Encephalitis

• Encephalitis is a medical emergency.
• Encephalitis has at least as high an incidence as purulent meningitis and motor neurone disease.  
• Lumbar puncture and neuroimaging are key to diagnosis. 
• Early diagnosis and treatment can reduce mortality and morbidity. 
• Survivors often have ongoing difficulties and will require referral to a range of allied professions, including neuropsychology, and to other sources of support and information such as the Encephalitis Society. 
• Encephalitis should be given equal weight to other acute neurological emergencies in undergraduate curricula.

Encephalitis is well recognised as a significant cause of mortality and morbidity worldwide. Studies have identified that encephalitis is more prevalent than previously considered, with an incidence of approximately 5–8 cases/100 000 per year (Granerod et al, 2013). It is estimated that there are up to 6000 cases of encephalitis in the UK per year. This means that at least a few patients with this condition will present to most district general hospitals each year (Ellul and Solomon, 2018).

The brain can be damaged in two ways – by the cause (for example the infection) and also by the resultant inflammation (or swelling).

There are two primary causes of encephalitis:

In some cases where patients are immune-compromised or where the cause cannot be identified, encephalitis can present in a slow and chronic form that may ultimately lead to death.

Diagnosis of encephalitis hinges crucially on results of analysis of the cerebrospinal fluid obtained by lumbar puncture which demonstrates evidence of central nervous system inflammation (Raschilas et al, 2002).

There is no single diagnostic test for encephalitis and diagnosis is centred around excluding other causes or illness, as well as utilising a range of tests that will contribute toward a diagnosis. This includes:

• a full patient history
• blood sampling and testing for HIV
• brain imaging (CT or MRI)
• electro-encephalogram (EEG)
• lumbar puncture (also known as spinal tap)
• tests measuring the presence of antibodies in autoimmune types (for example anti-NMDA receptor encephalitis)

On more rare occasions, and where diagnosis is presenting a challenge, a brain biopsy may be performed.

Early treatment with antiviral medications or immunotherapy is critical for viral and antibody-mediated encephalitis (Whitley et al, 1986; Armangue et al, 2014; Ellul and Solomon, 2018). Encephalitis remains a life-threatening inflammation of the brain, with a mortality of 10–30%.

Treatment will vary significantly depending on cause. Other treatment is in relation to the patient's presentation and symptoms. For example:

• monitoring of consciousness,
• respiration, and ventilation 
• sedation
• hydration
• anti-convulsants
• treatments to address common, secondary infections in immobile patients.

Support and information can be provided by the Encephalitis Society (www.encephalitis.info).