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) account for 50% of cases^[1]

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

SAH
Lyme disease
Brain abscess
Bacterial endocarditis
Toxic / metabolic encephalopathy

Altered mental status and fever

Infectious
- Sepsis
- Meningitis
- Encephalitis
- Cerebral malaria
- Brain abscess
Other
- Neuroleptic malignant syndrome
- Serotonin syndrome
- Malignant hyperthermia
- Sympathomimetic toxicity (cocaine, amphetamine, ketamine)
- Anticholinergic toxicity
- Heat stroke
- Delirium tremens
- Hypothalamic stroke
- Pheochromocytoma
- Thyroid storm

Evaluation

Brain MRI showing high signal in the temporal lobes and right inferior frontal gyrus secondary to HSV encephalitis.

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

Management

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

References

↑ Somand D, Meurer W. Central Nervous System Infections. EMCNA 2009; 27: 89-100.
↑ 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.
↑ Howes DS et al. Encephalitis Workup. Oct 12, 2015. http://emedicine.medscape.com/article/791896-workup#showall

Authors:

[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

[1]

[2]

[3]