Encephalitis

Question 1

Definition of encephalitis

Answer 1

Inflammation of the brain parenchyma that is associated with neurological dysfunction

Question 2

Aetiology of Encephalitis

Answer 2

• Most common cause is VIRAL INFECTION (Herpes virus is the most common group)
• A cause is only found 50% of the time
• Viral:
◦ Herpes virus
◦ Enteroviruses
◦ Parechoviruses

• Non-viral:
‣ Neisseria Meningitidis
‣ TB
‣ Syphilis
‣ Cryptococcus (fungal)
‣ Toxoplasma Gondi (parasitic)

Question 3

Pathophysiology of encephalitis

Answer 3

• In viral encephalitis, the virus would gain entry and replicate in areas such as the GI tract, skin, Urogenital or respiratory system.
• They would then spread to the CNS via the haematogenous route (via blood)
• Infection and inflammation of the brain parenchyma would then occur
• Autoimmune encephalitis would have auto-antibodies directed against normal brain components
• Would cause neurological dysfunction

Question 4

History and examination of encephalitis:

Answer 4

• Fever: Frequently seen with infectious causes. Exception is measles
• Altered mental state:
‣ Ranges from mild somnolence to coma. May have memory disturbances, bizarre behaviour, personality changes, disorientation, confusion, decreased consciousness
• Focal neurological deficit: Aphasia, hemiparesis, hemianopia, Babinski’s sign, cranial nerve deficits
• Decreased GCS
• Headache
• Seizures: generalised tonic clonic
• Rash: May see vesicular eruption with some viruses (HSV and varicella)
• May show some meningismus

Question 5

Risk factors for encephalitis

Answer 5

• Risk factors:
• Extremes of age (<1 or >65)
• Immunodeficiency
• Previous viral infection (resp, GI etc)
• Animal or insect bite
• Travel history

Question 6

Investigations for encephalitis

Answer 6

• FBC: would see lymphocytosis in viral causes
• Contrast CT scan: order in all patients with altered mental state, unless allergic to contrast (then MRI)
• Lumbar puncture for CSF analysis: first check to see if there is raised ICP
• Blood cultures + viral PCR/ throat swabs
• EEG: may show background slowing but cannot indicate cause

Question 7

Treatment for viral encephalitis

Answer 7

1) Aciclovir: All cases of suspected viral cause should be started on this ASAP, until the cause is determined. Give IV
+ Supportive care: all cases should be admitted. Transfer to HDU or ICU if severe symptoms. May require ventilation, ICP lowering therapy (mannitol) etc. May give phenytoin for seizures

Question 8

Prevention of encephalitis

Answer 8

Vaccinations for MMR etc. Improve sanitation etc

Question 9

Complications and prognosis of encephalitis

Answer 9

• Death: very high risk of death with untreated HSV encephalitis
• Neurological sequelae

Depends on underlying cause, immune status of the host etc
Fast treatment with aciclovir can reduce mortality and morbidity by a large amount