Encephalitis

Short description: Inflammation of the brain

Encephalitis

MRI scan image shows high signal in the temporal lobes and right inferior frontal gyrus in someone with herpes simplex encephalitis.
Specialty| Neurology, infectious disease
Symptoms| Headache, fever, confusion, stiff neck, vomiting[1]
Complications| Seizures, trouble speaking, memory problems, problems hearing[1]
Duration| Weeks to months for recovery[1]
Types| Herpes simplex, West Nile, rabies, Eastern equine, others[2]
Causes| Infection, autoimmune, certain medication, unknown[2]
Diagnostic method| Based on symptoms, supported by blood tests, medical imaging, analysis of cerebrospinal fluid[2]
Treatment| Antiviral medication, anticonvulsants, corticosteroids, artificial respiration[1]
Prognosis| Variable[1]
Frequency| 4.3 million (2015)[3]
Deaths| 150,000 (2015)[4]

Encephalitis is inflammation of the brain.[5] The severity can be variable with symptoms including reduction or alteration in consciousness, headache, fever, confusion, a stiff neck, and vomiting.[1][6] Complications may include seizures, hallucinations, trouble speaking, memory problems, and problems with hearing.[1]

Causes of encephalitis include viruses such as herpes simplex virus and rabies virus as well as bacteria, fungi, or parasites.[1][2] Other causes include autoimmune diseases and certain medications.[2] In many cases the cause remains unknown.[2] Risk factors include a weak immune system.[2] Diagnosis is typically based on symptoms and supported by blood tests, medical imaging, and analysis of cerebrospinal fluid.[2]

Certain types are preventable with vaccines.[5] Treatment may include antiviral medications (such as acyclovir), anticonvulsants, and corticosteroids.[1] Treatment generally takes place in hospital.[1] Some people require artificial respiration.[1] Once the immediate problem is under control, rehabilitation may be required.[2] In 2015, encephalitis was estimated to have affected 4.3 million people and resulted in 150,000 deaths worldwide.[3][4]

## Contents

* 1 Signs and symptoms
* 2 Cause
* 2.1 Viral
* 2.2 Bacterial and other
* 2.3 Limbic encephalitis
* 2.4 Autoimmune encephalitis
* 2.5 Encephalitis lethargica
* 3 Diagnosis
* 4 Prevention
* 5 Treatment
* 6 Prognosis
* 7 Epidemiology
* 8 Terminology
* 9 See also
* 10 References
* 11 Further reading
* 12 External links

## 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.[7] 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.[8]

## Cause

Rabies virus

In 30%-40% of encephalitis cases, the etiology remains unknown.[9]

### Viral

Viral infections are the usual cause of infectious encephalitis.[9] 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.[10] Other causes of acute viral encephalitis are rabies virus, poliovirus, and measles virus.[11]

Additional possible viral causes are arboviral flavivirus (St. Louis encephalitis, West Nile virus), bunyavirus (La Crosse strain), arenavirus (lymphocytic choriomeningitis virus), reovirus (Colorado tick virus), and henipavirus infections.[12][13] The Powassan virus is a rare cause of encephalitis.[14]

### Bacterial and other

It can be caused by a bacterial infection, such as bacterial meningitis,[15] or may be a complication of a current infectious disease such as syphilis (secondary encephalitis).[16]

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.[citation needed]

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.[17]

### 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.[18]

### Autoimmune encephalitis

Main page: Medicine: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 encephalitis are examples of autoimmune encephalitis.[19] 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.[20]

### Encephalitis lethargica

Main page: Medicine:Encephalitis lethargica

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.[21]

## Diagnosis

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.[22] Diagnosing encephalitis is done via a variety of tests:[23][24]

* 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[25] and Japanese encephalitis[26] 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.[27] Contraindication to Pertussis immunization should be observed in patients with encephalitis.[28]

## 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 blood–brain barrier. Some drugs such as isoniazid, pyrazinamide, linezolid, metronidazole, fluconazole, and some fluoroquinolones have good penetration to blood brain barrier.[29]Treatment (which is based on supportive care) is as follows:[30]

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.[31] 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%.[31] This is a significant difference as relapse may impact the severity and prognosis of disease and result in an increase in healthcare expenditure.[31]

The effectiveness of intravenous immunoglobulin for the management of childhood encephalitis is unclear. Systematic reviews 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.[32] 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.[32] Intravenous immunoglobulin for Japanese encephalitis appeared to have no benefit when compared with placebo (pretend) treatment.[32]

