  • Gold standard for confirmation
  • Sensitivity: 40–80%
  • Time:
    • MGIT: 1–3 weeks
    • LJ: 4–8 weeks

 Also allows drug susceptibility testing (DST)


 NUCLEIC ACID AMPLIFICATION TEST (NAAT)

✔ Xpert MTB/RIF

  • Detects:
    • MTB DNA
    • Rifampicin resistance

Feature

Value

Sensitivity

~60–80%

Specificity

~95–98%

Turnaround

~2 hours


✔ Xpert MTB/RIF Ultra (preferred)

  • Higher sensitivity (especially paucibacillary TBM)
  • Recommended by WHO


✔ PCR for TB

  • Variable sensitivity
  • Not standardized globally


 CSF ADA (Adenosine Deaminase)

  • Cutoff: >10 U/L suggests TBM
  • Sensitivity moderate, specificity limited

 Use as supportive, NOT diagnostic


 3. NEUROIMAGING 

CT Brain (contrast-enhanced)

Findings:

  • Basal meningeal enhancement (hallmark)
  • Hydrocephalus (communicating)
  • Infarcts (basal ganglia, MCA territory)
  • Tuberculomas (ring-enhancing lesions)


 MRI Brain (preferred modality)

Superior for:

  • Early meningeal inflammation
  • Brainstem involvement
  • Small infarcts
  • Cranial nerve enhancement


 Classic Radiological Triad 

  1. Basal meningeal enhancement
  2. Hydrocephalus
  3. Infarcts

 4. SYSTEMIC TB WORKUP(MANDATORY)

 Chest Imaging

  • Chest X-ray:
    • Active TB (~50%)
    • Miliary TB (important clue)
  • HRCT chest:
    • More sensitive

 Microbiology from Other Sites

  • Sputum AFB / culture
  • Gastric aspirate
  • Bronchoalveolar lavage

 Helps confirm disseminated TB


 5. BLOOD INVESTIGATIONS

Test

Finding

CBC

Anemia, lymphocytosis

ESR

Elevated

CRP

Mild-moderate ↑

LFT

Baseline before ATT

RFT

Baseline

HIV test

Mandatory

 HIV infection strongly associated with TBM


 6. IMMUNOLOGICAL TESTS (LIMITED ROLE)

 Mantoux Test (TST)

  • May be positive
  • False negative in:
    • Severe TB
    • HIV

 Interferon Gamma Release Assays (IGRA)

  • QuantiFERON-TB Gold
  • Indicates exposure, NOT active TB

 Not useful for diagnosing TBM


 7. WHEN NOT TO DO LUMBAR PUNCTURE 

Contraindications:

  • Raised ICP with focal deficits
  • Papilledema
  • Large mass lesion

Always do CT/MRI before LP in these cases


 8. DIAGNOSTIC CRITERIA 

 Uniform Case Definition (Marais Criteria)

Categories:

Category

Criteria

Definite TBM

CSF microbiological confirmation

Probable TBM

Score-based (clinical + CSF + imaging)

Possible TBM

Lower score

 Differential Diagnosis

  • Bacterial meningitis (acute, neutrophilic)
  • Viral meningitis (normal glucose)
  • Fungal meningitis (e.g., Cryptococcus neoformans)
  • Carcinomatous meningitis

Management 

1. PRINCIPLES OF THERAPY

  • Medical emergency → start empiric ATT immediately (do NOT wait for microbiological confirmation)
  • Prolonged therapy required due to:
    • Poor CSF drug penetration
    • High bacillary load
    • Risk of relapse
  • Always combine:
    • Antitubercular therapy (ATT)
    • Adjunctive corticosteroids
    • Management of complications (ICP, seizures, hyponatremia)

2. FIRST-LINE ANTITUBERCULAR THERAPY (DRUG-SENSITIVE TBM)

 Standard WHO/ATS Regimen

➤ Intensive Phase (2 months)

  • Isoniazid (H)
  • Rifampicin (R)
  • Pyrazinamide (Z)
  • Ethambutol (E)

➤ Continuation Phase (7–10 months)

  • Isoniazid + Rifampicin

 Total duration:
✔️ 9–12 months (preferred in TBM)
✔️ Many guidelines recommend 12 months for CNS TB


3. PHARMACOLOGY

PHARMACOLOGY

ADVERSE EFFECTS 

ISONIAZID (H)

Dose: 5 mg/kg/day (max 300 mg) (up to 10 mg/kg in severe TBM)

