Diagnostic Approach of Encephalitis

1. Ade Wijaya, MD – April 2021

2.  Acute encephalitis is a neurological emergency which
can cause severe disability or death, but can often be
treated if diagnosed promptly.
 Most common etiology: VIRAL, autoimmune.
Ellul M, Solomon T. Acute encephalitis–diagnosis and management. Clinical Medicine. 2018 Apr;18(2):155.
Granerod J. Cousens S. Davies NW. Crowcroft NS. Thomas SL. New estimates of incidence of encephalitis in England. Emerg Infect Dis. 2013;19:1455–62.

3. Encephalopathy = altered consciousness persisting for longer
than 24 hour, including lethargy, irritability or a change in
personality or behaviour
Encephalitis = encephalopathy AND 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 per μL)
 EEG findings suggestive of encephalitis
 Neuroimaging findings suggestive of encephalitis.
Granerod J. Ambrose HE. Davies NW, et al. Causes of encephalitis and differences in their clinical presentations in England: a multicentre, population-based
prospective study. Lancet Infect Dis. 2010;10:835–44.

4. Ellul M, Solomon T. Acute encephalitis–diagnosis and management. Clinical Medicine. 2018 Apr;18(2):155.

5. Ellul M, Solomon T. Acute encephalitis–diagnosis and management. Clinical Medicine. 2018 Apr;18(2):155.

6. Ellul M, Solomon T. Acute encephalitis–diagnosis and management. Clinical Medicine. 2018 Apr;18(2):155.

7.  CSF pleocytosis (>5 white cells x 109/L)
 Lymphocyte predominant
 Early state: could be PMN prodominant, WBC could
be normal
 Protein normal / raised
 PCR (could be normal in early state; repeat)
Saraya AW. Wacharapluesadee S. Petcharat S, et al. Normocellular CSF in herpes simplex encephalitis. BMC Res Notes. 2016;9:95. [
Cinque P. Cleator GM. Weber T, et al. The role of laboratory investigation in the diagnosis and management of patients with suspected herpes simplex encephalitis: a
consensus report. The EU Concerted Action on Virus Meningitis and Encephalitis. J Neurol Neurosurg Psychiatry. 1996;61:339–45.
Weil AA. Glaser CA. Amad Z. Forghani B. Patients with suspected herpes simplex encephalitis: rethinking an initial negative polymerase chain reaction result. Clin Infect
Dis. 2002;34:1154–7

8.  HSV encephalitis: abnormal in 90% cases  temporal
lobe lesions
 Autoimmune encephalitis: normal or subtly abnormal
 PET Scan may be indicated for paraneoplastic
evaluation, eg ovarian teratoma in young adult female
with anti NMDAr encephalitis

9.  EEG: non specific
 HIV testing: CMV encephalitis

10.  Undertaking a lumbar puncture is vital to distinguish
encephalitis from encephalopathy, and therefore to
guide management
 Imaging is not required before lumbar puncture unless
a specific contraindication is present
 Aciclovir is a time-critical life-saving treatment for
HSV encephalitis and should be commenced before
lumbar puncture if this is delayed for any reason