Abstract
Bell’s palsy is an idiopathic lower motor neurone palsy of the facial nerve. It is the most common cause of rapid-onset unilateral facial weakness, affecting approximately 1 in 5000 patients in the UK each year. A careful history and examination can usually exclude other causes of facial nerve paralysis. Seventy-one percent of affected patients regain full neurological function within a year. Timely treatment with prednisolone increases the likelihood of complete recovery. Ocular complications may occur if the patient cannot completely close the affected eye. This may be prevented by regular use of lubricants. Patients who do not recover nerve function may benefit from surgery to improve facial function and appearance.
The GP curriculum and Bell’s palsy
Manage primary contact with patients who have a common/important ENT, oral or facial problem Appreciate that pathology in other systems may lead to ENT-related symptoms Understand when urgent (or semi-urgent) referral to secondary care may be indicated Demonstrate knowledge of the scientific backgrounds of symptoms, diagnosis and treatment of ENT, oral and facial conditions Understand the significant quality-of-life impairment that may arise from common ENT and oral complaints
History and epidemiology
Bell’s palsy is named after Charles Bell, a Scottish surgeon and anatomist who, in 1821, published a paper describing the function of the facial nerve. He found that dividing the nerve in animals was painless, but led to facial muscle paralysis on the side of the lesion. The term ‘Bell’s palsy’ describes an idiopathic lower motor neurone palsy of the facial nerve. Several theories for its aetiology have been proposed: infection (namely reactivation of herpes simplex or varicella zoster virus), autoimmunity, and ischaemia, all of which may lead to neural inflammation and compression of the facial nerve in the facial canal. Compelling evidence for any of these hypotheses is lacking (Eviston, Croxson, Kennedy, Hadlock, & Krishnan, 2015).
The annual incidence of Bell’s palsy in the UK is 1 in 5000 (Anon, 2008). It most commonly occurs between the ages of 15 and 60 years (National Institute for Health and Care Excellence (NICE), 2012). It is almost always unilateral. Seven percent of affected patients have a recurrence (Pitts, Adour, & Hilsinger, 1988). It affects males and females equally. Bell’s palsy is more common in diabetic patients: a case control study showed that 24.8% of patients diagnosed with Bell’s palsy had diabetes mellitus, compared with 13.1% of age-matched controls (Paolino, Granieri, Tola, Panarelli, & Carreras, 1985). It is also more common in pregnancy.
Anatomy
The facial nerve arises from the pons and medulla, and carries motor fibres to the muscles of facial expression, stapedius and some muscles of mastication; taste sensory fibres to the anterior two thirds of the tongue via the chorda tympani; general sensory fibres to some skin of the external auditory meatus; and parasympathetic fibres to the pterygopalatine and submandibular ganglia (Moore & Daley, 2006).
On leaving the brainstem, the nerve crosses the posterior cranial fossa and enters the petrous temporal bone through the internal auditory meatus. It passes through the internal auditory meatus into the facial canal. Here the nerve divides, giving off the greater petrosal nerve (carrying parasympathetic fibres to the lacrimal glands), the nerve to stapedius and the chorda tympani.
The facial nerve exits the skull via the stylomastoid foramen. It divides again, giving off the posterior auricular branch as well as motor fibres to the posterior belly of digastric and stylohyoid. The main trunk of the nerve then enters the parotid gland and forms the parotid plexus, giving rise to five motor nerves: temporal, zygomatic, marginal mandibular, temporal and cervical. Figure 1 shows the pathways followed by the different fibres of the facial nerve.
Anatomy of the facial nerve.
Making the diagnosis
Patients with Bell’s palsy typically notice a unilateral facial weakness, which develops within 2 days. The severity can vary from a slight weakness to a complete paralysis. Patients are unable to move the affected side of their face, and may notice drooping of the mouth and an asymmetrical smile (NICE, 2012). Figure 2 shows a patient with a left-sided Bell’s palsy who demonstrates these signs. Weakness of the orbicularis oris can lead to difficulty chewing food and drooling of saliva. Incomplete eyelid closure and reduced innervation of the lacrimal glands leads to dry eyes. Taste and speech may be impaired. Occasionally, facial pain, ear pain or aural fullness precedes the nerve palsy.
