Can you create a concise study guide on central nervous system infections, including tuberculous meningitis, for medical students?

CNS Infections Study Guide for Medical Students

Initial Assessment and Emergency Management

All patients with suspected meningitis require immediate hospital admission with a goal arrival time within one hour, and antibiotics must be administered within 1 hour of hospital arrival. 1

Immediate Stabilization Steps

• Stabilize airway, breathing, and circulation first, then document Glasgow Coma Scale (GCS) score to assess severity 1
• Obtain blood cultures within the first hour before antibiotic administration 1
• Document presence or absence of: headache, altered mental status, neck stiffness, fever, rash, seizures, and signs of shock 1
• Place all patients in respiratory isolation with droplet precautions until meningococcal disease is excluded; discontinue after 24 hours of effective antibiotics 1

Lumbar Puncture Decision Algorithm

Proceed immediately with lumbar puncture if the patient is alert, oriented, and has no focal neurological deficits. 1

Absolute contraindications to immediate LP:

• Focal neurological signs or abnormal pupils 1
• Papilledema 1
• Continuous or uncontrolled seizures 1
• GCS ≤ 12 1
• Immunocompromised state 1
• History of CNS disease 1
• New onset seizure within 1 week 1

If LP is delayed, administer antibiotics immediately after blood cultures, then perform LP within 4 hours of antibiotic initiation to minimize impact on CSF culture results. 1

Empiric Antibiotic Therapy

For adults <60 years: Ceftriaxone 2g IV every 12 hours OR cefotaxime 2g IV every 6 hours 1

CSF Analysis Interpretation

• Perform Gram stain, cell count with differential, glucose, protein, and bacterial culture 1
• Suspect bacterial meningitis: Neutrophilic pleocytosis, low glucose, elevated protein 1
• Suspect tuberculous meningitis: Lymphocytic pleocytosis, CSF:plasma glucose <50%, elevated protein 2

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Tuberculous Meningitis (TBM)

TBM is a medical emergency requiring immediate empirical treatment; do not wait for microbiological confirmation. 3, 2

Clinical Presentation

Early phase (1-2 weeks): Malaise, headache, low-grade fever, personality change 4

Late phase (2-3 weeks): Protracted headache, stroke, meningismus, vomiting, confusion, focal neurologic findings 4

Untreated progression: Mental status deteriorates to stupor or coma 4

Diagnostic Approach

CSF findings suggestive of TBM:

• Lymphocytic-predominant pleocytosis 5, 2
• Elevated protein 5, 2
• CSF:plasma glucose <50% 2
• Elevated opening pressure (≥250 mm H₂O indicates need for urgent intervention) 6

Increase diagnostic yield by:

• Submitting large volume CSF samples 5, 2
• Performing repeat lumbar punctures if diagnosis remains uncertain 2
• Obtaining multiple samples for acid-fast bacilli smear and culture 5

Molecular diagnostics:

• PCR is highly specific but suboptimal sensitivity; a negative test does not rule out TBM 5
• Metagenomic and nanopore sequencing enhance detection but are limited by cost and access 7

Imaging:

• MRI is the imaging modality of choice, superior to CT for detecting basal meningeal enhancement, tuberculomas, hydrocephalus, and infarcts 8
• Chest radiography may reveal miliary pattern 9

Attempt tissue diagnosis whenever possible:

• Biopsy of lesions or diagnostic sampling from extra-neural sites (lung, gastric fluid, lymph nodes, liver, bone marrow) 2

Anti-Tuberculosis Treatment Regimen

Initiate immediate four-drug therapy: isoniazid, rifampicin, pyrazinamide, and ethambutol for the first 2 months. 3, 2

Preferred fourth drug:

• Adults: Ethambutol (preferred over streptomycin) 3
• Children: Replace ethambutol with ethionamide or an aminoglycoside because visual-acuity monitoring is difficult 3

Continuation phase:

• After 2 months, discontinue pyrazinamide and ethambutol when isolate is confirmed susceptible to isoniazid and rifampicin 3
• Continue isoniazid + rifampicin daily for an additional 7-10 months 3, 2

Total treatment duration: 9-12 months (preferably 12 months) 3, 2

Daily dosing is strongly preferred over intermittent regimens. 3

Adjunctive Corticosteroid Therapy

Adjunctive corticosteroids reduce mortality by approximately 25% and should be given to all patients with TBM, regardless of disease severity. 3, 2, 10

Adult dosing:

• Dexamethasone: 12 mg IV daily (or 0.4 mg/kg/day, max 12 mg) for 3 weeks, then taper over 3 weeks (total 6 weeks) 3
• Alternative: Prednisolone 60 mg oral daily, tapered over 6-8 weeks (60 mg × 4 weeks → 30 mg × 4 weeks → 15 mg × 2 weeks → 5 mg × 1 week) 3

Pediatric dosing:

• ≥25 kg: Dexamethasone 12 mg IV daily 3
• <25 kg: Dexamethasone 8 mg IV daily 3
• Same tapering schedule as adults 3

Critical timing: Corticosteroids must be started immediately before or concurrently with the first anti-TB dose; delay is not permitted 3

Mortality benefit is greatest in Stage II disease (lethargic presentation). 3

Critical Treatment Pitfalls

Most common critical error: Using a 6-month treatment course (adequate for pulmonary TB) instead of the required 9-12 months for CNS TB 3

Do not discontinue steroids abruptly: Complete the full 6-8 week taper regardless of clinical improvement to avoid life-threatening adrenal crisis 3

