Encephalitis

Question 1

Define encephalitis.

Answer 1

Inflammation of the brain parenchyma associated with neurological dysfunction.

Can be caused by infectious or non-infectious causes.

Question 2

What % of encephalitis cases have an identifiable aetiology?

Answer 2

An aetiological agent is only identified in around 50% of cases.

Question 3

What are the most common viral causes of encephalitis?

Answer 3

• HSV1 and 2 - HSV-1 causes 95% of cases in adults
• Arboviruses
• CMV
• EBV
• VZV
• HIV
• Measles
• Mumps
• Rabies
• Japanese B encephalitis
• West Nile virus
• Tick-borne encephalitis

Question 4

What are the most common non-viral causes of encephalitis?

Answer 4

• Bacterial meningitis
• TB
• Malaria
• Listeria
• Lyme disease
• Legionella
• Leptospirosis
• Aspergillosis
• Cryptococcus
• Schistosomiasis
• Typhus

Question 5

What is the pathophysiology of encephalitis? Which part of the brain is most commonly affected?

Answer 5

Virus usually gains entry and replicates in regional tissues before disseminating to the CNS by haematogenous or retrograge axonal transport.

HSV1 classically affects temporal and inferior frontal lobes

Question 6

What are the risk factors for encephalitis?

Answer 6

• Age <1 or >65years
• Immunodeficiency
• Blood/body fluid exposure
• Organ transplantation
• Animal or insect bites - mosquitoes, ticks, animals with rabies/brucellosis
• Travel
• Swimming/diving in warm freshwater or nasal/sinus irrigation

Question 7

What is the sequence of events in encephalitis?

Answer 7

1. Infectious prodrome (raised temp, lymphadenopathy, cold sores, conjunctivitis, meningeal signs)*
2. Then odd behaviour, reduced GCS, focal neurology or seizure

*if no infectious prodrome suspect encephalopathy

Question 8

List some non-infectious causes of encephalopathy ?

Answer 8

• hypoglycaemia
• hepatic encephalopathy
• diabetic ketoacidosis
• drugs
• hypoxic brain injury
• uraemia
• SLE
• Wernicke’s (give vit B1 if in doubt)

Question 9

What are the signs of encephalitis?

Answer 9

• Bizarre behaviour or confusion
• Reduced GCS or coma
• Focal neurological signs
• History of travel or animal bite

Question 10

What are the symptoms of encephalitis?

Answer 10

• Fever, rash, cough, (GI infection)
• Headache
• Seizures
• Some patients have meningism

Question 11

What investigations would you do for encephalitis?

Answer 11

Bloods:

• Cultures
• PCR for HSV
• Throat swab and MSU

Imaging:

• Contract enhanced CT - do before LP; normal in 1 in 3.
• EEG - lateralised periodic discharges at 2 Hz

Invasive:

• LP- elevated proteins and lymphocytosis. Send for viral PCR including HSV

Question 12

How do you manage encephalitis?

Answer 12

Mortality if untreated = 70%

• IV aciclovir within 30min of admission (10mg/kg TDS given over 1hr) for 14-21 days (specific therapies exist for CMV and toxoplasmosis)
• Supportive therapy, HDU or ICU if necessary
• Symptomatic treatment e.g. phenytoin for seizures

Question 13

What is the difference in management of viral encephalitis vs meningitis? How do you distinguish between the two ?

Answer 13

Viral meningitis - does not require treatment in the immunocompetent

Viral encephalitis - always requires antiviral treatment - differentiated from meningitis on clinical grounds: confusion, behavioural change, neurological deficits.

Question 14

What is the relation of cold sores to HSV encephalitis?

Answer 14

Peripheral lesions (e.g. cold sores) have no relation to the presence of HSV encephalitis