• Infection of brain parenchyma of the temporal lobes and inferior frontal lobe causing distinct neurologic abnormality
  • Pathophysiology
    • Gray matter is predominantly affected (cognitive / psychiatric signs, lethargy, seizure)


Clinical Features

  • New psychiatric symptoms (HSV)[2]
  • Cognitive deficits
    • Aphasia, amnesia, confusion
  • Seizure
  • Movement disorder (arboviruses)
  • Fever and meningeal signs are almost always present
  • Dysuria and pyuria (St. Louis encephalitis)
  • Extreme lethargy (West Nile encephalitis)

Differential Diagnosis

Altered mental status and fever


  • Imaging identifies abnormalities in medial temporal and inferior frontal gray matter in HSV[3]
    • CT Head - edema and petechial hemorrhage
    • MRI - increased T2 intensity
  • LP
    • Bloody tap consistent with HSV


often it is unclear which type of encephalitis is present and starting Acyclovir empirically is appropriate

HSV encephalitis

HZV encephalitis

CMV encephalitis

  • Ganciclovir 5mg/kg IV every 12hr OR
  • Foscarnet 90mg/kg IV every 12 hrs


Admit in all cases

See Also


  1. Somand D, Meurer W. Central Nervous System Infections. EMCNA 2009; 27: 89-100.
  2. Loring KE, Tintinalli JE: Central Nervous System and Spinal Infections, in Tintinalli JE, Kelen GD, Stapczynski JS (eds): Emergency Medicine, A Comprehensive Study Guide, ed 7. New York, McGraw-Hill, 2011, (Ch) 168:p 1175-1176.
  3. Howes DS et al. Encephalitis Workup. Oct 12, 2015. http://emedicine.medscape.com/article/791896-workup#showall