Encephalitis is inflammation of the brain. Severity is variable.
Causes of encephalitis include viruses such as herpes simplex virus or rabies, bacteria, fungus, or parasites. In many cases the cause remains unknown. 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 meningoencephalitis.
Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection. The majority of viral cases of encephalitis have an unknown cause, however the most common identifiable cause of viral encephalitis is from herpes simplex infection. Other causes of acute viral encephalitis are rabies virus, poliovirus, and measles virus.
Additional possible viral causes are arbovirus (St. Louis encephalitis, West Nile encephalitis virus), bunyavirus (La Crosse strain), arenavirus (lymphocytic choriomeningitis virus) and reovirus (Colorado tick virus). The Powassan virus is a rare cause of encephalitis.
===Bacterial and other=== It can be caused by a bacterial infection, such as bacterial meningitis, or may be a complication of a current infectious disease 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 or Bartonella henselae may also cause encephalitis.
Other bacterial pathogens, like Mycoplasma and those causing rickettsial disease, cause inflammation of the meninges and consequently encephalitis. A non-infectious cause includes acute disseminated encephalitis which is demyelinated.
===Limbic encephalitis=== Limbic encephalitis refers to inflammatory disease confined to the limbic system of the brain. The clinical presentation often includes disorientation, disinhibition, memory loss, seizures, and behavioral anomalies. MRI imaging reveals T2 hyperintensity in the structures of the medial temporal lobes, and in some cases, other limbic structures. Some cases of limbic encephalitis are of autoimmune origin.
Autoimmune encephalitis signs can include catatonia, psychosis, abnormal movements, and autonomic dysregulation. Antibody-mediated anti-N-methyl-D-aspartate-receptor encephalitis and Rasmussen encephalitis are examples of autoimmune encephalitis. Anti-N-methyl-D-aspartate-receptor encephalitis is the most common autoimmune form, and is accompanied by ovarian teratoma in 58 percent of affected women 18-45 years of age.
Encephalitis lethargica is identified by high fever, headache, delayed physical response, and lethargy. Individuals can exhibit upper body weakness, muscular pains, and tremors, though the cause of encephalitis lethargica is not currently known. From 1917 to 1928, an epidemic of encephalitis lethargica occurred worldwide.
People should only be diagnosed with encephalitis if they have a decreased or altered level of consciousness, lethargy, or personality change for at least twenty-four hours without any other explainable cause. Diagnosing encephalitis is done via a variety of tests:
*Brain scan, done by MRI, can determine inflammation and differentiate from other possible causes. *EEG, in monitoring brain activity, encephalitis will produce abnormal signal. *Lumbar puncture (spinal tap), this helps determine via a test using the cerebral-spinal fluid, obtained from the lumbar region. *Blood test *Urine analysis *Polymerase chain reaction (PCR) testing of the cerebrospinal fluid, to detect the presence of viral DNA which is a sign of viral encephalitis.
==Prevention== Vaccination is available against tick-borne and Japanese encephalitis and should be considered for at-risk individuals. Post-infectious encephalomyelitis complicating smallpox vaccination is avoidable, for all intents and purposes, as smallpox is nearly eradicated. Contraindication to Pertussis immunization should be observed in patients with encephalitis.
==Treatment== Treatment (which is based on supportive care) is as follows:
Pyrimethamine-based maintenance therapy is often used to treat Toxoplasmic Encephalitis (TE), which is caused by Toxoplasma gondii and can be life-threatening for people with weak immune systems. The use of highly active antiretroviral therapy (HAART), in conjunction with the established pyrimethamine-based maintenance therapy, decreases the chance of relapse in patients with HIV and TE from approximately 18% to 11%. In contrast, a normal encephalogram at the early stages of diagnosis is associated with high rates of survival. The number of cases of encephalitis has not changed much over time, with about 250,000 cases a year from 2005 to 2015 in the US. Approximately seven per 100,000 people were hospitalized for encephalitis in the US during this time.
Encephalitis with meningitis is known as meningoencephalitis. While encephalitis with involvement of the spinal cord is known as encephalomyelitis. composed of ἐν, en, "in" and κεφαλή, kephalé, "head", and the medical suffix -itis "inflammation".
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==External links== * [http://www.who.int/topics/encephalitis_viral/en/ WHO: Viral Encephalitis]
* Category:Infectious diseases Category:Inflammations Category:Acute pain Category:RTT