4.3 Pediatric Central Nervous System Infections

4.3 Pediatric Central Nervous System Infections

Central nervous system (CNS) infections in pediatric patients—including bacterial meningitis, viral (aseptic) meningitis, and encephalitis—are life-threatening medical emergencies. Prompt recognition, rapid diagnostic differentiation, and immediate initiation of targeted antimicrobial therapy are critical to prevent mortality and long-term neurological sequelae such as sensorineural hearing loss, cognitive impairment, seizure disorders, and hydrocephalus.

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Pathophysiology & Age-Specific Etiology

Infections of the CNS occur when pathogens breach the blood-brain barrier via hematogenous dissemination from mucosal colonization, direct extension from adjacent parameningeal structures (e.g., otitis media, sinusitis, mastoiditis), or direct inoculation following neurosurgery or penetrating head trauma.

Pathogens by Age Group

• Neonates (< 28 Days):
  • Group B Streptococcus (Streptococcus agalactiae): Most common neonatal pathogen, acquired vertically during vaginal delivery.
  • Escherichia coli (and other Gram-negative enteric bacilli such as Klebsiella).
  • Listeria monocytogenes: Transmitted transplacentally or during birth; resistant to cephalosporins.
• Infants & Children (> 28 Days to 17 Years):
  • Streptococcus pneumoniae: Leading cause of bacterial meningitis in post-neonatal infants and children. Associated with severe neurological morbidity and sensorineural hearing loss.
  • Neisseria meningitidis: Encapsulated Gram-negative diplococcus responsible for epidemic outbreaks; causes severe fulminant meningococcemia.
  • Haemophilus influenzae type b (Hib): Significantly reduced due to routine Hib conjugate vaccination, but remains a risk in unimmunized or under-immunized children.

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Clinical Presentation & Physical Examination

Clinical manifestations vary significantly based on patient age and developmental stage.

Infants (< 12 Months)

Infants rarely present with classic meningeal signs due to unclosed cranial fontanelles and immature motor responses. Clinical presentation is often subtle and non-specific:

• Fever or hypothermia (temperature instability)
• Tense, bulging anterior fontanelle (best assessed while the infant is seated and quiet)
• Paradoxical Irritability: The infant cries more intensely when held or rocked by parents due to positioning that stretches inflamed meninges.
• Poor feeding, vomiting, lethargy, or high-pitched inconsolable cry
• Hypotonia or focal seizure activity

Children & Adolescents (> 1 Year)

Presents with the classic diagnostic triad: Fever, Nuchal Rigidity, and Altered Mental Status.

• Severe headache and intense photophobia
• Nuchal Rigidity: Resistance and pain upon passive neck flexion.
• Kernig's Sign: With the patient supine, flex the hip and knee to 90 degrees; resistance or severe pain upon subsequent passive extension of the knee indicates meningeal irritation.
• Brudzinski's Sign: Involuntary flexion of the hips and knees when the patient's neck is passively flexed while supine.

Kernig's Sign: Flex hip/knee 90° ──► Pain on knee extension ──► Positive
Brudzinski's Sign: Passive neck flexion ──► Involuntary hip/knee flexion ──► Positive

Meningococcemia & Purpura Fulminans

Infection with Neisseria meningitidis can produce a fulminant systemic vasculitis:

• Initial petechial rash rapidly coalesces into ecchymotic, purpuric lesions (purpura fulminans).
• Triggers disseminated intravascular coagulation (DIC), profound septic shock, and bilateral adrenal hemorrhage (Waterhouse-Friderichsen syndrome).
• Emergency Isolation: Instigate immediate Droplet Precautions (mask, eye protection, gloves) in addition to Standard Precautions upon suspicion of meningococcal disease.

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Lumbar Puncture (LP) & CSF Analysis

Diagnostic evaluation requires lumbar puncture for cerebrospinal fluid (CSF) analysis, unless contraindications are present.

