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 with contrast - most sensitive investigation method in patients with encephalitis and the study of choice; however, CT may be more readily available and produce better quality imaging in an uncooperative patient (1)
• 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 (2)
• 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. (1)

References:

1. Ellul M, Solomon T. Acute encephalitis - diagnosis and management. Clin Med (Lond). 2018 Mar;18(2):155-159
2. Miller JM, Binnicker MJ, Campbell S, et al. Guide to utilization of the microbiology laboratory for diagnosis of infectious diseases: 2024 update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). Clin Infect Dis. 2024 Mar 5:ciae104.