Encephalitis

Inflammation of the brain, and sometimes also the meninges, usually due to a viral infection. Encephalitis varies in severity from mild, in which symptoms are barely noticeable, to serious and potentially life-threatening. Mild cases can be due to glandular fever (see infectious mononucleosis) or may be a complication of childhood diseases such as mumps or measles. The most common cause of life-threatening encephalitis is herpes simplex, particularly in people with HIV. Mild cases usually develop over several days and may cause only a slight fever and mild headache. In serious cases, symptoms develop rapidly and include weakness or paralysis, speech, memory, and hearing problems, and gradual loss of consciousness; coma and seizures may also occur. If the meninges are inflamed, other symptoms may develop, such as a stiff neck and abnormal sensitivity to light. Diagnosis is based on results of blood tests, CT scanning or MRI, EEG, lumbar puncture, and, rarely, a brain biopsy. Encephalitis due to herpes simplex is treated with intravenous infusion of the antiviral drug aciclovir, but there is no known treatment for encephalitis caused by other viral infections.