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There are currently three main treatments for facial nerve disorders:
Medical treatment for Bell's palsy can include the use of steroids, antiviral medications and/or botulinum therapy. Steroids, such as prednisone, prednisolone, and methylprednisolone, work by reducing the inflammatory reaction of the body. This is important since the inflammatory reaction can be more harmful than the disease process itself.
Antiviral medications, such as acyclovir, have been shown to help in Bell's palsy. They work by inhibiting viral replication, and the fact that they show a small improvement in recovery from Bell's palsy gives strength to the argument that viral infection plays a role in the disease.
When selected muscles of the face are overactive, clenched, or "hypertonic," one way to achieve more facial balance is to intentionally weaken selected muscles. Botulinum is often used for this purpose. It is a substance produced by the bacterium Clostridium Botulinum, and has the ability to temporarily paralyze muscle into which it is injected by blocking the release of neurotransmitters from the nerve fibers to the muscle cells, which are responsible for triggering muscle action. Botulinum is selectively injected into the areas that are overactive, and works within several days. It is an effective therapy for facial synkinesis, spasm, and contracture. It is also used to weaken the normal side of the face in facial paralysis, providing more symmetry to the two sides.
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The effects of botulinum administration last for three to six months. This can be advantageous because if the effect achieved is undesirable, its effect is not permanent. The drawback is that if the achieved effect is desirable, therapy needs to be repeated semi-annually. The development of antibodies to botulinum toxin can occur, though it is rare. This results in a loss of effectiveness of this treatment for certain patients. Sometimes, botulinum therapy is utilized to see what the effect of selective myectomy would be. If the effect is acceptable, myectomy may be performed to achieve a more permanent result.
Surgery for treating facial nerve problems can include facial nerve decompression, nerve repair and grafting, reinnervation techniques, regional muscle transfers, free muscle transfers, and static techniques.
Facial nerve decompression refers to the procedure whereby the facial nerve is exposed along the length of its bony canal in the temporal bone. It is indicated when the nerve dysfunction is related to compression of an inflamed nerve within the bony canal, causing a "choking" of the nerve in the confined space. There is evidence to suggest that in cases of Bell's palsy, when recovery is not seen after a certain time, this procedure can lead to overall better recovery than if it is not performed. The benefit, however, may be quite small, and the risks of surgery need to be weighed against this benefit.
During the procedure the facial nerve is
usually approached through a middle fossa craniotomy, and through
the mastoid bone directly behind the ear. Segments of the bony
canal are then unroofed, and the nerve carefully protected from
surgical trauma as the overlying bone is removed. By removing the
overlying bone, the nerve is free to expand, thus relieving the
compression that results in ischemia* and neurapraxia.
*ischemia: local lack of blood supply, due
to mechanical obstruction.
When the facial nerve is transected, and
there is no significant gap between the two ends of the nerve, the
first choice for repair of the nerve is to approximate the two
edges of the nerve and join them. Controversy surrounds the best
way to perform this connection, for example, whether microsutures
or glue-like substances provide a better connection. It is
generally agreed, however, that if the two ends come together in a
tension-free manner, it is better to repair the injury than to use
interposition grafting material.
When the facial nerve is injured or parts of
it lost, and there is a significant gap between the two nerve ends,
it is not feasible to perform a direct coaptation*. In these
situations, a nerve graft from another part of the body is used as
a cable to connect the two ends. Fibers from the proximal stump
then grow into and traverse the graft, and enter the distal stump.
From there, they are directed toward their targets. Regeneration
through these grafts can be quite variable, and often prove to be
unsatisfactory.
*coaptation: the joining together or fitting of two surfaces.
Significant research has gone into the development of substitutes for nerve autografts, including vein grafts, muscle cables, synthetic tubes, and biodegradable materials. There are some theoretical advantages to using some of these bio-artificial nerve regeneration conduits.
In the entubulation model, both the
properties of the walls of the chamber and the contents of the
chamber can be manipulated to promote regeneration. However, to
date, regeneration success rates through these graft materials have
not exceeded that through autografts, which remain the clinical
gold standard choice for this treatment.
Regardless which graft is used, the graft serves simply as a conduit for the extension of neural fibers from the proximal stump to the distal musculature.The fibers must extend from the injury site to the muscles of facial expression. Accomplishing this is a lengthy process.
It is not merely a question of bridging the gap between the two stumps. The entire distal stump serves only as a regeneration guide, the nerve fibers from the proximal stump cannot re-establish continuity with their distal attachments since these degenerate immediately following injury.
Sometimes the distal facial nerve and facial musculature are healthy, but the nerve is permanently and irreparably damaged near, or at the brainstem. In these cases, one approach to restoring facial movement is to bring neurons into the distal facial nerve from another nerve located in the vicinity of the distal facial nerve. Cutting all, or part of, a different motor nerve, such as that to the tongue or to the shoulder, involves creating a new motor deficit in order to give some neuronal "power" to the facial musculature.
