Encephalitis Health Dictionary

Inflammation of the brain. A notifiable disease. See: BRAIN DISORDERS. 

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.

Encephalitis means in?ammation or infection of the brain, usually caused by a virus; it may also be the result of bacterial infection. It occurs throughout the world and affects all racial groups and ages. Rarely it occurs as a complication of common viral disease such as measles, mumps, glandular fever, or chickenpox. It may occur with no evidence of infection elsewhere, such as in HERPES SIMPLEX encephalitis, the most common form seen in Europe and America. RABIES is another form of viral encephalitis, and the HIV virus which causes AIDS invades the brain to cause another form of encephalitis (see AIDS/HIV). In some countries – North and South America, Japan and east Asia and Russia

– there may be epidemics spread by the bite of mosquitoes or ticks.

The clinical features begin with in?uenza-like symptoms – aches, temperature and wretchedness; then the patient develops a headache with drowsiness, confusion and neck sti?ness. Severely ill patients develop changes in behaviour, abnormalities of speech, and deterioration, sometimes with epileptic seizures. Some develop paralysis and memory loss. CT (see COMPUTED TOMOGRAPHY) and MRI brain scans show brain swelling, and damage to the temporal lobes if the herpes virus is involved. ELECTROENCEPHALOGRAPHY (EEG), which records the brainwaves, is abnormal. Diagnosis is possible by an examination of the blood or other body ?uids for antibody reaction to the virus, and modern laboratory techniques are very speci?c.

In general, drugs are not e?ective against viruses – antibiotics are of no use. Herpes encephalitis does respond to treatment with the antiviral agent, aciclovir. Treatment is supportive: patients should be given painkillers, and ?uid replacement drugs to reduce brain swelling and counter epilepsy if it occurs. Fortunately, most sufferers from encephalitis make a complete recovery, but some are left severely disabled with physical defects, personality and memory disturbance, and epileptic ?ts. Rabies is always fatal and the changes found in patients with AIDS are almost always progressive. Except in very speci?c circumstances, it is not possible to be immunised against encephalitis.

Encephalitis lethargica is one, now rare, variety that reached epidemic levels after World War I. It was characterised by drowsiness and headache leading on to COMA. The disease occasionally occurs as a complication after mumps and sometimes affected individuals subsequently develop postencephalitic PARKINSONISM.

Inflammation of the brain and spinal cord due to infection

n. inflammation of the brain. It may be caused by a viral or bacterial infection or it may be due to an abnormal autoimmune process, such as an allergic response to a systemic viral illness or vaccination (see encephalomyelitis), a remote response to malignancy (paraneoplastic encephalitis), or a primary antibody-mediated autoimmune disorder. Recently a number of antibody-mediated encephalitides have been described (voltage-gated potassium receptor and *NMDA-receptor antibody being the commonest) that have characteristic clinical features and are often responsive to immunosuppressive therapies. Viral encephalitis is endemic in some parts of the world; it may also occur epidemically or sporadically. One form – encephalitis lethargica – reached epidemic proportions shortly after World War I and was marked by headache and drowsiness, progressing to coma (hence its popular name – sleepy sickness). Encephalitis can cause postencephalitic *parkinsonism. Another type of encephalitis that occurs sporadically is due to the herpes simplex virus.