Charlie had heard of Bell’s palsy before, even knew someone who had it once. So when the left side of his face started to droop he didn’t panic. Over the next two days he couldn’t close his eye or keep the left side of his mouth from drooling, but otherwise he felt pretty good. Still, he thought he should see the doctor.
The facial nerve is one of the twelve cranial nerves that arise directly from the brain. It runs in a long bony canal (Fallopian canal) through the bone surrounding the ear to innervate the muscles of the face. Disorders of the ear or the facial nerve itself may result in facial weakness or paralysis.
Bell’s palsy takes its name from Sir Charles Bell, who described the symptoms in the eighteenth century. It is characterized by partial or total weakness of the facial muscles. The cause is unknown. The overall incidence of Bell’s palsy is estimated at twenty to forty people per hundred thousand and about sixty thousand people are affected each year in the United States. The rate increases significantly when pregnancy, diabetes, and family history of facial paralysis is a factor.
Most people recover completely from Bell’s palsy, especially if the weakness is partial. But over 15 percent end up with some degree of permanent paralysis. Usually only one side of the face is involved, but paralysis may affect both sides and may recur on either side.
In addition to facial weakness of unknown cause (Bell’s palsy), there are several known causes of facial weakness. These include stroke, penetrating trauma that may damage the nerve, and cancer. But the cause of facial paralysis is known in only about 5 percent of all cases and none of these is Bell’s palsy.
Figure 29.1
Bell’s palsy causes mild to severe disfigurement, but 85 percent of patients with Bell’s recover fully without treatment. The patient in this illustration is attempting to contract the muscles on the left side of his face.
What Causes Bell’s Palsy?
The facial nerve has the longest course in a bony canal of all the nerves in the body. At one particular place near the inner ear, the facial canal is very narrow and constricting. It is thought that when a virus infects the facial nerve, as it can with any nerve, swelling in this narrow part of the canal causes enough pressure to cut off circulation and result in paralysis. Some people with Bell’s palsy have simultaneous infection of other cranial nerves, but those nerves do not stop working because they have room to swell. The viruses associated with Bell’s palsy include Epstein-Barr and Varicella-Zoster, both members of the herpes family. Bell’s palsy is not related to stroke.
Symptoms
The symptoms of Bell’s palsy peak within seventy-two hours of onset. Because the facial nerve has many branches, the symptoms vary widely. For example, besides innervating the muscles of the face, the facial nerve is a pathway for tearing, saliva, taste, and for contracting a small muscle in the middle ear. Symptoms of dysfunction may be seen in any of these areas.
Table 29.1
Symptoms of Bell’s Palsy
• Facial weakness or paralysis
• Twitching of facial muscles
• Drooping eyelid and corner of the mouth
• Dryness of eye or mouth
• Drooling
• Tearing from the eye
• Metallic taste from the front and side of the tongue
• Pain near the ear
• Tinnitus
• Dizziness
Diagnosis
Since Bell’s palsy is a diagnosis of exclusion, possible known causes must be ruled out before determining that the paralysis has no known cause. Unfortunately, because 85 percent of patients with Bell’s recover fully without treatment, investigation into treatable causes is frequently put off, resulting in a delay of treatment in those cases where it is needed. Other conditions that cause facial paralysis include Lyme disease, sarcoidosis, shingles, acoustic neuroma, facial nerve or brain tumors, ear infections, mastoiditis, cholesteatoma (a growth of the middle ear), and skull fracture.
The history and examination will focus on the onset of symptoms and signs of underlying causes. Special attention should be paid to eye closure and the cornea. When indicated, a CT scan, an MRI, and blood tests can be performed to rule out most underlying causes. Nerve conduction testing can provide information about the likelihood of not recovering from paralysis.
Treatment
The most important immediate need is to protect the cornea. When the eyelids do not close due to paralysis of the face, foreign material may have easy access to the cornea and lead to trauma or infection. Even a pillowcase can pose a danger during sleep with the eyelids open. The cornea quickly dries out when we cannot blink to lubricate it, causing itching, pain, or blurred vision. This may lead to permanent damage.
Moisture chambers and taping or patching the eye are necessary in advanced cases, along with ointments at night and frequent use of artificial tears during the day. The eyelids may need to be taped shut with special tape at night. An ophthalmologist can be very helpful in protecting the cornea and may need to sew the eyelids partially or totally shut if the cornea has been damaged.
With no treatment, 85 percent of people with Bell’s palsy begin to have some improvement within three weeks, but only 71 percent eventually regain normal facial movement. This is not deemed a good outcome, considering the nature of the deformity.
Steroids are effective in treating Bell’s palsy. Prednisone is commonly prescribed to be taken orally in tapering dosages over ten days. The initial adult dose is usually 40 to 60 mg per day; for children, 0.5 to 1.0 mg per kilogram per day. For maximum effect, treatment should begin within seventy-two hours of the onset of symptoms.
Antiviral medications, although effective in treating herpes-family viruses, have led to only small improvements in patients with Bell’s palsy. This may be due to delay in beginning treatment.
Surgical treatment of Bell’s palsy is only considered for people who experience complete paralysis and when nerve conduction tests indicate a poor prognosis. Early surgery is aimed at removing the bone from around the nerve to allow it room to swell. The conundrum is that this surgery, to be most effective, should be performed within two weeks of onset of symptoms. But it is not possible to be certain that surgery is necessary during that time, since this is the period when spontaneous recovery also occurs. The most effective decompression surgery is performed through the middle cranial fossa and usually requires a stay in the neurosurgical ICU as well as several days in the hospital.
If the paralysis becomes permanent, two surgical options may be possible. These include substituting another nerve for the facial nerve or performing cosmetic procedures that are similar to a face lift but with movement added. Gold weights may also be placed in the upper eyelid so gravity can close the eye at rest.
Synkinesis is a complication in which separate branches of the facial nerve fire simultaneously. For example, the eye may blink when you try to smile, giving the appearance of a grimace. The facial muscles are prone to spasm, and crocodile tear syndrome may occur in which tears form when you are eating. The latter symptoms are caused by regenerating nerve fibers following the wrong pathway.
Facial exercises are not effective when the face is completely paralyzed. However in partial weakness or when the muscles first begin to recover, facial exercises can strengthen the muscles and may help separate the function of the eye from the rest of the face.