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Bell's Palsy

Original Editor - Wendy Walker

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Introduction

Facial palsy, day 3

Bell's Palsy, or Bell Palsy, is facial paralysis which is caused by dysfunction of Cranial Nerve VII, the Facial Nerve.

Also known as Idiopathic Peripheral Facial Palsy, it is named after Sir Charles Bell [1774 to 1842], who was a Scottish surgeon, neurologist and anatomist.

It results in inability or reduced ability, to move the muscles on the affected side of the face ie. Facial Palsy or Facial Paralysis.

Bell's Palsy is an idiopathic condition, i.e. no specific cause has been conclusively established. It is a diagnosis of exclusion: once other causes of facial palsy have been eliminated, the patient is said to have Bell's Palsy[1].

Epidemiology

Population studies show an average incidence of 11 to 40 cases per 100,00 population[2][3].

It is the most common cause of acute unilateral facial paralysis, thought to cause between 60 and 75% of all unilateral facial palsy cases[1].

Mechanism of Injury / Pathological Process

The image shows how narrow the facial canal is, with the nerve surrounded by unyielding bone.
Facial nerve in the facial canal.

The facial nerve is damaged by inflammation within the nerve causing it to become enlarged[3], at the point where the nerve exits the skull through the stylomastoid foramen.

Ischaemia occurs as the nerve swells in its bony canal, blocking neural blood supply.

Having said that Bell's Palsy is a diagnosis of exclusion and that we are not certain what causes the nerve inflammation[4], there is evidence to suggest that in the majority of cases it is likely to be linked to Herpes Simplex infection[5][6].

For more information on the course of Cranial Nerve VII, please see the Facial Nerve page.

Clinical Presentation

Illustration of left sided flaccid facial palsy , position at rest. It shows the absence of horizontal forehead lines on the left, larger left eye and lower resting position of left corner of the mouth.
Left sided flaccid facial palsy, position at rest. Note absence of horizontal forehead lines on left side, left eye larger than right and a lower resting position of he left corner of the mouth.

Loss of control of the muscles on one side of the face is the main physical presentation. Typically the paralysis develops over 24 to 72 hours.

Some patients also report general malaise in the first few days of onset, as well as some pain in the region of the ipsilateral mastoid (known as otalgia), but many patients have no otalgia or malaise.

At onset, the paralysis may be complete, or partial (paresis) and although it frequently affects all branches of the facial nerve on the affected side, resulting in loss of control of that side of the mouth and the ipsilateral eye, in a few cases only one or two branches of the facial nerve are affected.

For a more detailed description of the clinical presentation, please see the Facial Palsy page.

Diagnostic Procedures

Bell's Palsy is essentially a diagnosis of exclusion, so once other causes of facial palsy have been eliminated, we call an isolated facial palsy Bell's Palsy, or Idiopathic Facial Palsy[1][7][8].

MRI scanning can be used to exclude other causes of facial nerve dysfunction[9], such as Facial Schwannoma or Acoustic Neuroma.

[10]

Differential Diagnosis

The following conditions also result in facial palsy:

  • Ramsay Hunt Syndrome - caused by Herpes Zoster infection (AKA Shingles)[9], generally the patient will have vesicles and involvement of other cranial nerves
  • Acoustic Neuroma - MRI scan should be used to exclude this[9]
  • Facial Schwannoma - caused by a tumour of the facial nerve; MRI scanning (with contrast) will show this
  • Surgical trauma can be a cause of injury to the facial nerve - the most common surgeries resulting in facial pasly are: removal of acoustic neuroma, mastoidectomy, parotidectomy
  • Neurological (consider Multiple Sclerosis, neurosasrcoidosis and Guillain-Barre Syndrome)
  • Infections[9], such as acute otitis media, Lyme Disease, cholesteatoma, viral infections including Epstein-Barr Virus
  • Neoplasm, particularly parotid malignancy, but also a number of brain tumours can (rarely) cause facial palsy, including meningioma
  • Trauma to the head, particularly the temporal bone, can result in facial palsy
  • Upper Motor Neurone [UMN] facial palsy, generally caused by Stroke - note, in many UMN causes the forehead does not suffer from paralysis

Risk factors

Medical Management

Corticosteroids - clear evidence of efficacy

Corticosteroid medication is generally considered to be the 1st line treatment for Bell's Palsy, providing the best results when treatment starts within 72 hours of the onset of symptoms[12][1][3]. There are a number of studies showing benefit for steroids given within this time-frame[13][14][15][16], and the 2016 Cochrane review Corticosteroids for Bell's Palsy (Idiopathic Facial Paralysis)[17] concludes "According to high‐quality evidence, 10 people with Bell's palsy need to be treated with corticosteroids to avoid one incomplete recovery. The available evidence from randomised controlled trials shows that corticosteroids significantly reduce the frequency of incomplete recovery from Bell's palsy."

