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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. [_2XU1D6YED]
View Image
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 retraining[2] ) 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.
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.
View Image
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.
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]
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]
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]
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]
No specific laboratory tests exist to confirm the diagnosis of Bell's palsy. Clinical setting determines tests that may be of value. Results of the following laboratory tests may confirm or suggest other potential causes in the differential diagnosis:
Complete blood count
Erythrocyte sedimentation rate
Thyroid function studies
Lyme titer
Serum glucose level
Rapid plasma reagin (RPR) or Venereal Disease Research Laboratory (VDRL) test
Human immunodeficiency virus (HIV) antibodies
Cerebral spinal fluid analysis
Immunoglobulin M (IgM), immunoglobulin G (IgG), and immunoglobulin A (IgA) titers for CMV; rubella; HSV; hepatitis A virus; hepatitis B virus; hepatitis C virus; VZV; M pneumoniae; and Borrelia burgdorferi
Bell's palsy remains a clinical diagnosis. Imaging studies are not indicated in the ED. Excluding other causes of facial palsy may require one of the following imaging studies, depending on clinical setting.
Facial CT scan or plain radiographs: Perform to rule out fractures or bony metastasis.
CT scan: Perform when the differential diagnosis includes stroke or CNS involvement from acquired immunodeficiency syndrome (AIDS).
MRI: Perform in patients with a suspected neoplasm of the temporal bone, brain, parotid gland, or other structure, or to evaluate for multiple sclerosis. MRI can visualize the course of the facial nerve through the intratemporal and extratemporal regions from the brain to the facial muscles and glands. MRI also may be considered in lieu of CT scan.
Electrodiagnosis of the facial nerve: These studies assess the function of the facial nerve. These tests are rarely performed on an emergent basis.[10]
Electromyography (EMG) and nerve conduction velocities produce a graphic readout of the electrical currents displayed by stimulating the facial nerve and recording the excitability of the facial muscles it supplies. Comparison to the contralateral side helps determine the extent of nerve injury and has prognostic implications. This is not part of the acute workup.
The nerve excitability test determines the threshold of the electrical stimulus needed to produce visible muscle twitching.
Electroneurography (ENoG) compares evoked potentials on the paretic side versus the healthy side.
The primary treatment of patients with Bell's palsy in the ED is pharmacological management. The remainder of care focuses on reassurance, eye care instructions, and appropriate follow-up care. [_2XU1D6YED]
Steroids: Inflammation and edema of the facial nerve is thought to cause the pathogenesis of Bell's palsy.[10] Anti-inflammatory medications such as corticosteroids are thoughts to counter these effects.
Older studies have shown conflicting results using steroids in treating Bell's palsy.[19] These studies have been limited in their size. However, 3 recent randomized controlled trials showed significant improvement in outcomes when prednisolone was started within 72 hours of symptom onset.[20, 21, 22]
Based on these 3 studies, steroids should be strongly considered to optimize outcomes. Once the decision to use steroids is made, the consensus is to start immediately.
Antiviral agents
Evidence evaluating the efficacy of antiviral medicines in Bell's palsy has shown limited benefit,[16, 23] with 3 recent randomized controlled trials showing no benefit.[20, 21, 22] However, there is evidence to suggest a large percentage of Bell's palsy cases may result from a viral infection.[16, 24] Therefore, antiviral agents may be reasonable in certain situations.
A 2009 Cochrane review analyzed 7 studies (1987 patients) from 1966 to 2008 looking at the efficacy of antivirals in the complete recovery from Bell's palsy. In their review, antivirals showed no significant benefit from placebo in the rate of incomplete recovery (relative risk [RR], 0.88; 95% confidence interval [CI], 0.65-1.18).[25]
Quant et al conducted a meta-analysis of published studies from 1984 to January 2009 to compare use of corticosteroids plus antiviral agents with corticosteroids alone on degree of facial muscle recovery in patients with Bell's palsy.[26] Six trials (representing pooled data of 1145 patients) were examined and included 574 patients who received corticosteroids alone and 571 patients who received corticosteroids and antiviral agents. The analysis showed no improved benefit for Bell's palsy with use of corticosteroids plus antivirals compared with corticosteroids alone (odds ratio, 1.50; 95% confidence interval [CI], 0.83-2.69; P=0.18).
Contrary to the Quant et al and the Cochrane meta-analysis, de Almeida et al found that, when combined with corticosteroids, antiviral agents were associated with greater risk reduction of borderline significance compared with corticosteroids alone (relative risk [RR], 0.75; 95% CI, 0.56-1.00; P =.05).[27] Their meta-analysis included 18 trials including 2786 patients. If antivirals are to be initiated, they should be done so in conjunction with corticosteroids. Future studies will be needed to determine which population will most benefit from antiviral therapy.
Eye care: Impaired eye closure and abnormal tear flow are common with Bell's palsy. These leave the eyes at risk for corneal drying and foreign body exposure. Manage with tear substitutes, lubricants, and eye protection.
Artificial tears: Use these during waking hours to replace diminished or absent lacrimation.
Lubricants are used during sleep. They may be used during waking hours if artificial tears cannot provide adequate protection. One disadvantage is blurred vision during waking hours.
Eyeglasses or shields protect the eye from injury and reduce drying by decreasing direct contact of air currents with the exposed cornea. Eye patches, however, are ineffective because unopposed third nerve function will result in corneal exposure despite best efforts to approximate eyelid margins.
The patient's primary care provider or consultant should provide close follow-up care. Documentation should chart the progress of the patient's recovery.
