View source for Encephalitis

{{Short description|Inflammation of the brain}}
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{{Infobox medical condition (new)
| name            = Encephalitis
| image           = Hsv_encephalitis.jpg
| caption         = [[Magnetic resonance imaging|MRI]] scan image shows high signal in the temporal lobes and right inferior frontal gyrus in someone with [[herpes simplex]] encephalitis.
| field           = [[Neurology]], [[Infectious disease (medical specialty)|infectious disease]]
| symptoms        = [[Headache]], [[fever]], [[confusion]], stiff neck, [[vomiting]]<ref name=NIH207Main/>
| complications   = [[Seizure]]s, trouble speaking, [[memory problem]]s, problems [[hearing]]<ref name=NIH207Main/>
| onset           =
| duration        = Weeks to months for recovery<ref name=NIH207Main/>
| causes          = Infection, autoimmune, certain medication, unknown<ref name=NIH2017Fact/>
| risks           =
| types           = [[Herpes simplex encephalitis|Herpes simplex]], [[West Nile encephalitis|West Nile]], [[rabies]], [[Eastern equine encephalitis|Eastern equine]], others<ref name=NIH2017Fact/>
| diagnosis       = Based on symptoms, supported by [[blood tests]], [[medical imaging]], analysis of [[cerebrospinal fluid]]<ref name=NIH2017Fact/>
| differential    =
| prevention      =
| treatment       = [[Antiviral medication]], [[anticonvulsants]], [[corticosteroids]], [[artificial respiration]]<ref name=NIH207Main/>
| medication      =
| prognosis       = Variable<ref name=NIH207Main/>
| frequency       = 4.3 million (2015)<!-- prevalence --><ref name=GBD2015Pre/>
| deaths          = 150,000 (2015)<ref name=GBD2015De/>
}}

'''Encephalitis''' ({{IPAc-en|US|ɛ|n|s|ɛ|f|ə|l|ˈ|aɪ|t|ɪ|s}}, {{IPAc-en|UK|ɛ|n|k|ɛ|f|ə|l|ˈ|aɪ|t|ɪ|s}}) is [[inflammation]] of the [[Human brain|brain]].<ref name="NHS2016">{{Cite web |date=2016 |title=Encephalitis |url=https://www.nhs.uk/Conditions/encephalitis/Pages/introduction.aspx |url-status=live |archive-url=https://web.archive.org/web/20170922022223/http://www.nhs.uk/Conditions/Encephalitis/Pages/Introduction.aspx |archive-date=22 September 2017 |access-date=29 October 2017 |website=NHS Choices |language=en}}</ref> The severity can be variable with symptoms including reduction or alteration in consciousness, [[aphasia]], [[headache]], [[fever]], [[confusion]], a [[stiff neck]], and [[vomiting]].<ref name=NIH207Main/><ref>{{Cite journal |vauthors=Ellul M, Solomon T |date=March 2018 |title=Acute encephalitis - diagnosis and management |journal=Clinical Medicine |volume=18 |issue=2 |pages=155–159 |doi=10.7861/clinmedicine.18-2-155 |pmc=6303463 |pmid=29626021}}</ref> Complications may include [[seizure]]s, [[hallucination]]s, trouble speaking, [[memory problem]]s, and problems with [[hearing]].<ref name="NIH207Main">{{Cite web |title=Meningitis and Encephalitis Information Page |url=https://www.ninds.nih.gov/health-information/disorders/meningitis |url-status=live |archive-url=https://web.archive.org/web/20171029065744/https://www.ninds.nih.gov/Disorders/All-Disorders/Meningitis-and-Encephalitis-Information-Page |archive-date=29 October 2017 |access-date=29 October 2017 |website=NINDS}}</ref>

