Encephalitis involves inflammation of the brain. Key causes are infections (e.g., viruses) and autoimmune disease.
A common and important treatable cause of encephalitis is herpes simplex virus (HSV). This may be:
- Herpes simplex virus type 1 (HSV-1) in older children and adults (HSV-1 is often associated with cold sores)
- Herpes simplex virus type 2 (HSV-2) in neonates, contracted at birth from genital herpes
Other viral causes include:
- Varicella zoster virus (VZV) (associated with chickenpox)
- Enterovirus
- Cytomegalovirus (associated with immunodeficiency)
- Epstein-Barr virus (infectious mononucleosis)
- Influenza virus
- Measles
- Mumps
- Rubella
Presentation
Presenting features of encephalitis include:
- Headache
- Altered consciousness
- Altered cognition
- Unusual behaviour
- Focal neurological symptoms
- Seizures
- Fever
Diagnosis
Key diagnostic tests include:
- Lumbar puncture, sending cerebrospinal fluid for viral PCR testing, including HSV, VZV and enterovirus
- MRI brain
- EEG in mild or ambiguous symptoms, but is not always routinely required
- Swabs can help establish the causative organism, such as throat and vesicle swabs
- HIV testing in all patients with encephalitis
Management
Intravenous antiviral medications are used to treat the suspected or confirmed underlying cause:
- Aciclovir treats herpes simplex virus (HSV) and varicella zoster virus (VZV)
- Ganciclovir treats cytomegalovirus (CMV)
Repeat lumbar puncture may be considered in HSV encephalitis to ensure successful treatment before stopping antivirals.
Most other viral causes are managed supportively.
Autoimmune encephalitis may be treated with immunotherapy, such as:
- Corticosteroids
- IV immunoglobulins
- Plasma exchange
Follow-up, support, and rehabilitation are required after encephalitis, with help in managing the complications.
Complications of Encephalitis
There is a long list of possible complications of encephalitis, including:
- Lasting fatigue and prolonged recovery
- Change in personality or mood
- Changes to memory and cognition
- Learning disability
- Behavioural problems
- Sleep disturbance
- Headaches
- Chronic pain
- Movement disorders
- Sensory disturbance
- Seizures
- Hormonal imbalance
Last updated May 2026
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