Editing Bell's palsy (section)

==Pathophysiology==
Bell's palsy is the result of a malfunction of the [[facial nerve]] ([[cranial nerve]] VII), which controls the [[muscle]]s of the face. Facial palsy is typified by an inability to move the muscles of facial expression. The paralysis is of the infranuclear/lower motor neuron type.

It is thought that as a result of [[inflammation]] of the facial nerve, pressure is produced on the nerve where it exits the skull within its bony canal (the [[stylomastoid foramen]]), blocking the transmission of neural signals or damaging the nerve. Patients with facial palsy for which an underlying cause can be found are not considered to have Bell's palsy ''per se''. Possible causes of facial paralysis include [[tumor]], [[meningitis]], [[stroke]], [[diabetes mellitus]], [[head injury|head trauma]] and inflammatory diseases of the cranial nerves ([[sarcoidosis]], [[brucellosis]], etc.). In these conditions, the neurologic findings are rarely restricted to the facial nerve. Babies can be born with facial palsy.<ref>[https://www.nlm.nih.gov/medlineplus/ency/article/001425.htm MedlinePlus Medical Encyclopedia: Facial nerve palsy due to birth trauma] {{webarchive|url=https://web.archive.org/web/20081001211231/http://www.nlm.nih.gov/medlineplus/ency/article/001425.htm |date=2008-10-01 }} retrieved 10 September 2008</ref> In a few cases, bilateral facial palsy has been associated with [[acute HIV infection]].

In some research, the [[herpes simplex virus]] type 1 (HSV-1) has been identified in a majority of cases diagnosed as Bell's palsy through endoneurial fluid sampling.<ref>{{cite journal | vauthors = Murakami S, Mizobuchi M, Nakashiro Y, Doi T, Hato N, Yanagihara N | title = Bell palsy and herpes simplex virus: identification of viral DNA in endoneurial fluid and muscle | journal = Annals of Internal Medicine | volume = 124 | issue = 1 Pt 1 | pages = 27–30 | date = January 1996 | pmid = 7503474 | doi = 10.7326/0003-4819-124-1_Part_1-199601010-00005 | s2cid = 22790049 }}</ref> Other research, however, identified, out of a total of 176 cases diagnosed as Bell's palsy, HSV-1 in 31 cases (18%) and [[herpes zoster]] in 45 cases (26%).<ref name=Furuta>{{cite journal | vauthors = Furuta Y, Ohtani F, Chida E, Mesuda Y, Fukuda S, Inuyama Y | title = Herpes simplex virus type 1 reactivation and antiviral therapy in patients with acute peripheral facial palsy | journal = Auris, Nasus, Larynx | volume = 28 Suppl | issue = Suppl | pages = S13–17 | date = May 2001 | pmid = 11683332 | doi = 10.1016/S0385-8146(00)00105-X }}</ref>

In addition, HSV-1 infection is associated with [[demyelination]] of nerves. This nerve damage mechanism is different from the above-mentioned—that edema, swelling, and compression of the nerve in the narrow bone canal are responsible for nerve damage. Demyelination may not even be directly caused by the virus but by an unknown [[immune system|immune]] response.