Encephalitis is inflammation of the parenchyma (the substance) of the brain and is a complex syndrome with many possible causes.1 The brain can be damaged in two ways – by the cause (for example the infection) and also by the resultant inflammation (or swelling). Encephalitis occurs at any age, to any gender or ethnicity and in any part of the world. There are two primary causes of encephalitis: infections and auto-immune malfunction (post-infectious and other non-post-infectious causes). 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.
In the United Kingdom it is estimated that there are 6000 people affected by the condition each year (based on capture–recapture models): 8.66 cases/100,000/year.2, but this is likely an underestimation of the true incidence. We don’t know how many people are living in our communities who have been affected by the condition and are living with its consequences (prevalence). Interestingly this is a higher incidence than many other conditions which have much higher public and clinical profiles, for example motor neurone disease and bacterial meningitis.
Mortality is considered to occur in up to three in every 10 cases and is higher than many other neurological diseases.3,4