Synkinesis is the result from miswiring of nerves of nerves after trauma after trauma.. This result is manifested through involuntary muscular movementsaccompanying movementsaccompanying voluntary movements. For example, voluntary smiling will induce an involuntary contraction of the eye muscles causing the eye to squint when the subject smiles.
Causes Almost all cases of synkinesis develop as a sequel to nerve trauma (the exception is when it is congenitally acquired as in Duane-Retraction Syndrome and Marcus Gunn phenomenon). phenomenon). Trauma to the nerve can be induced in cases such as surgical [1] [2] procedures, nerve inflammation, neuroma , and physical injury . [edit edit]Variations ]Variations Since synkinesis is ultimately an interaction of nerves with muscles (although glands can also be involved), almost all studied cases are relevant to the cranial nerves where they interact with many small cranial muscles, most of which are responsible for separate and unique functions. This is in contrast to areas of our body where miswiring of the larger muscles is clinically less evident due the size of the muscles. The two cases of synkinesis most commonly studied involve the facial muscles and the extraocular muscles. muscles. [edit edit]]Facial synkinesis Facial Synkinesis is a common sequelae to Idiopathic Facial Nerve Paralysis, Paralysis, also [3] called Bells Palsy or Facial Palsy . Bells Palsy, which occurs due to the compression of the seventh cranial nerve, results in a hemifacial paralysis due to non-functionality of the nerve. As the nerve attempts to recover, nerve miswiring results (see Mechanism of Action below). In patients with severe facial nerve [4] paralysis, facial synkinesis will inevitably develop . Additionally, a common treatment option for facial palsy is to use electrical stimulation. Unfortunately, this has been shown to be disruptive to normal re-innervation and can promote [5] the development of synkinesis . The most common symptoms of facial synkinesis [6] include :
Eye
closure with volitional contraction of mouth muscles
Midfacial movements with volitional eye closure
Neck tightness (Platysmal contraction) with volitional smiling
Hyperlacrimation(also
called Crocodile Tears)
A case where eating provokes excessive lacrimation. This has been attributed to neural interaction between the salivary glands and [7] the lacrimal glands . [edit]Extra-ocular muscle synkinesis
The six muscles around the eye (extraocular muscles) are innervated by three different cranial nerves: Abducens (6th nerve), Trochlear (4th nerve), and Oculomotor (3rd nerve). After nerve trauma around the eye, a combination of any two of these three cranial nerves have been shown to be involved with extra-ocular synkinesis. More over, while the abducens and the trochlear nerve each innervate one specific muscle, the oculomotor nerve has many functions including eyelid retraction and pupil constriction. Thus, during synkinesis, a variable of these functions are involved. Examples include:
On attempted abduction of an affected eye, the eye adducts and the eyelid retracts.
On attempted abduction, the eyes unreactive pupil constricts
This is an interaction between the abducens nerve and a branch of the oculomotor nerve. Voluntary activation of the abducens nerve (eye abduction) causes involuntary activation of the oculomotor nerve (eye [2] adduction and eyelid elevation). Another interaction, yet different, between the abducens nerve (eye [8] abduction) and the oculomotor nerve (pupil constriction) .
On attempted adduction with eye depression, the eyelid retracts.
This is a case reported in which voluntary activation of the trochlear nerve (eye depression + eye abduction) is involuntarily activating a branch of the [9] oculomotor nerve responsible for eyelid retraction .
Other less common variations of synkinesis involving the cranial nerves include:
Trigeminal-Abducens Synkinesis
After physical trauma to the skull, the muscle involved in eye abduction can become reinnervated by the branch of the trigeminal nerve involved in innervating the muscles of mastication(chewing muscles). Thus, involuntary [10] abduction of an involved eye will occur upon eating or chewing .
Trigeminal-Facial Synkinesis
After surgical trauma, the muscles of mastication can become reinnervated by the facial nerve as opposed to the trigeminal nerve. This causes weakness in voluntary chewing; also, facial movements such as blinking [1] cause the muscles to contract .