CSF:  Excellent (90–100%), unaffected by inflammation 


Mechanism: Prodrug (KatG) → inhibits InhA → ↓ mycolic acid → bactericidal 


Clinical role: Most important drug; highest early bactericidal activity; acts intra + extracellular; key for CSF sterilization 

Interactions: CYP inhibitor (less than rifampicin)

Hepatotoxicity (most important): ↑ risk with age, alcohol, liver disease 

Peripheral neuropathy: due to B6 deficiency → prevent with pyridoxine 25–50 mg/day (mandatory in ICU, pregnancy, DM, HIV) 


CNS toxicity: seizures, encephalopathy (overdose) 

Others: drug-induced lupus, rash, fever 

Monitoring: LFT baseline + periodic; neurological symptoms


RIFAMPICIN (R)

Dose: 10 mg/kg/day (max 600 mg) (15–20 mg/kg may improve survival)

CSF: Moderate (10–20%), ↑ with inflammation 


Mechanism: Inhibits DNA-dependent RNA polymerase → bactericidal 

Clinical role: Sterilizing activity; prevents relapse; shortens therapy 


Interactions (VERY IMPORTANT): Potent CYP450 inducer → ↓ antiepileptics, ART, steroids 

ICU note: Alters sedatives/analgesics

Hepatotoxicity: additive with INH + PZA 


Orange discoloration: urine, tears, sweat (benign) 


Flu-like syndrome: intermittent dosing 

Hematologic: thrombocytopenia, hemolysis (rare) 

Renal: interstitial nephritis (rare) 

Monitoring: LFT, CBC (if prolonged), mandatory interaction review

PYRAZINAMIDE (Z)

Dose: 20–25 mg/kg/day 

CSF:  Excellent (≈ plasma levels) 


Mechanism: → pyrazinoic acid → disrupts membrane energetics; inhibits fatty acid synthesis → bactericidal in acidic pH 


Clinical role: Active in acidic intracellular sites (macrophages, caseous necrosis); reduces bacterial load rapidly 

TBM advantage: effective in necrotic meningeal lesions

Hepatotoxicity (dose-related): most hepatotoxic drug 

Hyperuricemia: ↓ uric acid excretion → gout risk 

Arthralgia: common 

GI: nausea, vomiting 

Photosensitivity


Monitoring: LFT (very important), uric acid (if symptomatic)

ETHAMBUTOL (E)

Dose: 15–20 mg/kg/day 

CSF: Variable (better with inflammation) 


Mechanism: Inhibits arabinosyl transferase (EmbB) → ↓ arabinogalactan → bacteriostatic 


PK: Renal excretion → dose adjust in CKD 


Clinical role: Prevents resistance; companion drug in intensive phase 

Limitation: Less reliable CSF penetration vs INH/PZA

Optic neuritis (most important): ↓ visual acuity, central scotoma, red-green color loss (early) 

-Dose-related, reversible if early 

Peripheral neuropathy (rare)


Hyperuricemia (rare)

Monitoring (CRUCIAL): baseline visual acuity, color vision (Ishihara), monthly visual check 

-Stop drug immediately if symptoms occur

4. ALTERNATIVE 4TH DRUG (IMPORTANT ICU POINT)

 Some guidelines prefer replacing ethambutol with:

 STREPTOMYCIN

  • Better CSF penetration in inflamed meninges
  • Dose: 15 mg/kg IM

Limitation

  • Ototoxicity
  • Nephrotoxicity

5. ADJUNCTIVE CORTICOSTEROIDS 

 REGIMEN (Standard)

Dexamethasone IV(Duration: 1–2 weeks)

  • 0.3–0.4 mg/kg/day (usually divided q6–8h or continuous)
  • Switch to oral prednisolone with starting dose 1 mg/kg/day and gradual taper over next 4–6 weeks

 BENEFITS (EVIDENCE-BASED)

  • ↓ Mortality
  • ↓ Neurological sequelae
  • ↓ cerebral edema
  • ↓ vasculitis & infarcts

Mechanism

  • Reduces host inflammatory response → prevents brain damage

6. MANAGEMENT OF DRUG-RESISTANT TBM

Drug-Resistant TB Meningitis (DR-TBM): How do you know it’s resistant?

you prove it microbiologically whenever possible, but in TBM you often have to suspect it clinically and act early because delays are dangerous.