Patient with left-sided Bells’ palsy.
On examination there will be facial asymmetry when the patient is asked to demonstrate voluntary facial movements (NICE, 2012). It is possible to distinguish between upper and lower motor neurone lesions by asking the patient to wrinkle their forehead. In a lower motor neurone palsy (occurring either in the pons or outside the brainstem), the patient will not be able to wrinkle their forehead on the affected side, as the final common pathway to the muscles is interrupted. In an upper motor neurone palsy (occurring between the primary motor cortex and the facial nerve nucleus), the patient is still able to wrinkle their forehead on the affected side. This is because the upper facial motor nucleus, which supplies nerve fibres to the frontalis, receives input from both cerebral cortices. In contrast, the lower facial motor nucleus only receives input from the contralateral hemisphere. As a result, the lower part of the face is weak in both upper and lower motor neurone lesions. Possible serious causes of an upper motor neurone facial palsy include stroke, infections such as syphilis or human immunodeficiency virus, vasculitis, tumours and multiple sclerosis.
Differential diagnosis of lower motor neurone facial nerve palsy.
Source: Patient UK (2013a).
Cholesteatoma visible on the superior part of the tympanic membrane. They can also have a waxy appearance.
The extent of facial weakness can be recorded using the House–Brackmann facial nerve grading system (House and Brackmann, 1985). This rates facial nerve function from one (normal) to six (complete paralysis) and is useful for assessing the degree of impairment and monitoring recovery. A pictorial version (Fig. 4) of the scale is also available, which may be easier to use and less subjective (Lazarini, Mitre, Takatu, & Tidei, 2006).
Pictorial representation of the House–Brackmann grading scale for facial nerve palsy.
Assess whether the cornea is fully covered when the eyes are closed: if it is not, taping and ocular lubricants are required to prevent corneal ulceration. If there is uncertainty regarding the diagnosis, or the patient has recurrent or bilateral Bell’s palsy, discuss the patient with an ear, nose and throat (ENT) specialist to arrange an urgent review.
Treatment of Bell’s palsy
Medication
In 2010, the Cochrane Collaboration published a systematic review and meta-analysis of eight randomised controlled trials (RCTs), comparing the likelihood of incomplete recovery of facial nerve function 6 months or more after randomisation with groups receiving placebo or corticosteroids. They found that 23% of patients who received corticosteroids failed to completely recover nerve function, compared with 33% of patients who received the placebo. The number needed to treat with corticosteroids to prevent one case of incomplete recovery was 10. The steroid doses and route of administration varied between the trials (Salinas, Alvarez, Daly, & Ferreira, 2010).
One large RCT randomised patients to receive aciclovir alone, corticosteroids alone, aciclovir and corticosteroids, or placebo alone. The patients were followed up for 9 months. The results did not show a significant improvement in recovery of nerve function in patients who received aciclovir compared with those who did not (Sullivan et al., 2007).
NICE (2012) advises: ‘for people presenting within 72 hours of the onset of symptoms, consider prescribing prednisolone’. The doses recommended come from the doses used in the two of the largest RCTs included in the Cochrane review. The doses are either 25 mg prednisolone twice daily for 10 days or 60 mg prednisolone once daily for 5 days followed by a reduction in dose of 10 mg per day over the next 5 days, to complete the 10 days of treatment. Prescribing aciclovir is not recommended, this is due to there being no evidence of benefit. There is insufficient evidence to recommend acupuncture as a treatment for Bell’s palsy.
Eye care
The orbicularis oculi muscle is supplied by the facial nerve. Loss of tone here leads to the main ocular complication of Bell’s palsy: corneal exposure. Untreated, this can lead to serious, sight-threatening infections of the cornea (microbial keratitis). However, prophylactic measures can be carried out safely in primary care (Lee, Currie, & Collin, 2004).