[edit]Mechanism of action There are three proposed mechanisms for synkinesis: aberrant nerve regeneration, interneuronal ephaptic transmission, and nuclear hyperexcitability. [edit]Aberrant nerve regeneration The aberrant nerve regeneration hypothesis is the most widely accepted [11] mechanism for synkinesis . The hypothesis states that, after trauma, axons project from the facial nucleus to incorrect peripheral muscle groups. These aberrant branches can simultaneously innervate different subdivisions of the [4] facial nerve . For example: compression to the facial nerve causes a lesion and the set of axons that innervates the orbicularis oris (mouth muscle) degenerate. Once the compression has relieved, regeneration of axons from the lesion site begins. This time though, only 50% of the set of axons that innervate the orbicularis oris successfully reinnervate the original site. The other half aberrantly branched off and innervated the orbicularis oculi(eye muscle). Thus, when the patient purses their lips, the ipsilateral eye will squint. The hypothesis assumes that disorganized regeneration occurs at the site of the [12] lesion. On the contrary, recent research by Choi and Raisman has provided a more thorough understanding of synkinesis through aberrant axonal regeneration. Their study has shown that regenerating axons become disorganized throughout the length of the nerve and not only at the site of the lesion. Previously, many developed treatment strategies (that inevitably failed) were invented based on the original hypothesis by only focusing on the lesion site for improving the organization of regeneration. The new modification to the hypothesis could allow for better success in developing treatments. [edit]Ephaptic transmission Ephaptic
transmission is when two nerves communicate with each other via an artificial synapse between nerves. Healthy peripheral nerves are insulated with a
myelin sheath that helps to both enhance electric transmission and to prevent cross-talk between parallel nerves. After a lesion, it has been observed that regenerating nerves might not be myelinated effectively. Consequently, the two nerve fibers can come into contact and provide a means for an impulse to be directly conducted through the nerve membrane. An example to clarify this is having two uninsulated electrical wires placed adjacent to each other. Thus, the two nerves are able to cross-talk and send action potentials in both [13] directions . [edit]Nuclear hyperexcitability The basis of this hypothesis is as follows: after a lesion, axonal degeneration (via Wallerian degeneration) occurs. The post-synaptic cell consequently becomes deprived of input and becomes more sensitive to neurotransmitters (e.g. creating additional receptors). Subsequently, residual undamaged axons in the same premise of the lesion can provide a source of neurotransmitter to the deprived post-synaptic cell. Since the post-synaptic cell is hypersensitive, the neurotransmitters that reach it from an axon of another nerve will successfully provide stimulation. This consequently creates undesired peripheral movement [14] (i.e. synkinesis) .
Since synkinesis has been reported in patients within 12 months, the nuclear [11] hyper-excitability hypothesis is being supported by more researchers . Furthermore, axonal regeneration is a slow process (~1 mm/day growth) and regeneration at this rate of the facial nerve would roughly take 48 months. Since synkinesis is observed much earlier, aberrant regeneration and ephaptic communication fail to explain for this observation thus providing evidence that nuclear hyper-excitability is an important factor in the mechanism of [15] synkinesis development. .
Although these three mechanisms have been argued for and against in various ways, it has become more accepted that synkinesis develops through a combination of these mechanisms. [edit]Measuring synkinesis Until May 2007, there was no clinical scale to measure synkinesis. A study led by [6] Mehta et al. has validated the use of a newly designed instrument to evaluate facial synkinesis called the Synkinesis Assessment Questionnaire (SAQ). The
instrument, consisting of nine questions, was found to be both reliable and valid. In addition, it is simple, easy to administer, and inexpensive. Its analyses can allow for treatment options to be evaluated.
[edit]Treatment Experimental
research for treatment has been mostly focused on facial synkinesis due to its abundant prevalence compared to extra-ocular synkinesis. Additionally, since the extra-ocular muscles are hidden within the orbits, there is a limit on the
type of practical treatments that can be established (e.g. massage). Established treatments for synkinesis in general include surgery; furthermore, facial synkinesis has the benefit of less invasive treatments such as facial retraining, biofeedback, mime therapy, and Botox. Theory/evidence General : Based on limited research and anecdotal evidence, it appears that both therapists and their
patients have noted improvements in patients' facial symmetry following mime therapy. Some research suggests that mime therapy patients may improve by one grade on the House-Brackmann scale. This commonly-used scale assigns a grade of one to six based on how completely the patient is able to close his or her eyes and whether or not synkinesis is present. Synkinesis is defined as involuntary facial movements, such as grimacing, that accompany voluntary movements, such as closing of the eyes.
