Appropriate Tests


Cerebrospinal fluid examination, diagnostic imaging and electroencephalography to support clinical diagnosis.

Herpes simplex virus infection is the most common cause of sporadic disease; in the absence of conflicting evidence, appropriate therapy should be instituted.

In otherwise undiagnosed, severe, progressive encephalitis, Brain biopsy may be required as a last resort.

See also Meningitis.

Viral infection

Consideration of seasonal and geographic factors, recent travel, age, and sexual activity may assist in defining the likely viral agent.

If appropriate: Throat swab, Nasopharyngeal swab/aspirate, Cerebrospinal fluid examination; Faeces for Virus detection, culture.

If there is a past history of exposure to sick horses or bats, Hendra virus Ab serology or Australian bat lyssavirus antibodies (see Rabies virus Ab) may be indicated.

Travel history is vital in diagnosing a wide range of vector borne encephalitis (ie, West Nile, Japanese encephalitis, Nipah virus and many others)

Herpes simplex virus infection


Autoimmune especially NMDA receptor antibody mediated encephalitis

Autoimmune mediated encephalitis with appropriate tests being Neuronal Ab, NMDA receptor Ab, Voltage gated potassium channel Ab. Cerebrospinal fluid examination is preferred for detection of NMDA receptor antibodies.

Arbovirus infections, especially

  • Australian encephalitis
  • Kunjin

Arbovirus Ab.

Enteroviruses, especially

  • Coxsackieviruses
  • Echoviruses

Enterovirus Ab, Enterovirus PCR on CSF or stool.

Infectious mononucleosis

Monospot, Full blood count, White cell count differential, Electrolytes, Liver function tests, Epstein-Barr virus serology on serum, quantitiative.

EBV PCR on serum or CSF.

HIV infection

See HIV infection, AIDS.

Measles, including

  • Acute infection
  • SSPE

Serum, CSF - Measles virus Ab; Measles PCR on blood, urine or CSF. CSF immunoglobulin studies (oligoclonal bands).

Rubella is a rare cause: Rubella Ab should be requested if measles antibodies/PCR negative.



Varicella zoster infection

CSF cell count and differential Varicella zoster  IgG, Varicella zoster  PCR of vesicle or CSF.


Rubella is a rare cause: Rubella Ab should be requested if measles antibodies negative.

Progressive multifocal leukoencephalopathy

A rare demyelinating disorder affecting immunosuppressed patients, due to JC virus (a Polyomavirus).

Mycoplasma infection


Mycoplasma pneumoniae antibodies, IgG, IgM PCR, specific culture media eg A8 Toxoplasma antibodies IgG/IgM.

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