Introduction
Background
Bell's palsy is a unilateral, peripheral facial paresis or paralysis that has an abrupt onset and no detectable cause. Bell palsy is one of the most common neurologic disorders affecting the cranial nerves, and it is certainly the most common cause of facial paralysis worldwide. Although this syndrome was first described in 1821, by the Scottish anatomist and surgeon Sir Charles Bell, much controversy still surrounds its etiology and management.
Left-sided Bell's palsy.
The onset of Bell's palsy can be frightening for patients, who often fear they have had a stroke or have a tumor and that the distortion of their facial appearance will be permanent. Consequently, patients with Bell's palsy frequently present to the ED before seeing any other health care professional.
It is imperative to keep in mind that Bell's palsy is a diagnosis of exclusion. Other disease states or conditions that present as facial palsies are often misdiagnosed as idiopathic. In addition to excluding other causes of facial paralysis, the role of the ED clinician consists of the following:
- Initiate appropriate treatment.
- Protect the eye.
- Arrange appropriate medical follow-up care.
Under Investigation
Variety nonpharmacologic measures have been used to treat Bell's palsy, including physical therapy (eg, facial exercises,1 neuromuscular retraining2 ) and acupuncture.3 No adverse effects of these treatments have been reported. Reviews suggest that physical therapy may result in faster recovery and reduced sequelae, but further randomized controlled trials are needed to confirm any benefit.
Pathophysiology
The precise pathophysiology of Bell's palsy remains an area of continuing debate. A popular theory proposes that inflammation and swelling of the facial nerve results in compression of the nerve within the temporal bone. This has been seen in MRI scans with facial nerve enhancement.4
The facial nerve courses through a portion of the temporal bone commonly referred to as the facial canal. The first portion of the facial canal, the labyrinthine segment, is narrowest; the meatal foramen in this segment has a diameter of only about 0.66 mm. Given the tight confines of the facial canal, it seems logical that inflammatory, demyelinating, ischemic, or compressive processes may impair neural conduction at this site.
Anatomy
The facial nerve (seventh cranial nerve) has 2 components. The larger portion comprises efferent fibers that stimulate the muscles of facial expression. The smaller afferent portion contains taste fibers to the anterior two thirds of the tongue, secretomotor fibers to the lacrimal and salivary glands, and some pain fibers.
The facial nerve.
Pathway
The path of the facial nerve is complex; this may be the reason the nerve is vulnerable to injury. Two portions of the facial nerve leave the brain at the cerebellopontine angle, traverse the posterior cranial fossa, dive into the internal acoustic meatus, pass through the facial canal in the temporal bone, then angle sharply backwards, where they pass behind the middle ear and exit the cranium at the stylomastoid foramen. From here, the facial nerve bisects the parotid gland, and then terminal branches extend from the parotid plexus to innervate the muscles of facial expression.
Frequency
United States
The incidence of Bell's palsy in the United States is approximately 25 cases per 100,000 persons.5 The condition affects approximately 1 person in 65 in a lifetime. However, the incidence is significantly higher in persons with diabetes mellitus than in those without diabetes.6
Bell's palsy can also be recurrent, occurring about 7% of the time.7 Rarely, bilateral simultaneous Bell's palsy can occur at a rate of less than 1% of unilateral facial nerve palsy.8,9
International
The incidence is similar to that in the United States,7,10 with the highest incidence reported in Japan.11
Mortality/Morbidity
Bell's palsy can cause aesthetic, functional, and psychological disturbances in patients who have residual nerve dysfunction during their recovery phase or in patients with incomplete healing.
- Partial paralysis
- Motor synkinesis (involuntary movement accompanying a voluntary movement)
- Autonomic synkinesis (involuntary lacrimation after a voluntary muscle movement)
Race
Incidence of Bell palsy appears to be slightly higher in persons of Japanese descent.
Sex
No difference exists in sex distribution in patients with Bell's palsy.7,10 In women, the overall incidence of Bell's palsy during pregnancy is comparable to that of all women of childbearing age; however, the incidence is high in the third trimester and correspondingly low during early pregnancy.12
Age
The incidence of Bell's palsy increases between the ages of 10 and 30 years. Bell's palsy is least common in persons younger than 10 years and most common in those older than 70 years.10
Clinical
History
Most patients presenting to the ED suspect they have suffered a stroke or have an intracranial tumor. The most common complaint is of weakness on one side of the face.
