How to objectively measure the facial nerve recovery level and synkinesis after Bell’s palsy?
Measuring is “seeing”.
Why is it so important to measure the level of facial nerve recovery? The answer is very simple: What we can measure, we can manage! At Crystal Touch clinic we always start our rehabilitation programs with measuring the recovery level of the facial nerve and doing the Synkinetic Correlation Test, before we decide on the composition of a program. We need to know objectively how far the facial nerve has already regenerated and what is the level of synkinetic correlation between the muscles before we begin the rehabilitation.
Nerve Conduction Study (NCS)
The importance of NCS after a facial palsy can be compared to that of an X-ray examination in case of a broken leg. If one has a broken leg, before a doctor can tell you what is the best way to recover it, he needs to make an X-ray scan, so he knows where and how the bone is broken. No doctor will start an operation to fix the broken bones without making an X-ray.
The same is with the facial nerve. The Nerve Conduction Study is like an X-ray for the facial nerve. By analyzing the response of the facial muscles to electrical stimuli, we can objectively measure to what extent each branch of the facial nerve has regenerated. This enables us to “see” the functionality level of the facial nerve. In turn, these results let us understand what we need to do during the rehabilitation to help improve the patient’s condition.
Synkinetic Correlation Test (SCT)
A different technique, with a different approach to analysis, helps us to measure the level of synkinetic correlation between the facial muscles that are involved in synkinetic movements. While some subjective methods of measuring synkinesis do exist, at Crystal Touch we have developed an objective quantitative measurement protocol to evaluate the intensity of synkinesis. This helps us to determine the starting point of the rehabilitation program, as well as to measure the progress of our patients.
Watch the video or read the article below to learn more about NCS and SCT.
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Nerve Conduction Study (measuring recovery level)
Synkinetic Correlation Test (measuring synkinesis)
Q&A
Nerve Conduction Study
As the name suggests, Nerve Conduction Study allows us to measure how well the nerve, in our case the facial nerve, is able to conduct electric signals between the brain and the facial muscles.
To perform the measurements, we use electromyograph, manufactured by Neurosoft. With this device, we can measure and record the responses of facial muscles to external stimulation. The analysis of those responses allows us to evaluate the recovery level of a facial nerve.
Nerve Conduction Study for the muscles of locomotion (muscles of the body) is a common modality if there are doubts about the proper functioning of the nerves or muscles. It is used regularly in neurological studies.
According to our experience, the nerve conduction study for the facial nerve is not very widely used in most countries. It is commonly used in the countries of ex. Soviet Union: Russia, Ukraine, Belarus, etc. It is sometimes used in Brazil and in the Far East countries. In Western Europe, the United States and Canada, it is not a standard practice and is used very rarely. This is most probably because Bell’s palsy is not a high priority for the health institutions since it does not present a direct danger or risk to the health or the life of a patient. It is a damage to only one single nerve of our body. The other reason could be that the equipment and the procedure of this test are rather expensive.
Extended protocol for NCS by Crystal Touch clinic
We have made some changes to the standard NCS protocol, to measure the facial nerve recovery level with more details. The protocol for NCS has been already used by other institutions working with facial palsy patients. At our clinic, we made some changes to the standard protocol to make the measurement more precise, to see a better picture of each facial nerve branch recovery level.
The usual standard protocol uses 3 or 4 points (3 or 4 muscles). We have extended this to 6 muscles and muscles groups: (1) Frontal muscle, (2) Orbicularis Oculi muscle, (3) Nasalis and Levator Labii Superioris, (4) two Zygomatic muscles, (5) circular muscle of the mouth, and (6) musculus Mentalis and musculus Depressor Anguli Oris. You can see the recording points for these muscles on Image 1.
Suggested article: Facial muscles and their functions.
To make the measurements more precise, we have also amended the usual nerve stimulation practice. Usually, the stimulation is done just behind and in front of the earlobe for all the muscles that will be measured. Instead, we position our stimulating electrode on each and every branch of the facial nerve. This way, we send a very narrowly directed stimulation signal that allows us to evaluate the recovery level of each facial nerve branch. Image 2 shows the stimulation points. Yellow circles show the placement of anode and blue circles show the placement of cathode.
