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Tests and diagnosis

By Mayo Clinic staff

Questions about symptoms, risk factors and medical history are important in making a diagnosis of encephalitis. Diagnostic tests that may be needed include the following:

  • Brain imaging. Brain imaging is often the first test if symptoms and patient history suggest the possibility of encephalitis. The images may reveal swelling of the brain or another condition that may be causing the symptoms, such as a tumor. Technologies may include magnetic resonance imaging (MRI), which can produce detailed cross-sectional and 3-D images of the brain, or computerized tomography (CT), which produces cross-sectional images.
  • Spinal tap (lumbar puncture). With a spinal tap, the doctor inserts a needle into the lower back to extract cerebrospinal fluid (CSF), the protective fluid that surrounds the brain and spinal column. A particular profile of blood cells and immune system proteins can indicate the presence of infection and inflammation in the brain. In some cases, samples of CSF can be tested in a laboratory to identify the causative virus or other infectious agent.
  • Other lab tests. Your doctor or other members of the care team may take samples of blood, urine, or excretions from the back of the throat. These can be tested in the laboratory to identify some of the viruses or other infectious agents that can cause encephalitis.
  • Electroencephalogram (EEG). Your doctor may order an electroencephalogram (EEG), a test in which a series of electrodes are affixed to the scalp. The EEG records the electrical activity of the brain. Certain abnormal patterns in this activity may be consistent with a diagnosis of encephalitis.
  • Brain biopsy. Rarely, a procedure to remove a small sample of brain tissue (brain biopsy) is used if symptoms are worsening, treatments are having no effect, and there is no working diagnosis.
Treatments and drugs Preparing for your appointment
References
  1. Encephalitis and meningitis fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm. Accessed March 8, 2011.
  2. Encephalitis. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/sec16/ch217/ch217c.html. Accessed March 10, 2011.
  3. Johnson RP, et al. Viral encephalitis in adults. http://www.uptodate.com/home/index.html. Accessed March 10, 2011.
  4. Hardarson HS. Acute viral encephalitis in children and adolescents: Clinical manifestations and diagnosis. http://www.uptodate.com/home/index.html. Accessed March 10, 2011.
  5. Beckham J, et al. Encephalitis. In: Mandell G, et al., eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa.: Churchill Livingstone Elsevier; 2009. http://www.mdconsult.com/books/page.do?sid=1129246002&eid=4-u1.0-B978-0-443-06839-3..00087-4&isbn=978-0-443-06839-3&type=bookPage&sectionEid=4-u1.0-B978-0-443-06839-3..00087-4&uniqId=237025740-4. Accessed March 10, 2011.
  6. Hardarson HS. Acute viral encephalitis in children and adolescents: Pathogenesis and etiology. http://www.uptodate.com/home/index.html. Accessed March 10, 2011.
  7. Information on arboviral enchephalitides. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/arbor/arbdet.htm. Accessed March 8, 2011.
  8. Hardarson HS. Acute viral encephalitis in children and adolescents: Treatment and prevention. http://www.uptodate.com/home/index.html. Accessed March 10, 2011.
  9. Insect repellant use and safety. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/qa/insect_repellent.htm. Accessed March 15, 2011.
  10. A parent's guide to insect repellent. American Academy of Pediatrics. http://patiented.aap.org/content.aspx?aid=5556. Accessed March 11, 2011.
  11. Acyclovir. National Center for Biotechnology Medicine. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000533. Accessed March 22, 2011.
  12. Ganciclovir injection. National Center for Biotechnology Medicine. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000889. Accessed March 22, 2011.
DS00226 May 5, 2011

© 1998-2013 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "EmbodyHealth," "Enhance your life," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.

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