Investigations

The investigation of encephalitis should include:

• a physical examination - which includes a detailed neurological examination
• a medical history - activities of the past several days (to detect any contact with insects, animals or recent travel) (1)
  
  
• throat swabs, stool culture
• CT - a late sign is bilateral low density regions in both temporal lobes seen with herpes simplex encephalitis; not very useful for early diagnosis, but essential before lumbar puncture
• MRI - most sensitive investigation method in patients with encephalitis (2)
• lumbar puncture after CT screening: usually shows raised protein and lymphocytic pleocytosis - identify organism; polymerase chain reaction now available at specialist centres for identification of organism. There may be oligoclonal bands in the CSF (3)
• viral and immunological studies of serum and CSF; paired studies are required to show rising titres.
• EEG - in herpetic encephalitis, the EEG shows diffuse slowing with periodic discharges; this is more useful than a CT scan in the first week.

Reference:

• 1. National Institute of Neurological Disorders and Stroke 2004. Meningitis and Encephalitis Fact Sheet.
• 2. Tunkel A.R. et al. The Management of Encephalitis: Clinical Practice Guidelines by the Infectious Diseases Society of America. Clinical Infectious Diseases 2008; 47:303-27
• 3. Philip Rice. Viral meningitis & encephalitis. Medicine 2005;33:4