ACUTE FACIAL PARALYSIS
• Typical cases of acute facial paralysis are diagnosed based on examination and do not require additional evaluation.
• All patients with acute facial paralysis should have a complete neurologic and head and neck examinations.
• The presence of atypical features such as a slowly progressive course, failure to improve, recurrent attacks, or other neurologic findings should prompt additional evaluation with computed tomography (CT) or magnetic resonance imaging (MRI) of the head and a specialist consultation.
• Steroid therapy, such as prednisone1 60–80 mg daily for 7 days,
initiated within 3 days of onset of the facial paralysis, increases the chances of recovery
• The use of antiviral therapy remains controversial without strong evidence of benefit, but valacyclovir (Valtrex)1 1000 mg three times daily for 7 days may be beneficial in patients with severe paralysis.
• Eye care with artificial tears, ophthalmic ointments at night, and eye protection should be used in patients with severe facial paralysis.
1 Not FDA approved for this indication.
Acute facial nerve paralysis, or Bell’s palsy, is a common disorder manifesting with the acute to subacute onset of unilateral paralysis of the muscles of facial expression. The Scottish physician Sir Charles Bell described cases of facial paralysis due to trauma in the 1800s, and the idiopathic condition carries his name today. However, there are many possible causes of facial paralysis, and each patient requires a careful history and complete neurologic examination to exclude these possibilities.
Epidemiology and Risk Factors
The annual incidence rate is between 13 and 34 cases per 100,000 population. All age ranges can be affected, but persons between the ages of 15 and 40 years are most commonly affected. Diabetics, pregnant women in the third trimester, and women in the immediate postpartum period are at increased risk. There is no gender, race, or geographic predilection.
The seventh cranial, or facial, nerve arises from the pontomedullary junction and runs in close proximity to the eighth cranial nerve to the internal auditory meatus. The nerve then runs through the bony fallopian canal before exiting the skull at the stylomastoid foramen.
The labyrinthine portion of the fallopian canal is very narrow, and it is postulated that swelling of the nerve results in compression in this region.
Three branches arise from the facial nerve within the fallopian canal. The greater petrosal nerve arises from the geniculate ganglion, passes to the pterygopalatine ganglion, and eventually supplies innervation to the lacrimal and palatine glands. The second branch is the nerve to the stapedius muscle in the middle ear. The final branch is the chorda tympani, which supplies taste sensation from the anterior two thirds of the tongue.
The pathophysiology of Bell’s palsy is uncertain, but a viral cause is the most commonly accepted hypothesis. Many different viruses have been associated with facial paralysis, with herpes simplex virus (HSV) having the strongest evidence. HSV-1 DNA has been detected by polymerase chain reaction assay in endoneural fluid in patients with Bell’s palsy undergoing facial nerve decompression.
Herpes zoster is another virus associated with facial nerve paralysis.
Herpes zoster oticus (Ramsey Hunt syndrome) is diagnosed when vesicles are seen in the external auditory canal or on the auricle. Other viruses implicated include cytomegalovirus, Epstein–Barr virus, adenovirus, rubella, mumps, influenza B, and coxsackievirus.
The histopathology of the facial nerve supports an inflammatory etiology with findings similar to those seen in herpes zoster infection. The perineurium is edematous, with diffuse infiltration of inflammatory cells between nerve bundles and surrounding the intraneural vessels.
The clinical presentation of Bell’s palsy is typically dramatic and very stereotypical. Pain behind the ear in the region of the mastoid can precede the onset of weakness by hours to days. Weakness of the muscles of facial expression on one side progresses over a period up to 48 hours. Progression over more prolonged periods raises the possibility of a neoplasm affecting the nerve. The degree of weakness can range from quite subtle to complete paralysis of all muscles of facial expression. Typical features include inability to close the eye, sagging of the eyelid, loss of the nasolabial fold, and inability to wrinkle the forehead muscles. Sparing of the forehead muscles suggests a central or upper motor neuron lesion because these muscles receive bilateral innervation. Additional symptoms that may be reported include hyperacusis due to paralysis of the stapedius muscle, loss of taste in the anterior tongue due to involvement of the chorda tympani, and decreased tearing due to dysfunction of the parasympathetic innervation of the lacrimal gland. However, most patients actually report increased tearing from the affected eye owing to diminished blinking.
