encephalitis

Question 1

definition

Answer 1

Encephalitis is defined as inflammation of the brain parenchyma associated with neurological dysfunction[1] such as altered state of consciousness, seizures, personality changes, cranial nerve palsies, speech problems, and motor and sensory deficits. It is the result of direct inflammation of the brain tissue, as opposed to the inflammation of the meninges (meningitis), and can be the result of infectious or non-infectious causes. An aetiological agent is only identified in around 50% of cases.

Question 2

causes

Answer 2

Virus: Most common in the UK is HSV. Other viruses are herpes zoster, mumps, adenovirus, coxsackie, echovirus, enteroviruses, measles, EBV, HIV, rabies (Asia), Nipah (Malaysia) and arboviruses transmitted by mosquitoes, e.g. Japanese B encephalitis (Asia), St. Louis and
West Nile encephalitis (USA).

Non-viral: (rare) e.g. syphilis, Staphylococcus aureus.
Immunocompromised: CMV, toxoplasmosis, Listeria.

Autoimmune or paraneoplastic: May be associated with antibodies e.g. anti-NMDA or anti-VGKC.

Question 3

signs and symptoms

Answer 3

• fever
• rash
• altered mental state
• meningismus (neck stiffness, photophobia, headache) – usually with meningus involvement
• seizures

Question 4

risk factors

Answer 4

age under 1 or over 65 years, immunodeficiency, viral infections, body fluid exposure, organ transplantation, animal or insect bites, location, and season.

Question 5

investigations

Answer 5

Blood: FBC (raised lymphocytes), U&E (SIADH may occur), glucose (compare with CSF glucose), viral serology, ABG.

MRI/CT: Excludes mass lesion. HSV produces characteristic oedema of the temporal lobe on MRI.

Lumbar puncture: raised Lymphocytes, raised monocytes, raised protein, glucose usually normal. CSF culture is difficult, viral PCR is now first line.

EEG: May show epileptiform activity, e.g. spiking activity in temporal lobes.

Brain biopsy: Now very rarely performed.