eMedicine Specialties > Ophthalmology > Neurologic Disorders

Bell Palsy

Author: Thomas R Hedges III, MD, Director of Neuro-Ophthalmology, New England Eye Center; Professor, Departments of Neurology and Ophthalmology, Tufts University School of Medicine
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Updated: Oct 30, 2009

Introduction

Background

Bell palsy is an acute, idiopathic, unilateral, peripheral, lower-motor-neuron facial-nerve paralysis that gradually resolves over time in 80-90% of cases. Its cause is unknown, though it appears to be a polyneuritis with possible viral, inflammatory, autoimmune, and ischemic etiologies. Increasing evidence implicates herpes simplex type I and herpes zoster virus reactivation from cranial-nerve ganglia.¹

Determining whether facial-nerve paralysis is peripheral or central is a key step in the diagnosis. A lesion involving the central motor neurons above the level of the facial nucleus in the pons causes weakness of the lower face alone. Thorough history taking and examination, including the ears, nose, throat, and cranial nerves, must be performed. If the clinical findings are doubtful or if paralysis lasts longer than 6-8 weeks, further investigations, including gadolinium-enhanced MRI of the temporal bones and pons, should be considered.²

Bell palsy is more common in adults, in people with diabetes, and in pregnant women than in others. Bell palsy recurs in 3-10% of patients, either on the same side or on the opposite side of the face. Recurrent or bilateral disease should suggest myasthenia gravis.³

Treatment overview

Treatment of Bell palsy should be conservative and guided by the severity and probable prognosis in each particular case. Studies have shown the benefit of high-dose corticosteroids for acute Bell palsy.^4,5 Although antiviral treatment has been used in recent years, evidence is now available indicating that it may not be useful.⁴ Electrodiagnostic tests (eg, stapedius reflex test, evoked facial-nerve electromyography [EMG], audiography) may help improve the accuracy of prognosis in difficult cases.

Topical ocular therapy is useful in all cases, except for those in which the condition is severe or prolonged. In these cases, surgical management is best. Several procedures are aimed at protecting the cornea from exposure and achieving facial symmetry. These procedures help eliminate the need for constant use of lubrication drops or ointments, they may improve cosmesis, and they may be needed to preserve vision on the affected side.

Anatomy

The facial nerve travels a 30-mm interosseous course through the internal auditory canal (with the eighth cranial nerve) and through the internal fallopian canal in the petrous temporal bone. This bony confinement limits the amount that the nerve can swell and thereby cause acute paralysis.

The facial nerve arises from its nucleus in the pons and exits at the cerebellopontine angle, where the nervus intermedius (which is responsible for lacrimation, salivation, and taste) and the nerve to the stapedius muscle joint are. The facial nerve travels with the vestibulocochlear nerve through the internal auditory canal and the facial (fallopian) canal in the temporal bone. The parasympathetic fibers directed toward the pterygopalatine ganglion and lacrimal gland exit at the geniculate ganglion as the greater petrosal nerve.

While coursing through the temporal bone, a branch leaves to the stapedius and proceeds distally as the chorda tympani to supply the salivary glands.

The facial nerve exits the stylomastoid foramen and divides into 5 branches in the parotid gland to innervate the facial muscles.

Pathophysiology

By definition, Bell palsy is idiopathic. Possible etiologies include infections, particularly herpes simplex (but also herpes zoster, Lyme disease, syphilis, Epstein-Barr viral infection, cytomegalovirus, HIV, and mycoplasma); inflammation alone; and microvascular disease (diabetes mellitus and hypertension).^6,7,8,9

Frequency

United States

The rate is 20-30 cases per 100,000 population.¹

International

The rate worldwide is approximately 10-30 cases per 100,000 population.

Mortality/Morbidity

• This condition is 4.5 times more common in people with diabetes, 3.3 times more common in pregnant women, and more common in people with immunocompromise or preeclampsia than in others.³
• Indicators of a poor prognosis are age older than 60 years, no recovery by 3 weeks, complete facial palsy, severe pain, and severe degeneration of the facial nerve (as assessed by means of evoked EMG testing).

Sex

The incidences are roughly equal in men and women.

Age

Bell palsy is rare in children. Peak ages are 20-40 years. The disease also occurs in elderly persons aged 70-80 years.¹⁰

Clinical

History

See Physical.

Physical

• Early symptoms
• Weakness of the facial muscles
• Poor eyelid closure
• Aching of the ear or mastoid (60%)
• Alteration of taste (57%)
• Hyperacusis (30%)
• Tingling or numbness of the cheek/mouth
• Epiphora
• Ocular pain
• Blurred vision
• Early ocular complications
• Lagophthalmos
• Paralytic ectropion of the lower lid
• Corneal exposure
• Brow droop
• Upper eyelid retraction
• Decreased tear output/poor tear distribution
• Loss of nasolabial fold
• Corneal erosion, infection, and ulceration (rare but may occur)
• Late ocular manifestations
• Mild, generalized mass contracture of the facial muscles, rendering the affected palpebral fissure narrower than the opposite one (after several months)
• Aberrant regeneration of the facial nerve with motor synkinesis
• Reversed jaw winking (ie, contracture of the facial muscles with twitching of the corner of the mouth or dimpling of the chin occurring simultaneously with each blink)
• Autonomic synkinesis (ie, crocodile tears-tearing with chewing)
• Rare, permanent, disfiguring facial paralysis
• Classification for facial nerve deficits¹¹

1. Normal 
2. Mild dysfunction (normal symmetry at rest, ability to close lids with minimal effort and slight asymmetry, ability to move mouth with maximal effort)
3. Moderate dysfunction (mild asymmetry, no functional impairment, ability to close lids and move mouth with maximal effort) 
4. Moderately severe dysfunction (obvious asymmetry, no movement of brows, unable to close lids completely, inability to move corner of mouth) 
5. Severe dysfunction (only barely perceptible motion, obvious asymmetry with droop of mouth and absent nasolabial fold, slight movement of eyelids)
6. Total paralysis

Causes

By definition, Bell palsy is idiopathic. Possible etiologies include infections (herpetic, Lyme disease, Epstein-Barr viral infection, cytomegalovirus, HIV, and mycoplasma), inflammation, and microvascular disease (diabetes mellitus and hypertension).^6,7

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