How NCS is done
When we do a nerve conduction study, we place a stimulating electrode successively on the 6 points explained before. Through the stimulating electrode, we send small electrical signals. We use three power levels of the signals: 10mA, 20mA and then 30mA (these levels of stimulation do not cause pain). The resulting graphs on the screen show us how the facial muscles, depending on which branch of the facial nerve we stimulate, react to that signal. For the purpose of measurements, we assume that facial muscles themselves are working properly and only the facial nerve is damaged.
Depending on the intensity of stimulation and on the shape and amplitude of electrical response from the muscles, we can conclude how well or how poorly the respective branch of the facial nerve has recovered.
Examples of NCS results
Healthy subject
Let’s take a look at some examples of nerve conduction study of a normal, healthy person. Six images below show NCS results for each stimulation point on both sides of the face. We can see that both the right side (top graph) and the left side (bottom graph) produce practically identical responses to a minimum stimulation of 10mA. This means that the facial nerve on both sides conducts the signals with the same efficiency and that the facial nerve is healthy on both sides.
Graphs are identical in shape, amplitude, and latency. The peak means how much time it takes for the electrical signal to reach the facial muscle from the point of stimulation and to generate maximum contraction.
Subject with long-standing facial palsy
What happens when the facial nerve becomes damaged? On the two images below, you can see an example of long-standing facial palsy, a female subject, 56 years old, two years since the onset. On both images, lines 1, 2 and 3 show the affected side (right-hand side) and lines 5, 6 and 7 show the healthy side (left-hand side). Each line represents different stimulation intensity, with lines 1 and 5 showing 10mA, 2 and 6 – 20mA, 3 and 7 – the maximum, 30mA.
This is m.Frontalis, a frontal muscle. The nerve is working normally on the healthy side (lines 5, 6 and 7). On the affected side, we see a quite modest response to the minimum stimulation (line 1). At the higher levels of stimulation (lines 2 and 3), we see already larger signals but they are different in shape, latency and amplitude from the healthy side.
The very similar picture on the circular muscle of the eye. As we can see here, identical signals on the healthy side for all levels of stimulation (lines 5, 6 and 7). And we see very modest responses on the affected side. It indicates that although two years have passed since the onset, the recovery level of this nerve branch is relatively poor.
The difference in response to the stimulation on the affected side compared to the healthy side does not mean that the nerve on the affected side is dead. If it was dead, then the response graphs would be flat, regardless of the stimulation level. It is not dead, it is working. The difference means that not all of the fibers that had been damaged have regained their connection with their respective facial muscles. In addition, the quality of electrical insulation of the recovered nerve fibers is lower than it is on the healthy side.
Let’s take a closer look at the other muscles.
m.Nasalis, the muscle that lifts the upper lip and wrinkles the nose. The situation here is similar to the ones before. The healthy side is almost identical at each stimulation level (lines 5, 6 and 7) and there is a smaller response on the affected side (lines 1, 2 and 3).
Musculi Zygomatici, the muscles that produce a smile. We can see in the first part of all lines (the peak that goes down) fairly identical responses, provided that the level of stimulation is high. In the second peak (the peak that goes up), we can see that there is a lower recovery in one of the two muscles. That peak corresponds to the Zygomatic major muscle.
m.Orbucularis Oris, the circular muscle of the mouth. Graphs also show very clear differences between the healthy and affected side.
We can also see a quite noticeable difference between healthy and affected side in m.Mentalis and m.Depressor Anguli Oris, the muscles that pull down the mouth corner and pull up the chin. They often stand in the way of balanced smiling. As we can see, the recovery level of Depressor Anguli Oris is quite high, so the response signal is big. Respectively, this muscle, even with the relatively low level of recovery is very much able and capable of resisting the smile in patients with long-standing facial palsy.
