Editing Trigeminal neuralgia (section)

==Causes==
{{See also|Pathophysiology of nerve entrapment}}
The trigeminal nerve is a mixed cranial nerve responsible for sensory data such as [[tactition]] (pressure), [[thermoception]] (temperature), and [[nociception]] (pain) originating from the face above the jawline; it is also responsible for the motor function of the [[muscles of mastication]], the muscles involved in chewing but not facial expression.<ref>{{cite web | vauthors = Pazhaniappan N |title=The Trigeminal Nerve (CN V) |url=https://teachmeanatomy.info/head/cranial-nerves/trigeminal-nerve/ |publisher=TeachMeAnatomy |access-date=5 April 2021 |date=15 August 2020}}</ref>

Several theories exist to explain the possible causes of this [[pain]] syndrome. It was once believed that the nerve was compressed in the opening from the inside to the outside of the skull; but leading research indicates that it is an enlarged or lengthened blood vessel – most commonly the [[superior cerebellar artery]] – compressing or throbbing against the microvasculature of the trigeminal nerve near its connection with the [[pons]].<ref>{{cite journal | vauthors = Nurmikko TJ, Eldridge PR | title = Trigeminal neuralgia--pathophysiology, diagnosis and current treatment | journal = British Journal of Anaesthesia | volume = 87 | issue = 1 | pages = 117–132 | date = July 2001 | pmid = 11460800 | doi = 10.1093/bja/87.1.117 | doi-access = free }}</ref> Such a compression can injure the nerve's protective myelin sheath and cause erratic and hyperactive functioning of the nerve. This can lead to pain attacks at the slightest stimulation of any area served by the nerve as well as hinder the nerve's ability to shut off the pain signals after the stimulation ends. This type of injury may rarely be caused by an [[aneurysm]] (an outpouching of a [[blood vessel]]); by an [[arteriovenous malformation]] (AVM);<ref name="SinghBharatha2014">{{cite journal | vauthors = Singh N, Bharatha A, O'Kelly C, Wallace MC, Goldstein W, Willinsky RA, Aviv RI, Symons SP | title = Intrinsic arteriovenous malformation of the trigeminal nerve | journal = The Canadian Journal of Neurological Sciences. Le Journal Canadien des Sciences Neurologiques | volume = 37 | issue = 5 | pages = 681–683 | date = September 2010 | pmid = 21059518 | doi = 10.1017/S0317167100010891 | doi-access = free }}</ref> by a [[tumor]]; such as an [[arachnoid cyst]] or [[meningioma]] in the [[cerebellopontine angle]];<ref name=Babu1991>{{cite journal | vauthors = Babu R, Murali R | title = Arachnoid cyst of the cerebellopontine angle manifesting as contralateral trigeminal neuralgia: case report | journal = Neurosurgery | volume = 28 | issue = 6 | pages = 886–887 | date = June 1991 | pmid = 2067614 | doi = 10.1097/00006123-199106000-00018 }}</ref> or by a traumatic event, such as a car accident.<ref>{{cite book| vauthors = Croft SM, Foreman AC |title=Whiplash injuries : the cervical acceleration/deceleration syndrome|year=2002|publisher=Williams & Wilkins|location=Baltimore|isbn=978-0-7817-2681-8|page=481|url=https://books.google.com/books?id=De5LdqgeSf4C&q=trigeminal+neuralgia+injury&pg=PA481|edition=3rd|url-status=live|archive-url=https://web.archive.org/web/20170314140758/https://books.google.com/books?id=De5LdqgeSf4C&pg=PA481&dq=trigeminal+neuralgia+injury&hl=en&sa=X&ei=O24nU5HoKIv8ywOIhYCoAw&redir_esc=y#v=onepage&q=trigeminal%20neuralgia%20injury&f=false|archive-date=2017-03-14}}</ref>

Short-term peripheral compression is often painless.<ref name=Okeson2005/> Persistent compression results in local demyelination with no loss of axon potential continuity. Chronic nerve entrapment results in demyelination primarily, with progressive axonal degeneration subsequently.<ref name=Okeson2005/> It is, "therefore widely accepted that trigeminal neuralgia is associated with demyelination of axons in the [[Gasserian ganglion]], the dorsal root, or both."<ref name="Okeson 2005 115">{{cite book| vauthors = Okeson JP |title=Bell's orofacial pains: the clinical management of orofacial pain|year=2005|publisher=Quintessence Publishing Co, Inc|isbn=0-86715-439-X|page=115|chapter-url=http://www.quintpub.com/display_detail.php3?psku=B439X|editor=Lindsay Harmon|chapter=6|url-status=live|archive-url=https://web.archive.org/web/20140112055333/http://www.quintpub.com/display_detail.php3?psku=B439X|archive-date=2014-01-12}}</ref> It has been suggested that this compression may be related to an aberrant branch of the superior cerebellar artery that lies on the trigeminal nerve.<ref name="Okeson 2005 115"/> Further causes, besides an aneurysm, multiple sclerosis or cerebellopontine angle tumor, include: a posterior fossa tumor, any other expanding lesion or even brainstem diseases from strokes.<ref name="Okeson 2005 115"/>

Trigeminal neuralgia is found in 3–4% of people with multiple sclerosis, according to data from seven studies.<ref>{{cite journal | vauthors = Foley PL, Vesterinen HM, Laird BJ, Sena ES, Colvin LA, Chandran S, MacLeod MR, Fallon MT | title = Prevalence and natural history of pain in adults with multiple sclerosis: systematic review and meta-analysis | journal = Pain | volume = 154 | issue = 5 | pages = 632–642 | date = May 2013 | pmid = 23318126 | doi = 10.1016/j.pain.2012.12.002 | s2cid = 25807525 }}</ref><ref>{{cite journal | vauthors = De Santi L, Annunziata P | title = Symptomatic cranial neuralgias in multiple sclerosis: clinical features and treatment | journal = Clinical Neurology and Neurosurgery | volume = 114 | issue = 2 | pages = 101–107 | date = February 2012 | pmid = 22130044 | doi = 10.1016/j.clineuro.2011.10.044 | s2cid = 3402581 }}</ref>  It has been theorized that this is due to damage to the [[spinal trigeminal complex]].<ref name=Cruccu2009>{{cite journal | vauthors = Cruccu G, Biasiotta A, Di Rezze S, Fiorelli M, Galeotti F, Innocenti P, Mameli S, Millefiorini E, Truini A | title = Trigeminal neuralgia and pain related to multiple sclerosis | journal = Pain | volume = 143 | issue = 3 | pages = 186–191 | date = June 2009 | pmid = 19171430 | doi = 10.1016/j.pain.2008.12.026 | s2cid = 24353039 | hdl = 11573/361397 }}</ref> Trigeminal pain has a similar presentation in patients with and without MS.<ref name=Simone2005>{{cite journal | vauthors = De Simone R, Marano E, Brescia Morra V, Ranieri A, Ripa P, Esposito M, Vacca G, Bonavita V | title = A clinical comparison of trigeminal neuralgic pain in patients with and without underlying multiple sclerosis | journal = Neurological Sciences | volume = 26 | issue = S2 | pages = s150–s151 | date = May 2005 | pmid = 15926016 | doi = 10.1007/s10072-005-0431-8 | s2cid = 23024675 }}</ref>

[[Postherpetic neuralgia]], which occurs after [[shingles]], may cause similar symptoms if the trigeminal nerve is damaged, called [[Ramsay Hunt syndrome type 2]].

When there is no apparent structural cause, the syndrome is called [[idiopathic]].