Central Nervous System Infections (Incl. Meningitis, Encephalitis, Abcess)

INTRODUCTION

Key symptoms: headache, seizures, altered conscious state

Meningitis: classic triad—headache, photophobia, neck stiffness Others: malaise, vomiting, fever, drowsiness

Bacterial causes: Strep. pneumoniae, H. influenzae (esp. children), Neisseria meningitidis (can take form of meningitis, septicaemia [meningococcaemia] or both)

Also—Listeria monocytogenes, M. tuberculosis, Group B Strep, Strep. agalactiae (esp. newborn), Staph spp. Gm–ve bacilli, Treponema pallidum

Viral causes: enteroviruses (Coxsackie, echovirus, poliovirus), mumps, HSV type 1, 2 or 6, Varicella zoster, EBV, HIV

Fungi: cryptococcus, Histoplasma capsulatum

Autoimmune encephalitis

BACTERIAL MENINGITIS

Basically a childhood infection (↑ risk 6–12 mths).

Infancy (clinical features)

• Fever, pallor, vomiting ± altered conscious state

• Lethargy

• Increasing irritability with drowsiness

• Refusal to feed, indifference to mother

• Neck stiffness (not always present)

• Cold extremities (a reliable sign)

• May be bulging fontanelle

Children over 3 years, adolescents, adults

• Meningeal irritation more obvious (e.g. headache, fever, vomiting, neck stiffness)

• Later: delirium, altered conscious state

• ± Kernig sign (Fig. C1) or Brudzinski sign (more reliable sign)

Note: Antibiotics may mask symptoms. Suspect meningitis if fever >3 days in reasonably well child on antibiotics. If significant delay with investigations, do not withhold treatment.

Fulminating

• Dramatic sudden-onset shock, purpura (does not blanch on pressure) ± coma

• Usually due to meningococcal septicaemia, also H. influenzae type B, Streptococcus pneumoniae

Note: Septic shock may ensue without signs of meningitis.

Treatment (suspected meningitis)

• First: oxygen + IV access and consult

• Take blood for culture (within 30 minutes of assessment)

• For child give bolus of 10–20 mL/kg of N saline with additional boluses up to 60 mL/kg if signs of hypoperfusion

• Admit to hospital for lumbar puncture (preliminary CT scan to assess safety of LP in adults)

• Dexamethasone 0.15 mg/kg up to 10 mg IV (shown to improve outcome)

• Start with antibiotic: antibiotics of proven value—ceftriaxone, cefotaxime, penicillin, meropenem. Choice directed by knowledge of organism and known susceptibility.

• Ceftriaxone 2 g (child: 50 mg/kg up to 2 g) IV statim then 12 hrly for 4 d

  or

  Cefotaxime 2 g (child: 50 mg/kg up to 2 g) IV 6 hrly for 3–5 d

Treatment (meningococcaemia—all ages)

Treatment is extremely urgent once suspected (e.g. petechial or purpuric rash on trunk and limbs). It should be given before reaching hospital.

Empirical treatment:

• benzylpenicillin 60 mg/kg IV (max. 2 g) statim (continue ...