Causes of encephalitis include [[virus]]es such as [[herpes simplex virus]] and [[rabies virus]] as well as [[bacteria]], [[fungi]], or [[parasites]].<ref name=NIH207Main/><ref name=NIH2017Fact/> Other causes include [[autoimmune diseases]] and certain medications.<ref name="NIH2017Fact">{{Cite web |title=Meningitis and Encephalitis Fact Sheet |url=https://www.ninds.nih.gov/health-information/disorders/meningitis |url-status=live |archive-url=https://web.archive.org/web/20171029065418/https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Meningitis-and-Encephalitis-Fact-Sheet |archive-date=29 October 2017 |access-date=29 October 2017 |website=National Institute of Neurological Disorders and Stroke}}</ref> In many cases the cause remains unknown.<ref name=NIH2017Fact/> Risk factors include a [[immunosuppression|weak immune system]].<ref name=NIH2017Fact/> Diagnosis is typically based on symptoms and supported by [[blood tests]], [[medical imaging]], and analysis of [[cerebrospinal fluid]].<ref name=NIH2017Fact/>

Certain types are preventable with [[vaccine]]s.<ref name=NHS2016/> Treatment may include [[antiviral medications]] (such as [[acyclovir]]), [[anticonvulsants]], and [[corticosteroids]].<ref name=NIH207Main/> Treatment generally takes place in hospital.<ref name=NIH207Main/> Some people require [[artificial respiration]].<ref name=NIH207Main/> Once the immediate problem is under control, [[Rehabilitation (neuropsychology)|rehabilitation]] may be required.<ref name=NIH2017Fact/> In 2015, encephalitis was estimated to have affected 4.3&nbsp;million people and resulted in 150,000 deaths worldwide.<ref name="GBD2015Pre">{{Cite journal |vauthors=Vos T, Allen C, Arora M, Barber RM, Bhutta ZA, Brown A, Carter A, Casey DC, Charlson FJ, Chen AZ, Coggeshall M, etal |date=October 2016 |title=Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990-2015: a systematic analysis for the Global Burden of Disease Study 2015 |journal=Lancet |volume=388 |issue=10053 |pages=1545–1602 |doi=10.1016/S0140-6736(16)31678-6 |pmc=5055577 |pmid=27733282 |collaboration=GBD 2015 Disease and Injury Incidence and Prevalence Collaborators}}</ref><ref name="GBD2015De">{{Cite journal |vauthors=Wang H, Naghavi M, Allen C, Barber RM, Bhutta ZA, Carter A, Casey DC, Charlson FJ, Chen AZ, Coates MM, Coggeshall M, etal |date=October 2016 |title=Global, regional, and national life expectancy, all-cause mortality, and cause-specific mortality for 249 causes of death, 1980-2015: a systematic analysis for the Global Burden of Disease Study 2015 |journal=Lancet |volume=388 |issue=10053 |pages=1459–1544 |doi=10.1016/S0140-6736(16)31012-1 |pmc=5388903 |pmid=27733281 |collaboration=GBD 2015 Mortality and Causes of Death Collaborators}}</ref>

==Signs and symptoms==
Adults with encephalitis present with acute onset of [[fever]], [[headache]], [[confusion]], and sometimes seizures. Younger children or [[infants]] may present with irritability, [[poor appetite]] and fever.<ref>{{Cite web |title=Symptoms of encephalitis |url=http://www.nhs.uk/Conditions/Encephalitis/Pages/Symptoms.aspx |url-status=live |archive-url=https://web.archive.org/web/20150105142821/http://www.nhs.uk/Conditions/Encephalitis/Pages/Symptoms.aspx |archive-date=5 January 2015 |access-date=5 January 2015 |website=NHS}}</ref> [[Neurological]] examinations usually reveal a [[drowsy]] or confused person. [[Stiff neck]], due to the irritation of the [[meninges]] covering the brain, indicates that the patient has either [[meningitis]] or [[meningoencephalitis]].<ref>{{Cite book |url=https://books.google.com/books?id=KI5p3pADvSsC&q=meningoencephalitis+symptoms+stiff+neck&pg=PA90 |title=Meningitis |vauthors=Shmaefsky B, Babcock H |date=2010-01-01 |publisher=Infobase Publishing |isbn=978-1-4381-3216-7 |archive-url=https://web.archive.org/web/20151030224553/https://books.google.com/books?id=KI5p3pADvSsC&pg=PA90&dq=meningoencephalitis+symptoms+stiff+neck&hl=en&sa=X&ved=0CCsQ6AEwAGoVChMIk7_kzqCSxwIVQYsNCh2nzwvd#v=onepage&q=meningoencephalitis%2520symptoms%2520stiff%2520neck&f=false |archive-date=2015-10-30 |url-status=live}}</ref>

