Encephalitis

Question 1

Define:

Answer 1

Inflammation of the brain parenchyma

Question 2

Aetiology/risk factors:

Answer 2

Most commonly due to a viral infection

Viral causes:

• Herpes Simplex Virus = the most common cause in the UK
• Varicella Zoster virus
• Coxsackie
• HIV
• mumps
• Adenovirus
• Japanese encephalitis

Non-viral (rare):

• syphilis
• S. aureus

If immunocompromised:

• CMV
• Toxoplasmosis
• Listeria

Autoimmune or paraneoplastic

Question 3

Epidemiology:

Answer 3

7.4/100,000 = UK incidence

Question 4

Symptoms:

Answer 4

Most cases are self-limiting and mild
Subacute onset (hrs to days)
Headaches
Fever
Vomiting
Behavioural changes - odd behaviour and confusion
History of seizures
Focal neurological symptoms (dysphagia and hemiplegia)
Travel history
Fever, rash, lymphadenopathy, cold sores and conjunctivitis

Question 5

Signs:

Answer 5

• Reduce consciousness
• Bizarre encephalopathic behaviour
• 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 - FBC (lymphocytes increased if there is an infection), U+Es (SIADH can cause encephalitis), glucose, viral serology, ABG, Toxoplasma IgM titre and malaria film

MRI/CT:
o Exclude mass lesion
o HSV causes oedema of the temporal lobe on MRI
o Meningeal enhancement suggests meningoencephalitis
o MRI if allergic to contrast

Lumbar puncture:
o	High lymphocytes 
o	High monocytes 
o	High protein 
o	Glucose is usually normal or low
o	Viral PCR – 95% specific for HSV-1

EEG

Brain biopsy - rarely needed