Encephalitis
| Encephalitis Classification and external resources | |
| ICD-10 | A83-A86, B94.1, G05 |
|---|---|
| ICD-9 | 323 |
| DiseasesDB | 22543 |
| eMedicine | emerg/163 |
| MeSH | D004660 |
Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. An inflammation that includes both the brain and the spinal cord is called encephalomyelitis (Longe 2006). While the term encephalitis also includes inflammations resulting from a bacterial infection, sometimes an inflammation of the brain specifically caused by a bacterial infection is labelled as cerebritis (Krapp and Wilson 2005). Certain parasitic protozoal infestations, like by toxoplasma or Naegleria fowleri, also can cause encephalitis in people with compromised immune systems.
Encephalitis often is accompanied by an inflammation of the brain's covering (the meninges), a condition called meningitis. Although encephaltis and meningitis are distinctly different diseases, they often share signs and symptoms of inflammation of the meninges (Chamberlin and Narins 2005).
Brain damage occurs as the inflamed brain pushes against the skull, and can lead to death.
Overview
Inflammation is a localized protective response of a body's living tissue to injury, infection, irritation, or allergy. Inflammation is characterized by the following quintet: redness (rubor), heat (calor), swelling (tumor), pain (dolor), and dysfunction of the organs involved (functio laesa). It is part of the innate immune system, that is, the immediate "first-line" of defense to illness or pathogens. Inflammation is usually indicated by using the English suffix "-itis", such as appendicitis, laryngitis, pancreatitis, hepatitis, and encephalitis for inflammation of the appendix, larynx, pancreas, liver, and brain, respectively.
Inflammation is not "healthy" nor "unhealthy" on its own. Inflammation helps fight disease or injury, such as by remove pathogens and debris, and walling off infection from spreading. However, it comes at the cost of suspending the body's normal immune and catabolic processes. In the short term, this is often a valid trade-off, but in the long term it causes progressive damage.
Encephalitis results in the brain's tissues becoming swollen, which can lead to a headache or fever, or even more severe symptoms (Longe 2006). In the United States, there are about 2,000 cases of encephalitis reported each year to the Centers for Disease Control (Longe 2006).
There are two basic forms of encephalitis. Primary encephalitis occurs when the virus directly infects the brain. Secondary encephalitis occurs when the virus first infects another organ and only secondarily enters the brain, or when thre si a post-infectious immune reaction to a viral infection somewhere else in the body (Longe 2006; Chamberlin and Narins 2005). Secondary infections can occur with chickenpox, measels, mumps, and rubella (Longe 2006). Encephalitis may also occur in response to vaccination against a viral disease or by infection by prions, a a type of infectious agent made only of protein, lacking the nucleic acids that are part of viruses.
Primary encephalitics can have an epidemic or sporadic cause. Epidemic encephalitis is part of an outbreak, such as the polio virus (Longe 2006; Chamberlin and Narins 2005). Arthropod-borne viral encephalitis, where the viruses live in mosquitoes and animal hosts that transmit the disease, is responsible for most epidemic viral encephalitis (Longe 2006). Sporadic encephalitis or non-epidemic encephalitis can happen to people at any time of the year, with the most common form caused by herpes simplex virus type 1 (HSV-1) and another being mumps (Longe 2006; Chamberlin and Narins 2005).
Causes and 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. Another symptomn of Encephalitis is hallucination.
Etiology
Encephalitis may be caused by a variety of afflictions. One such affliction is rabies.
Diagnosis
Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present with 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 against specific viral agent (such as herpes simplex virus) or by polymerase chain reaction that amplifies the RNA or DNA of the virus responsible.
Treatment
Treatment is usually symptomatic. Reliably tested specific antiviral agents are available only for a few viral agents (e.g. acyclovir for herpes encephalitis) 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. There have only been a small number of isolated cases 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.
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).
ReferencesISBN links support NWE through referral fees
- Chamberlin, S. L., and B. Narins. 2005. The Gale Encyclopedia of Neurological Disorders. Detroit: Thomson Gale. ISBN 078769150X.
- Krapp, Kristine M., and Jeffrey Wilson. 2005. The Gale encyclopedia of children's health: infancy through adolescence. Detroit: Thomson Gale. ISBN 0787692417.
- Longe, J. L. 2005. The Gale Encyclopedia of Alternative Medicine. Farmington Hills, Mich: Thomson/Gale. ISBN 0787693960.
- Longe, J. L. 2006. The Gale Encyclopedia of Medicine. Detroit: Thomson Gale. ISBN 1414403682.
External links
- http://www.encephalitis.info (only resource of its kind in the world 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
http://www.garrettmtaylor.com/" a website about Garrett Taylor a 2 year old who lost his life after a battle with encephalitis
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