===Limbic encephalitis===
{{Main|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.<ref>{{Cite book |last=Larner |first=A. J. |url=https://books.google.com/books?id=hO_lWEDsJYMC&q=limbic+encephalitis+definition&pg=PA156 |title=Neuropsychological Neurology: The Neurocognitive Impairments of Neurological Disorders |date=2013-05-02 |publisher=Cambridge University Press |isbn=978-1-107-60760-6 |archive-url=https://web.archive.org/web/20151030055159/https://books.google.com/books?id=hO_lWEDsJYMC&pg=PA156&dq=limbic+encephalitis+definition&hl=en&sa=X&ved=0CCIQ6AEwAWoVChMIxouQj-2RxwIVBaKACh1J3w-x#v=onepage&q=limbic%2520encephalitis%2520definition&f=false |archive-date=2015-10-30 |url-status=live}}</ref>

===Encephalitis lethargica===
{{main|Encephalitis lethargica}}

[[Encephalitis lethargica]] is identified by high fever, [[headache]], delayed physical response, and [[lethargy]]. Individuals can exhibit upper body [[weakness]], [[muscular pain]]s, and [[tremor]]s, though the cause of encephalitis lethargica is not currently known. From 1917 to 1928, an epidemic of encephalitis [[lethargica]] occurred worldwide.<ref>{{NINDS|encephalitis-lethargica|Encephalitis Lethargica}}</ref>

==Cause==
[[File:Rabies Virus EM PHIL 1876.JPG|thumb|Rabies virus]]
In 30%-40% of encephalitis cases, the etiology remains unknown.<ref name=":1">{{Cite web |date=2021-08-08 |title=Encephalitis |url=https://www.hopkinsmedicine.org/health/conditions-and-diseases/encephalitis |access-date=2024-01-09 |website=www.hopkinsmedicine.org |language=en}}</ref>
===Viral===
{{main|Viral encephalitis|Herpesviral encephalitis}}
Viral infections are the usual cause of infectious encephalitis.<ref name=":1" /> 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.<ref>{{Cite book |title=Harrison's Principles of Internal Medicine |vauthors=Roos KL, Tyler KL |date=2015 |publisher=McGraw-Hill Education |isbn=978-0-07-180215-4 |edition=19 |location=New York, NY |chapter=Meningitis, Encephalitis, Brain Abscess, and Empyema |access-date=2017-11-17 |chapter-url=http://accessmedicine.mhmedical.com/content.aspx?bookid=1130&sectionid=79734335 |archive-url=https://web.archive.org/web/20171117122546/http://accessmedicine.mhmedical.com/content.aspx?bookid=1130&sectionid=79734335 |archive-date=2017-11-17 |url-status=live}}</ref> Other causes of acute viral encephalitis are [[rabies virus]], [[poliovirus]], and [[measles virus]].<ref>{{Cite journal |vauthors=Fisher DL, Defres S, Solomon T |date=March 2015 |title=Measles-induced encephalitis |journal=QJM |volume=108 |issue=3 |pages=177–182 |doi=10.1093/qjmed/hcu113 |pmid=24865261 |doi-access=free}}</ref>

