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Learning objectives

  • Presentation of encephalitis as a stroke mimic
  • Appropriate investigations
  • Managing the patient with suspected encephalitis


  • Encephalitis is an inflammatory process involving the brain parenchyma
  • Associated with clinical or laboratory evidence of neurological dysfunction
  • May mimic stroke particularly if affects dominant temporal lobe with dysphasia


  • Herpes simplex virus types 1 and 2, Varicella zoster virus, CMV
  • Enteroviruses, Adenovirus, Parechovirus, measles virus, HIV
  • St Louis encephalitis, West Nile encephalitis (WNE): Extreme lethargy
  • Autoimmune (main tumour associations in brackets) see below
  • Acute disseminated encephalomyelitis, Bickerstaff's encephalitis


  • Confusion/Delirium,change in personality or behaviour
  • Coma. seizures, obtunded, cold sores, lethargy
  • Headache, altered speech, amnesia, temporal lobe seizures


  • Infectious processes
  • Encephalopathy
  • Autoimmune processes such as ADEM or autoimmune encephalitis


  • FBC: Raised WCC, U&E, Raised CRP, Low Na
  • CSF: >5 white cells x 10 9 /L predominantly lymphocytes with normal or moderately raised protein and glucose is normal.
  • CSF PCR for HSV highly sensitive and specific in immunocompetent adults
  • HIV test in all
  • EEG findings suggestive of encephalitis
  • CT head: may show hypoattenuation and oedema and even hydrocephalus
  • MRI: T2 and FLAIR signal hyperintensities abnormal in 90% of cases of HSV encephalitis involving medial temporal lobes. Temporal lobe and limbic abnormalities are seen in HSV and HHV-6 encephalitis
  • Antibodies: NMDAR antibody encephalitis and LGI-1 antibody
  • Antibodies against neuronal surface antigens: NMDAR antibody encephalitis (ovarian teratoma)
  • Antibodies to LGI-1 encephalitis (thymoma)
  • Antibodies against intracellular antigens: anti-Hu (small cell lung tumour), anti-Ma (testicular tumours), anti-GAD


  • ABC and airways management if low GCS. Supportive care. May need a period of ITU and support.
  • With recovery there may be long terms cognitive and amnestic and other issues
  • Aciclovir is a time-critical life-saving treatment for HSV encephalitis and should be commenced if diagnosis suspected before lumbar puncture if this is delayed. Aciclovir treatment for 14 days then repeat LP to ensure PCR negative.
  • Autoimmune encephalitis: corticosteroids intravenously or orally. Intravenous Ig or plasma exchange are often also used, especially in those failing to improve


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