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Tests and diagnosis
By Mayo Clinic staffDiagnosing encephalitis may involve:
- Spinal tap (lumbar puncture). One common way to diagnose encephalitis is to analyze the cerebrospinal fluid surrounding your brain and spinal cord. A needle inserted into your lower spine (below the level of the spinal cord) extracts a sample of fluid for laboratory analysis, which may reveal the presence of an infection or an increased white blood count — a signal that your immune system is fighting an infection. Your cerebrospinal fluid may also be slightly bloody if hemorrhages have occurred. Diagnosis of herpes simplex encephalitis can be difficult, but advances in using sensitive DNA methods have allowed detection of the virus in spinal fluid.
- Electroencephalography (EEG). This procedure measures the waves of electrical activity produced by your brain. It's often used to diagnose and manage seizure disorders. A number of small electrodes are attached to your scalp with paste or an elastic cap as you recline. You remain still during the test, but at times you may be asked to breathe deeply and steadily for several minutes or to stare at a patterned board. At times, a light may be flashed in your eyes. These actions are meant to stimulate your brain. The electrodes pick up the electrical impulses from your brain and send them to the EEG machine, which records your brain waves on a moving sheet of paper. An abnormal EEG result may suggest encephalitis, but a normal result does not rule out the disease.
- Brain imaging. A computerized tomography (CT) or magnetic resonance imaging (MRI) scan may reveal swelling of your brain. Or it may reveal another condition with signs and symptoms that are similar to encephalitis, such as a concussion. If encephalitis is suspected, brain imaging is often done before a spinal tap to look for evidence of elevated intracranial pressure.
- Brain biopsy. Very rarely, if diagnosis of herpes simplex encephalitis isn't possible using DNA methods or by CT or MRI scans, your doctor may take a small sample of your brain tissue. This sample is analyzed in the laboratory to see if the virus is present. Your doctor may also try treatment with antiviral medications before suggesting brain biopsy.
- Blood testing. Your doctor can confirm the presence of West Nile virus in your body by drawing a sample of your blood for laboratory analysis. If you have West Nile virus, an analysis of your blood sample may show a rising level of an antibody to the virus, a positive DNA test for the virus or a positive culture of the virus.
References
- 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 21, 2009.
- Tyler KL. West Nile virus infection in the United States. Archives of Neurology. 2004;61:1190.
- Johnson RP. Viral encephalitis in adults. http://www.uptodate.com/home/index.html. Accessed March 12, 2009.
- Willoughbly RE Jr, et al. Encephalitis, meningoencephalitis, acute disseminated encephalomyelitis, and acute necrotizing encephalopathy. In: Long SS, et al. Principles and Practice of Pediatric Infectious Diseases. 3rd ed. Philadelphia, Pa.: Churchill Livingstone; 2008. http://www.mdconsult.com/das/book/body/127224884-3/819357724/1679/50.html#4-u1.0-B978-0-443-06687-0..50049-7--cesec19_1078. Accessed March 21, 2009.
- Eastern equine encephalitis fact sheet. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/arbor/eeefact.htm. Accessed March 21, 2009.
- St. Louis encephalitis fact sheet. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/sle/Sle_FactSheet.html. Accessed March 21, 2009.
- LaCrosse encephalitis. Directors of Health Promotion and Education. http://www.dhpe.org/lacenceph.asp. Accessed March 21, 2009.
- Peters CJ. Infections caused by arthropod- and rodent-borne viruses. In: Fauci AS, et al. Harrison's Principles of Internal Medicine. 17th ed. New York, N.Y.: McGraw-Hill Medical; 2008. http://www.accessmedicine.com/content.aspx?aID=2895916. Accessed March 21, 2009.
- Encephalitis. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec16/ch217/ch217c.html. Accessed March 21, 2009.
- Voelker R. Effects of West Nile virus may persist. Journal of the American Medical Association. 2008;299:2135.
- Insect repellant use and safety. Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvbid/westnile/qa/insect_repellent.htm. Accessed March 22, 2009.
- Follow safety precautions when using DEET on children. American Academy of Pediatrics. http://www.aap.org/family/wnv-jun03.htm. Accessed March 22, 2009.