Additional possible viral causes are [[Arbovirus|arboviral]] [[flavivirus]] ([[Saint Louis encephalitis|St. Louis encephalitis]], [[West Nile virus]]), [[bunyavirus]] (La Crosse strain), [[arenavirus]] (lymphocytic choriomeningitis virus), [[Reoviridae|reovirus]] (Colorado tick virus), and [[henipavirus]] infections.<ref>{{cite journal |last1=Kennedy |first1=P. G. E. |title=Viral encephalitis: causes, differential diagnosis, and management |journal=Journal of Neurology, Neurosurgery, and Psychiatry |date=March 2004 |volume=75 Suppl 1 |issue=Suppl 1 |pages=i10–15 |doi=10.1136/jnnp.2003.034280 |pmid=14978145 |pmc=1765650 }}</ref><ref>{{Cite book |title=Henipavirus |vauthors=Broder CC, Geisbert TW, Xu K, Nikolov DB, Wang LF, Middleton D, Pallister J, Bossart KN |year=2012 |isbn=978-3-642-29818-9 |series=Current Topics in Microbiology and Immunology |volume=359 |pages=197–223 |chapter=Immunization strategies against henipaviruses |doi=10.1007/82_2012_213 |pmc=4465348 |pmid=22481140}}</ref> The [[Powassan virus]] is a rare cause of encephalitis.<ref>{{Cite web |date=4 December 2018 |title=Symptoms & Treatment {{!}} Powassan {{!}} CDC |url=https://www.cdc.gov/powassan/symptoms.html |url-status=live |archive-url=https://web.archive.org/web/20190626032132/https://www.cdc.gov/powassan/symptoms.html |archive-date=26 June 2019 |access-date=26 June 2019 |website=www.cdc.gov |language=en-us}}</ref>

===Bacterial===
It can be caused by a [[bacteria]]l infection, such as bacterial [[meningitis]],<ref>{{Cite book |url=https://books.google.com/books?id=KLBZ85zbTeYC&q=bacterial+meningitis+inflmation+of+encepha+definition&pg=PA113 |title=Johns Hopkins Internal Medicine Board Review: Certification and Recertification |vauthors=Ashar BH, Miller RG, Sisson SD |date=2012-01-01 |publisher=Elsevier Health Sciences |isbn=978-1-4557-0692-1 |archive-url=https://web.archive.org/web/20151129111640/https://books.google.com/books?id=KLBZ85zbTeYC&pg=PA113&dq=bacterial+meningitis+inflmation+of+encepha+definition&hl=en&sa=X&ved=0CGAQ6AEwCGoVChMI8PLmjZqSxwIVS6KACh03_QJ_#v=onepage&q=bacterial%2520meningitis%2520inflmation%2520of%2520encepha%2520definition&f=false |archive-date=2015-11-29 |url-status=live}}</ref> or may be a complication of a current infectious disease such as [[syphilis]] (secondary encephalitis).<ref>{{Cite journal |vauthors=Hama K, Ishiguchi H, Tuji T, Miwa H, Kondo T |date=2008-01-01 |title=Neurosyphilis with mesiotemporal magnetic resonance imaging abnormalities |journal=Internal Medicine |volume=47 |issue=20 |pages=1813–1817 |doi=10.2169/internalmedicine.47.0983 |pmid=18854635 |doi-access=free}}</ref>

Other bacterial pathogens, like ''[[Mycoplasma]]'' and those causing [[rickettsial disease]], cause inflammation of the meninges and consequently encephalitis. [[Lyme disease]] or ''[[Bartonella henselae]]'' may also cause encephalitis.{{citation needed|date=August 2015}}

===Other infectious causes===

Certain [[parasitic]] or [[protozoa]]l infestations, such as [[toxoplasmosis]] and [[malaria]] can also cause encephalitis in people with [[immune deficiency|compromised]] [[immune system]]s.