Diagnosis and Differential Diagnosis
There is no specific diagnostic test for Bell’s palsy. The diagnosis is based on a typical history and examination. Atypical features mandate a search for other causes. A slowly progressive course, parotid gland mass, or involvement in selected branches of the facial nerve can suggest neoplastic compression. Vesicles over the ear or internal auditory canal suggests herpes zoster infection. Patients should be asked about preceding fevers, rashes, and arthralgias, which can prompt evaluation for Lyme disease. However, in the absence of these features, routine serologic testing is not recommended. Sarcoid is a rare cause of usually bilateral facial paralysis. The onset of facial paralysis in the setting of head injury, particularly in the presence of ipsilateral hearing loss, should prompt imaging of the skull base to rule out a temporal bone fracture (Box 1).
|Differential Diagnosis of Acute Facial Nerve Paralysis|
Idiopathic cases account for 65%
• Herpes zoster
• Herpes simplex
• Lyme disease
• Epstein–Barr virus
• Human immunodeficiency virus
• Acute otitis media
• Chronic otitis media
Temporal bone fractures
Metabolic and Toxic
Carbon monoxide poisoning (rare)
Treatment of Bell’s palsy can be divided into three categories: general medical therapy, specific medical therapy, and surgical therapy.
General medical care includes proper eye care. Reduced blinking and inability to completely close the eye increases the risk of corneal abrasion and ulceration. Artificial tears and ophthalmic ointments can prevent these complications. Patients should be instructed to use proper eye protection to prevent injuries. Facial muscle massage and facial nerve stimulation have no evidence to support their use.
Specific medical therapy includes glucocorticoid and antiviral medications. Glucocorticoid therapy has been demonstrated to be effective in both meta-analyses and randomized trials. The two largest trials of glucocorticoid and antiviral therapy demonstrated benefit for steroids but no benefit for antiviral therapy when used either alone or in combination with steroids. Treatment in these trials was begun within 72 hours of onset of paralysis and consisted of relatively high dose prednisolone (Millipred)1 50 to 60 mg daily for 10 days. Antiviral therapy evaluated included acyclovir (Zovirax)1 400 mg five times daily for 10 days and valacyclovir (Valtrex)1 1000 mg three times daily for 7 days, neither of which showed benefit.
Smaller, lower-quality studies have suggested a benefit of combining antiviral therapy with glucocorticoids, particularly in patients with more severe baseline dysfunction.
Surgical decompression of the facial nerve is not recommended. A 2011 Cochrane review and a 2001 review by the American Academy of Neurology both found no good evidence supporting this treatment modality. Only two small randomized studies showed no differences in outcome between surgical and medical therapy.
Monitoring and Complications
The overall prognosis of Bell’s palsy is favorable. In one study of untreated patients, 85% showed signs of recovery within 3 weeks. Ultimately, 71% experienced complete recovery and an additional 13% were felt to have only slight residual weakness. The degree of weakness at onset is an important prognostic indicator: 94% of patients with incomplete paralysis experienced complete recovery. The absence of any improvement, no matter how small, at 3 to 4 months should raise concern regarding the diagnosis and lead to a search for alternative etiologies.
Motor nerve conduction studies, or electroneurography, can be used to help predict prognosis in selected patients. Patients with incomplete lesions that have an excellent prognosis do not require further evaluation. Motor nerve conduction studies involve stimulating the facial nerve electrically and recording muscle responses with surface electrodes over appropriate muscles. The amplitude of the evoked muscle response on the affected side at 10 days can be compared to the unaffected side, giving an estimate of the degree of axonal loss. A 90% drop in amplitude predicts less than complete recovery, and loss greater than 98% predicts significant residual weakness and synkinesis.
In severe cases of facial paralysis, attention to good eye care as previously discussed is important to prevent eye damage and vision loss.
During recovery from severe nerve injury, axonal regrowth may be misdirected, resulting in synkinesis. Voluntary activation of one muscle group can cause activation of other muscles. Attempts at blinking can result in twitching of the mouth, or smiling can cause involuntary blinking. Misdirection of autonomic fibers can result in the syndrome of “crocodile tears,” involuntary lacrimation while eating.
Recurrent attacks of facial paralysis on the ipsilateral or contralateral side occur in up to 15% of patients even after many years. Additional recurrences are quite rare, being reported at a rate between 1% and 3%.
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