Original Editor - Wendy Walker
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 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.
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.
Population studies show an average incidence of 15 to 30 cases per 100,00 population.
It is the most common cause of acute unilateral facial paralysis, thought to cause between 60 and 75% of all unilateral facial palsy cases.
Mechanism of Injury / Pathological Process
The facial nerve is damaged by inflammation within the nerve causing it to become enlarged, at the point where the nerve exits the skull through the stylomastoid foramen.
Ischemia 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, there is some evidence to suggest that in the majority of cases it is likely to be linked to Herpes Simplex infection.
For more information on the course of Cranial Nerve VII, please see the Facial Nerve page.
Loss of control of the muscles on one side of the face is the main physical presentation.
Some patients also report general malaise in the first few days on onset, as well as some pain in the region of the ipsilateral mastoid (known as otalgia), but many of 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.
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.
MRI scanning can be used to exclude other causes of facial nerve dysfunction, such as Facial Schwannoma or Acoustic Neuroma.
Corticosteroids and antiviral medication are generally considered to be the 1st line treatment for Bell's Palsy, providing the best results when treatment starts within 72 hours of onset of symptoms. There are a number of studies showing benefit for steroids given within this time-frame.
However, many studies do not demonstrate any advantage of using antiviral medication combined with corticosteroids over corticosteroids along.
The Cochrane review "Antiviral treatment for Bell's palsy" Idiopathic facial paralysi,s concludes:"Moderate-quality evidence from randomised controlled trials showed no additional benefit from the combination of antivirals with corticosteroids compared to corticosteroids alone for the treatment of Bell's palsy of various degrees of severity. Moderate-quality evidence showed a small but just significant benefit of combination therapy compared with corticosteroids alone in severe Bell's palsy."
Physiotherapy management of the facial paralysis or weakness is as detailed in the section on Facial Palsy.
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.
The following conditions also result in facial palsy:
- Ramsay Hunt Syndrome - caused by Herpes Zoster infection (AKA Shingles), generally the patient will have vesicles and involvement of other cranial nerves
- Acoustic Neuroma - MRI scan should be used to exclude this
- Facial Schwannoma - caused by a tumour of the facial nerve; MRI scanning (with contrast) will show this
- Neurological (consider Multiple Sclerosis, Guillain-Barre Syndrome
- Infections, such as acute otitis media, cholesteatoma, viral infections including Epstein-Barr Virus
- Neoplasm, particularly parotid malignancy
- Upper Motor Neurone [UMN] facial palsy, generally caused by Stroke - note, the forehead will not suffer from paralysis in UMN causes.
- In 2012 the Guideline Development Subcommittee of the American Academy of Neurology published a review Evidence-based guideline update: steroids and antivirals for Bell palsy, looking specifically at studies published since 2000. This consisted of 9 studies, 2 of which were rated Class 1 (high methodological quality).
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 Cochrane Review Antiviral treatment for Bell's palsy reviewed the effect of antiviral therapy alone concludes:"Moderate-quality evidence from randomised controlled trials showed no additional benefit from the combination of antivirals with corticosteroids compared to corticosteroids alone or in combination with other therapy for the treatment of Bell's palsy of various degrees of severity. They identified 10 trials looking at patients with all degrees (mild through to severe) of Bell's Palsy, aged 14 to 84 years. Moderate-quality evidence showed a small but just significant benefit of combination therapy compared with corticosteroids alone in severe Bell's palsy."
The charity Facial Palsy UK has a page on Bell's Palsy.
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