II. Causes: Viral (most cases)

  1. Common
    1. Herpes Simplex Encephalitis (Very poor prognosis)
      1. Adults: Herpes Simplex Virus I
      2. Neonates: Herpes Simplex Virus II
    2. Arbovirus
      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. California Encephalitis (generally benign)
      5. Venezuelan equine Encephalitis (generally benign)
      6. West Nile Virus Encephalitis (severe in elderly)
    3. Mumps (Generally benign)
  2. Uncommon
    1. Enterovirus
    2. Varicella Zoster Virus
    3. Epstein-Barr Virus
    4. Influenza
    5. Rabies (rare in U.S.)
  3. Immunocompromised
    1. Cytomegalovirus (AIDS)

III. Causes: Other (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. Cerebral Edema
    1. Mannitol
    2. Corticosteroids
      1. Only for specific indications
      2. Avoid in Herpes Simplex Virus
  2. Seizure control
  3. Specific empiric Management if cause suspected (Keep high level of suspicion for treatable etiologies)
    1. HSV Encephalitis: Acyclovir IV
      1. Start Acyclovir empirically for Encephalitis case and continue until diagnosis is excluded
    2. CMV Encephalitis (AIDS): 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. Fuchs and Yamamoto (2012) APLS, Jones and Bartlett, Burlington, p. 180-3

Images: Related links to external sites (from Google)

Ontology: Encephalitis (C0014038)

Definition (MSHFRE) Inflammation de l'encéphale due à une infection (bactérienne, parasitaire ou virale), à un processus auto-immun, à des toxines, ou à d'autres étiologies. Les infections virales sont une étiologie fréquente des encéphalites.
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 (MEDLINEPLUS)

Encephalitis is an inflammation of the brain. The usual cause is a viral infection, but bacteria can also cause it. Cases can range from mild to severe. For mild cases, you could have flu-like symptoms. Serious cases can cause

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

For mild cases, you may just need rest, plenty of fluids and a pain reliever. For severe cases, you might need to be hospitalized. Fortunately, encephalitis is uncommon in the United States.

NIH: National Institute of Neurological Disorders and Stroke

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 267578009, 45170000, 267682000, 192736002
French ENCEPHALITE, Encéphalite SAI, Encéphalite
English ENCEPHALITIS, Encephalitis, NOS, Encephalitis NOS, Encephalitis, BRAIN INFLAMM, INFLAMM BRAIN, ENCEPH, encephalitis, encephalitis (diagnosis), Brain Inflammation, Brain Inflammations, Inflammation, Brain, Encephalitis NOS (disorder), Encephalitis [Disease/Finding], brain inflammation, inflammation of the brain, Encephalitis (disorder), brain; inflammation, cerebral; inflammation, inflammation; brain, inflammation; cerebral
Portuguese ENCEFALITE, Encefalite NE, Encefalite, Inflamação do Encéfalo
Spanish ENCEFALITIS, Encefalitis NEOM, Inflamación del Encéfalo, Inflamacion del Encefalo, Encephalitis, Encephalitis NOS, encefalitis (trastorno), encefalitis, SAI (trastorno), encefalitis, SAI, encefalitis, Encefalitis
German ENZEPHALITIS, Enzephalitis NNB, Enzephalitis, Entzündung, Gehirn
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
Russian ENTSEFALIT, ЭНЦЕФАЛИТ
Croatian UPALA MOZGA, ENCEFALITIS
Polish Zapalenie mózgu
Hungarian Encephalitis k.m.n., Encephalitis

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.
Definition (MSH) Inflammation of brain parenchymal tissue as a result of viral infection. Encephalitis may occur as primary or secondary manifestation of TOGAVIRIDAE INFECTIONS; HERPESVIRIDAE INFECTIONS; ADENOVIRIDAE INFECTIONS; FLAVIVIRIDAE INFECTIONS; BUNYAVIRIDAE INFECTIONS; PICORNAVIRIDAE INFECTIONS; PARAMYXOVIRIDAE INFECTIONS; ORTHOMYXOVIRIDAE INFECTIONS; RETROVIRIDAE INFECTIONS; and ARENAVIRIDAE INFECTIONS.
Concepts Disease or Syndrome (T047)
MSH D018792
ICD10 A86
SnomedCT 187400005, 192694006, 34476008, 154321007, 266190006, 186503001
English Encephalitis, Viral, Viral encephalitis, NOS, 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), [X]Unspecified viral encephalitis (disorder), Encephalomyelitis, Infectious, Viral, Encephalomyelitis, Viral Infectious, Infectious Encephalomyelitis, Viral, Viral Infectious Encephalomyelitis, Encephalitis in viral disease NOS (disorder), Encephalitis, Viral [Disease/Finding], encephalities viral, encephalitis viral, Encephalitis viral NOS, Encephalitis viral, Viral encephalitis, Viral encephalitis (disorder), encephalitis; viral, viral; encephalitis, Encephalitis - viral, 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, Encephalitis - viral, Viral encephalitis NOS, Viral encephalitis, [X]encefalitis viral no especificada, [X]encefalitis viral no especificada (trastorno), encefalitis en enfermedad viral, SAI (trastorno), encefalitis en enfermedad viral, SAI, encefalitis viral (trastorno), encefalitis viral, encefalitis virósica, 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
Russian ENTSEFALIT VIRUSNYI, ENTSEFALOMIELIT INFEKTSIONNYI VIRUSNYI, VIRUSNYI ENTSEFALIT, ВИРУСНЫЙ ЭНЦЕФАЛИТ, ЭНЦЕФАЛИТ ВИРУСНЫЙ, ЭНЦЕФАЛОМИЕЛИТ ИНФЕКЦИОННЫЙ ВИРУСНЫЙ
Korean 상세불명의 바이러스 뇌염
Croatian ENCEFALITIS, VIRUSNI, VIRUSNI ENCEFALITIS
Polish Zapalenie mózgu wirusowe
Hungarian Viralis encephalitis, virusos encephalitis, virusos encephalitis k.m.n.