Antivirals - unclear if any additional benefit

Although some patients are also prescribed antivirals, many studies do not demonstrate any advantage of using antiviral medication combined with corticosteroids over corticosteroids alone. 

The conclusions & recommendations were: For patients with new-onset Bell's palsy, steroids are highly likely to be effective and should be offered to increase the probability of recovery of facial nerve function [this conclusion was based on 2 Class 1 studies, Level A, & the risk difference was 12.8%-15%]. They concluded that for new-onset Bell's Palsy, antiviral agents in combination with steroids do not increase the probability of facial functional recovery by >7%, but "because of the possibility of a modest increase in recovery, patients might be offered antivirals (in addition to steroids" [Level C evidence]. They also remark "patients offered antivirals should be counselled that a benefit from antivirals has not been established, and, if there is a benefit, it is likely that it is modest at best".

  • The 2019 Cochrane review "Antiviral treatment for Bell's palsy"[18] Idiopathic facial paralysis concludes:"Corticosteroids alone were more effective than antivirals alone on rates of incomplete recovery (667 participants, 2 trials); antivirals and corticosteroids combined were more effective than placebo or no treatment (658 participants, 2 trials); and there was no clear benefit from antivirals alone over placebo (658 participants, 2 trials). Although, based on data from two trials (656 participants), we found no clear difference in the occurrence of side effects between people receiving both antivirals and corticosteroids, compared to those receiving corticosteroids alone, this evidence is too uncertain for us to draw conclusions."

[19]

Physiotherapy Interventions

For physiotherapy interventions please see Facial Palsy page; for an assessment format see Lower Motor Neuron Facial Palsy Assessment page.

It is also important to provide information on care of the eye in order to prevent formation of corneal ulcer: see advice page on Dry Eye. Referral to an opthalmologist should be considered.

A number of people with Bell's Palsy suffer from Xerostomia, or Dry Mouth. This occurs because two of the three main salivary glands receive their parasympathetic nerve supply from the facial nerve: the sublingual and glossopharyngeal glands. (The parotid gland is not innervated by the facial nerve, so is unaffected.) See the advice page on Dry Mouth.

Bell's Palsy patients with long term facial paralysis may also start to experience dental problems: see advice page on Dental Issues in Facial Palsy.

Prognosis

Approximately 70% of patients who have Bell's Palsy will have complete recovery within approximately 8 weeks,[20][21][22]as in these cases the Facial Nerve has suffered the mildest degree of nerve damage ie. neuropraxia, and there is no permanent damage to the axons; see the Classification of Peripheral Nerve Injury page for more details.

The remaining 30% will suffer long term sequelae ranging from mild to severe, which can include facial weakness, synkinesis, involuntary movements, and persistent lachrymation.[1][12][23]In these cases the Facial Nerve has suffered axonotmesis damage as explained in the Classification of Peripheral Nerve Injury page.