Cerebrospinal Fluid (CSF) Differentiating Profile

Contraindications to Immediate Lumbar Puncture

1. Signs of Increased ICP or Impending Brainstem Herniation: Focal neurological deficits, papilledema, pGCS ≤ 8, Cushing's triad, unreactive/asymmetric pupils.
2. Severe Hemodynamic Instability or Septic Shock: LP positioning (flexed lateral decubitus) compromises airway and venous return.
3. Severe Thrombocytopenia or Coagulopathy: Risk of epidural hematoma and spinal cord compression.
4. Infection at the LP Insertion Site: Risk of introducing bacteria into the subarachnoid space.

• Critical Rule: If LP is delayed for neuroimaging (Head CT) or due to clinical instability, NEVER DELAY ANTIMICROBIAL THERAPY. Administer empiric IV antibiotics and blood cultures immediately before sending the patient for CT.

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Age-Specific Antimicrobial Coverage & Adjunctive Therapy

Empiric antimicrobial selection must cover age-specific bacterial pathogens and breach the blood-brain barrier at meningeal therapeutic concentrations.

Empiric Regimens by Age Group

• Neonates (< 28 Days):
  • Ampicillin (100 mg/kg IV q6h) PLUS Cefotaxime (50 mg/kg IV q6h) OR Gentamicin (2.5 mg/kg IV q8h).
  • Rationale: Ampicillin provides essential coverage against Listeria monocytogenes and Group B Streptococcus. Cefotaxime covers Gram-negative enterics (E. coli).
  • Avoid Ceftriaxone in Neonates: Ceftriaxone is contraindicated in neonates because it displaces bilirubin from albumin, increasing the risk of kernicterus, and precipitates with intravenous calcium-containing solutions (biliary sludging).
• Infants & Children (> 28 Days to 17 Years):
  • Vancomycin (15-20 mg/kg IV q6h) PLUS Ceftriaxone (50 mg/kg IV q12h; max 2 g/dose) OR Cefotaxime (75 mg/kg IV q6h).
  • Rationale: High-dose Ceftriaxone/Cefotaxime treats N. meningitidis and sensitive S. pneumoniae. Vancomycin is added to cover ceftriaxone-resistant Streptococcus pneumoniae strains.

Adjunctive Dexamethasone Therapy

• Administer Dexamethasone 0.15 mg/kg IV q6h for 4 days in infants and children > 6 weeks of age with suspected or confirmed Hib or S. pneumoniae meningitis.
• Timing: Must be administered prior to or concurrently with the first dose of IV antibiotics. Dexamethasone inhibits inflammatory cytokine release triggered by antibiotic-induced bacterial lysis, significantly reducing the incidence of sensorineural hearing loss.

Empirical Acyclovir for Encephalitis

• Add Acyclovir 20 mg/kg IV q8h in neonates or children presenting with signs of encephalitis (focal seizures, temporal lobe involvement on EEG/MRI, vesicles, or severe lethargy) to treat suspected Herpes Simplex Virus (HSV-1 or HSV-2) encephalitis.

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Encephalitis vs. Meningitis

Unlike meningitis (inflammation restricted to the meninges), encephalitis involves inflammation of the brain parenchyma itself.

• Clinical Hallmarks: Prominent altered mental status, personality/behavioral changes, acute psychosis, focal neurological deficits (hemiparesis, cranial nerve palsies), and focal motor seizures.
• Etiology: Primarily viral (HSV-1, Enteroviruses, Arboviruses, EBV).
• Diagnosis: CSF PCR for viral DNA/RNA, EEG (showing temporal lobe periodic sharp wave complexes characteristic of HSV), and brain MRI.

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Clinical Scenario

A 3-month-old infant is brought to the ED with a 2-day history of fever (39.1°C), poor feeding, and extreme irritability. Physical exam reveals a tense, bulging anterior fontanelle and paradoxical irritability when held by the mother. Blood cultures are drawn. Before lumbar puncture is performed, the infant exhibits a brief 45-second focal seizure. The emergency nurse immediately establishes IV access, administers empiric IV Vancomycin (20 mg/kg), Ceftriaxone (50 mg/kg), and Dexamethasone (0.15 mg/kg), and prepares the infant for a non-contrast head CT to rule out mass effect prior to performing the LP.