Encephalitis
Basics
Description
Description
- Acute inflammation of the brain
- 20,000 cases in the U.S. annually
- Mortality: 10%
- Inflammatory reaction occurs within brain parenchyma with destruction of neurons, parenchymal edema, and petechial hemorrhages
- Route of CNS infection usually hematogenous:
- Respiratory or GI tract
- Blood transfusion
- Organ transplant
- Neural migration occurs with rabies, herpes simplex virus (HSV), and varicella zoster virus (VZV) encephalitis
Etiology
Etiology
- Viral is most common
- Noninfectious
- Autoimmune, paraneoplastic, collagen vascular disease
- 50% of cases have no identifiable cause
Specific Viruses
- HSV:
- 10–20% of all encephalitides
- Primary or reactivation
- Early treatment improves prognosis
- Arbovirus:
- 10–15% of all encephalitides
- Zoonotic transmission (mosquitoes, ticks) in warm months
- Eastern equine causes fulminant encephalitis:
- Tropism for the hippocampus
- Abrupt onset of headache, fever, vomiting progressing to coma
- Western equine occurs mostly in the western 2/3 of the U.S.:
- Often preceded by nonspecific upper respiratory/GI tract symptoms
- Japanese – most prevalent arboviral encephalitis worldwide:
- Indolent course of fever, headache, myalgias, and fatigue followed by confusion, delirium, masklike facies, and parkinsonism, seizures, brainstem dysfunction, coma, and death
- Flavivirus:
- West Nile virus – increased incidence in North America:
- Found in mosquitoes and birds
- Febrile illness, often with rash
- Headache
- Lymphadenopathy
- Polyarthropathy
- Increased morbidity/mortality in elderly patients
- Flaccid paralysis can lead to respiratory failure with 50% mortality
- West Nile virus – increased incidence in North America:
- Enteroviral:
- Occurs mainly in children <10 yr old
- Relatively benign course with little or no long-term sequelae
- Measles encephalitis:
- Occurs several days to 2–3 wk after primary infection and rash, or after years of latent infection
- Abrupt onset and rapid progression to coma
- Seizures common (50–60%)
- Postimmunization incidence of 1 per 1 million vaccinated
- HIV encephalitis:
- Lower CD4 counts predispose to encephalitis
- Typical features include motor spasticity and dementia
- Involvement of white matter with extensive neural degeneration
- Rhabdovirus: Rabies
- CNS infection in the absence of systemic infection
Nonviral
- Mycoplasma pneumoniae
- Toxoplasma gondii
- Rickettsia rickettsii
- Mycobacterium tuberculosis
- Borrelia burgdorferi
- Bartonella henselae
Immunocompromised/HIV Patients
- Histoplasma
- Cryptococcus neoformans
- VZV
- Listeria monocytogenes
- Cytomegalovirus (CMV)
- T. gondii
- Human herpesvirus type 6 (HHV-6)
Autoimmune
- Anti-LGI1 encephalitis
- Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis
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Citation
Schaider, Jeffrey J., et al., editors. "Encephalitis." 5-Minute Emergency Consult, 6th ed., Lippincott Williams & Wilkins, 2020. Emergency Central, emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307594/1.3/Encephalitis.
Encephalitis. In: Schaider JJJ, Barkin RMR, Hayden SRS, et al, eds. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307594/1.3/Encephalitis. Accessed December 7, 2024.
Encephalitis. (2020). In Schaider, J. J., Barkin, R. M., Hayden, S. R., Wolfe, R. E., Barkin, A. Z., Shayne, P., & Rosen, P. (Eds.), 5-Minute Emergency Consult (6th ed.). Lippincott Williams & Wilkins. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307594/1.3/Encephalitis
Encephalitis [Internet]. In: Schaider JJJ, Barkin RMR, Hayden SRS, Wolfe RER, Barkin AZA, Shayne PP, Rosen PP, editors. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. [cited 2024 December 07]. Available from: https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307594/1.3/Encephalitis.
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