Various symptoms resembling meningitis may be present. An examination may show signs of meningeal irritation (especially neck stiffness), increased intracranial pressure or other neurologic symptoms (such as muscle weakness, mental confusion, speech problems, and abnormal reflexes). The patient may have a skin rash, mouth ulcers, and signs of involvement of other organs (e.g., the liver and lungs).
- A lumbar puncture test and cerebrospinal fluid (CSF) examination show clear fluid, high pressure, high white-blood cell count and protein levels (indicating inflammation). Blood may be present in the CSF.
- Sometimes the virus can be detected in CSF, blood, or urine through a laboratory test called "viral culture." However, this test is cumbersome and rarely useful. In some cases viral "PCR" (which stands for "polymerase chain reaction," a test able to detect very tiny amounts of viral DNA) is used to identify the virus. Health care providers also rely on serology tests (serologies detect some proteins called antibodies, which are produced in response to an specific virus) to provide evidence of viral infection.
- An EEG (a test of the electrical activity of the brain) may provide indirect clues for the diagnosis of encephalitis. Some EEG wave patterns may suggest a seizure disorder, or point to a specific virus as cause of the infection. Certain EEG wave patterns can suggest encephalitis due to herpes, for instance.
- A brain MRI, which provides high-quality pictures of the brain, or a CAT scan of the head may be used to determine the presence or absence of internal bleeding or focal areas of brain inflammation.
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