WOTD: Encephalitis

Fig 1 - CT scan of a normal brain. Fig 2 - Contrast material showing the infected area around the brain Photograph: Paul Traughber, M.D.

"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 or may be a complication of childhood diseases such as mumps and 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 conciousness, 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.

"encephalitis". British Medical Association (2007). Illustrated Medical Dictionary. 2nd ed. London: Dorling Kindersley (DK). p199.