Encephalitis

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Encephalitis
Hsv encephalitis.jpg
MRI scan image shows high signal in the temporal lobes and right inferior frontal gyrus in someone with HSV 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 encephalitis, 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] Severity is variable.[1] Symptoms may include headache, fever, confusion, a stiff neck, and vomiting.[1] Complications may include seizures, hallucinations, trouble speaking, memory problems, and problems with hearing.[1]

Causes of encephalitis include viruses such as herpes simplex virus or rabies, bacteria, fungus, or parasites.[2][1] Other causes include autoimmune diseases and certain medication.[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 medication (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]

Signs and symptoms[edit]

Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present irritability, poor appetite and fever.[6] 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.[7]

Cause[edit]

Rabies virus

Viral[edit]

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.[8] Other causes of acute viral encephalitis are rabies virus, poliovirus, and measles virus.[9]

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).[10] The Powassan virus is a rare cause of encephalitis.

Bacterial and other[edit]

It can be caused by a bacterial infection, such as bacterial meningitis,[11] or may be a complication of a current infectious disease syphilis (secondary encephalitis).[12]

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.[13]

Limbic encephalitis[edit]

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.[14]

Autoimmune encephalitis[edit]

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.[15]

Encephalitis lethargica[edit]

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.[16]

Diagnosis[edit]

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.[17] Diagnosing encephalitis is done via a variety of tests:[18]

  • 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.[19]

Prevention[edit]

Vaccination is available against tick-borne[20] and Japanese encephalitis[21] 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.[22] Contraindication to Pertussis immunization should be observed in patients with encephalitis.[23]

Treatment[edit]

Treatment (which is based on supportive care) is as follows:[24]

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.[25] 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%.[25] This is a significant difference as relapse may impact the severity and prognosis of disease and result in an increase in healthcare expenditure.[25]

Prognosis[edit]

Identification of poor prognostic factors include thrombocytopenia, cerebral edema, status epilepticus, and thrombocytopenia.[26] In contrast, a normal encephalogram at the early stages of diagnosis is associated with high rates of survival.[26]

Epidemiology[edit]

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 population per year. In tropical countries, the incidence is 6.34 per 100,000 per year.[27] The incidence of Encephalitis has not changed much over time, with an incidence of encephalitis in the US of 250,000 from 2005 to 2015. Approximately seven per 100,000 patients were hospitalized for encephalitis in the US during this time.[26] 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 population per year.[28]

Terminology[edit]

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",[29] composed of ἐν, en, "in" and κεφαλή, kephalé, "head", and the medical suffix -itis "inflammation".[30]

See also[edit]

References[edit]