## Prognosis

Identification of poor prognostic factors include cerebral edema, status epilepticus, and thrombocytopenia.[33] In contrast, a normal encephalogram at the early stages of diagnosis is associated with high rates of survival.[33]

## Epidemiology

Encephalitis deaths per million persons in 2012

0-0

1-1

2-2

3-4

5-9

10-14

15-24

25-45

The 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.[34] 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.[33] In 2015, encephalitis was estimated to have affected 4.3 million people and resulted in 150,000 deaths worldwide.[4][3] Herpes simplex encephalitis has an incidence of 2–4 per million of the population per year.[35]

## Terminology

Encephalitis with meningitis is known as meningoencephalitis, while encephalitis with involvement of the spinal cord is known as encephalomyelitis.[2]

The word is from Ancient Greek ἐγκέφαλος, enképhalos 'brain',[36] composed of ἐν, en, 'in' and κεφαλή, kephalé, 'head', and the medical suffix -itis 'inflammation'.[37]

## See also

## References

1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 "Meningitis and Encephalitis Information Page". https://www.ninds.nih.gov/Disorders/All-Disorders/Meningitis-and-Encephalitis-Information-Page.
2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 "Meningitis and Encephalitis Fact Sheet". https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Meningitis-and-Encephalitis-Fact-Sheet.
3. ↑ 3.0 3.1 3.2 "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". Lancet 388 (10053): 1545–1602. October 2016. doi:10.1016/S0140-6736(16)31678-6. PMID 27733282.
4. ↑ 4.0 4.1 4.2 "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". Lancet 388 (10053): 1459–1544. October 2016. doi:10.1016/S0140-6736(16)31012-1. PMID 27733281.
5. ↑ 5.0 5.1 "Encephalitis" (in en). 2016. https://www.nhs.uk/Conditions/encephalitis/Pages/introduction.aspx.
6. ↑ "Acute encephalitis - diagnosis and management". Clinical Medicine 18 (2): 155–159. March 2018. doi:10.7861/clinmedicine.18-2-155. PMID 29626021.
7. ↑ "Symptoms of encephalitis". http://www.nhs.uk/Conditions/Encephalitis/Pages/Symptoms.aspx.
8. ↑ Meningitis. Infobase Publishing. 2010-01-01. ISBN 9781438132167. https://books.google.com/books?id=KI5p3pADvSsC&q=meningoencephalitis+symptoms+stiff+neck&pg=PA90.
9. ↑ 9.0 9.1 "Encephalitis" (in en). 2021-08-08. https://www.hopkinsmedicine.org/health/conditions-and-diseases/encephalitis.
10. ↑ "Meningitis, Encephalitis, Brain Abscess, and Empyema". Harrison's Principles of Internal Medicine (19 ed.). New York, NY: McGraw-Hill Education. 2015. ISBN 9780071802154. http://accessmedicine.mhmedical.com/content.aspx?bookid=1130&sectionid=79734335. Retrieved 2017-11-17.
11. ↑ "Measles-induced encephalitis". QJM 108 (3): 177–182. March 2015. doi:10.1093/qjmed/hcu113. PMID 24865261.
12. ↑ "Viral encephalitis: causes, differential diagnosis, and management". Journal of Neurology, Neurosurgery, and Psychiatry 75 (Suppl 1): i10–i15. March 2004. doi:10.1136/jnnp.2003.034280. PMID 14978145. PMC 1765650. http://jnnp.bmj.com/content/75/suppl_1/i10.
13. ↑ "Immunization strategies against henipaviruses". Current Topics in Microbiology and Immunology 359: 197–223. 2012. doi:10.1007/82_2012_213. ISBN 978-3-642-29818-9. PMID 22481140.
14. ↑ "Symptoms & Treatment | Powassan | CDC" (in en-us). 4 December 2018. https://www.cdc.gov/powassan/symptoms.html.
15. ↑ Johns Hopkins Internal Medicine Board Review: Certification and Recertification. Elsevier Health Sciences. 2012-01-01. ISBN 978-1455706921. https://books.google.com/books?id=KLBZ85zbTeYC&q=bacterial+meningitis+inflmation+of+encepha+definition&pg=PA113.
16. ↑ "Neurosyphilis with mesiotemporal magnetic resonance imaging abnormalities". Internal Medicine 47 (20): 1813–1817. 2008-01-01. doi:10.2169/internalmedicine.47.0983. PMID 18854635.
17. ↑ "Encephalitis: Practice Essentials, Background, Pathophysiology". MedScape. 2018-08-07. http://emedicine.medscape.com/article/791896-overview#a4.