- Postauricular pain: Approximately 50% of patients experience pain in the mastoid region.7 The pain frequently occurs simultaneously with the paresis, but precedes the paresis by 2-3 days in about 25% of patients.
- Tear flow: Two thirds of patients complain about tear flow.7 This is due to the reduced function of the orbicularis oculi in transporting the tears. Fewer tears arrive at the lacrimal sac and overflow occurs. The production of tears is not accelerated.
- Altered taste: While only one third of patients complain about taste disorders,7 four fifths of patients show a reduced sense of taste. Patients may fail to note reduced taste because of normal sensation in the uninvolved side of the tongue.
- Dry eyes
- Hyperacusis: Impaired tolerance to typical levels of noise as a result of paralysis of the stapedius muscle.7
Physical
Findings of facial paralysis are easily recognizable on physical examination. A careful, complete examination excludes other possible causes of facial paralysis. Strongly consider other etiologies if all branches of the facial nerve are not affected.
- Weakness and/or paralysis from involvement of the facial nerve affects the entire face (upper and lower) on the affected side. Focus attention on the voluntary movement of the upper part of the face on the affected side: in supranuclear lesions such as a cortical stroke (upper motor neuron; above the facial nucleus in the pons), the upper third of the face is spared while the lower two thirds are paralyzed. The orbicularis, frontalis, and corrugator muscles are innervated bilaterally, which explains the pattern of facial paralysis in these cases.10
- Eye closure on the affected side may be partially or completely impaired. On attempting to close the eye, the patient may demonstrate the Bell phenomenon: the eye on the affected side rolls upward and inward.
- All the other cranial nerves should be tested; results should be normal.
- Tympanic membranes should be normal; the presence of inflammation, vesicles, or other signs of infection raises the possibility of complicated otitis media.
- Concurrent rash or vesicles along the ear canal, pinna, mouth should raise the suspicion for Ramsey-Hunt syndrome (Zoster sine herpete).
- Bilateral facial palsies should prompt a workup for other causes besides Bell's palsy, although Bell's palsy is the most common etiology.9
Causes
The etiology of Bell's palsy remains unclear, although vascular, infectious, genetic, and immunologic causes have all been proposed. Patients with other diseases or conditions (eg, Lyme disease)13 sometimes develop a peripheral facial nerve palsy, but these are not classified as Bell's palsy (see Differentials).
- Viral infections: Clinical and epidemiologic data lend credence to an infectious origin, with inflammation and/or a related autoimmune response resulting in local demyelination of the facial nerve. Pathogens leading the list include herpes simplex virus type 1 (HSV-1); herpes simplex virus type 2 (HSV-2); human herpesvirus (HHV); varicella-zoster virus (VZV); influenza B; adenovirus; coxsackievirus; Ebstein-Barr virus; hepatitis A, B, and C viruses; cytomegalovirus (CMV); and rubella virus.14,15,16
- Mycoplasma infection: Bell's palsy may be a complication of M pneumoniae infection, sometimes in the absence of respiratory symptoms.17
- Genetics: A family history of Bell's palsy has been reported in approximately 4% of cases. Inheritance in such cases may be autosomal dominant with low penetration. Which predisposing factors are inherited is unclear.18
More on Bell Palsy |
 Overview: Bell Palsy |
| Differential Diagnoses & Workup: Bell Palsy |
| Treatment & Medication: Bell Palsy |
| Follow-up: Bell Palsy |
| Multimedia: Bell Palsy |
| References |
| Next Page » |
References
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Further Reading
Keywords
Bell's palsy, Bell palsy, facial nerve paralysis, facial paralysis, idiopathic facial paralysis, unilateral facial paralysis, cranial nerve VII paralysis, seventh cranial nerve paralysis, neurologic disorder, paralysis on one side of face, weakness on one side of face, drooling, tearing from eyes, upper respiratory infection, URI, viral infection, herpes simplex virus, HSV
