What causes encephalitis?
Encephalitis is inflammation of the brain, caused either by an infection invading the brain or through the immune system attacking the brain in error. It is broadly divided into four main categories or types:
Inflammation that occurs as a direct and almost immediate result of an infection – usually viral. No apparent cause can be identified in over half of all cases of infectious encephalitis.
When the immune system reacts to a previous infection and starts to produce antibodies which, instead of fighting an infection that may not be present, are sent to the brain where they cause inflammation. Precisely why the immune system malfunctions like this is not known.
When the immune system mistakes a non-infectious agent inside the brain as a threat and starts attacking it with antibodies this causes otherwise ‘normal’ brain tissue to inflame and swell. The reason for the immune system attacking healthy brain tissue in this way remains a mystery.
There are two main types of chronic encephalitis: Subacute Sclerosing Panencephalitis and Progressive Multifocal Leukodystrophy (PML). Subacute sclerosing panencephalitis is usually a complication of measles and extremely rare. PML is equally rare and normally affects only those people with a severely weakened immune system.
Whatever its cause, encephalitis is a serious condition, which if left untreated or undiagnosed can be life-threatening and have severe long-term complications.