Encephalitis

Question 1

Define

Answer 1

Inflammation of the brain parenchyma

Can be infectious or non-infectious

Question 2

What’s the aeitiology?

Answer 2

Most commonly due to VIRAL INFECTION

Aetiological agent only identified in 50% of cases

Viral Causes:

Herpes Simplex Virus - MOST COMMON in the UK

VZV

Mumps

Adenovirus

Coxsackie

EBV

HIV

Japanese encephalitis

Flaviviruses

Non-Viral (RARE) :

Syphilis

TB

Neisseria meningitides

Staphylococcus aureus

Fungal infections: cyptococcus, candida, coccidiodes

In immunocompromised patients:

CMV

Toxoplasmosis

Listeria

Autoimmune or Paraneoplastic:

Associated with certain antibodies (e.g. anti-NMDA, anti-VGKC)

Question 3

What are the risk factors?

Answer 3

age under 1 or over 65

Immunodeficiency

Viral infections

Organ transplantation

Question 4

What’s the epidemiology?

Answer 4

UK incidence: 7.4/100,000

Due to HIV cases have reduced

Question 5

What are the presenting symptoms?

Answer 5

In most cases, encephalitis is self-limiting and mild

Subacute onset (hours to days)

Fever

Rash

Vomiting

Evidence of meningeal inflammation may also present (headache, photophobia, neck stiffness)

Behavioural changes

Altered mental state

History of seizures

Focal neurological symptoms (e.g. dysphagia, hemiplegia)

May also have a cough, GI infection symptoms

Obtain a detailed TRAVEL HISTORY

Question 6

What are the signs?

Answer 6

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 (bilateral optic disc swelling)

Focal neurological signs

MMSE may reveal cognitive/psychiatric disturbance

Question 7

What are the appropriate investigations?

Answer 7

Bloods

FBC - high lymphocytes (indicates viral cause)

U&Es - SIADH may occur as a result of encephalitis, hyponatraemia

LFTs (may be elevated)

Glucose

Viral serology

ABG

Peripheral blood smear

Blood cultures

Throat swab, nasophargeal aspirate, sputum culture may also be done for respiratory infection.

Chest x-ray

MRI/CT

Exclude mass lesion

HSV causes oedema of the temporal lobe on MRI

Lumbar Puncture (CSF analysis, culture, serology or PCR)

High lymphocytes

High monocytes

High protein

Glucose is usually normal

Viral PCR

EEG - may show epileptiform activity, background slowing

Investigations to consider: urine culture, stool culture, PCR blood, Brain biopsy (rarely needed)