Recent developments in Bell's palsy

Introduction

General practitioners in the United Kingdom will see about one patient with Bell's palsy every two years. Increasing evidence shows that the way the patient is managed has an important effect on outcome. Untreated Bell's palsy leaves some patients with major facial dysfunction and a reduced quality of life. Of patients with Bell's palsy registered by general practitioners between 1992 and 1996 a fifth were referred for specialist opinion, just over a third received oral steroids, and 0.6% received aciclovir.1 Improving outcomes requires coordination between specialists and general practitioners so that patients are treated during the critical first 72 hours. We outline recent developments in Bell's palsy and current best evidence in its management.

Sources and selection criteria

We canvassed specialists with an interest in acute facial palsy and incorporated the latest consensus from key publications and systematic reviews. We performed a hierarchical literature search through Medline, CINAHL, SUMSearch, bmj.com, Lancet Neurology Network, Bandolier, Health Technology Assessment, Clinical Evidence, and the Cochrane Library. Both authors are otolaryngologists with an interest in neurotology and facial palsy.

Incidence and pathophysiology

Bell's palsy accounts for almost three quarters of all acute facial palsies, with the highest incidence in the 15 to 45 year old age group (table 1).2 The annual incidence in the UK population is around 20 per 100 000, with one in 60 people being affected during their lifetime. Men and women are equally affected, although the incidence is higher in pregnant women (45 cases per 100 000).

Increasing evidence implies that the main cause of Bell's palsy is latent herpes viruses (herpes simplex virus type 1 and herpes zoster virus), which are reactivated from cranial nerve ganglia. Sensitive polymerase chain reaction techniques have isolated herpes virus DNA from the facial nerve during acute palsy.3 Inflammation of the nerve initially results in a reversible neurapraxia, but ultimately Wallerian degeneration ensues. Herpes zoster virus shows more aggressive biological behaviour than herpes simplex virus type 1 because it spreads transversely through the nerve by way of satellite cells.

Symptoms

The most alarming symptom of Bell's palsy is paresis; up to three quarters of affected patients think they have had a stroke or have an intracranial tumour. The palsy is often sudden in onset and evolves rapidly, with maximal facial weakness developing within two days. Associated symptoms may be hyperacusis, decreased production of tears, and altered taste (table 2).

Patients may also mention otalgia or aural fullness and facial or retroauricular pain, which is typically mild and may precede the palsy. Severe pain suggests herpes zoster virus and may precede a vesicular eruption and progression to Ramsay Hunt syndrome. Features may be consistent with a mild polyneuropathy. A slow onset progressive palsy with other cranial nerve deficits or headache raises the possibility of a neoplasm.

Examination

Bell's palsy causes a peripheral lower motor neurone palsy, which manifests as the unilateral impairment of movement in the facial and platysma muscles, drooping of the brow and corner of the mouth, and impaired closure of the eye and mouth. Bell's phenomenon—upward diversion of the eye on attempted closure of the lid—is seen when eye closure is incomplete.

A central upper motor neurone deficit causes weakness of the lower face only (fig 1). More complex segmental deficits may be caused by peripheral facial nerve lesions. Patients with facial palsy require careful examination of the other cranial nerve and cerebellar function. The modified House-Brackmann facial grading scale allows consistent documentation of facial palsy (see table on bmj.com).5

Fig 1

Lesion of right upper motor neurone causes central pattern of facial weakness on left. Lesion of right lower motor neurone causes facial palsy on right. Adapted from Dresner6

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Assessment of the ear should include pneumatic otoscopy and tuning fork tests. Polyposis or granulations in the ear canal may suggest cholesteatoma or malignant otitis externa. Vesicles in the conchal bowl, soft palate, or tongue suggest Ramsay Hunt syndrome (see fig A on bmj.com).

The examination should exclude masses in the head and neck. A deep lobe parotid tumour may only be identified clinically by careful examination of the oropharynx and ipsilateral tonsil to rule out asymmetry (fig 2). Erythema migrans on the limbs or trunk with a history of tick bite implies Lyme disease, which may cause facial palsy.7

Fig 2

Woman with segmental facial palsy showing reduced elevation of right eyebrow and closure of right eye. A malignant mass was found in the right parotid gland. Reproduced with patient's permission

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Investigations

Serum testing for rising antibody titres to herpes virus is not a reliable diagnostic tool for Bell's palsy. Salivary polymerase chain reaction for herpes simplex virus type 1 or herpes zoster virus is more likely to confirm virus during the replicating phase, but these tests remain research tools. Serological tests for Lyme disease (IgM, IgG) are essential to exclude this disease in endemic areas, and magnetic resonance imaging has revolutionised the detection of tumours. Typically, the hearing threshold is not affected in Bell's palsy, but stapedius reflexes may be reduced or absent. Topognostic tests and electroneurography may give useful prognostic information but remain research tools.8

Zoster sine herpete

Herpes zoster virus has traditionally been associated with Ramsay Hunt syndrome, with typical cutaneous vesicles and cochleovestibular dysfunction. Vesiculation may not necessarily appear (zoster sine herpete) or may be delayed in up to half of patients. Dermatomal pain and dysaesthesia before vesiculation is termed preherpetic neuralgia and may be the only clinical indicator that herpes zoster virus is involved. Zoster sine herpete is thought to be the cause of almost a third of facial palsies previously diagnosed as idiopathic.9

Bell's palsy in children

Bell's palsy is a much less common cause of facial palsy in children under 10 years of age. These children therefore merit careful review to identify an alternative cause, including acute suppurative ear disease. Lyme disease may be responsible for as many as half the cases in endemic areas.

Outcomes

Overall, Bell's palsy has a fair prognosis without treatment, with almost three quarters of patients recovering normal mimetical function and just over a tenth having minor sequelae. A sixth of patients are left with either moderate to severe weakness, contracture, hemifacial spasm, or synkinesis. Patients with a partial palsy fair better, with 94% making a full recovery. The outcome is worse when herpes zoster virus infection is involved in partial palsy. In patients who recover without treatment, major improvement occurs within three weeks in most. If recovery does not occur within this time, then it is unlikely to be seen until four to six months, when nerve regrowth and reinnervation have occurred. By six months it is clear who will have moderate to severe sequelae. Box 1 lists the poor prognostic indicators of Bell's palsy.

In facial palsies caused by herpes simplex virus or herpes zoster virus there remains a strong correlation between the peak severity of the palsy and the outcome. As yet there is no reliable investigation or test at presentation that can indicate who will make a full recovery.

Treatment

The main aims of treatment in the acute phase of Bell's palsy are to speed recovery and to prevent corneal complications. Treatment should begin immediately to inhibit viral replication and the effect on subsequent pathophysiological processes that affect the facial nerve. Psychological support is also essential, and for this reason patients may require regular follow up.

Follow up

Patients with Bell's palsy should start treatment immediately and be referred to a specialist as soon as possible. In a few cases the diagnosis may be subsequently reassigned.2 Patients should receive psychological support and eye care during follow up. Long term sequelae may be missed if patients are not monitored for a full year.

A multidisciplinary team approach (general practitioners, otolaryngologists, ophthalmologists, plastic surgeons, physiotherapists, and psychologists) is essential when there is no prospect of further recovery of facial nerve function. Synkinesis and facial spasm, common features of partially recovered deficits, can be effectively managed with subcutaneous or intramuscular injections of botulinum toxin. Facial reanimation may be possible by a combination of static and dynamic surgical techniques and may result in functional as well as cosmetic improvements. Weighting of the upper lid improves eye closure.