The rare but typically deadly forms of encephalitis, [[primary amoebic meningoencephalitis]] and [[Granulomatous amoebic encephalitis]], are caused by free-living [[amoeba]].<ref>{{Cite web |date=2024-06-24 | title=Free Living Amebic Infections | url=https://www.cdc.gov/dpdx/freelivingamebic/index.html }}</ref>

===Autoimmune encephalitis===
{{Main|Autoimmune encephalitis}}

Autoimmune encephalitis signs can include [[catatonia]], [[psychosis]], [[abnormal]] movements, and autonomic [[dysregulation]]. Antibody-mediated anti-N-methyl-D-aspartate-receptor encephalitis and [[Rasmussen's encephalitis|Rasmussen encephalitis]] are examples of autoimmune encephalitis.<ref>{{Cite journal |vauthors=Armangue T, Petit-Pedrol M, Dalmau J |date=November 2012 |title=Autoimmune encephalitis in children |journal=Journal of Child Neurology |volume=27 |issue=11 |pages=1460–1469 |doi=10.1177/0883073812448838 |pmc=3705178 |pmid=22935553}}</ref>

[[Anti-NMDA 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.<ref>{{Cite journal |vauthors=Dalmau J, Graus F |date=March 2018 |title=Antibody-Mediated Encephalitis |journal=The New England Journal of Medicine |volume=378 |issue=9 |pages=840–851 |doi=10.1056/NEJMra1708712 |pmid=29490181 |s2cid=3623281 |hdl-access=free |hdl=2445/147222}}</ref>

Another autoimmune cause includes [[acute disseminated encephalitis]], a [[demyelinating disease]] which primarily affects children.<ref>{{EMedicine|article|791896|Encephalitis}}</ref>

==Diagnosis==
[[File:Spinal tap newborn.JPG|thumb|Spinal tap on a newborn]]
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.<ref>{{Cite journal |vauthors=Venkatesan A, Tunkel AR, Bloch KC, Lauring AS, Sejvar J, Bitnun A, Stahl JP, Mailles A, Drebot M, Rupprecht CE, Yoder J, Cope JR, Wilson MR, Whitley RJ, Sullivan J, Granerod J, Jones C, Eastwood K, Ward KN, Durrheim DN, Solbrig MV, Guo-Dong L, Glaser CA |date=October 2013 |title=Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the international encephalitis consortium |journal=Clinical Infectious Diseases |volume=57 |issue=8 |pages=1114–1128 |doi=10.1093/cid/cit458 |pmc=3783060 |pmid=23861361}}</ref> Diagnosing encephalitis is done via a variety of tests:<ref>{{Cite web |title=Encephalitis: Diagnosis |url=http://www.nhs.uk/Conditions/Encephalitis/Pages/Diagnosis.aspx |url-status=live |archive-url=https://web.archive.org/web/20150716081924/http://www.nhs.uk/Conditions/Encephalitis/Pages/Diagnosis.aspx |archive-date=2015-07-16 |access-date=2015-08-05 |website=NHS Choices}}</ref><ref>{{Cite journal |vauthors=Kneen R, Michael BD, Menson E, Mehta B, Easton A, Hemingway C, Klapper PE, Vincent A, Lim M, Carrol E, Solomon T |date=May 2012 |title=Management of suspected viral encephalitis in children - Association of British Neurologists and British Paediatric Allergy, Immunology and Infection Group national guidelines |journal=The Journal of Infection |volume=64 |issue=5 |pages=449–477 |doi=10.1016/j.jinf.2011.11.013 |pmid=22120594}}</ref>
* 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 Encephalitis|tick-borne]]<ref>{{Cite web |title=Tick-borne Encephalitis: Vaccine |url=https://www.who.int/ith/vaccines/tbe/en/ |archive-url=https://web.archive.org/web/20131203053717/http://www.who.int/ith/vaccines/tbe/en/ |archive-date=3 December 2013 |access-date=2 April 2013 |website=International travel and health |publisher=World Health Organization}}</ref>  and [[Japanese encephalitis]]<ref>{{Cite web |title=Japanese encephalitis |url=https://www.who.int/immunization/topics/japanese_encephalitis/en/ |archive-url=https://web.archive.org/web/20131203031151/http://www.who.int/immunization/topics/japanese_encephalitis/en/ |archive-date=3 December 2013 |access-date=2 April 2013 |website=Immunization, Vaccines and Biologicals |publisher=World Health Organization}}</ref>  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.<ref>{{Cite web |date=January 2016 |title=CDC Media Statement on Newly Discovered Smallpox Specimens |url=https://www.cdc.gov/media/releases/2014/s0708-NIH.html |url-status=live |archive-url=https://web.archive.org/web/20160520220838/http://www.cdc.gov/media/releases/2014/s0708-NIH.html |archive-date=2016-05-20 |access-date=2016-05-19 |website=www.cdc.gov}}</ref> [[Contraindication]] to [[Pertussis]] immunization should be observed in patients with encephalitis.<ref>{{Cite web |title=Contraindications and Precautions to Commonly Used Vaccines in Adults |url=https://www.cdc.gov/vaccines/schedules/hcp/imz/adult-contraindications.html |archive-url=https://web.archive.org/web/20150823024025/http://www.cdc.gov/vaccines/schedules/hcp/imz/adult-contraindications.html |archive-date=2015-08-23 |access-date=2015-08-05 |website=Vaccines |publisher=Center for Disease Control}}</ref>