There have been few randomized controlled trials involving mime therapy. Researchers have noted that more (and stronger) evidence from well-designed trials is necessary before mime therapy is integrated into evidence-based clinical practice.
Researchers hope to learn more about the potential mechanisms of mime therapy. It has been suggested, but not proven, that mime therapy may cause changes in the nervous system. Some suspect that this success is due to the relearning of motor skills by patients, or it may be due to the fact that patients are working in cooperation with a therapist who gives them full attention.
R ecent
research : A recent review of clinical trial treatments for Bell's palsy looked at the use of
mime therapy and electromyogram (EMG) biofeedback, among other possible treatments. Researchers concluded that there were not enough randomized controlled trials to properly analyze whether the techniques under review were effective.
By 2003, reportedly more than 1,000 patients had been successfully treated with mime therapy in Nijmegen, the Netherlands. Treatment was initially monitored with the House-Brackmann scale and later with the Sunnybrook Facial Grading System (the Sunnybrook Facial Scale is an internationallyused grading system for judging facial paralysis; some research has shown the Sunnybrook scale to be more reliable than House-Brackmann.) Both reporting systems showed that patients who underwent mime therapy had improved facial symmetry at rest and in motion, and that synkinesis had decreased following treatment.
Additional research in the Netherlands showed that, compared to a control group, patients who underwent mime therapy improved by 20 points on a facial symmetry grading system; the patients also reduced the severity of paresis (paralysis) by 0.6 of a grade point. Results were measured in two ways: Symmetry was measured with the Sunnybrook Facial Grading System, and the degree of paralysis was measured with the House-Brackmann Facial Grading system.
[edit]Mime therapy [20]
Mime therapy was introduced in the Netherlands in 1980 . It was initially designed to treat facial palsy by improving symmetry of the face both at rest and during movement. It was then later observed that people who had post-facial palsy synkinesis also benefited from this therapy. It wasnt until 2003 that Beurskens and Heymans were able to experimentally conclude that mime therapy was indeed a good treatment choice for synkinesis. Furthermore, later studies by Beurskens et al. have shown that benefits obtained from mime therapy are stable [21] 1 year after therapy . Current mime therapy consists of a combination of procedures designed to promote symmetry of the face at rest and during movement and control synkinesis. The components include: massage, stretching [3] exercises, exercises to coordinate both halves of the face, etc. . The overall aim of mime therapy is to develop a conscious connection between the use of facial muscles and emotional expression. So while facial retraining therapy is much more focused on treating slight synkinetic movements, mime therapy aims to increase the overall vigor of the muscles through active exercises, while in the process of doing so, teaching the face to decrease unwanted synkinetic movements. Mime therapy typically begins as soon as a patient exhibits synkinesis, which studies indicate may occur three months after the development of facial paralysis. Mime therapy currently includes about 10, 45-minute sessions, held weekly. In the first session, the therapist typically explains the treatment plan, measures the current status of paresis through the use of a grading system, photos and video, and then offers a prognosis. Each session starts with an exchange of information. This is followed by massage of the face and neck, along with breathing and relaxation exercises. The patient then engages in exercises to coordinate movements of both sides of the face, in order to reduce synkinesis. This training is followed by speech exercises. The session ends with exercises that focus on facial expressions. While patients may mimic therapists at first to learn how to perform the exercises properly, the goal of mime therapy is for patients to learn how to communicate effectively by controlling their facial expressions and movements.
Patients
often use a mirror when performing facial exercises, which helps them to gauge their progress and to observe the severity of their synkinesis. Practicing
at home between therapy sessions is an essential part of mime therapy. Practice includes self-massage of the face and neck for 10-15 minutes daily, breathing and relaxation exercises, and other facial exercises that are to be done in a specific order. Follow-up typically extends for 3-6 months after a patient completes treatment. continue to do stretching exercises on their own after therapy ends.
Patients
usually
Goals of therapy: Mime therapy generally has two goals: 1) to improve symmetry of the face, whether it is in motion or at rest; and 2) to control the involuntary facial movements known as synkinesis. When these goals are met, a patient's face appears less affected; facial expressions are more easily read; and the patient may have fewer difficulties with eating, drinking, and speaking. As a result, the patient's self-esteem may improve. Patients typically begin to see benefits from mime therapy after about one month of treatment
House Brackman Facial Nerve Grading System Reference: House JW, Brackman DE. Facial nerve grading system. Otolaryngol Head Neck Surg. 1985:93,146-147.