 1) MICROBIOLOGICAL CONFIRMATION (GOLD STANDARD APPROACH)

A. Rapid molecular tests (first line)

  • Xpert MTB/RIF (CBNAAT)
    • Detects Mycobacterium tuberculosis DNA + rifampicin resistance
    • Turnaround: ~2 hours
    • Works on CSF
    • Key point: Rifampicin resistance = surrogate marker of MDR-TB
  • Line Probe Assay (LPA)
    • Detects mutations:
      • rpoB → rifampicin resistance
      • katG/inhA → isoniazid resistance
    • Can be done on CSF (if bacillary load adequate)

B. Culture + Drug Susceptibility Testing (DST)

  • Liquid culture (MGIT) or solid media
  • Gives full resistance profile (H, R, FQ, second-line drugs)

 Limitation in TBM:

  • CSF is paucibacillary
  • Yield is low
  • Takes weeks

 Therefore: treatment decisions often precede confirmation

2) CLINICAL DIAGNOSIS (VERY IMPORTANT IN EXAMS & ICU)

You must suspect DR-TBM when expected response does not occur.

 A. Lack of clinical improvement

  • No improvement after 2–4 weeks of adequate ATT
  • Persistent:
    • Fever
    • Altered sensorium
    • Neurological deficits

 B. Clinical deterioration despite therapy

  • Worsening GCS
  • New focal deficits
  • New cranial nerve palsy
  • Seizures

 C. Radiological progression

  • Increasing hydrocephalus
  • New infarcts
  • Enlarging tuberculomas

 D. Persistent CSF abnormalities

  • Ongoing:
    • High protein
    • Low glucose
    • Pleocytosis

 DIFFERENTIAL: Don’t mislabel everything as resistance ,Before calling it DR-TBM, exclude:

 1. Paradoxical reaction (COMMON)

  • Clinical worsening after initial improvement
  • Due to immune response

 Management:

  • Continue same ATT
  • Increase steroids

 2. IRIS (in HIV)

  • After starting ART
  • Mimics treatment failure

 3. Poor compliance / malabsorption

  • Vomiting
  • Drug interactions (e.g., rifampicin ↓ drug levels)

 4. Inadequate regimen / dosing errors

  • Wrong dose
  • Missing drugs

 5. Complications

  • Hydrocephalus
  • Infarction
  • Raised ICP

 3) WHEN TO STRONGLY SUSPECT DR-TBM 

 Risk factors

  • Previous TB treatment (especially incomplete)
  • Known contact with MDR-TB
  • High TB burden areas (like India)
  • HIV co-infection
  • Treatment default history

 MDR-TB / RR-TB REGIMEN

Use second-line drugs with good CNS penetration:

Core drugs:

  • Fluoroquinolones (Levofloxacin, Moxifloxacin)
  • Linezolid
  • Cycloserine
  • Ethionamide
  • Bedaquiline (in selected cases)

 CSF PENETRATION 

Good penetration:

  • Isoniazid
  • Pyrazinamide
  • Linezolid
  • Cycloserine
  • Fluoroquinolones

Poor penetration:

  • Ethambutol
  • Aminoglycosides (except inflamed meninges)


Duration

  • ≥18–24 months


7. MANAGEMENT IN SPECIAL SITUATIONS

 HIV CO-INFECTION

  • Start ATT immediately
  • Start ART after:
    • 2–8 weeks (to reduce IRIS risk)

—IRIS (Immune Reconstitution Inflammatory Syndrome)

  • Paradoxical worsening after ART
  • Treatment:
    • Continue ATT
    • Add/increase steroids

— PREGNANCY

Safe:

  • Isoniazid
  • Rifampicin
  • Ethambutol

Avoid:

  • Streptomycin (ototoxic to fetus)

 CHILDREN

  • Same regimen (weight-based dosing)
  • Steroids strongly recommended

8. MONITORING DURING THERAPY

 Clinical

  • GCS, focal deficits
  • Signs of raised ICP

 Lab

  • LFTs (hepatotoxic drugs)
  • Renal function
  • Electrolytes

 Special

  • Vision (ethambutol)
  • Audiometry (streptomycin)

9. Management of Complications

 Raised ICP / Hydrocephalus

  • Mannitol / hypertonic saline
  • VP shunt / EVD if obstructive hydrocephalus

 Seizures

  • Antiepileptics (Levetiracetam preferred)

 Hyponatremia

  • Differentiate:
    • SIADH → fluid restriction
    • CSW → saline replacement

 Stroke (TB vasculitis)

  • Continue ATT + steroids
  • Role of antiplatelets individualized

Prognosis

Poor Prognostic Factors:

  • Stage III disease
  • Delayed treatment
  • HIV coinfection
  • Hydrocephalus
  • Infarcts

 Complications

  • Hydrocephalus
  • Cranial nerve palsies
  • Stroke (basal ganglia infarcts)
  • Cognitive impairment
  • Hearing loss