==Treatment==
An ideal drug to treat brain infection should be small, moderately lipophilic at pH of 7.4, low level of plasma protein binding, volume of distribution of litre per kg, does not have strong affinity towards binding with [[P-glycoprotein]], or other [[efflux pumps]] on the surface of the [[blood–brain barrier]]. Some drugs such as [[isoniazid]], [[pyrazinamide]], [[linezolid]], [[metronidazole]], [[fluconazole]], and some [[fluoroquinolones]] have good penetration of the blood brain barrier.<ref name="pmid20930076">{{Cite journal |vauthors=Nau R, Sörgel F, Eiffert H |date=October 2010 |title=Penetration of drugs through the blood-cerebrospinal fluid/blood-brain barrier for treatment of central nervous system infections |journal=Clinical Microbiology Reviews |volume=23 |issue=4 |pages=858–883 |doi=10.1128/CMR.00007-10 |pmc=2952976 |pmid=20930076}}</ref> Treatment (which is based on supportive care) is as follows:<ref>{{MedlinePlus|001415|Encephalitis}}</ref>
{{columns-list|colwidth=30em|
* [[Antiviral]] medications (if virus is cause)
* [[Antibiotics]], (if bacteria is cause)
* [[Steroids]] are used to reduce brain swelling
* [[Sedatives]] for restlessness
* [[Acetaminophen]] for fever
* [[Occupational therapy|Occupational]] and [[physical therapy]] (if brain is affected post-infection)
}}

[[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.<ref name="Connollyetal2017">{{Cite journal |vauthors=Connolly MP, Goodwin E, Schey C, Zummo J |date=February 2017 |title=Toxoplasmic encephalitis relapse rates with pyrimethamine-based therapy: systematic review and meta-analysis |journal=Pathogens and Global Health |volume=111 |issue=1 |pages=31–44 |doi=10.1080/20477724.2016.1273597 |pmc=5375610 |pmid=28090819}}</ref> 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%.<ref name="Connollyetal2017" /> This is a significant difference as relapse may impact the severity and prognosis of disease and result in an increase in healthcare expenditure.<ref name="Connollyetal2017" />

