Viral Encephalitis

Aka: Viral Encephalitis, Encephalitis

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II. Causes: Viral (most cases)

  1. Causative organism identified in only half of cases
  2. Common
    1. Enterovirus Meningitis (50.9% of all Meningitis cases in adults)
    2. Herpes Simplex Encephalitis (8.3% of all Meningitis cases in adults, Very poor prognosis)
      1. Adults: Herpes Simplex Virus I
      2. Neonates: Herpes Simplex Virus II
    3. Varicella Zoster Virus (15% of cases)
    4. Mumps (Generally benign)
    5. Arbovirus (1.1% of all Meningitis causes in adults)
      1. Eastern Equine Encephalitis (70-90% poor prognosis)
      2. Western equine Encephalitis (2-20% poor prognosis)
      3. St. Louis Encephalitis (2-20% poor prognosis)
      4. Powassan Encephalitis (Tick Borne Illness, 50% with Cognitive Impairment, 10-15% mortality)
      5. California Encephalitis (generally benign)
      6. Venezuelan equine Encephalitis (generally benign)
      7. West Nile Virus Encephalitis (severe in elderly)
      8. Japanese Encephalitis (severe disease is uncommon, but 30% mortality when it occurs)
        1. Limited to travelers to rural and periurban Southeast Asia, Western Pacific
  3. Uncommon
    1. Parvovirus B19
    2. Epstein-Barr Virus
    3. Influenza
    4. Rabies (rare in U.S.)
  4. Immunocompromised
    1. Cytomegalovirus (AIDS)

III. Causes: Other non-viral (uncommon)

  1. Bacterial causes
    1. Tuberculosis (15% of cases)
    2. Listeria (10% of cases)
    3. Borrelia Burgdorferi (Lyme Disease)
    4. Bartonella Henselae (Cat Scratch Disease)
    5. Rickettsia rickettsii (Rocky Mountain Spotted Fever)
    6. Mycoplasma pneumoniae
    7. Treponema pallidum (Syphilis)
    8. Anaplasmosis
    9. Ehrlichiosis
  2. Fungal causes
    1. Cryptococcus
    2. Coccidioides
    3. Histoplasma
  3. Parasitic causes
    1. Taenia solium (Cysticercosis)
    2. Plasmodium Falciparum (Malaria)
    3. Toxoplasma gondii (Toxoplasmosis)
    4. Trypanosoma cruzi (Chagas Disease)
  4. Miscellaneous causes
    1. NMDA Encephalitis (very common in age <30 years old)

IV. Symptoms

  1. Sudden high fever
  2. Severe Headache
  3. Meningismus (e.g. Stiff neck)
  4. Altered Level of Consciousness
    1. Lethargy
    2. Mental confusion
    3. Coma
  5. Behavior change
  6. Seizure
  7. Dysarthria
  8. Dysphasia
  9. Nausea and Vomiting
  10. Photophobia
  11. Hemiparesis
  12. Cranial Nerve deficits
  13. Visual Field loss

V. Signs

  1. Variable signs depending on involvement and organism
    1. See HSV Encephalitis
    2. See West Nile Virus Encephalitis (C0043124)
  2. Tremor
    1. Tongue
    2. Lips
    3. Hands
  3. Other neurologic changes
    1. Ataxia
    2. Spastic paralysis
    3. Deep Tendon Reflexes exaggerated
    4. Signs of Increased Intracranial Pressure

VI. Differential Diagnosis

  1. See Altered Level of Consciousness Causes
  2. See Drug Induced Altered Level of Consciousness Causes

VII. Labs

  1. See Altered Level of Consciousness for general labs
  2. Complete Blood Count (CBC)
    1. Mild Leukocytosis
    2. Mild Lymphocytosis
  3. Serum Electrolytes and Glucose
  4. Specific testing
    1. Strep Throat swab
    2. Influenza nasal swab
    3. St Loius Encephalitis serum IgM
    4. West Nile Virus serum IgM
    5. Western Equine Encephalitis serum IgM
    6. Mycoplasma pneumoniae IgM
    7. Lyme Disease Screening
    8. Serum RPR for Syphilis
    9. CMV culture from urine or Saliva (Test Sensitivity approaches 100%)
    10. Varicella culture from vessicles
    11. Herpes culture from Vesicles, mucous membranes and urine
  5. Cerebrospinal Fluid (CSF)
    1. Initial tests
      1. CSF Gram Stain
      2. CSF Culture
      3. CSF Protein
      4. CSF Glucose
      5. CSF Cell Count with differential
    2. Typical non-specific findings
      1. Increased Intracranial Pressure
      2. Increased Protein
      3. Lymphocytic Pleocytosis
    3. CSF Antigens (indicated if CSF findings not consistent with Bacterial Meningitis)
      1. CSF HSV PCR (Send in all cases of suspected Encephalitis)
      2. CSF enterovirus PCR

VIII. Imaging

  1. CT Head
    1. Indicated prior to Lumbar Puncture if focal neurologic findings or signs of Increased Intracranial Pressure
  2. MRI Brain
    1. See HSV Encephalitis for HSV specific findings
    2. CMV Encephalitis
      1. Periventricular intracranial calcifications
      2. Cerebral dysgenesis
    3. Congenital Toxoplasmosis
      1. Multiple ring-enhancing lesions
    4. Cysticercosis
      1. Cystic lesions with variable calcifications
      2. Ring enhancement suggests cyst degeneration

IX. Management

  1. Empiric HSV management
    1. Start Acyclovir empirically for all Encephalitis cases
      1. Acyclovir 10 mg/kg IV over 1 hour every 8 hours
      2. Continue until diagnosis is excluded by HSV CSF PCR
  2. Cerebral Edema
    1. Mannitol
    2. Corticosteroids
      1. Only for specific indications
      2. Avoid in Herpes Simplex Virus
  3. Seizure control
  4. Specific empiric Management if cause suspected (Keep high level of suspicion for treatable etiologies)
    1. HSV Encephalitis
      1. Acyclovir IV (see dosing above)
    2. CMV Encephalitis (AIDS)
      1. Ganciclovir or Foscarnet
    3. Rocky Mountain Spotted Fever
      1. Doxycycline for any age where this is strongly suspected (causes tooth staining in under age 8 years)
    4. Cat-Scratch Disease Encephalitis
      1. Azithromycin or
      2. Doxycycline
    5. Mycoplasma pneumoniae Encephalitis
      1. Azithromycin or
      2. Doxycycline
    6. Lyme Encephalitis
      1. Ceftriaxone 75-100 mg/kg up to 2 grams IV q24 hours
    7. Influenza Encephalitis
      1. Oseltamivir (Tamiflu)

X. Course

  1. Symptomatic: weeks to months

XI. Prognosis

  1. Mortality during acute illness: 10%
  2. High rate of Disability following infection
    1. Variable depending on specific etiology

XII. References

  1. (2016) Sanford Guide, accessed 4/11/2016
  2. Fuchs and Yamamoto (2012) APLS, Jones and Bartlett, Burlington, p. 180-3
  3. Mailles (2009) Clin Infect Dis 49(12):1838-47 +PMID:19929384 [PubMed]
  4. Singh (2015) Neurology 84(4):359-66 +PMID:25540320 [PubMed]

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