Encephalitis

Background

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)

Microbiology

HSV
HZV
EBV
CMV
Rabies
Arboviruses (West Nile, St. Louis equine)

Clinical Features

New psychiatric symptoms (HSV)^[1]
Cognitive deficits
1. Aphasia, amnesia, confusion
Seizure
Movement disorder (arboviruses)
Fever and meningeal signs are almost always present

Diagnosis

CT Head
1. Medial temporal and inf frontal grey matter c/w HSV
LP
1. Bloody tap c/w HSV

DDX

Meningitis
SAH
Lyme disease
Brain abscess
Bacterial endocarditis
Toxic / metabolic encephalopathy

Treatment

Often it is unclear which type of encephalitis is present and starting Acyclovir empirically is appropriate. In addition to the pathogens below, possible causes can include West Nile Virus, EBV, HIV, toxoplasmosis, or rabies.

HSV encephalitis

Acyclovir 10mg/kg (10-15mg/kg for pediatrics) every 8hrs

HZV encephalitis

Acyclovir 10mg/kg every 8hr

CMV encephalitis

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

Tick Associated (Borrelia burgdorferi, Ehrlichiosis or Rickettsia)

Doxycycline 200 mg IV once followed by 100 mg IV twice daily

Disposition

Admit in all cases

Source

↑ 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.

Authors:

[1] 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.

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