It is important to check for lagophthalmos at rest (incomplete closure of the eye lids) and for Bell’s reflex (the tendency for the eyes to roll back when the eyelids are closed to protect the cornea, which is present in over 50% of patients (Francis & Loughhead, 1984). Figure 5 shows Bell’s reflex in a healthy subject. A large degree of lagophthalmos and a poor Bell’s reflex are indications of high risk to the cornea, this should necessitate discussion with ophthalmology. Conversely, a white, non-painful eye with a small degree of lagophthalmos and good Bell’s reflex, thus removing the cornea from exposure, is common and can be safely managed in the community using intensive ocular lubrication.
Positive Bell’s reflex. Note there is no cornea or iris visible: only the white of the eye is seen.
All cases of Bell’s palsy should be prescribed ocular lubrication: this should consist of a viscous e.g. paraffin-based ointment before bed (such as Lacrilube® or VitAPos®) with a regular drop such as hypromellose 0.3% or similar by day, up to hourly in frequency. The taping of an eye suffering from lagophthalmos is also essential at night; show the patient how to close the lid with their finger and secure it in place with a small horizontal strip of 2-cm-wide micropore tape after instillation of lubricating ointment.
Advice for patients
You can reassure patients that most people with Bell’s palsy recover normal facial nerve function within a year, even without steroid treatment. An observational study that followed 1011 untreated patients with Bell’s palsy over the year following their diagnosis found that: 71% recovered normal facial function; 13% had minor sequelae; and 16% had permanently reduced facial nerve function. Most patients showed signs of spontaneous recovery within 3 weeks (Pietersen, 1982). A RCT of 551 patients compared facial nerve recovery (grade 1 on the House–Brackmann scale) in patients who received prednisolone and those who received placebo. At 3 months, 83% of the patients who received prednisolone had recovered completely, compared with 64.7% of patients receiving placebo. By 9 months, 94.4% of patients receiving prednisolone, and 85.2% of patients receiving placebo, had recovered (Sullivan et al., 2007). Poor prognostic factors include delayed administration of prednisolone (beyond 72 hours), complete facial nerve paralysis, associated hearing loss or taste impairment, recurrent Bell’s palsy, increasing age and hypertension.
Resources for patients.
Patients might find it difficult to remove food debris from the weaker side of their mouth, so regular thorough tooth-brushing is recommended. Artificial saliva may be needed. Patients may wish to massage the facial muscles.
Complications
Complications of Bell’s palsy include incomplete resolution of facial nerve weakness, exposure of the cornea leading to dry eyes and corneal ulceration, synkinesis (involuntary muscle twitching), gustatory hyperlacrimation or ‘crocodile tears’ (caused by misdirection of regenerating nerve fibres to the lacrimal glands, rather than the salivary glands), and muscle contractures (Eviston et al., 2015).
Patients who develop complications or who have residual weakness after 6 months should be referred to secondary care. Treatment options at this point include: botulinum toxin injections for contractures or excessive lacrimation; surgery to lift the eyelid and improve facial symmetry; and specialist facial physiotherapy (Eviston et al., 2015).
Follow-up and prognosis
Patients should be followed up within a month of diagnosis to assess for some recovery of nerve function. If there is no improvement after a month, NICE (2012) recommends urgent referral to ENT. This is a useful opportunity to reiterate the importance of eye protection and good dental hygiene. Discuss the natural history of Bell’s palsy with patients and advise them to return for assessment if they have not recovered normal nerve function after 6 months.
Key points
Bell’s palsy is a diagnosis of exclusion: a careful neurological and ENT exam is required to rule out other causes of facial nerve palsy Starting oral prednisolone within 72 hours significantly improves the chance of full neurological recovery For patients with corneal exposure, eye protection with ocular lubricants and lid taping is essential Bell’s palsy that is recurrent, bilateral, or does not improve after 1month requires urgent referral to ENT
Footnotes
Acknowledgement
We would like to thank Dr Helen Carslaw for her help with the writing of this article under the InnovAiT ‘buddy’ scheme.