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)

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

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. Resources: Patients

  1. Encephalitis Global Support Website
    1. http://communities.msn.com/encephalitisglobal

XIII. 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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Related Studies

Ontology: Encephalitis (C0014038)

Definition (MEDLINEPLUS)

Encephalitis is an inflammation of the brain. Usually the cause is a viral infection, but bacteria can also cause it. It can be mild or severe. Most cases are mild. You may have flu-like symptoms. With a mild case, you may just need rest, plenty of fluids, and a pain reliever.

Severe cases need immediate treatment. Symptoms of severe cases include

  • Severe headache
  • Sudden fever
  • Drowsiness
  • Vomiting
  • Confusion
  • Seizures

In babies, additional symptoms may include constant crying, poor feeding, body stiffness, and bulging in the soft spots of the skull.

Severe cases may require a stay in the hospital. Treatments include oral and intravenous medicines to reduce inflammation and treat infection. Patients with breathing difficulties may need artificial respiration. Some people may need physical, speech, and occupational therapy once the illness is under control.

NIH: National Institute of Neurological Disorders and Stroke

Definition (NCI) An acute inflammatory process affecting the brain parenchyma. Causes include viral infections and less frequently bacterial infections, toxins, and immune-mediated processes.
Definition (MSH) Inflammation of the BRAIN due to infection, autoimmune processes, toxins, and other conditions. Viral infections (see ENCEPHALITIS, VIRAL) are a relatively frequent cause of this condition.
Definition (CSP) inflammation of the brain due to infection, autoimmune processes, toxins, and other conditions; viral infections are a relatively frequent cause of this condition.
Concepts Disease or Syndrome (T047)
MSH D004660
SnomedCT 267682000, 192736002, 267578009, 45170000
LNC LP20690-1
French ENCEPHALITE, Encéphalite SAI, Encéphalite
Portuguese ENCEFALITE, Encefalite NE, Encefalite, Inflamação do Encéfalo
Spanish ENCEFALITIS, Encefalitis NEOM, Inflamación del Encéfalo, encefalitis, SAI (trastorno), encefalitis, SAI, encefalitis (trastorno), encefalitis, Encefalitis
German ENZEPHALITIS, Enzephalitis NNB, Enzephalitis, Entzündung, Gehirn
English Encephalitis NOS, Encephalitis, BRAIN INFLAMM, INFLAMM BRAIN, ENCEPH, encephalitis, encephalitis (diagnosis), Brain Inflammation, Brain Inflammations, Inflammation, Brain, Encephalitis [Disease/Finding], brain inflammation, inflammation of the brain, Encephalitis NOS (disorder), ENCEPHALITIS, Encephalitis (disorder), brain; inflammation, cerebral; inflammation, inflammation; brain, inflammation; cerebral, Encephalitis, NOS
Dutch encefalitis NAO, cerebraal; ontsteking, hersenen; ontsteking, ontsteking; cerebraal, ontsteking; hersenen, encefalitis, Encefalitis, Hersenontsteking, Ontsteking, hersen-
Italian Encefalite NAS, Infiammazione del cervello, Encefalite
Japanese 脳炎NOS, ノウエン, ノウエンNOS, 脳炎
Swedish Hjärninflammation
Czech mozek - zánět, encefalitida, zánět mozku, Encefalitida, Encefalitida NOS
Finnish Aivotulehdus
Polish Zapalenie mózgu
Hungarian Encephalitis k.m.n., Encephalitis
Norwegian Encefalitt, Hjernebetennelse

Ontology: Viral Encephalitis (C0243010)

Definition (MSHFRE) Inflammation du parenchyme de l'encéphale ayant pour étiologie une infection virale. L'encéphalite peut être une manifestation primaire ou secondaire des infections par les : Togaviridae, Herpesviridae, Adenoviridae, Flaviviridae, Bunyaviridae, Picornaviridae, Paramyxoviridae, Orthomyxoviridae, Retroviridae, Arenaviridae.
Concepts Disease or Syndrome (T047)
MSH D018792
ICD10 A86
SnomedCT 187400005, 266190006, 154321007, 192694006, 186503001, 34476008
English Encephalitis, Viral, Unspecfd viral encephalitis, Unspecified viral encephalitis, [X]Unspecfd viral encephalitis, [X]Unspecified viral encephalitis, Encephalitis in viral dis NOS, Encephalitis in viral disease NOS, INFECT ENCEPH VIRAL, VIRAL ENCEPH, ENCEPH INFECT VIRAL, ENCEPH VIRAL, Viral Encephalitis, viral encephalitis, viral encephalitis (diagnosis), Encephalomyelitis, Infectious, Viral, Encephalomyelitis, Viral Infectious, Infectious Encephalomyelitis, Viral, Viral Infectious Encephalomyelitis, Encephalitis, Viral [Disease/Finding], encephalitis viral, Encephalitis viral NOS, Encephalitis - viral, Viral encephalitis NOS, [X]Unspecified viral encephalitis (disorder), Encephalitis in viral disease NOS (disorder), Encephalitis viral, Viral encephalitis, Viral encephalitis (disorder), encephalitis; viral, viral; encephalitis, Viral encephalitis, NOS
Dutch encefalitis viraal NAO, virusencefalitis, encefalitis; viraal, viraal; encefalitis, Niet gespecificeerde virale encefalitis, virale encefalitis, Encefalitis, virale, Encefalomyelitis, infectieuze virale, Infectieuze encefalomyelitis, virale, Virale encefalitis
French Encéphalite virale SAI, Encéphalite virale, Encéphalo-myélite virale, Encéphalomyélite virale
German virale Enzephalitis, Enzephalitis durch Viren NNB, Virusenzephalitis, nicht naeher bezeichnet, Virale Enzephalitis, Enzephalitis, Virus-, Virusenzephalitis, Enzephalomyelitis, infektiöse, virale, Infektiöse Enzephalomyelitis, virale
Italian Encefalite virale NAS, Encefalomielite virale infettiva, Encefalite virale
Portuguese Encefalite viral NE, Encefalite vírica, Encefalite viral, Encefalite Viral, Encefalomielite Infecciosa Viral
Spanish Encefalitis vírica, Encefalitis vírica NEOM, encefalitis virósica, encefalitis vírica, [X]encefalitis viral no especificada (trastorno), encefalitis en enfermedad viral, SAI (trastorno), [X]encefalitis viral no especificada, encefalitis en enfermedad viral, SAI, encefalitis viral (trastorno), encefalitis viral, Encefalitis viral, Encefalitis Viral, Encefalomielitis Infecciosa Viral, Encefalomielitis Viral Infecciosa
Japanese ウイルス性脳炎NOS, ウイルスセイノウエン, ウイルスセイノウエンNOS, 脳炎-ウイルス性, ウイルス性脳炎, ウイルス脳炎
Swedish Hjärninflammation, viral
Czech encefalitida virová, Virová encefalitida NOS, Virová encefalitida
Finnish Aivojen virustulehdus
Korean 상세불명의 바이러스 뇌염
Polish Zapalenie mózgu wirusowe
Hungarian Viralis encephalitis, virusos encephalitis, virusos encephalitis k.m.n.
Norwegian Viral encefalitt, Virusencefalitt, Encefalomyelitt, infeksiøs viral, Infeksiøs viral encefalomyelitt, Encefalitt, viral