encephalitis, general term used to describe a diffuse inflammation of the brain and spinal cord, usually of viral origin, often transmitted by mosquitoes, in contrast to a bacterial infection of the meninges (membrane surrounding the brain and spinal cord), known as meningitis. Diagnostic symptoms include capillary congestion, small hemorrhages into perivascular spaces, accumulation of plasma cells and lymphocytes, and increased pressure and protein content of cerebrospinal fluid.

Among the several forms of viral brain inflammation are rabies, polio, and two types transmitted by the mosquito: equine encephalitis in its various forms and St. Louis encephalitis. The latter two have appeared in epidemic form in the United States and are characterized by high fever, prolonged coma (which is responsible for the disease being known as a "sleeping sickness"; see also trypanosomiasis), and convulsions sometimes followed by death. Encephalitis that results as a complication of another systemic infection is known as parainfectious encephalitis and can follow such diseases as measles (rubeola), influenza, and scarlet fever. The AIDS virus also infects the brain and produces dementia in a predictably progressive pattern. Although no specific treatment can destroy the virus once the disease has become established, many types of encephalitis can be prevented by immunization.

Inflammation of the brain, most often due to infection, usually with a virus. One class of encephalitis (including multiple sclerosis) attacks the myelin sheath that insulates nerve fibres rather than the neurons themselves. In most cases, symptoms include fever, headache, lethargy, and coma. Convulsions are most common in infants. Characteristic neurological signs include uncoordinated, involuntary movements and localized weakness. The symptoms and a lumbar puncture (to obtain cerebrospinal fluid for analysis) may establish the presence but not the cause. Treatment usually aims to relieve the symptoms and ensure quiet rest. Various symptoms may remain after recovery.

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Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. It can be caused by a bacterial infection such as bacterial meningitis spreading directly to the brain (primary encephalitis), or may be a complication of a current infectious disease like rabies or syphilis (secondary encephalitis). Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Lyme disease may also cause encephalitis. Bartonella henselae can also lead to this. Brain damage occurs as the inflamed brain pushes against the skull, and can lead to death.

Symptoms

Patients with encephalitis suffer from fever, headache and photophobia with weakness and seizures also common. Less commonly, stiffness of the neck can occur with rare cases of patients also suffering from stiffness of the limbs, slowness in movement and clumsiness depending on which specific part of the brain is involved. The symptoms of encephalitis are caused by the brain's defense mechanisms activating to get rid of the infection.

Etiology

Encephalitis may be caused by a variety of afflictions. One such affliction is rabies. Encephalitis may also be caused by HIV. The major causes of encephalitis outbreaks all over the world are viruses like Japanese Encephalitis, West Nile, Chandipura virus, St. Louis Encephalitis, Equine Encephalitis, La Crosse encephalitis, Murray Valley encephalitis virus, California encephalitis virus, Tick-borne meningoencephalitis, Herpes simplex, Influenza A virus. Less common are e.g. RSSE (Russian spring-summer encephalitis) viruses.

Diagnosis

Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present irritability, anorexia and fever.

Neurological examinations usually reveal a drowsy or confused patient. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningeoncephalitis. Examination of the cerebrospinal fluid obtained by a lumbar puncture procedure usually reveals increased amounts of protein and white blood cells with normal glucose, though in a significant percentage of patients, the cerebrospinal fluid may be normal. CT scan often is not helpful, as cerebral abscess is uncommon. Cerebral abscess is more common in patients with meningitis than encephalitis. Bleeding is also uncommon except in patients with herpes simplex type 1 encephalitis. Magnetic resonance imaging offers better resolution. In patients with herpes simplex encephalitis, electroencephalograph may show sharp waves in one or both of the temporal lobes. Lumbar puncture procedure is performed only after the possibility of prominent brain swelling is excluded by a CT scan examination. Diagnosis is often made with detection of antibodies in the cerebrospinal fluid against a specific viral agent (such as herpes simplex virus) or by polymerase chain reaction that amplifies the RNA or DNA of the virus responsible (such as varicella zoster virus).

Treatment

Treatment is usually symptomatic. Reliably tested specific antiviral agents are available only for a few viral agents (e.g. acyclovir for herpes simplex virus) and are used with limited success for most infection except herpes simplex encephalitis. In patients who are very sick, supportive treatment, such as mechanical ventilation, is equally important.

Encephalitis lethargica

Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1917 to 1928, resulting in millions of deaths worldwide. Those who survived sank into a semi-conscious state that lasted for decades until the Parkinsons drug L-dopa was used to revive those still alive in the late 1960s by Oliver Sacks.

There have been only a small number of isolated cases in the years since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be either a bacterial agent or an autoimmune response following infection.

Herpes simplex encephalitis

Herpes simplex encephalitis is caused by the herpes simplex virus that manifests in oral cold sores or genital sores. When this triggers brain inflammation, which occurs in 10% of cases of encephalitis (2 cases per million people), half of all untreated patients die (1 case per million people). Brain damage, partial paralysis, seizures, hallucinations and an altered state of consciousness are all common symptoms. HSE can be passed from mother to child during birth in rare cases, where symptoms include lethargy, tremors, irritability, seizures and poor feeding in the first two weeks after birth.

Limbic system encephalitis

In a small number of cases, called limbic encephalitis, the pathogens responsible for encephalitis attack primarily the limbic system (a collection of structures at the base of the brain responsible for basic autonomic functions).

See also

References

External links

• http://www.encephalitis.info resource providing evidence based support to people affected and professionals
• WHO: Encephalitis
• eMedicine-1 and eMedicine-2 Information on the causes, symptoms, and treatment options for Encephalitis.
• Encephalitis Global, Inc. Website offering information and support to encephalitis survivors, caregivers and loved ones. Encephalitis Global Inc. is a USA 501(c)(3) public charity; annual FACES Encephalitis Conference information available at the website.
• A case study of a Limbic Encephalitis patient
• A website about Garrett Taylor a 2 year old who lost his life after a battle with encephalitis