18. ↑ Larner, A. J. (2013-05-02). Neuropsychological Neurology: The Neurocognitive Impairments of Neurological Disorders. Cambridge University Press. ISBN 9781107607606. https://books.google.com/books?id=hO_lWEDsJYMC&q=limbic+encephalitis+definition&pg=PA156.
19. ↑ "Autoimmune encephalitis in children". Journal of Child Neurology 27 (11): 1460–1469. November 2012. doi:10.1177/0883073812448838. PMID 22935553.
20. ↑ "Antibody-Mediated Encephalitis". The New England Journal of Medicine 378 (9): 840–851. March 2018. doi:10.1056/NEJMra1708712. PMID 29490181.
21. ↑ encephalitis_lethargica at NINDS
22. ↑ "Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the international encephalitis consortium". Clinical Infectious Diseases 57 (8): 1114–1128. October 2013. doi:10.1093/cid/cit458. PMID 23861361.
23. ↑ "Encephalitis: Diagnosis". NHS Choices. http://www.nhs.uk/Conditions/Encephalitis/Pages/Diagnosis.aspx.
24. ↑ "Management of suspected viral encephalitis in children - Association of British Neurologists and British Paediatric Allergy, Immunology and Infection Group national guidelines". The Journal of Infection 64 (5): 449–477. May 2012. doi:10.1016/j.jinf.2011.11.013. PMID 22120594.
25. ↑ "Tick-borne Encephalitis: Vaccine". International travel and health. World Health Organization. https://www.who.int/ith/vaccines/tbe/en/.
26. ↑ "Japanese encephalitis". Immunization, Vaccines and Biologicals. World Health Organization. https://www.who.int/immunization/topics/japanese_encephalitis/en/.
27. ↑ "CDC Media Statement on Newly Discovered Smallpox Specimens". January 2016. https://www.cdc.gov/media/releases/2014/s0708-NIH.html.
28. ↑ "Contraindications and Precautions to Commonly Used Vaccines in Adults". Vaccines. Center for Disease Control. https://www.cdc.gov/vaccines/schedules/hcp/imz/adult-contraindications.html.
29. ↑ "Penetration of drugs through the blood-cerebrospinal fluid/blood-brain barrier for treatment of central nervous system infections". Clinical Microbiology Reviews 23 (4): 858–883. October 2010. doi:10.1128/CMR.00007-10. PMID 20930076.
30. ↑ Template:MedlinePlus
31. ↑ 31.0 31.1 31.2 "Toxoplasmic encephalitis relapse rates with pyrimethamine-based therapy: systematic review and meta-analysis". Pathogens and Global Health 111 (1): 31–44. February 2017. doi:10.1080/20477724.2016.1273597. PMID 28090819.
32. ↑ 32.0 32.1 32.2 "Intravenous immunoglobulin for the treatment of childhood encephalitis". The Cochrane Database of Systematic Reviews 2017 (10): CD011367. October 2017. doi:10.1002/14651858.CD011367.pub2. PMID 28967695.
33. ↑ 33.0 33.1 33.2 "Epidemiology and outcomes of acute encephalitis". Current Opinion in Neurology 28 (3): 277–282. June 2015. doi:10.1097/WCO.0000000000000199. PMID 25887770.
34. ↑ "The incidence of acute encephalitis syndrome in Western industrialised and tropical countries". Virology Journal 5 (134): 134. October 2008. doi:10.1186/1743-422X-5-134. PMID 18973679.
35. ↑ "Herpes simplex encephalitis : from virus to therapy". Infectious Disorders Drug Targets 11 (3): 235–250. June 2011. doi:10.2174/187152611795768088. PMID 21488834.
36. ↑ "Woodhouse's English-Greek Dictionary" (in de). The University of Chicago Library. http://artflx.uchicago.edu/cgi-bin/efts/dicos/woodhouse_test.pl?keyword=^Brain, subs..
37. ↑ 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 “encéphalite” ). 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 “encephalitis” in the Online Etymology Dictionary). Retrieved 11 March 2017.

## Further reading

* "Viral encephalitis: a review of diagnostic methods and guidelines for management". European Journal of Neurology 12 (5): 331–343. May 2005. doi:10.1111/j.1468-1331.2005.01126.x. PMID 15804262.
* "Encephalitis caused by pathogens transmitted through organ transplants, United States, 2002-2013". Emerging Infectious Diseases 20 (9): 1443–1451. September 2014. doi:10.3201/eid2009.131332. PMID 25148201.
* National Center for Biotechnology Information. "Encephalitis". PubMed Health. National Library of Medicine. https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0024785/.