Resources

The charity Facial Palsy UK has a page on Bell's Palsy.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Eviston TJ, Croxson GR, Kennedy PGE, et al Bell's palsy: aetiology, clinical features and multidisciplinary care Journal of Neurology, Neurosurgery & Psychiatry 2015;86:1356-1361
  2. ↑ Katusic SK; Beard CM; Wiederholt WC; Bergstralh EJ; Kurland LT Incidence, clinical features, and prognosis in Bell's palsy, Rochester, Minnesota, 1968-1982. Ann Neurol.  1986; 20(5):622-7
  3. ↑ 3.0 3.1 3.2 Somasundara, D., & Sullivan, F. (2017). Management of Bell's palsy. Australian prescriber, 40(3), 94–97. https://doi.org/10.18773/austprescr.2017.030
  4. ↑ Peitersen,E. Bell's Palsy; the spontaneous course of 2,500 peripheral facial nerve palsies of different etiologies. Acta Oto-Laryngologica. Supplementum 2002;549:4-30
  5. ↑ Holland NJ, Weiner GM. Recent developments in Bell's Palsy. BMJ 2004; 329(7465):553-7
  6. ↑ Murakami, S. et al. Bell palsy and herpes simplex virus: identification of viral DNA in endoneurial fluid and muscle. Ann. Intern. Med. 124, 27–30 (1996).
  7. ↑ Ahmed A. When is facial paralysis Bell palsy? Current diagnosis and treatment. Cleve Clin J Med. 2005;72(5):398-401, 405
  8. ↑ Zhao H, Zhang X, Tang Y, Zhu J, Wang X, Li S: Bell's Palsy: Clinical Analysis of 372 Cases and Review of Related Literature. Eur Neurol 2017;77:168-172. doi: 10.1159/000455073
  9. ↑ 9.0 9.1 9.2 9.3 Zimmermann, J., Jesse, S., Kassubek, J. et al. Differential diagnosis of peripheral facial nerve palsy: a retrospective clinical, MRI and CSF-based study. J Neurol 266, 2488–2494 (2019). https://doi.org/10.1007/s00415-019-09387-w
  10. ↑ Osmosis. Bell's Palsy - causes, symptoms, diagnosis, treatment, pathology. Available from: http://www.youtube.com/watch?v=ic1hKbk4CKc[last accessed 23/4/2020]
  11. ↑ 11.0 11.1 11.2 11.3 Khan AJ, Szczepura A, Palmer S, et al. Physical therapy for facial nerve paralysis (Bell's palsy): An updated and extended systematic review of the evidence for facial exercise therapy. Clin Rehabil. 2022;36(11):1424-1449. doi:10.1177/02692155221110727
  12. ↑ 12.0 12.1 Shi J, Lu D, Chen H, et al. Efficacy and Safety of Pharmacological and Physical Therapies for Bell's Palsy: A Bayesian Network Meta-Analysis. Front Neurol. 2022;13:868121. Published 2022 Apr 18. doi:10.3389/fneur.2022.868121
  13. ↑ Engstrom M, Berg T, Stjernquist-Desatnik A, Axelsson S, Pitkaranta A, Hultcrantz M, et al. Prednisolone and valaciclovir in Bell's palsy: a randomised, double-blind, placebo-controlled, multicentre trial. Lancet Neurol. 2008;(11):993-1000
  14. ↑ Sullivan FM, Swan IR, Donnan PT, Morrison JM, Smith BH, McKinstry B, et al. Early treatment with prednisolone or acyclovir in Bell's palsy. N Engl J Med. 2007;357(16):1598-607
  15. ↑ Axelsson S, Berg T, Jonsson L, Engström M, Kanerva M, Stjernquist-Desatnik A. Bell's palsy - the effect of prednisolone and/or valaciclovir versus placebo in relation to baseline severity in a randomised controlled trial. Clin Otolaryngol. 2012;37(4):283-90
  16. ↑ Berg T, Bylund N, Marsk E, Jonsson L, Kanerva M, Hultcrantz M, et al. The effect of prednisolone on sequelae in Bell's palsy. Arch Otolaryngol Head Neck Surg. 2012; 138(5):445-9
  17. ↑ Madhok VB, Gagyor I, Daly F, Somasundara D, Sullivan M, Gammie F, Sullivan F. Corticosteroids for Bell's palsy (idiopathic facial paralysis). Cochrane Database of Systematic Reviews 2016, Issue 7. Art. No.: CD001942. DOI: 10.1002/14651858.CD001942.pub5. Accessed 22 April 2025.
  18. ↑ Gagyor I, Madhok VB, Daly F, Sullivan F. Antiviral treatment for Bell's palsy (idiopathic facial paralysis). Cochrane Database of Systematic Reviews 2019, Issue 9. Art. No.: CD001869. DOI: 10.1002/14651858.CD001869.pub9. Accessed 22 April 2025.
  19. ↑ FacialPalsyUK. What is the treatment for Bell's palsy and Ramsay Hunt syndrome? Available from: http://www.youtube.com/watch?v=vIVCg6lHFcg [last accessed 23/4/2020]
  20. ↑ Peitersen E. Bell's palsy: the spontaneous course of 2,500 peripheral facial nerve palsies of different etiologies. Acta Otolaryngol Suppl. 2002;(549):4-30. PMID: 12482166.[1]
  21. ↑ Morgenlander JC, Massey EW. Bell's Palsy. Ensuring the best possible outcome. Postgraduate Medicine 1990;88(5):157‐61, 164.
  22. ↑ Baugh, R.F., Basura, G.J., Ishii, L.E., et al. (2013) Clinical practice guideline: Bell's palsy. Otolaryngology - Head and Neck Surgery 149(3 Suppl), S1-S27
  23. ↑ Schirm J, Mulkens PS. Bell's palsy and herpes simplex virus. APMIS. 1997 Nov; 105(11):815-23


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