Over time, the nerve which has become most popular for this purpose is the hypoglossal nerve, which controls tongue movement. The motor deficit that results from cutting the nerve to reroute it is usually well tolerated, and compensated for by the hypoglossal nerve on the other side of the tongue. In addition, it has become popular not to cut the entire hypoglossal nerve, but to transect it only partially, so that some fibers go to the tongue, while some are rerouted to the facial musculature.
The major advantage of using reinnervation techniques is that native delicate facial muscles remain intact. Because of that, facial movement that is achieved through nervous system input to these muscles is much more delicate than movement that would be achieved by bringing non-native musculature into the face. Natural resting tone is maintained, and at rest the two sides of the face can balance quite nicely.
The disadvantages are that new motor deficits are created, and that to achieve facial movement, the patient has to make a voluntary tongue movement, thus driving facial movement via the hypoglossal nerve. With training, this voluntary movement can look and feel very natural, but it requires patience and practice to learn the skill. The final disadvantage is a phenomenon called, mass movement. Because the hypoglossal nerve is hooked to the main trunk of the facial nerve, eliciting movement in this manner,causes all regions of the face to move at once,. This means that when a person tries to voluntarily smile, there is some simultaneous eye closure. Also, initiating a subtle facial movement can lead to a full strength contraction of the entire hemiface.
Modifications to the hypoglossal facial
transfer to decrease the severity of these problems have been
described, including limiting the nerve hookup to the lower
division of the facial nerve only, and addressing the upper face
with other techniques, such as temporalis transfer and gold weight
lid implantation.
Many surgeons have
attempted to utilize one branch of the healthy, contralateral
facial nerve for reinnervation purposes, by bridging the branch to
the main trunk of the facial nerve on the diseased side via a sural
nerve autograft. The obvious beauty of this technique is that it
will result in both sides of the face contracting simultaneously,
and naturally. Involuntary emotional smiling would then occur. The
drawback of the technique is that there are many fewer axons in an
isolated branch of the donor facial nerve, so often the graft is
too weak to restore meaningful motion to the diseased side. Despite
this, some surgeons obtain excellent results using it.
Like any muscle, if the muscles of facial expression are not used for many months, they undergo atrophy and scarring. Even if neural input is restored, muscles lose their ability to contract properly. In cases of prolonged denervation (more than 1-2 years), reinnervation techniques like the hypoglossal facial transfer described above, are not good options. When reinnervation surgery is not an option, another strategy is used. Muscle tissue is transferred into the face, and placed into some of the same vectors as the native musculature. Using this technique, contraction of the newly transferred muscle "imitates" the native facial muscles, and permits smiling, eye closure, and eversion of the lower lip.
Regional muscle transfer is a technique in which a muscle found in the head and neck area is loosened from its normal bed and rotated into the face along a smiling vector. The native blood supply to the muscle is maintained, so there is no need for microsurgical vessel hookup. The native neural supply to the transferred muscle is also maintained, so that to create the smile effect, the patient must voluntarily initiate a contraction of the transferred muscle. In the past, the masseter muscle was described as a potential muscle for transfer, but it was not able to be placed into quite the right vector to achieve a natural appearing smile, and has fallen somewhat out of favor. Currently, two most popular muscles for regional transfer for facial reanimation are the temporalis muscle transfer and the anterior belly of the digastric muscle.
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Occasionally regional muscle transfer is not possible. Examples of this are a patient who has had previous ear surgery, the status of whose temporalis muscle is in question, a patient in whom a temporalis transfer has failed, and a patient whose disease required resection of a large amount of soft tissue in the face, who requires more bulk than the temporalis can offer for the restoration of facial contour.
Over the past 30 years, reconstructive surgeons have developed the ability to transfer segments of skin, muscle, and bone from one part of the body to another by harvesting the tissue on a vascular pedicle, and then hooking the artery and vein back up to donor vessels in the area where the reconstruction is required. This new surgical technology has been useful in facial reanimation because it has allowed surgeons to bring new muscle into the face for reanimation purposes. The first muscle used for this purpose was the gracilis, a thin muscle located in the thigh. It was transferred into the face, secured to the cheek bone and the corner of the mouth, and hooked up to the local vascular supply. Since then, many other muscles have been utilized for free tissue transfer for facial paralysis, though the gracilis continues to be the most popular. Among other muscles, the latissimus dorsi, the pectoralis minor, the serratus anterior, and the rectus abdominis muscles have been utilized.
The gracilis free muscle transfer can involve either a one stage operation or a two stage operation, depending on where the nerve input will come to cause muscle contraction. If the goal is to restore a spontaneous smile and the opposite facial nerve is intact, then a cross facial nerve graft can be placed nine to twelve months earlier, and when growing axons reach through the graft, the muscle can be brought up to the paralyzed side, and its nerve can be attached to the previously placed cross face nerve graft.
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If, however, the opposite facial nerve is also affected (for example, Mobiius syndrome), then the gracilis can be brought into the face and its nerve attached immediately to the nerve that drives the masseter muscle.To elicit facial movement using this technique, the patient needs to make a conscious effort to bite down. This triggers the nerve which has been transferred to the gracilis muscle, causing the muscle to contract and lift the corner of the mouth.
