Bacterial meningitis

Definition

• Bacterial infection of meninges

Etiology

• Adults
  • Streptococcus pneumoniae
  • Neisseria meningitidis
  • Listeria monocytogenes in immunocompromised, elderly, alcoholics, adn diabetes
  • Haemophilus influenzae
• Infants:
  • Group B Streptococcus
  • Escherichia coli
  • Haemophilus influenza
  • Listeria monocytogenes
• Head trauma or neurosurgery
  • Staphylococcus aureus
  • Gram-negatives

Risk factors

• Immunosuppression
• Diabetes
• Splenic dysfunction or splenectomy (e.g. sickle cell)
• Alcoholism
• Recent neurosurgery
• CSF leak
• Shunt infections
• Head trauma
• Chronic otitis media

Presentation

• Typically, an acute onset of headache with fever and vomiting after viral prodrome
• Bacterial vs. aseptic/viral meningitis
• Headache or neck pain (70-80%)
• Fever (75%)
• Altered level of consciousness (70%)
• Clinical signs
  • Brudzinski's sign (unhelpful)
  • Kernig's sign (may be specific)
  • Jolt test (very sensitive)
  • Seizures or focal neurological deficits (rare, poor prognosis)
  • Rash (purpuric with Neisseria)
• Ask about recent travel and sick contacts

Investigations

• Lab
  • CBC with differential
  • Electrolytes
  • Liver enzymes
  • Blood cultures
• Imaging
  • CT head to rule out abscess or increased ICP
  • MRI head if suspicion for herpes encephalitis
    • Temporal lobe enhancement (usually unilateral)
• Other
  • Lumbar puncture after CT head

CSF Interpretation

• Gram stain positive
• Glucose <1.0
• CSF:blood glucose <0.23
• Protein >2.2
• WBC >2000
• PMNs >1180

Management

• Blood cultures before antibiotics
• Start empiric antibiotics and dexamethasone
  • Infants
  • Children
  • Adults
    • Ceftriaxone 2g bid
    • vancomycin 1g q12h
    • +/- ampicillin 2g 14h if >50
    • Dexamethasone 10mg q6h x72h
    • +/- acyclovir
  • >65 years old
    • Treat like immunocompromised
• CT head if reduced or altered level of consciousness
• Lumbar puncture
• Adjust antibiotics based on Gram stain and cultures

Complications

• Cerebral edema with raised ICP
• Hydrocephalus
• Seizures
• Arterial ischemia or infarction
• SIADH
• Subdural effusion or subdural empyema
• Venous sinus thrombosis
• Cranial nerve palsies, especially deafness