  1. ^ a b c d e f g h i j k l "Meningitis and Encephalitis Information Page". NINDS. Archived from the original on 29 October 2017. Retrieved 29 October 2017. 
  2. ^ a b c d e f g h i j "Meningitis and Encephalitis Fact Sheet". National Institute of Neurological Disorders and Stroke. Archived from the original on 29 October 2017. Retrieved 29 October 2017. 
  3. ^ a b c GBD 2015 Disease and Injury Incidence and Prevalence Collaborators (8 October 2016). "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. doi:10.1016/S0140-6736(16)31678-6. PMC 5055577Freely accessible. PMID 27733282. 
  4. ^ a b c GBD 2015 Mortality and Causes of Death Collaborators (8 October 2016). "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. doi:10.1016/S0140-6736(16)31012-1. PMC 5388903Freely accessible. PMID 27733281. 
  5. ^ a b "Encephalitis". NHS Choices. 2016. Archived from the original on 22 September 2017. Retrieved 29 October 2017. 
  6. ^ "Symptoms of encephalitis". NHS. Archived from the original on 5 January 2015. Retrieved 5 January 2015. 
  7. ^ Shmaefsky, Brian; Babcock, Hilary (2010-01-01). Meningitis. Infobase Publishing. ISBN 9781438132167. Archived from the original on 2015-10-30. 
  8. ^ Roos, Karen L.; Tyler, Kenneth L. (2015). "Meningitis, Encephalitis, Brain Abscess, and Empyema". Harrison's Principles of Internal Medicine (19 ed.). New York, NY: McGraw-Hill Education. ISBN 9780071802154. 
  9. ^ Fisher, D. L.; Defres, S.; Solomon, T. (2015). "Measles-induced encephalitis". QJM. 108 (3): 177–182. doi:10.1093/qjmed/hcu113. PMID 24865261. 
  10. ^ Kennedy, P. G. E. (2004-03-01). "Viral Encephalitis: Causes, Differential Diagnosis, and Management". Journal of Neurology, Neurosurgery & Psychiatry. 75 (Suppl 1): i10–5. doi:10.1136/jnnp.2003.034280. PMC 1765650Freely accessible. PMID 14978145. Archived from the original on 2015-10-02. 
  11. ^ Ashar, Bimal H.; Miller, Redonda G.; Sisson, Stephen D. (2012-01-01). Johns Hopkins Internal Medicine Board Review: Certification and Recertification. Elsevier Health Sciences. ISBN 1455706922. Archived from the original on 2015-11-29. 
  12. ^ Hama, Kiwa; Ishiguchi, Hiroshi; Tuji, Tomikimi; Miwa, Hideto; Kondo, Tomoyoshi (2008-01-01). "Neurosyphilis with Mesiotemporal Magnetic Resonance Imaging Abnormalities". Internal Medicine. 47 (20): 1813–7. doi:10.2169/internalmedicine.47.0983. PMID 18854635. Archived from the original on 2016-01-31. 
  13. ^ "Encephalitis: Practice Essentials, Background, Pathophysiology". Archived from the original on 2015-08-03. 
  14. ^ Larner, A. J. (2013-05-02). Neuropsychological Neurology: The Neurocognitive Impairments of Neurological Disorders. Cambridge University Press. ISBN 9781107607606. Archived from the original on 2015-10-30. 
  15. ^ Armangue, Thaís; Petit-Pedrol, Mar; Dalmau, Josep (2012-11-01). "Autoimmune Encephalitis in Children". Journal of child neurology. 27 (11): 1460–9. doi:10.1177/0883073812448838. PMC 3705178Freely accessible. PMID 22935553. 
  16. ^ encephalitis_lethargica at NINDS
  17. ^ 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; International Encephalitis, Consortium. (October 2013). "Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the international encephalitis consortium". Clinical Infectious Diseases. 57 (8): 1114–28. doi:10.1093/cid/cit458. PMID 23861361. 
  18. ^ "Encephalitis: Diagnosis". NHS Choices. Archived from the original on 2015-07-16. Retrieved 2015-08-05. 
  19. ^ Kneen R, Michael BD, Menson E, Mehta B, Easton A, Hemingway C, Klapper PE, Vincent A, Lim M, Carrol E, Solomon T (2012). "Management of suspected viral encephalitis in children - Association of British Neurologists and British Paediatric Allergy, Immunology and Infection Group national guidelines". J. Infect. 64 (5): 449–77. doi:10.1016/j.jinf.2011.11.013. PMID 22120594. 
  20. ^ "Tick-borne Encephalitis: Vaccine". International travel and health. World Health Organization. Archived from the original on 3 December 2013. Retrieved 2 April 2013. 
  21. ^ "Japanese encephalitis". Immunization, Vaccines and Biologicals. World Health Organization. Archived from the original on 3 December 2013. Retrieved 2 April 2013. 
  22. ^ "CDC Media Statement on Newly Discovered Smallpox Specimens". www.cdc.gov. Archived from the original on 2016-05-20. Retrieved 2016-05-19. 
  23. ^ "Contraindications and Precautions to Commonly Used Vaccines in Adults". Vaccines. Center for Disease Control. Archived from the original on 2015-08-23. Retrieved 2015-08-05. 
  24. ^ MedlinePlus Encyclopedia Encephalitis
  25. ^ a b c Connolly MP, Goodwin E, Schey C, Zummo J (2017). "Toxoplasmic encephalitis relapse rates with pyrimethamine-based therapy: systematic review and meta-analysis". Pathogens and global health. 111 (1): 31–44. doi:10.1080/20477724.2016.1273597. PMID 28090819. 
  26. ^ a b c Venkatesan, A (June 2015). "Epidemiology and outcomes of acute encephalitis". Current Opinion in Neurology. 28 (3): 277–82. doi:10.1097/WCO.0000000000000199. PMID 25887770. 
  27. ^ Jmor F, Emsley HC, et al. (October 2008). "The incidence of acute encephalitis syndrome in Western industrialised and tropical countries". Virology Journal. 5 (134): 134. doi:10.1186/1743-422X-5-134. PMC 2583971Freely accessible. PMID 18973679. 
  28. ^ Rozenberg, F; Deback C; Agut H (June 2011). "Herpes simplex encephalitis: from virus to therapy". Infectious Disorders Drug Targets. 11 (3): 235–250. doi:10.2174/187152611795768088. PMID 21488834. 
  29. ^ "Woodhouse's English-Greek Dictionary" (in German). The University of Chicago Library. Retrieved 2013-01-10. 
  30. ^ 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” Archived 2017-11-05 at the Wayback Machine.). 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[edit]

External links[edit]

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External resources