14th June 2023

Clinical presentation

Encephalopathy refers to altered consciousness persisting for longer than 24 hours, including lethargy, irritability or change in personality or behaviour. Encephalitis is defined as encephalopathy with evidence of CNS inflammation, demonstrated by at least two of:

• Fever
• Seizures or focal neurological findings attributable to the brain parenchyma
• CSF pleocytosis – more than 4 white cells/µL
• EEG findings suggestive of encephalitis
• Neuroimaging finding suggestive of encephalitis

Other clinical features include:

• Photophobia and neck stiffness
• Features of raised intracranial pressure including severe headache, nausea and vomiting
• Focal neurological deficits
• Non-specific viral prodrome symptoms (fever, myalgia, arthralgias)
• Rashes may be seen in varicella, hand-foot-mouth disease, rickettsia.
• Lymphadenopathy and hepatosplenomegaly may be seen in Ebstein Barr virus, varicella zoster virus, and cytomegalovirus infections.
• Features of parkinsonism if basal ganglia involvement in Japanese encephalitis.

The most common aetiology of encephalitis are viral causes, as outlined below, with Herpes Simplex Virus type 1 being the most common cause. More rarely, bacteria, fungi or parasites can cause encephalitis.