Do not stop anti-TB therapy early even if CSF parameters have normalized. 3

Monitoring and Follow-Up

• Perform repeat lumbar punctures early in therapy to monitor CSF cell count, glucose, and protein 3
• Conduct regular neurological examinations to detect improvement or deterioration 3
• Monitor liver function for hepatotoxicity from isoniazid, rifampicin, and pyrazinamide 3
• Watch for steroid-related complications: hyperglycemia, gastrointestinal bleeding, invasive bacterial infections 3

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Complications of CNS Tuberculosis

Hydrocephalus

Hydrocephalus occurs in 40-85% of patients with chronic meningitis, with greater severity in children. 6

Obstructive hydrocephalus, if untreated, causes increased intracranial pressure progressing to fatal brain herniation. 6

Immediate neurosurgical consultation is indicated for:

• Hydrocephalus requiring ventriculoperitoneal shunt placement 3, 6
• Paraparesis or spinal cord compression 3
• Tuberculous cerebral abscesses 3
• Progressive neurological deficits despite optimal medical therapy 3

External ventricular drain placement is indicated in most patients with obstructive hydrocephalus to prevent brain herniation. 6

Cerebrovascular Complications

Cerebrovascular complications occur frequently and include:

• Cerebral infarcts 6
• Subarachnoid hemorrhage 6
• Intracranial hemorrhage 6
• Venous sinus thrombosis 6

Therapeutic anticoagulation is contraindicated in TBM-related cerebral infarcts:

• Full-dose anticoagulation increases major bleeding risk 6- to 7.7-fold compared with antiplatelet therapy 3
• Therapeutic anticoagulation has not been shown to reduce stroke progression or improve outcomes in TBM-related inflammatory arteritis 3
• When craniectomy is planned, withhold antiplatelet agents (e.g., aspirin) until after the procedure 3

VTE prophylaxis:

• Immobilized TBM patients should receive low-dose prophylactic subcutaneous low-molecular-weight heparin 3
• Prophylactic anticoagulation does not contraindicate concurrent aspirin use 3

Respiratory and Hemodynamic Failure

One-third of adults with bacterial meningitis develop hemodynamic or respiratory failure during their clinical course. 6

Mechanisms of death in TBM:

• Brain herniation with compression of respiratory and cardiovascular centers 6
• Septic shock with coagulopathy contributing to fatal hemorrhagic complications 6
• Acute respiratory failure requiring mechanical ventilation 6

Long-Term Sequelae

Neurological deficits occur in approximately 50% of adults with bacterial meningitis. 6

Severe sequelae include:

• Hearing loss (34%) 6
• Seizures (13%) 6
• Motor deficits (12%) 6
• Cognitive defects (9%) 6
• Hydrocephalus (7%) 6
• Visual loss (6%) 6

Nearly half of TBM patients exhibit impaired cognition. 7

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Special Populations

HIV-Positive Patients

Delay antiretroviral therapy (ART) for 8 weeks after starting anti-TB treatment, even when CD4 <50 cells/µL, to reduce the risk of severe or fatal neurological immune reconstitution inflammatory syndrome (IRIS). 3

ART regimen selection:

• Dolutegravir-based regimens are preferred for patients receiving rifampicin, but rifampicin reduces dolutegravir plasma exposure by approximately 26%, which may require dose adjustment 3
• Avoid cobicistat-containing regimens when co-administered with rifampicin because rifampicin markedly lowers cobicistat levels, leading to sub-therapeutic antiretroviral concentrations 3

For moderate to severe paradoxical TB-IRIS: Prednisone 1.25 mg/kg/day significantly lowers the need for hospitalization 3

All patients with suspected or proven tuberculosis should be offered HIV testing. 2

Drug-Resistant Tuberculosis

Suspected or confirmed drug-resistant TB meningitis should be managed in specialized centers with expertise in regimen adaptation and close monitoring. 3

Drug-resistant TBM is increasingly recognized and poses significant challenges to both diagnosis and treatment, with high mortality risks. 7

Pediatric Considerations

Children with CNS tuberculosis should ideally be managed by a pediatrician with expertise in pediatric tuberculosis or with input from a pediatric infectious diseases unit. 2

In children, replace ethambutol with ethionamide or an aminoglycoside because visual-acuity monitoring is difficult in young patients. 3

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Pathogenesis and Pathophysiology

Mycobacterium tuberculosis disseminates from the primary site of infection and overcomes protective barriers to enter the CNS. 11

Once in the CNS, M. tuberculosis induces an inflammatory response involving both peripheral and resident immune cells, initiating a cascade of pathologic mechanisms. 11

The granulomatous inflammatory response contributes to neurotoxicity. 12

CNS TB can manifest as:

• Tuberculous meningitis (most common presentation) 4
• Intracranial tuberculomas 4, 8
• Spinal tuberculous arachnoiditis 4, 8
• Tuberculous abscess 8

Spinal infection may result in spondylitis, arachnoiditis, and/or focal intramedullary tuberculomas. 8

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Emerging Therapies and Research Priorities

Investigational regimens: Fluoroquinolones and higher-dose intravenous rifampicin are currently being evaluated in clinical trials for CNS tuberculosis 3

Host-directed therapies targeting immune modulation and oxidative stress show promise in improving outcomes, particularly for drug-resistant TBM. 12

Novel approaches being explored:

• Intrathecal drug administration 12
• Nanoparticle-based drug delivery 12
• Artificial intelligence for early diagnosis, disease monitoring, and personalized treatments 7

Substantial knowledge and evidence gaps remain, highlighting current research priorities in TBM diagnosis and treatment. 10