## External links

* WHO: Viral Encephalitis

Classification|

* ICD-10: A83-A86, B94.1, G05
* ICD-9-CM: 323
* MeSH: D004660
* DiseasesDB: 22543

|

External resources|

* MedlinePlus: 001415
* eMedicine: emerg/163

* v
* t
* e

Diseases of the nervous system, primarily CNS (G04–G47, 323–349)

Inflammation|

| Brain|

* Encephalitis
* Viral encephalitis
* Herpesviral encephalitis
* Limbic encephalitis
* Encephalitis lethargica
* Cavernous sinus thrombosis
* Brain abscess
* Amoebic

|

Spinal cord|

* Myelitis: Poliomyelitis
* Demyelinating disease
* Transverse myelitis
* Tropical spastic paraparesis
* Epidural abscess

Both/either|

* Encephalomyelitis
* Acute disseminated
* Myalgic
* Meningoencephalitis

Brain/
encephalopathy|

| Degenerative|

| Extrapyramidal and
movement disorders|

* Basal ganglia disease
* Parkinsonism
* PD
* Postencephalitic
* NMS
* PKAN
* Tauopathy
* PSP
* Striatonigral degeneration
* Hemiballismus
* HD
* OA

* Dyskinesia
* Dystonia
* Status dystonicus
* Spasmodic torticollis
* Meige's
* Blepharospasm
* Athetosis
* Chorea
* Choreoathetosis
* Myoclonus
* Myoclonic epilepsy
* Akathisia

* Tremor
* Essential tremor
* Intention tremor
* Restless legs
* Stiff-person

|

Dementia|

* Tauopathy
* Alzheimer's
* Early-onset
* Primary progressive aphasia
* Frontotemporal dementia/Frontotemporal lobar degeneration
* Pick's
* Dementia with Lewy bodies
* Posterior cortical atrophy

* Vascular dementia

Mitochondrial disease|

* Leigh syndrome

Demyelinating|

* autoimmune
* Multiple sclerosis
* Neuromyelitis optica
* Schilder's disease
* hereditary
* Adrenoleukodystrophy
* Alexander
* Canavan
* Krabbe
* ML
* PMD
* VWM
* MFC
* CAMFAK syndrome
* Central pontine myelinolysis
* Marchiafava–Bignami disease
* Alpers' disease

Episodic/
paroxysmal|

| Seizure/epilepsy|

* Focal
* Generalised
* Status epilepticus
* Myoclonic epilepsy

|

Headache|

* Migraine
* Familial hemiplegic
* Cluster
* Tension

Cerebrovascular|

* TIA
* Amaurosis fugax
* Transient global amnesia
* Acute aphasia

* Stroke
* MCA
* ACA
* PCA
* Foville's
* Millard–Gubler
* Lateral medullary
* Medial medullary
* Weber's
* Lacunar stroke

Sleep disorders|

* Insomnia
* Hypersomnia
* Sleep apnea
* Obstructive
* Congenital central hypoventilation syndrome
* Narcolepsy
* Cataplexy
* Kleine–Levin
* Circadian rhythm sleep disorder
* Advanced sleep phase disorder
* Delayed sleep phase disorder
* Non-24-hour sleep–wake disorder
* Jet lag

CSF|

* Intracranial hypertension
* Hydrocephalus/NPH
* Choroid plexus papilloma
* Idiopathic intracranial hypertension
* Cerebral edema
* Intracranial hypotension

Other|

* Brain herniation
* Reye's
* Hepatic encephalopathy
* Toxic encephalopathy
* Hashimoto's encephalopathy

Spinal cord/
myelopathy|

* Syringomyelia
* Syringobulbia
* Morvan's syndrome
* Vascular myelopathy
* Foix–Alajouanine syndrome
* Spinal cord compression

Both/either|

| Degenerative|

| SA|

* Friedreich's ataxia
* Ataxia–telangiectasia

|

MND|

* UMN only:
* Primary lateral sclerosis
* Pseudobulbar palsy
* Hereditary spastic paraplegia

* LMN only:
* Distal hereditary motor neuronopathies
* Spinal muscular atrophies
* SMA
* SMAX1
* SMAX2
* DSMA1
* Congenital DSMA
* SMA-PCH
* SMA-LED
* SMA-PME
* Progressive muscular atrophy
* Progressive bulbar palsy
* Fazio–Londe
* Infantile progressive bulbar palsy

* both:
* Amyotrophic lateral sclerosis

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