Encephalitis

Question 1

Definition

Answer 1

Inflammation of the brain parenchyma

Question 2

Aetiology/Risk factors

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

· 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 3

Epidemiology

Answer 3

UK incidence: 7.4/100,000

Question 4

Presenting 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 on physical examination

Answer 5

· 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 6

Investigations

Answer 6

· Bloods
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

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

· Lumbar Puncture
o High lymphocytes
o High monocytes
o High protein
o Glucose is usually normal
o Viral PCR

· EEG - may show epileptiform activity

· Brain biopsy (rarely needed)