“Inflammation of brain parenchyma”
- Gallstones, recent biliary tract procedure or previous cholangitis.
- Medication e.g. COCP, fibrates.
- Lipid-rich diet (increased incidence of gallstones).
- Primary viral infection (primary encephalitis)
- Epidemic e.g. coxsackievirus, poliovirus, arbovirus, echovirus
- Sporadic e.g. cytomegalovirus, herpes simplex (HSV-1 or HSV-2 in immunocompromised), varicella-zoster, rabies, mumps, lymphocytic choriomeningitis
- Reactivation of latent viral infection e.g. HIV-associated encephalopathy and dementia, subacute sclerosing panencephalitis (measles reactivation), HSV-1 and herpes zoster encephalitis, progressive multifocal leukoencephalopathy
- Rarely, SARS-CoV2 has been reported to cause encephalitis
- Secondary immunological complication
- With possible progression to acute disseminated encephalomyelitis -> inflammatory demyelination of the brain
- Immune system targets CNS antigens resembling viral proteins
- A complication of measles, rubella, chickenpox, mumps, smallpox vaccine, live-virus vaccines, influenza A/B, enterovirus, EBV, HepA, HepB or HIV
- Acute encephalitis:
- Inflammation and oedema occurs in CNS structures.
- Direct viral invasion of brain parenchyma damages neurons.
- Severe infection can cause brain haemorrhagic necrosis.
- Acute disseminated encephalomyelitis:
- Multifocal areas of perivenous demyelination, absence of virus in the brain
- Altered mental status
- Seizures and focal neurological deficits
- GI or respiratory prodrome
- Status epilepticus or coma = poor prognosis due to severe brain inflammation
- Phantosmia (olfactory hallucination) indicates temporal lobe involvement -> HSV encephalitis
- Contrast-enhanced MRI -> can show orbitofrontal and temporal oedema, demyelination, basal ganglia, thalamic abnormalities)
- Excludes lesions which may mimic viral encephalitis
- CSF analysis (PCR for HSV/other viruses with serologic tests) -> lymphocytic leucocytosis, normal glucose, elevated protein, absence of pathogens
- Brain biopsy if patient is worsening, has responded poorly to treatment or has an undiagnosed lesion
- Supportive care
- Treatment of fever, dehydration, electrolyte imbalance, seizures
- Antiviral drugs
- Acyclovir for HSV or varicella-zoster virus encephalitis
- Antibiotics until bacterial meningitis excluded
- If immunologic: corticosteroids e.g. prednisolone and plasma exchange/IV immunoglobulins
- Permanent neurological deficits in survivors of severe infection