Opinions widely vary on referral to a specialist. Some specific referral indications are listed below:
Neurologist: Consult a neurologist when other neurologic signs are identified on physical examination and for an atypical presentation of Bell's palsy.
Ophthalmologist: Consult an ophthalmologist for any unexplained ocular pain or abnormal findings on physical examination of the eyes.
Otolaryngologist: Consult an otolaryngologist for patients with persistent paralysis, prolonged weakness of the facial muscles, or recurrent weakness.
Surgeon: Surgery to decompress the facial nerve is occasionally recommended for patients with Bell's palsy. Patients with a poor prognosis, identified by facial nerve testing or persistent paralysis, appear to benefit the most from surgical intervention. However, studies have been mixed as far as benefit from surgery.[28] It is recommended that if surgery is decided, it should be within 14 days from onset of symptoms.[10]
Watchful waiting is an option for management of Bell's palsy, because most cases resolve without medication. However, some individuals with Bell's palsy never fully recover. For both classes of medications listed below, there are clinical trials that support their efficacy and trials that dispute it.
These agents have anti-inflammatory properties and cause profound and varied metabolic effects. They modify the body's immune response to diverse stimuli.
Clinical Context:
Therapeutic success may be the result of anti-inflammatory effect, which presumably decreases compression of the facial nerve in the facial canal.
Prednisone at an initial dose of 1 mg/kg/d up to 60 mg should be strongly considered within 72 hours of onset of symptoms if no contraindications exist.
Prednisone is a potent drug with a potential for side effects. While older studies are mixed in showing efficacy,[19] 3 recent, double-blinded, randomized controlled trials showed benefit if treatment was started within 72 hours.[20, 21, 22]
The best prednisone regimen for Bell's palsy is a short burst (up to 10 d), but steroid taper may also be used.
Caution should be given to patients who are immunocompromised, pregnant, or have poorly controlled diabetes, severe peptic ulcer disease, an active infection, sarcoidosis, or sepsis.
High-dose steroids (>120 mg/d of prednisone) have been safely used to treat Bell's palsy in patients with diabetes;[29, 30] however, optimal dosing has not been established. Caution should be given in these cases due to the risk of hyperglycemia.
Consider using antivirals within 72 hours if there is a high suspicion for HSV or VZV as a cause.
Administer acyclovir (Zovirax) 400 mg PO 5 times/d for 10 d. Evidence supports HSV as a major cause of Bell's palsy. If VZV is suspected, higher doses may be needed (800 mg PO 5 times/d). However, evidence of efficacy with acyclovir has been mixed.[23] Two recent trials showed no additional benefit with the addition of acyclovir to prednisolone.[20, 22]
Valacyclovir (Valtrex), 500 mg PO twice a day for 5 days, may be used instead of acyclovir. Although more expensive, this may lead to better compliance. If VZV is the cause, higher doses may be needed (1000 mg PO tid). However, evidence of efficacy with valacyclovir has been mixed.[16, 23, 24] A recent trial showed no additional benefit with the addition of high-dose valacyclovir to prednisolone.[21] Because of increased cost and increased risk of side effects with higher doses, valacyclovir cannot be routinely recommended at this time.
Two recent reviews showed no benefit of antivirals,[26, 25] while 1 recent review showed some benefit with the use of antivirals plus steroids.[27]
Most patients with Bell's palsy recover without any cosmetically obvious deformities; however, approximately 5% are left with an unacceptably high degree of sequelae.
Incomplete motor regeneration
The largest portion of the facial nerve comprises efferent fibers that stimulate muscles of facial expression. Suboptimal regeneration of this portion results in paresis of all or some of these facial muscles.
This manifests as (1) oral incompetence, (2) epiphora (excessive tearing), and (3) nasal obstruction.
Incomplete sensory regeneration
Dysgeusia (impairment of taste) may result.
Ageusia (loss of taste) may result.
Dysesthesia (impairment of sensation or disagreeable sensation to normal stimuli) may result.
Aberrant reinnervation of the facial nerve
During regeneration and repair of the facial nerve, some neural fibers may take an unusual course and connect to neighboring fibers. This aberrant reconnection produces unusual neurologic pathways.
When voluntary movements are initiated, they are accompanied by involuntary movements (eg, the movement of a closed eye following that of the uncovered one). These involuntary movements accompanying voluntary movement are termed synkinesis.
The natural course of Bell's palsy varies from early complete recovery to substantial nerve injury with permanent sequelae. Prognostically, patients fall into 3 groups:
Group 1 - Complete recovery of facial motor function without sequelae
Group 2 - Incomplete recovery of facial motor function, but no cosmetic defects are apparent to the untrained eye
Group 3 - Permanent neurologic sequelae that are cosmetically and clinically apparent
Patients who experience incomplete facial paralysis during the acute phase have an excellent prognosis for full recovery. Patients demonstrating complete paralysis are at higher risk for severe sequelae.[7]
Other factors that determine worsening prognosis are history of recurrence,[31] diabetes,[29] increased age, longer onset of time to recovery, presence of postauricular pain, abnormal taste, stapedius reflex, and tearing.[7]
Of patients with Bell's palsy, 85% achieve complete recovery, 10% have some persistent asymmetry of facial muscles, and 5% experience severe sequelae.
The prognosis in pregnant women with Bell's palsy may be slightly worse than it is in nonpregnant women with Bell's palsy.[12]
Bilateral Bell's palsy is thought to share the same prognosis as unilateral Bell's palsy.[8]
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