The effectiveness of [[Intravenous therapy|intravenous]] [[immunoglobulin]] for the management of childhood encephalitis is unclear. [[Systematic review]]s have been unable to draw firm conclusions because of a lack of [[randomised]] [[double-blind]] studies with sufficient numbers of patients and sufficient follow-up.<ref name=":0">{{Cite journal |vauthors=Iro MA, Martin NG, Absoud M, Pollard AJ |date=October 2017 |title=Intravenous immunoglobulin for the treatment of childhood encephalitis |journal=The Cochrane Database of Systematic Reviews |volume=2017 |issue=10 |article-number=CD011367 |doi=10.1002/14651858.CD011367.pub2 |pmc=6485509 |pmid=28967695}}</ref> There is the possibility of a benefit of intravenous immunoglobulin for some forms of childhood encephalitis on some indicators such as length of hospital stay, time to stop spasms, time to regain consciousness, and time to resolution of neuropathic symptoms and fever.<ref name=":0" />  Intravenous immunoglobulin for [[Japanese encephalitis]] appeared to have no benefit when compared with [[placebo]] (pretend) treatment.<ref name=":0" />

==Prognosis==
Identification of poor prognostic factors include [[cerebral edema]], [[status epilepticus]], and [[thrombocytopenia]].<ref name="Venkatesan2015">{{Cite journal |vauthors=Venkatesan A |date=June 2015 |title=Epidemiology and outcomes of acute encephalitis |journal=[[Current Opinion in Neurology]] |volume=28 |issue=3 |pages=277–282 |doi=10.1097/WCO.0000000000000199 |pmid=25887770 |s2cid=21041693}}</ref> In contrast, a normal [[encephalogram]] at the early stages of diagnosis is associated with high rates of survival.<ref name="Venkatesan2015" />

==Epidemiology==
[[File:Encephalitis world map-Deaths per million persons-WHO2012.svg|thumb|upright=1.3|Encephalitis deaths per million persons in 2012 {{Div col|small=yes|colwidth=10em}}{{legend|#ffff20|0-0}}{{legend|#ffc020|1-1}}{{legend|#ffa020|2-2}}{{legend|#ff9a20|3-4}}{{legend|#f08015|5-9}}{{legend|#e06815|10-14}}{{legend|#d85010|15-24}}{{legend|#d02010|25-45}}{{div col end}}]]
The [[incidence (epidemiology)|number of new cases a year]] of acute encephalitis in Western countries is 7.4 cases per 100,000 people per year. In tropical countries, the incidence is 6.34 per 100,000 people per year.<ref name="Jmor">{{Cite journal |vauthors=Jmor F, Emsley HC, Fischer M, Solomon T, Lewthwaite P |date=October 2008 |title=The incidence of acute encephalitis syndrome in Western industrialised and tropical countries |journal=Virology Journal |volume=5 |issue=134 |article-number=134 |doi=10.1186/1743-422X-5-134 |pmc=2583971 |pmid=18973679 |doi-access=free}}</ref> 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.<ref name="Venkatesan2015" /> In 2015, encephalitis was estimated to have affected 4.3&nbsp;million people and resulted in 150,000 deaths worldwide.<ref name=GBD2015De/><ref name=GBD2015Pre/> Herpes simplex encephalitis has an incidence of 2–4 per million of the population per year.<ref name="Rozenberg">{{Cite journal |vauthors=Rozenberg F, Deback C, Agut H |date=June 2011 |title=Herpes simplex encephalitis: from virus to therapy |journal=Infectious Disorders Drug Targets |volume=11 |issue=3 |pages=235–250 |doi=10.2174/187152611795768088 |pmid=21488834}}</ref>

==Terminology==

Encephalitis with [[meningitis]] is known as [[meningoencephalitis]], while encephalitis with involvement of the spinal cord is known as [[encephalomyelitis]].<ref name=NIH2017Fact/>

