|
Overview
Bell’s palsy is a neurological
disorder caused by damage to the seventh cranial
nerve, also known as the facial nerve, which
results in weakness or paralysis on one side of
the face. The paralysis causes distortion of
facial features and interferes with normal
functions, such as closing the eye and eating.
Patients often fear that they have suffered a
stroke, with permanent damage to their health and
appearance, but Bell’s palsy is not related to
that condition.
The onset of Bell’s palsy is
usually sudden. Many people wake up in the morning
and find that one side of their face is paralyzed.
Milder symptoms include tingling around the lips
or a dry eye and usually progress quickly,
reaching maximum severity in 48 hours or less.
Anatomy
The facial nerve controls the muscles that move
the eyebrows, close the eyes, and move the mouth
and lips. It also controls the tear glands, one of
the salivary glands, and the taste buds in the
front of the tongue.
Electrochemical signals are relayed
between the brain and many facial muscles by 7000
nerve fibers that comprise the facial nerve. When
the facial nerve is damaged, as in Bell’s palsy,
the action of each nerve fiber is disrupted.
Because the facial nerve controls several
functions, several symptoms occur.
Incidence and Prevalence
Bell’s palsy affects about 40,000 people in the
United States every year. It affects approximately
1 person in 65 during a lifetime. It is more
commonly seen in young adults and persons of
Japanese descent have a slightly higher incidence
of the condition. Bell’s palsy is the most common
cause of facial paralysis worldwide and one of the
most common neurological disorders involving a
cranial nerve.
Causes
Viral infections such as herpes,
mumps, or HIV, and bacterial infections such as
Lyme disease or tuberculosis can cause
inflammation and swelling of the facial nerve that
causes Bell’s palsy. A tumor, skull facture, or
neurological condition caused by chronic disease
(e.g., diabetes, Guillain-Barre syndrome) can also
lead to Bell’s palsy.
Risk Factors
Conditions that compromise the
immune system, such as HIV, increase the risk for
Bell’s palsy. Stress, pregnancy, and diabetes are
also risk factors. Diabetics are more than 4 times
as likely to develop the disorder compared to the
general population.
Other risk factors include the
following:
-
Bacterial infections such as Lyme
disease or typhoid fever
-
Neurological disorders such as
Guillain-Barre syndrome,
multiple sclerosis, and myasthenia gravis
-
Traumatic injury to the head or
face
-
Tumor causing nerve compression
-
Viruses such as influenza, the
common cold, or infectious mononucleosis
Signs and Symptoms
The most common symptoms are facial
weakness or paralysis, a dry eye or mouth, and
problems tasting. The severity of symptoms depends
on the extent of facial nerve damage and varies
from mild weakness to complete paralysis. Bell’s
palsy usually affects both the upper and lower
parts on one side of the face. Both sides of the
face are affected in less than 1% of cases.
Symptoms usually come on suddenly,
often following recovery from a recent upper
respiratory infection or other virus. Several
hours before the onset of facial weakness, many
people experience pain behind the ear or in the
back of the head. In addition to paralysis, other
symptoms include:
-
Dizziness
-
Drooling
-
Dry mouth
-
Facial twitching
-
Hypersensitivity to sound
-
Inability to blink or close the
eye, tearing, and dry eyes
-
Impaired sense of taste
-
Impaired speaking
Bell’s palsy is self-limiting.
Symptoms do not spread beyond the face and do not
worsen once they "peak." Between 60% and 80% of
patients experience complete recovery within a
short time, whether or not they receive treatment.
Others are left with varying degrees of facial
disfigurement, paralysis, or muscle spasms.
Recovery varies from a few days to
a few months, depending on the amount of the
damage to the facial nerve. Approximately 7% of
patients experience a recurrence.
Diagnosis
A diagnosis of Bell’s palsy is
often based on symptoms and by ruling out other
disorders. Other conditions that may cause facial
paralysis include facial tumors, certain cancers,
and autoimmune diseases. The physician can usually
exclude other disorders by taking the patient’s
history of symptoms, and by examining the head,
neck, ears, and eyes.
During the physical examination,
the doctor observes the patient’s range of
movement in different parts of the face (e.g.,
raising and lowering the eyebrows, closing both
eyes). If one eyebrow cannot be raised or can only
be lifted slightly, it suggests that one side of
the face is weaker. Similarly, if one eye cannot
be closed tightly, it indicates a problem with the
controlling muscles. If paralysis or muscle
weakness is noted in another part of the body,
Bell’s palsy may be ruled out, through diagnostic
testing.
Imaging scans
such as computerized tomography (CT) scan or
magnetic resonance imaging (MRI) are used to
detect infection, tumor, bone fracture, or other
abnormality in and around the facial nerve.
Hearing and balance
tests are used to determine if the nerve
responsible for hearing is also damaged and assess
injury to the inner ear. Tests can be performed to
evaluate the eye’s ability to produce tears.
The sense of taste also can be evaluated to
determine the location and severity of a facial
nerve lesion.
Electromyograph
(EMG) assesses injury by electrically stimulating
the facial nerve. Electrical current is applied to
the skin over the nerve and nerve function is
determined by the amount of current needed to
cause contraction of the facial muscles. The test
is often repeated to assess disease progression
and the extent of injury.
