Encephalitis

• Infection of the brain parenchyma causing clouding of the sensorium
• Some overlap with meningitis

Differential Diagnosis

• Infectious
  • Viruses
    • Enteroviruses
    • Eastern or Western equine encephalitis, Japanese encephalitis, Murray Valley encephalitis, St. Louis encephalitis, West Nile virus
    • Rabies virus
    • Hendra virus
    • Nipah virus
    • Tickborne encephalitis, La Crosse virus, Powassan virus
  • Bacteria
    • Mycoplasma pneumoniae
    • Listeria monocytogenes
    • Borrelia burgdorferi (Lyme disease)
    • Coxiella burnetii
    • Bartonella henselae or B. quintana
  • Other
    • Cryptococcus neoformans
    • Toxoplasma gondii
    • Bayliscarias procyonis
    • Prion disease (CJD)
• Non-infectious (including post-infectious)
  • Acute disseminated encephalomyelitis (ADEM)
  • Vasculitis
  • Collagen vascular disorders
  • Paraneoplastic syndromes

Investigations

• Lumbar puncture for viral culture or PCR
• MRI is the best neuroimaging; CT if MRI not available
• EEG is rarely helpful except to rule out non-convulsive status epilepticus

Management

• Acyclovir for suspected HSV or VZV encephalitis