Encephalitis, or acute inflammation of the brain, is usually caused by a viral infection or a mistaken immune system attack on the brain tissue. Early symptoms include photophobia or extreme light sensitivity, fever, irritability, and headaches. Encephalitis is rarely life-threatening and is most common in children and older adults. It is also a risk for people with compromised immune systems, such as those with HIV. Doctors can use an EEG to identify the typical brain changes that suggest encephalitis.

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