While excellent results can be obtained using free muscle transfer, the surgical procedure is delicate, time consuming, and not guaranteed to yield an improved aesthetic result. There can be problems with excess bulk of the muscle in the face, poor excursion of the transferred muscle, and free flap failure. These factors need to be carefully considered before such an operative plan is undertaken.
While many people focus upon the lack of movement of the affected side in facial paralysis, another critical issue is the position and function of structures in the resting state. Facial paralysis causes a drooping of the corner of the mouth that leads to drooling, collapse of the side of the nose (resulting in nasal blockage), and a widening of the space between the upper and lower eyelids, exposing the eye more than is ordinary. The affected eyebrow is usually lower than the other side, and the blink reflex is lost.
A number of procedures have been designed to correct these malpositionings, to improve cosmetic appearance and to restore function. The decision about which option to pursue lies with each patient, and his/her specific areas of concern.p
Rehabilitation of the paralyzed eye is accomplished by one of several techniques. The eyebrow can be repositioned by performing a unilateral brow lift, and matching the brow height with the other side. This can be done with very small incisions, using endoscopes to guide the surgery.
The eyelids can be addressed using implantable eyelid springs so that gravity assists with eye closure. There are also implantable eyelid springs which offer mechanical assistance with eye closure. Another technique to decrease eye exposure is to place several stitches from the upper lid to the lower lid where the two lids meet at the corner of the eye. This technique, called a canthoplasty, is excellent for eye protection, but does produces an asymmetry between the two eyes which is often noticeable.
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The collapse of the nasal sidewall, often seen in facial paralysis, is called nasal valve collapse, and can be remedied either from the outside or the inside of the nose.
Outside techniques involve placing strips of suspension material from the cheekbone, under the skin, to the nasal sidewall, and suspending the nasal sidewall in its anatomic position. This can be done in conjunction with static sling procedures for the corner of the mouth.
To widen the nasal cavity from the inside, small cartilage grafts can be inserted into the framework of the nose, to widen the cavity slightly, or to stiffen the lowest part of the nose so that it does not get pulled in and block the passage when the patient breathes in through the nose.
Static sling techniques are used to reposition the corner of the mouth without
requiring a muscle transfer surgical procedure. These are useful
for patients who are either not candidates for lengthy surgery, or
in whom muscle transfers have healed poorly or failed. The
technique is simple, and involves securing a rigid piece of
material from the cheekbone, under the skin, down to the corner of
the mouth at the junction of the upper and lower lip. There is
debate over which material is best suited for this purpose. Fascia
lata, a tough sheath like material from the thigh, as been widely
used and is favored because it is an autologous* material. There
are commercially available synthetic and allogenic materials
(materials from organ banks) that are now achieving popularity for
these static slings. All types of materials have distinct
advantages and disadvantages, and these need to be well understood
when choosing which is right for an individual patient.
*autologous material: something from the
patient's own body.
In older patients with aging skin, there is often a looseness, or laxity, to the soft tissue of entire face. This has led to the implementation of facelift type techniques to improve facial symmetry. It differs from a standard facelift in that the paralyzed side of the face is pulled significantly more than the normal side, and the sides are made to "match" as closely as possible. This technique has found a substantial place in the management of partial paralysis or poor recovery from Bell's palsy and Ramsey-Hunt Syndrome.
After damage or injury to the facial nerve, including after any type of tissue manipulation for facial paralysis, it is critical to optimize the cosmetic and functional outcome by learning to control facial movement. Physical therapy uses facial neuromuscular retraining to optimize the motor control of the facial muscles. A comprehensive review of the literature supports the use of neuromuscular retraining, in both the acute stage (less than one year since injury or surgery) and in the post acute stages of recovery. The use of electrical stimulation to improve the motor control in the face is not recommended, and it is a treatment technique that is not supported in the literature.
Neuromuscular retraining uses selective motor training techniques to facilitate symmetrical movement and to control undesired gross motor activity (synkinesis). Tools such as surface electromyography (EMG) and specific mirror exercises provide augmented sensory information to enhance neural adaptation and learning. Motivation through individualized instruction, and active patient participation are crucial to success. Because each patient presents differently, there are no generic lists of exercises. Although each patient's program differs, some general principles apply. For example, it is imperative the movement of the face be initiated slowly, not rapidly. Small movements, rather than large motions of the facial muscles are taught to improve coordination and accuracy.
The length of treatment time and number of physical therapy session varies from patient to patient, and typically depends on patient's motivation, compliance, need for EMG, third party payers, and geographic location affecting scheduling. Patients are typically seen for an hour initial evaluation. Follow-up appointments are usually 30 minutes and can be as frequent as once per week or as infrequent as once every 4-6 weeks over the course of 4-6 months. Some patients are followed for up to one year.
Although neuromuscular retraining cannot restore perfect function, it can make a difference in facial muscle control with the ultimate goal of improved physical function, enhanced cosmesis, and increased self confidence.
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