Encephalitis

Question 1

Definition

Answer 1

Inflammation of the brain parenchyma

Question 2

Aetiology (viral)

Answer 2

• Most commonly due to VIRAL INFECTION

• Viral Causes:
o Herpes Simplex Virus - MOST COMMON in the UK
o VZV
o Mumps
o Adenovirus
o Coxsackie
o EBV
o HIV
o Japanese encephalitis

Question 3

Aetiology (other)

Answer 3

• Non-Viral (RARE)
o Syphilis
o Staphylococcus aureus

• In immunocompromised patients
o CMV
o Toxoplasmosis
o Listeria

• Autoimmune or Paraneoplastic
o Associated with certain antibodies (e.g. anti-NMDA, anti-VGKC)

Question 4

Epidemiology

Answer 4

UK incidence: 7.4/100,000

Question 5

Presenting symptoms

Answer 5

• 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 6

Signs on physical examination

Answer 6

• Reduce consciousness
• Deteriorating GCS
• Seizures
• Pyrexia

• Signs of Meningism:
o Neck stiffness
o Photophobia
o Kernig’s test positive

• Signs of raised ICP:
o Cushing’s Response: hypertension + bradycardia + irregular breathing
o Papilloedema

• Focal neurological signs
• MMSE may reveal cognitive/psychiatric disturbance

Question 7

Investigations (bloods)

Answer 7

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

Question 8

Investigations (lumbar puncture)

Answer 8

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

Question 9

Investigations (other)

Answer 9

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

• EEG - may show epileptiform activity
• Brain biopsy (rarely needed)