Laboratory tests
can help the physician determine the underlying
cause. For example, a blood test for Lyme disease
may be ordered if there is a chance that the
patient was bitten by a deer tick.
Treatment
There is no curative treatment for
Bell’s palsy. Symptoms, especially in the eyes,
are treated to prevent permanent damage. Treatment
also attempts to reduce inflammation of the facial
nerve.
Eye Care
Bell’s palsy usually affects the eye on the
affected side of the face. Continuous eye care is
required until the condition resolves. Patients
are often unable to blink or close their eyelid
completely, which can lead to eye problems and
permanent damage, if the eye is not cared for
properly.
Blinking and closing the eyelid
helps move tears across the eye and into its
drainage channels. Tears are continuously produced
to maintain moisture in the eye, remove metabolic
waste products and environmental debris (e.g.,
dust, ash), keep the eye's outer surface smooth,
and deliver nutrients to underlying tissues.
When the eyelid is unable to blink
or close, tears are not moved across the eye
surface and the eye dries out. The closed eyelid
holds moisture in and on the surface of the eye
during sleep. If the lid does not close during
sleep, the uncovered cornea is exposed to the
environment. This causes dryness and possibly
injury because of exposure to foreign bodies.
Patients experience a gritty feeling in their eye,
dryness, and burning.
Daytime treatment of the eye is
relatively simple. Artificial tears are
instilled about every 2 hours to keep the eye
moist and patients can manually close the affected
eye to keep moisture in and debris out. Sunglasses
can help protect the eye from injury and reduce
dryness by decreasing exposure to wind.
At night or during sleeping, a
heavy lubricant is usually placed in the eye and
the eyelid is taped shut to reduce dryness and the
risk for injury.
Medication
Corticosteroids, such as prednisone, are
used to reduce swelling and inflammation of the
facial nerve. Whether or not this treatment speeds
up healing and improves the chances for complete
recovery has not been determined. Once the
decision has been made to utilize corticosteroids,
they should be started within 2 days after
symptoms develop. Treatment is continued for 1 to
2 weeks.
Treatment with antiviral agents
such as acyclovir may be beneficial. Acyclovir and
prednisone used together are more effective than
prednisone alone. The acyclovir-prednisone
combination is most effective when begun as soon
as possible after the onset of symptoms. One
recent study found that patients had a 100%
recovery rate when treated within 3 days of
symptom onset, compared to an 84% recovery rate
when treatment was delayed 4 days or longer.
Surgery
If patients do not completely recover, surgical
treatment may be indicated. These complex
procedures are performed on the facial nerves and
muscles in order to reduce distortion of facial
features and help restore function (e.g., eye
closure). The three main procedures are facial
nerve repair and nerve graph, nerve substitution,
and muscle transposition. These procedures are not
able to completely restore normal function, but
they can significantly improve facial function and
appearance.
Facial nerve repair
is the most effective procedure to restore facial
function in patients who have suffered nerve
damage from an accident or during surgery. It
involves microscopic repair of a nerve that has
been cut. A nerve graph replaces one that
has been removed.
Nerve substitution
is indicated when the nerve cannot be repaired in
the conventional manner. In this procedure,
another cranial nerve involved in facial movement
is connected to the damaged nerve and takes over
its function.
Muscle transposition
is used in patients who have had facial paralysis
for at least 2 years and are unlikely candidates
for nerve repair or substitution. This procedure
involves the transfer of a neuromuscular unit (a
muscle with its original nerve supply) to the
affected area. The temporalis muscle or masseter
muscle (two muscles in the face that are not
controlled by the facial nerve) are moved and
connected to the corner of the mouth to provide
movement in the lower part of the face. In free
muscle transfer, muscles from the leg are
moved to the face to provide bulk and function.
In addition to these procedures, a
brow or facelift may be necessary to reduce facial
drooping. The lower eyelid, which may begin to
droop and turn outward (called ectropion) because
of the lack of muscle tone, can be tightened with
corrective surgery. Weights can be
implanted into the eyelid to help the eye blink
and close.
Surgical removal of the bone near
the nerve, known as decompression surgery,
is performed in severe cases when the facial nerve
is seriously deteriorating. These patients are at
risk for permanent paralysis and have a poor
prognosis without aggressive intervention.
Research has shown that this procedure is
effective in improving outcomes in a select group
of patients. To be effective, the surgery must be
performed within 2 weeks of the onset of symptoms.
Physical Therapy
A special form of physical therapy called
facial retraining can help minimize the
asymmetrical appearance of the face that occurs
when one side is weakened. It improves muscle
mobility, even when therapy is initiated years
after the onset of Bell’s palsy. Hemifacial spasm
may be relieved with botulinum toxin injections.
Other Therapies
Many patients incorporate alternative health care
remedies such as acupuncture, Traditional Chinese
Medicine, and homeopathy regimens into their
treatment. Facial exercises may improve muscle
tone and help the facial nerve recover. Exercises
for Bell’s palsy patients have been developed by
physical therapists and other specialists.
Prevention
Currently, there is no way to
prevent Bell’s palsy. |
