Encephalitis

Question 1

What are the causes of encephalitis?

Answer 1

• Direct invasion of cerebellum by neurotoxic virus (e.g. HSV)
• Post-infectious encephalopathy of delayed brain swelling following neuroimmunological response to antigen
• Slow virus infection (e.g. HIV or subacute sclerosing pan-encephalitis following measles); in UK:
  > Most common UK:
  • Enterovirus
  • Respiratory viruses (influenza)
  • Herpes (HSV (rare cause of childhood encephalitis), VZV, HHV-6)
  *70% mortality from untreated HSV encephalitis *
  • Other = chickenpox, bacteria & fungus (very rare), mosquitos (Japanese encephalitis), ticks (tick-borne encephalitis), mammals (rabies encephalitis)

Question 2

What are the signs and symptoms?

Answer 2

• Same as per meningitis (may not be able to differentiate clinically -> begin treatment for both)
• Main = fever, altered consciousness, seizures (differentiate potentially by behavioural change)

Question 3

What is the management for encephalitis?

Answer 3

1. IV acyclovir (high-dose) 3 weeks – HSV is a rare cause but complications are major, so treat empirically
2. IV administration – E.G. 8.9kg child, 76cm long, 8.5 months old – use BNF-c:
   - 500mg/m2 every 8 hours for 21 days (in simplex encephalitis)

Body surface area calculation:
Body surface area (m^2 )= √(body weight (kg)*height (cm))/3600
Body surface area = 0.43m2 -> (500 x 0.43) 215mg
IV administration -> reconstitute to: 25mg/mL with water
5mg/mL with NaCl
5mg/mL -> 215 / 5 = 43mL of NaCl + 215mg aciclovir

Other:
	CMV - add in ganciclovir and Foscarnet
	VZV - acyclovir/ganciclovir 
	EBV - acyclovir 
	Supportive care – fluids, ventilation, etc.