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Tuberculous Meningitis (TBM) — Comprehensive Review

1. CAUSE & EPIDEMIOLOGY

• TBM accounts for ~5% of all extrapulmonary TB cases
• In the U.S., incidence declined steadily until ~1985, when a 16% annual increase occurred — driven largely by HIV (tuberculosis may be the first clinical manifestation of HIV; among patients with full-blown AIDS, the incidence is nearly 500 times that of the general population)
• In developing countries (especially sub-Saharan Africa), TB is ~25 times more frequent than in the U.S., again largely due to HIV prevalence
• In more than half of TBM cases, evidence of old pulmonary lesions or a miliary pattern is found on chest X-ray — Adams & Victor; Harrison's Principles of Internal Medicine, 22nd Ed.

2. PATHOPHYSIOLOGY

Step 1 — Primary Infection and Hematogenous Seeding

1. Hematogenous seeding of the meninges and subpial brain parenchyma → formation of subpial or subependymal tubercles (Rich foci)
2. Rupture of one or more tubercles into the subarachnoid space → bacterial discharge triggers intense meningeal inflammation

Step 2 — Basal Meningeal Exudate

• Pontine and interpeduncular cisterns
• Third ventricular floor and subthalamic region
• Optic chiasm
• Undersurfaces of the temporal lobes

Step 3 — Cascade of Injury

3. CLINICAL FEATURES

Prodrome (1–2 weeks before diagnosis)

• Low-grade fever, malaise, anorexia, irritability
• Headache (>50% of cases)
• Lethargy, confusion

Established Disease

• Neck stiffness (75%), Kernig's sign, Brudzinski's sign
• Cranial nerve palsies — especially oculomotor (CN III, IV, VI) — present in ~20% at diagnosis
• Papilledema — from raised ICP
• Hypothermia and hyponatremia (SIADH)
• Seizures (especially in children)
• Focal deficits from arteritis and infarction

CSF Findings (Lumbar Puncture — cornerstone of diagnosis)

4. RADIOLOGY

CT Scan

• Basal cistern obliteration — isoattenuating or slightly hyperattenuating exudate fills the interpeduncular and sylvian cisterns; enhances with IV contrast
• Communicating hydrocephalus — dilatation of lateral, third, and fourth ventricles; seen in 50% of adults and 85% of children
• Most sensitive/specific CT criteria for TBM:
  • Linear enhancement of the middle cerebral artery cisterns
  • Obliteration of CSF spaces around normal vascular enhancement
  • Y-shaped enhancement at the junction of the suprasellar and MCA cisterns
  • Asymmetry of enhancement
• Infarcts — basal ganglia, internal capsule, brainstem (from perforator arteritis)
• Tuberculomas — small rounded lesions, iso- or hypoattenuating, with variable vasogenic edema; ring enhancement with central caseation ("target sign")

MRI (Superior to CT)

• Post-contrast T1: Marked basal meningeal enhancement (see image below)
• FLAIR: High-signal abnormalities in basal ganglia from subacute infarction
• ADC maps/DWI: Restricted diffusion in subacute infarcts; tuberculomas may show restricted or elevated diffusion
• T2: Caseating tuberculomas show characteristically low signal (due to solid proteinaceous content); non-caseated lesions are T2-bright
• Differential for basal enhancement: fungal meningitis, neurosarcoidosis, carcinomatous meningitis

1. Basal meningeal enhancement
2. Hydrocephalus
3. Cerebral/brainstem infarction — ROSEN's Emergency Medicine; Grainger & Allison's Diagnostic Radiology

5. TREATMENT

Antituberculous Chemotherapy

Total treatment duration for TBM is 9–12 months — significantly longer than pulmonary TB (6 months), due to poor CNS drug penetration and high mortality/morbidity.

• Initial 2 months: INH + RIF + PZA + ethionamide or aminoglycoside (in place of EMB, which has poor CNS penetration)
• Continuation phase 7–10 months: INH + RIF

• INH and PZA have excellent CSF penetration
• RIF has moderate penetration (enhanced with inflammation)
• EMB has poor CSF penetration — reason for substitution in pediatric TBM

Adjunctive Corticosteroids (HIGH-QUALITY EVIDENCE — STRONGLY RECOMMENDED)

• 0.4 mg/kg/day IV, tapering by 0.1 mg/kg/week for 4 weeks
• Then oral: 4 mg/day, tapering by 1 mg/week for 4 weeks
• Total: ~6–8 weeks

• Prednisolone 4 mg/kg/day (or dexamethasone 0.6 mg/kg/day) for 4 weeks, then taper over 2–4 weeks

Note: In PLWH (HIV), a recent placebo-controlled study demonstrated no mortality benefit from adjunctive dexamethasone. This is an important exception to the general recommendation.

CSF Monitoring

Management of HIV Co-infection

Surgical Management

• Hydrocephalus — ventriculoperitoneal shunt or external ventricular drainage (required in up to 25% of advanced cases)
• Tuberculous cerebral abscess — drainage
• Paraparesis from spinal cord compression — Murray & Nadel's Respiratory Medicine; Harrison's; Adams & Victor's

6. COMPLICATIONS

Acute Complications

Chronic/Long-term Complications

If left untreated, TBM is uniformly fatal. — Robbins Pathology; Murray & Nadel; Tintinalli's Emergency Medicine

Recent Evidence (2024–2026)

• Lancet Infect Dis 2026 — Clinical Practice Guideline for TBM (PMID 40840485): The most current guideline, published February 2026, providing updated evidence-based recommendations for TBM management.
• JAMA Network Open 2024 — Global Case Fatality of Bacterial Meningitis (PMID 39093565): Systematic review/meta-analysis over 80 years confirms the persistently high mortality of TBM compared to other bacterial meningitides.
• Biomedicine & Pharmacotherapy 2025 — Rifampicin Neuroprotection (PMID 40024057): Systematic review of rifampicin's neuroprotective properties, relevant to understanding its role beyond antimicrobial activity in TBM.

Summary