The doctor will often question a patient about their travel history. Geographic location and seasonal occurrence can help identify the specific cause of encephalitis. The doctor will often do a physical exam that includes looking for insect bites and will probably complete a neurologic evaluation. The physician often will order some blood tests, including a
complete blood count (CBC). Depending on the patient's unique situation, the doctor may perform one or more of the following tests:
- An imaging study of the brain such as a CT scan or magnetic resonance imagining (MRI) is often done. MRI is the procedure of choice if herpes encephalitis is suspected.
- A study called polymerase chain reaction (PCR)
to detect genetic material of the virus has greatly improved the diagnosis of herpes encephalitis. Variations of this test are used by the CDC and some state agencies to identify the various other virus types that may cause encephalitis.
- A reading of the electrical activity of the brain with an EEG can detect irregularities. Herpes encephalitis produces a characteristic EEG pattern.
- A lumbar puncture, also known as a spinal tap, may be necessary to isolate and identify the virus. During this procedure, the doctor applies local numbing medication and then inserts a needle into the lower back to collect fluid from the space around the spinal column for analysis.
- The virus may also be isolated from tissue or blood.
- Brain biopsy is an option although it is rarely done and usually only if the other tests do not give an answer.
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