The word is from [[Ancient Greek]] {{Lang|grc|{{Script|Greek|ἐγκέφαλος}}}}, {{Lang|grc-latn|enképhalos}} 'brain',<ref>{{Cite web |title=Woodhouse's English-Greek Dictionary |url=http://artflx.uchicago.edu/cgi-bin/efts/dicos/woodhouse_test.pl?keyword=^Brain,%20subs. |archive-url=https://web.archive.org/web/20170305002545/http://artflx.uchicago.edu/cgi-bin/efts/dicos/woodhouse_test.pl?keyword=%5EBrain%2C%20subs. |archive-date=2017-03-05 |access-date=2013-01-10 |publisher=The University of Chicago Library |language=de}}</ref> composed of {{Lang|grc|{{Script|Greek|ἐν}}}}, {{Lang|grc-latn|en}}, 'in' and {{Lang|grc|{{Script|Greek|κεφαλή}}}}, {{Lang|grc-latn|kephalé}}, 'head', and the medical suffix ''-itis'' 'inflammation'.<ref>The word seems to have had a meaning of "lithic imitation of the human brain" at first, according to the ''Trésor de la langue française informatisé'' (cf. the article on [http://www.cnrtl.fr/etymologie/encéphalite "encéphalite"] {{webarchive|url=https://web.archive.org/web/20171105194524/http://www.cnrtl.fr/etymologie/enc%C3%A9phalite |date=2017-11-05 }}). The first use in the medical sense is attested from the early 19th century in French (J. Capuron, ''Nouveau dictionnaire de médecine, chirurgie...'', 1806), and from 1843 in English respectively (cf. the article [http://www.etymonline.com/index.php?allowed_in_frame=0&search=encephalitis "encephalitis"] in the ''Online Etymology Dictionary''). Retrieved 11 March 2017.</ref>

== See also ==
{{columns-list|colwidth=30em|
* [[Bickerstaff's encephalitis]]
* [[Cerebritis]]
* [[La Crosse encephalitis]]
* [[Primary amoebic meningoencephalitis]]
* [[Sappinia amoebic encephalitis]]
* [[Wernicke's encephalopathy]]
* [[World Encephalitis Day]]
* [[Zika virus]]
}}
{{clear}}

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{Cite journal |vauthors=Steiner I, Budka H, Chaudhuri A, Koskiniemi M, Sainio K, Salonen O, Kennedy PG |date=May 2005 |title=Viral encephalitis: a review of diagnostic methods and guidelines for management |journal=European Journal of Neurology |volume=12 |issue=5 |pages=331–343 |doi=10.1111/j.1468-1331.2005.01126.x |pmid=15804262 |s2cid=8986902 |doi-access=free}}
* {{Cite journal |vauthors=Basavaraju SV, Kuehnert MJ, Zaki SR, Sejvar JJ |date=September 2014 |title=Encephalitis caused by pathogens transmitted through organ transplants, United States, 2002-2013 |journal=Emerging Infectious Diseases |volume=20 |issue=9 |pages=1443–1451 |doi=10.3201/eid2009.131332 |pmc=4178385 |pmid=25148201}}
* {{Cite web |last=National Center for Biotechnology Information |title=Encephalitis |url=https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0024785/ |archive-url=https://web.archive.org/web/20210828073601/https://misuse.ncbi.nlm.nih.gov/error/abuse.shtml |archive-date=2021-08-28 |access-date=2015-08-05 |website=PubMed Health |publisher=National Library of Medicine}}
{{refend}}

== External links ==
* [https://web.archive.org/web/20060516005130/http://www.who.int/topics/encephalitis_viral/en/ WHO: Viral Encephalitis]
{{Medical condition classification and resources

| DiseasesDB      = 22543
 | ICD10           = {{ICD10|A|83||a|80}}-{{ICD10|A|86||a|80}}, {{ICD10|B|94|1|b|90}}, {{ICD10|G|05||g|00}}
 | ICD9            = {{ICD9|323}}
 | MedlinePlus     = 001415
 | eMedicineSubj   = emerg
 | eMedicineTopic  = 163
 | MeshID          = D004660
}}
{{Commons}}

{{Scholia|topic}}
{{Diseases of the nervous system}}

{{Authority control}}

[[Category:Encephalitis| ]]
[[Category:Infectious diseases]]
[[Category:Inflammations]]
[[Category:Acute pain]]
[[Category:Wikipedia medicine articles ready to translate]]