That’s a short version of a description of the nerve conduction study. Of course, in the course of our rehabilitation program, we monitor the changes in the condition of the nerve. We usually do the nerve conduction study during the very first visit of our patient to the clinic. We do the second measurement after completion of the first module of rehabilitation, after or during the fourth visit of the patient to the clinic. We do a control measurement to see how well the recovery of the nerve has progressed.
Synkinetic Correlation Test
Existing measurement methods for synkinesis (subjective)
There are several methods to evaluate synkinesis that already exist:
- Most of them are questionnaires: how you feel this, how you feel that and so on. It is being either assessed by the patient himself or herself or by the therapist. Then a certain score is given, depending on the visual observations of the patient or of the therapist. In the course of rehabilitation, you observe the change of that score.
- There are also some methods with video evaluation of synkinesis. This means that you sit in front of a video camera and it records the movements of parts of your face. The computer compares the movement of your healthy side and the affected side. So it measures, actually, the differences in the movements of your healthy side and affected side and that way it measures synkinesis by visual observation.
- As far as we know at the moment, except for Synkinetic Correlation Test that we have developed in our clinic, no other instrumental tests are available to measure synkinesis quantitatively.
How Synkinetic Correlation Test is performed
When we do the Synkinetic Correlation Test, we place a total of four recording electrodes on the face. First, we put two electrodes on the upper part of the face: on the frontal muscle and m.Orbicularis Oculi (circular muscle of the eye). The other two electrodes we place on the Zygomatic muscles and the chin area: m.Mentalis and m.Depressor Anguli Oris. In this way, we are measuring the two areas which are the most involved in synkinetic patterns.
Ocular-oral synkinesis means that when the patient closes or blinks the eye, the mouth corner usually involuntarily moves. Sometimes the neck and the chin area are also involved. The other way around, oral-ocular synkinesis manifests when the patient smiles, puckers the lips or blows the cheeks and then the eye involuntarily closes. So the eye fissure becomes more narrow.
Muscle “driver” and muscle “follower” in the synkinetic movement
As the contraction of one muscle forces the correlated synkinetic contraction of the other, we have named the muscle that initiates the movement – “master”, and the muscle that follows the movement in synkinetic involvement – “slave”. Or we can call it a “driver” and the “follower”.
Norm: no synkinetic movement
On the left side of Image 3 below, where you see “NORM”, is the recording of a healthy side, with no synkinesis. The two upper graphs show a recording of rhythmical blinking. This is an electrical representation of blinking. The blue graph shows the signal recorded from the circular muscle of the eye. When a healthy person or a healthy side of a patient is blinking, we can see that a very small effort is involved. The amplitudes of graphs are small because the intensity of muscle contractions is low. In this case, during blinking, the muscles around the mouth (green graph) are not involved at all. The signal remains unchanged.
The two lower graphs show the measurement during rhythmical smiling. We can observe the same pattern when a healthy subject or a healthy side of FP patient’s face makes a rhythmical light smile. As we can see, very small efforts are necessary to produce a smile (the fourth line), because there is no resistance from muscles-antagonists. Also, the eye area (third line) remains totally, nicely relaxed and uninvolved during rhythmical light smiling.
Synkinesis: a patient after long-standing facial palsy
When we look at the synkinetic pattern (right side of Image 3), we can see a totally different picture. First, when the person is blinking (the first, dark blue top line), we can see that it involves a lot of effort by the circular muscle of the eye. Of course, those efforts are “spilling over” to the other muscles, which means, in this case, the muscles around the mouth (the second, bright blue line). So we can see the synkinetic movement with a lot of efforts applied. This effort is seen in both the “master” and the “follower” muscles.
There is a phenomenon which is called Reciprocal Inhibition. This means when the agonist muscle contracts, the antagonist muscle normally relaxes. It happens automatically. On the healthy side, as we can see, there is very little physical effort necessary to produce the facial movement. However, on the synkinetic side, we see a lot of efforts involved. As we see from the recordings of a healthy subject, this kind of effort normally should not be necessary to produce regular blinking or smiling.
Why synkinetic movements require so much effort?
