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encephalitis

Also see - meningoencephalitis - encephalomyelitis - viral encephalitis Etiology: 1) infection - viral encephalitis (48%) - Herpes simplex virus (19%) - reactivation of latent infection - Varicella zoster virus (11%) - acute infection or reactivation of latent infection - increased risk with HIV1 infection - enterovirus - encephalitis viruses - West Nile virus (9%) - Epstein-Barr virus (3%) - HIV1 infection* (2%) - rabies virus - bacterial infection - cat scratch disease* (Bartonella henselae) - tuberculosis* - Q fever* (Coxiella burnetti) - tularemia* (Francisella tularensis) - Mycoplasma infection* - protozoan infection - toxoplasmosis* 2) autoimmune disease (22%) - sarcoidosis* - histiocytic necrotizing lymphadenitis* (Kikuchi's disease) - anti-NMDA receptor encephalitis - voltage-gated potassium channel antibody 3) malignancy - lymphoma* 4) idiopathic (30%) [4] * acute encephalitis associated with regional lymphadenopathy Epidemiology: - enterovirus: late summer or fall - West Nile virus: mosquito-borne infection, summer or fall (June-October) - rabies: bite from infected mammal, generally bat Pathology: - inflammation of the brain parenchyma Clinical manifestations: - HSV1: fever, altered mental status, temporal lobe epilepsy - Herpes zoster: dermatomal cutaneous lesions variably present - enterovirus: fever, altered mental status, variable rash, oral lesions - West Nile virus: fever, altered mental status, muscle weakness variable (asymmetric flaccid paralysis possible), parkinsonism, rarely seizures - Rabies virus: paresthesias at site of innoculation, hydrophobia, progressive obtundation [6] Laboratory: - CSF analysis - CSF cell count: - lymphocyte predominance (pleocytosis) - ~20% of infectious encephalitis without pleocytosis [10] - CSF herpes simplex virus DNA (all cases of encephalitis) [6] - CSF varicella-zoster virus DNA - CSF enterovirus RNA - West Nile virus IgM in CSF - CSF Rabies virus RNA - NMDA receptor IgG in CSF - nape of neck biopsy (nuchal skin biopsy) for immunohisochemstry (rabies) - also see paraneoplastic limbic encephalitis - see ARUP consult [1] Special laboratory: - electroencephalography [6] Radiology: - MRI - bilateral temporal lobe involvement with HSV1 Complications: - mortality 9% during hospitalization & 17% at 1 year - factors associated with poor outcome [4] - age >= 65 years - immunocompromise - coma - acute thrombocytopenia - need for mechanical ventilation Differential diagnosis: - autoimmune encephalitis - insidious onset, positive nonspecific serum antibodies suggest other diagnosis [9] Management: - acyclovir for HSV1 & Herpes zoster - supportive care for enterovirus, West Nile virus & rabies - see specific etiology - see meningitis for empiric antibiotic coverage - prognosis - minimal or no disability at hospital discharge in 49% of patients & 60% of patients at 1 year - prophylaxis for close contacts of patient with rabies [6]

Interactions

disease interactions

Related

differential diagnosis of regional lymphadenopathy & acute encephalitis

Specific

Bickerstaff brainstem encephalitis encephalitis lethargica; sleeping sickness; von Economo's disease encephalomyelitis GABA-A receptor antibody encephalitis limbic encephalitis meningoencephalitis paraneoplastic brainstem encephalitis; paraneoplastic rhombencephalitis Rasmussen's encephalitis Rassmusen's encephalitis viral encephalitis

General

encephalopathy inflammation

References

  1. ARUP Consult: Encephalitis, Infectious The Physician's Guide to Laboratory Test Selection & Interpretation https://www.arupconsult.com/content/encephalitis-infectious
  2. Glaser CA, Honarmand S, Anderson LJ et al Beyond viruses: clinical profiles and etiologies associated with encephalitis. Clin Infect Dis. 2006 Dec 15;43(12):1565-77 PMID: 17109290
  3. Tunkel AR, Glaser CA, Bloch KC et al The management of encephalitis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2008 Aug 1;47(3):303-27 PMID: 18582201 (corresponding National Guideline Clearinghouse entry withdrawn Dec 2013)
  4. Singh TD et al. The spectrum of acute encephalitis: Causes, management, and predictors of outcome. Neurology 2015 Jan 27; 84:1 PMID: 25540320 http://www.neurology.org/content/early/2014/12/24/WNL.0000000000001190
  5. Wyllie E, Rincon SP, Pierce VM Case 16-2015 - A 9-Year-Old Girl with Loss of Consciousness and Seizures. N Engl J Med 2015; 372:2050-2058. May 21, 2015 PMID: 25992750 http://www.nejm.org/doi/full/10.1056/NEJMcpc1501149
  6. Medical Knowledge Self Assessment Program (MKSAP) 17, 19 American College of Physicians, Philadelphia 2015, 2021 - Medical Knowledge Self Assessment Program (MKSAP) 19 Board Basics. An Enhancement to MKSAP19. American College of Physicians, Philadelphia 2022
  7. Venkatesan A, Geocadin RG. Diagnosis and management of acute encephalitis: A practical approach. Neurol Clin Pract. 2014 Jun;4(3):206-215. PMID: 25110619 Free PMC Article
  8. Venkatesan A, Tunkel AR, Bloch KC et al Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the international encephalitis consortium. Clin Infect Dis. 2013 Oct;57(8):1114-28. PMID: 23861361 Free PMC Article
  9. Flanagan EP et al. Autoimmune encephalitis misdiagnosis in adults. JAMA Neurol 2022 Nov 28; [e-pub]. PMID: 36441519 PMCID: PMC9706400 Free PMC article https://jamanetwork.com/journals/jamaneurology/fullarticle/2799083
  10. Habis R et al. Absence of cerebrospinal fluid pleocytosis in encephalitis. Clin Infect Dis 2024 Aug 3; PMID: 39096271 https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciae391/7726814 - Bloch K, Glaser C. A clear and present danger: Encephalitis due to infection with normocellular cerebrospinal fluid. Clin Infect Dis 2024 Aug 3; [e-pub]. PMID: 39096272 https://academic.oup.com/cid/advance-article-abstract/doi/10.1093/cid/ciae387/7726813 - Hebant B, et al. Absence of Pleocytosis in Cerebrospinal Fluid does not Exclude Herpes Simplex Virus Encephalitis in Elderly Adults. J Am Geriatr Soc. 2015. PMID: 26096420
  11. NINDS Encephalitis and Meningitis Information Page https://www.ninds.nih.gov/Disorders/All-Disorders/Meningitis-and-Encephalitis-Information-Page - Meningitis and Encephalitis Fact Sheet https://www.ninds.nih.gov/disorders/patient-caregiver-education/fact-sheets/meningitis-and-encephalitis-fact-sheet