Neuroanatomy

The VIIth cranial (facial) nerve is largely motor in function (some sensory fibres from external acoustic meatus, fibres controlling salivation and taste fibres from the anterior tongue in the chorda tympani branch). It also supplies the stapedius (so a complete nerve lesion will alter auditory acuity on the affected side). From the facial nerve nucleus in the brainstem, fibres loop around the VI nucleus before leaving the pons medial to VIII and passing through the internal acoustic meatus. It passes through the petrous temporal in the facial canal, widens to form the geniculate ganglion (taste and salivation) on the medial side of the middle ear whence it turns sharply (and the chorda tympani leaves), to emerge through the stylomastoid foramen to supply all the muscles of facial expression including the platysma.

Presentation

Weakness of the muscles of facial expression and eye closure. The face sags and is drawn across to the opposite side on smiling. Voluntary eye closure may not be possible and can produce damage to the conjunctiva and cornea.

• In partial paralysis, the lower face is generally more affected.
• In severe cases, there is often demonstrable loss of taste over the front of the tongue and intolerance to high-pitched or loud noises. It may cause mild dysarthria and difficulty with eating.

The most common system used for describing the degree of paralysis is the House-Brackmann scale, where 1 is normal power and 6 is total paralysis.¹

It is important to identify whether the patient has an upper motor neurone (UMN) or lower motor neurone (LMN) lesion to assist in identifying the cause.

• In an LMN lesion the patient can't wrinkle their forehead - the final common pathway to the muscles is destroyed. Lesion must be either in the pons, or outside the brainstem (posterior fossa, bony canal, middle ear or outside skull).
• In an UMN lesion, the upper facial muscles are partially spared because of alternative pathways in the brainstem, i.e. the patient can wrinkle their forehead (unless there is bilateral lesion) and the sagging of the face seen with LMN palsies is not as prominent. There appear to be different pathways for voluntary and emotional movement.

Cerebrovascular accidents usually weaken voluntary movement, often sparing involuntary movements (e.g. spontaneous smiling). The much rarer selective loss of emotional movement is called mimic paralysis and is usually due to a frontal or thalamic lesion.

Aetiology^2,3

• If bilateral, particularly consider Guillain-Barré syndrome or Lyme disease.
• If recurrent, particularly consider lymphoma, sarcoidosis and Lyme disease.
• In children, particularly consider Lyme disease and middle ear disease.

Characteristic features

Acute lower motor neurone (LMN) palsy

Acute LMN palsy can present at any age but is most frequently seen at age 20-50 years, affecting both sexes equally. Incidence is around 30 cases per 100,000 per year, and is slightly higher in pregnant women (45 per 100,000).³ There is usually a rapid onset of unilateral facial paralysis. Aching pain below the ear or in the mastoid area is also common and may suggest middle ear or herpetic cause if severe. There may be hyperacusis and patients with lesions proximal to the geniculate ganglion may be unable to produce tears and have loss of taste.

Bell's palsy⁸

• Originally described by Sir Charles Bell in 1821. Incidence 20 per 100,000 between ages 10-40 years but 59 per 100,000 over age 65 years.
• There may be a familial component.⁹
• In the past no cause was found in the majority of cases of LMN facial nerve palsy and these were labelled as idiopathic (i.e. Bell's palsy).
• The incidence is higher in people with diabetes than with non-diabetics.
• Approximately 7% of patients have a recurrence.
• Recent work suggests that a large number of these cases may be due to herpetic viral infection - particularly herpes simplex type 1, or varicella (herpes) zoster.^2,3,10

Ramsay Hunt's syndrome

LMN facial nerve palsy specifically due to varicella (herpes) zoster. Pain is often a prominent feature and vesicles are seen in the ipsilateral ear, on the hard palate and/or on the anterior two thirds of the tongue. It can include deafness and vertigo and other cranial nerves can be affected. When the rash is absent it is known as zoster sine herpete. Immunodeficiency is a risk factor.¹¹

Investigations

• Serology - Lyme, herpes and zoster (paired samples 4-6 weeks apart). It may not influence management but may reveal aetiology.
• Check blood pressure in children with Bell's palsy (2 case reports of aortic coarctation presenting with facial nerve palsy and hypertension).¹²
• The following tests are rarely done but, combined with a good understanding of the neuroanatomy, can determine the level of the palsy:
  • Schirmer tear test (reveals a reduced flow of tears on the side of a palsy affecting the greater palatine nerve).
  • Stapedial reflex (an audiological test, absent if the stapedius muscle is affected).
  • Electrodiagnostic studies (generally a research tool) reveal no changes in involved facial muscles for the first three days but a steady decline of electrical activity often occurs over the next week and will identify the 15% with axonal degeneration.

Management

Ideally this should be a multidisciplinary approach, encompassing ophthalmologists, ENT surgeons, plastic surgeons and psychologists.¹³

General measures

• Reassurance - the majority of cases resolve spontaneously - see Prognosis, below.
• Eye care - ophthalmologists play an important role in preventing irreversible blindness from corneal exposure. This may be successfully achieved by using lubricating drops hourly and eye ointment at night ± an eye patch. Botulinum toxin or surgery (upper lid weighting or tarsorraphy) may also be required temporarily.¹³ After the cornea has been protected but recovery is thought to be unlikely, longer-term management of eyelid and facial reanimation may be arranged.