So why so much effort is needed to produce the movement, as seen on Image 3 (right side)? The answer is very clear – because something is resisting the movement. In the case of blinking, this “something” is the muscle that is called m.Levator Palpebrae Superior, the muscle that lifts the upper eyelid. The tricky thing about this muscle is that it does not belong to the system of the facial nerve. It belongs to the other nerve, Nervus Oculomotorius. It is the nerve that moves the eyeballs. That is why, when the facial palsy strikes it is very easy to open the eye, but practically impossible to close it.
Motor overflow
When a muscle remains contracted (in our case it is the muscle that opens the eyelid) for an extended period of time without relaxation or stretching, it becomes stiff. So the brain gets used to keeping this muscle contracted and would not let it go when it is time to close the eye or to blink. Even after the connection between the circular muscle of the eye and the brain has been restored. The same would happen if you walk with you arm lifted up for three days. It will be very difficult for you to put the arm down because the brain will get used to contracting the deltoid muscle so much, that it would not be able to relax it that easily. That is why the muscle that closes the eyelid (a part of the circular muscle of the eye) needs to put a lot of efforts to overcome the resistance. I’m sure that those of you who have experienced synkinesis, especially ocular-oral synkinesis, know that feeling. When you have a feeling that you have to make an extra effort to close your eye, and if you make that effort, your mouth corner involuntarily moves outwards. This is called motor overflow.
Example of Synkinetic Correlation Analysis
Unaffected side
Images 4 and 5 show the example of SCA of one of our patients. You can see very clearly that the healthy side is producing the same signals as we have seen on the previous Image (Image 3). No efforts whatsoever: neutral expression, eyes closed, rhythmical blinking; a light smile and a broad smile – nothing special, the eye area remains uninvolved.
Affected side
We see a totally different picture on the affected side of the same person. As we can see, the person is making an effort to produce a certain facial expression. It is a completely different picture because the brain is exercising a lot of effort. It is not because the muscles are weak, it is the other way around. The muscles are putting too much effort, much more than necessary, to contract.
That is why the excitation in the motor cortex (where these signals are produced) spreads out to the adjacent areas and also engages other muscles. In the case of blinking, it spreads to the muscles around the mouth area. You can see very clearly the pattern of contractions of the muscles around the mouth on the affected side when squeezing the eyes, is completely different than the pattern on the healthy side.
The same you can see when the person smiles, you can see the same correlation. That is why the method is called Synkinetic Correlation. There is a certain correlation between the muscle “master” and muscle “slave”. Due to motor overflow, the excitation spreads out and involves muscles that are normally not involved in a regular mimetic pattern.
Healthy side and affected side show two completely different expressions
Image 6 shows the original photos of the person with two facial expressions: closing the eye and smiling. Image 7 shows these expressions of the affected side, mirrored. Image 8 shows the expressions of the healthy side, mirrored.
We can see very clearly the facial expressions that each side is showing. The expression that is produced by the healthy side (Image 8) is the intended expression. This is the normal facial expression that would be if both sides were healthy.
When we mirror the affected side (Image 7) we see a totally different facial expression and we can see that this expression involves a lot of effort. You can see that all antagonists are working against each other. The person is trying to squeeze the eye but the muscles Frontalis and Corrugator Supercilii are contracted and are pulling the eye up. They are not letting the eyebrow go down. Also, when the muscles want to move the mouth corners in the same direction as on the healthy side, the antagonists are resisting very heavily. That is why we have this very characteristic over-tensed expression of the face. As we can see when the patient tries to smile, the affected side uses a lot of extra effort, especially in the area below the mouth corner that actually resists the intended action of smiling.
Why the length of recovery influences the effort exerted during facial expressions
During the long recovery period, especially after re-connection has started to take place, we experience the motor contractions. So, in the course of those many months, and for some of you even years, this mimetic pattern of applying too much effort, becomes a habit. It becomes a habit of the brain and with positive feedback from the contracting muscles, it becomes a conditioned reflex.
This is why, here in the clinic, we believe that synkinesis is not a result of aberrant regeneration. If you would like to learn more about synkinesis and its cause, according to our research, take a look at our Scientific Work.