Grade
Desc ription
Measurement*
Function %
Estimated Function %
I
Normal
8/8
100
100
II
Slight
7/8
76 - 99
80
III
Moderate
5/8 - 6/8
51 - 75
60
3/8 - 4/8
26 - 50
40
IV
Moderately
Severe
V
Severe
1/8 - 2/8
1 - 25
20
VI
Total
0/8
0
0
* "Measurement" is determined by measuring the superior movement of the mid-portion of the superior eye brow and the lateral movement of the oral commissure. A scale point of 1 is assigned for each 0.25 cm of motion up to 1 cm. for both eye brow and commissure movement. The points are then added together. Thus, a total of 8 points can be obtained, if each structure moves 1 cm.
** "Description" is defined as follows: Grade
Description
I
Normal
Characteristics
Normal facial function in all nerve branches
y
Gross:
Slight weakness o n clos e ins pectio n,
s light s ynkines is . y
At Res t:
Normal t one & Symmet ry. II
Slight
y
M ot i on:
Fo rehead: Goo d t o mo derat e mo vemen t . Eye: Co mplet e clo sure wit h mi ni mum eff o rt . t h: Sli ght asymme t ry. M ou
y
y
III
M o derat e
y
Obvio us but no t dis figur ing facial as ymmet ry . Synkineis i is no ticeable but no t s ever e. May have hemi-facial s pas m or co nt ra ctur e. At Res t: Normal t one & Symmet ry. Gross:
M ot i on:
Fo rehead: Sli ght t o mo derat e mo vemen t . Eye: Co mplet e clo sure wit h eff o rt . t h: Sli ght weakn ess wit h maxi mum M ou eff o rt .
y
Gross:
As ymmet ry is dis figur ing and/or weakness .
o bvio us facial y
IV
erat ely M od
Severe
Normal t one & Symmet ry. y
y
Severe
M ot i on:
Fo rehead: No mo vemen t. Eye: In co mplet e eye clo sure. t h: Asymmet ri cal wit h maxi mum eff o rt . M ou
y
V
At Res t:
y
Only s light, bar ely no ticeable, mo vement. At Res t: A s ymmet rical facial appearance. Gross:
M ot i on:
Fo rehead: No mo vemen t. Eye: In co mplet e clo sure. t h: Sli ght mo vemen t. M ou VI
To tal
No faci al fun cti on
References 1. ^
a b
Rubin
DI, Matsumoto JY, Suarez GA, Auger RG. (1999). "Facial trigeminal synkinesis associated with a
trigeminal schwannoma.". Neurology 53 (3): 635±7. PMID 10449135. 2. ^
a b
Buckley EG, Ellis FD, Postel E, Saunders T (2005). "Postraumatic Abducens to Oculomotor Nerve
Misdirection". J ournal of AAPOS 9 (1): 12±16.doi:10.1016/j.jaapos.2004.11.011. PMID 15729274. 3. ^
a b
Beurskens CH, Heymans PG. (2006). "Mime therapy improves facial symmetry in people with long-term
facial nerve paresis: a randomised controlled trial.". Aust J Physiother. 4. ^
a b c d
52
(3): 177±83. PMID 16942452.
Nakamura K, Toda N, Sakamaki K, Kashima K, Takeda N. (2003). "Biofeedback rehabilitation for
prevention of synkinesis after facial palsy.". Otolaryngol Head Neck Surg. 128 (4): 539± 43. doi:10.1016/S0194-5998(02)23254-4. PMID 12707658. 5.
^
Manikandan N. (2007). "Effect of facial neuromuscular re-education on facial symmetry in patients with
Bell's palsy: a randomized controlled trial.".
C lin
Rehabil..
21
(4): 338±
43.doi:10.1177/0269215507070790. PMID 17613574. 6. ^
a b
Mehta RP, WernickRobinson M, Hadlock TA. (2007). "Validation of the Synkinesis Assessment
Questionnaire.". Laryngoscope. 117 (5): 923±6.doi:10.1097/MLG.0b013e3180412460. PMID 17473697.