Encephalitis

Question 1

Define

Answer 1

Inflammation of neuronal cells i.e. the brain parenchyma Leads to altered mental status

In many cases mild and self-limiting

Question 2

Causes

Answer 2

Usually as a result of a viral infection

• Virus: most commonly HSV
  Also many other viral causes from travelling abroad
  
  • VZV
  • Mumps
  • Adenovirus
  • Coxsackie
  • EBV
  • HIV
  • Japanese encephalitis
• Non-viral (RARE): syphilis, S. aureus
• Immunocompromised: CMV, toxoplasmosis, listeria
• Autoimmune or paraneoplastic: associated with antibodies

Question 3

Epidemiology

Answer 3

UK incidence: 7.4/100,000

Question 4

Symptoms

Answer 4

• In most cases, encephalitis is self-limiting and mild
• Subacute onset (hours to days)
• Headache
• Fever
• Vomiting
• Neck stiffness
• Photophobia
• Behavioural changes
• Drowsiness
• Confusion
• History of seizures
• Focal neurological symptoms (e.g. dysphagia, hemiplegia)
• Obtain a detailed TRAVEL HISTORY

Question 5

Signs

Answer 5

Reduce consciousness

Deteriorating GCS

Seizures

Pyrexia

Signs of Meningism:

• Neck stiffness
• Photophobia
• Kernig’s test positive

Signs of raised ICP:

• Cushing’s Response: hypertension + bradycardia + irregular breathing
• Papilloedema

Focal neurological signs

MMSE may reveal cognitive/psychiatric disturbance

Question 6

Investigations

Answer 6

Bloods

• FBC - high lymphocytes (indicates viral cause)
• U&Es - SIADH may occur as a result of encephalitis
• Glucose
• Viral serology
• ABG

MRI/CT

• Exclude mass lesion
• HSV causes oedema of the temporal lobe on MRI

Lumbar Puncture

• High lymphocytes
• High monocytes
• High protein
• Glucose is usually normal
• Viral PCR

EEG - may show epileptiform activity

Brain biopsy (rarely needed)