Bell's palsy management¹⁴

• Steroids: prednisolone 25 mg twice a day should be given to patients over the age of 16 presenting within 72 hours. There is no evidence to support its use after 72 hours. There is no evidence supporting the use of steroids in children.¹⁵ Acyclovir is no longer recommended, either alone or with steroids.
• Referral:
  • Consider referral to an ENT or neurology specialist if:
    • The diagnosis is in doubt
    • The palsy is bilateral
    • There is a recurrence
    • There is no improvement in paralysis after one month
  • Refer to an ophthalmologist if the cornea is exposed despite attempting to close the eyelid.
  • Refer to a plastic surgeon with special interest in facial reconstruction if there is residual paralysis after 6-9 months.
• Surgery: surgical transmastoid decompression of the facial nerve in severe cases is being investigated but cannot currently be recommended.^3,16 Where nerve fails to regenerate, cosmetic surgery to elevate the mouth or anastomosis of the hypoglossal nerve to the facial nerve may help.

Facial palsy in children^17,18

Most cases of facial palsy in children were classified as idiopathic, although the cause increasingly being identified after thorough investigation. Radiological investigation is required if there is a history of trauma. Spontaneous resolution usually occurs but, in one series, steroids were used in one patient and surgical decompression was required in another.

Prognosis^14,19

Full recovery occurs in about 80% of the cases, 15% experience some kind of permanent nerve damage and 5% remain with severe sequelae.

Poor prognostic features:

• Complete palsy or severe degeneration (electrophysiology)
• No signs of recovery by three weeks
• Age >60
• Severe pain
• Ramsay Hunt's syndrome (herpes zoster virus)
• Associated with either hypertension, diabetes, or pregnancy

Those with axonal degeneration may not show any re-innervation for three months and recovery may be partial or not at all. Synkinesis is often seen, e.g. blinking causes the angle of the mouth to contract. Also aberrant parasympathetic re-innervation may cause symptoms such as gustatory lacrimation ('crocodile tears'). Symptoms can be helped by subcutaneous or intramuscular injections of botulinum toxin.²

Document references

1. House JW, Brackman DE; House Brackman Facial Nerve Grading System 2010.
2. Holland NJ, Weiner GM; Recent developments in Bell's palsy. BMJ. 2004 Sep 4;329(7465):553-7.
3. Gilden DH; Clinical practice. Bell's Palsy. N Engl J Med. 2004 Sep 23;351(13):1323-31.
4. Rosted P, Woolley DR; Bell's Palsy following acupuncture treatment--a case report. Acupunct Med. 2007 Jun;25(1-2):47-8. [abstract]
5. Serrano P, Hernandez N, Arroyo JA, et al; Bilateral Bell palsy and acute HIV type 1 infection: report of 2 cases and review. Clin Infect Dis. 2007 Mar 15;44(6):e57-61. Epub 2007 Feb 8. [abstract]
6. Mutsch M, Zhou W, Rhodes P, et al; Use of the inactivated intranasal influenza vaccine and the risk of Bell's palsy in Switzerland. N Engl J Med. 2004 Feb 26;350(9):896-903. [abstract]
7. Stowe J, Andrews N, Wise L, et al; Bell's palsy and parenteral inactivated influenza vaccine. Hum Vaccin. 2006 May-Jun;2(3):110-2. Epub 2006 May 11. [abstract]
8. Bruce Lo; Bell's Palsy, eMedicine, Feb 2010.
9. Qin D, Ouyang Z, Luo W; Familial recurrent Bell's palsy. Neurol India. 2009 Nov-Dec;57(6):783-4. [abstract]
10. Murakami S, Mizobuchi M, Nakashiro Y, et al; Bell palsy and herpes simplex virus: identification of viral DNA in endoneurial fluid and muscle. Ann Intern Med. 1996 Jan 1;124(1 Pt 1):27-30. [abstract]
11. Goldani LZ, da Silva LF, Dora JM; Ramsay Hunt syndrome in patients infected with human immunodeficiency virus. Clin Exp Dermatol. 2009 Dec;34(8):e552-4. Epub 2009 Jun 1. [abstract]
12. Margabanthu G, Brooks J, Barron D, et al; Facial palsy as a presenting feature of coarctation of aorta. Interact Cardiovasc Thorac Surg. 2003 Mar;2(1):91-3. [abstract]
13. Rahman I, Sadiq SA; Ophthalmic management of facial nerve palsy: a review. Surv Ophthalmol. 2007 Mar-Apr;52(2):121-44. [abstract]
14. Bell's Palsy, Clinical Knowledge Summaries (September 2008)
15. Ashtekar CS, Joishy M, Joshi R; Best evidence topic report. Do we need to give steroids in children with Bell's Emerg Med J. 2005 Jul;22(7):505-7. [abstract]
16. Yanagihara N, Hato N, Murakami S, et al; Transmastoid decompression as a treatment of Bell palsy. Otolaryngol Head Neck Surg. 2001 Mar;124(3):282-6. [abstract]
17. Cha HE, Baek MK, Yoon JH, et al; Clinical features and management of facial nerve paralysis in children: analysis J Laryngol Otol. 2009 Dec 22:1-5. [abstract]
18. Shargorodsky J, Lin HW, Gopen Q; Facial Nerve Palsy in the Pediatric Population. Clin Pediatr (Phila). 2010 Feb 4. [abstract]
19. Finsterer J; Management of peripheral facial nerve palsy. Eur Arch Otorhinolaryngol. 2008 Jul;265(7):743-52. Epub 2008 Mar 27. [abstract]

Internet and further reading

• Reich SG. Bell palsy: Which side? Video demonstartion. Neurology; January 2007

Acknowledgements