Constraint-Induced Sound Therapy for Sudden Sensorineural Hearing Loss

 

by Neil Bauman, Ph.D.

November 4, 2016

 

A man explained,

My wife suffers from tinnitus after sudden partial hearing loss in one ear. In her reading, she came across “Constraint-Induced Sound Therapy” and its potential benefits. Do you recommend this technique?

Constraint-Induced Sound Therapy (CIST) for single-sided Sudden Sensorineural Hearing Loss (SSHL) is quite a new technique. Published research on it didn’t come out until January of 2014 so I doubt many hearing health care professionals know much about it yet.

I think constraint-induced sound therapy is a cool treatment and is worth considering if you have just had sudden sensorineural hearing loss in one ear. Unfortunately, in your wife’s case, it probably is too late for her as you need to begin CIST as soon as possible after the sudden hearing loss—and certainly not more than 5 days later.

Before we look at the details of constraint-induced sound therapy, let’s look a bit more at what exactly sudden sensorineural hearing loss is.

What Is Sudden Sensorineural Hearing Loss?

The CIST researchers defined sudden sensorineural hearing loss this way.

1. Sudden sensorineural hearing loss is a hearing loss that occurs either instantaneously or over a period of up to three days.
2. Sudden sensorineural hearing loss is an inner ear hearing loss (sensorineural) as opposed to a middle ear (conductive) hearing loss.
3. Sudden sensorineural hearing loss is defined as an acute hearing loss of at least 30 decibels (dB) that occurs at three or more consecutive test frequencies on a standard audiogram.
4. For their purposes, CIST researchers define sudden sensorineural hearing loss as occurring in just one ear. (However, in truth, it can occur in both ears at the same time, although this is less common than sudden hearing loss occurring in just one ear.)

Causes of Sudden Sensorineural Hearing Loss

There are a number of causes of sudden sensorineural hearing loss. About 10% of the time, the cause is known—such as Meniere’s disease, head trauma, Autoimmune Inner Ear Disease (AIED), Cogan’s syndrome, genetic disorders, ototoxic drugs or retrocochlear disorders related to vestibular schwannomas, auditory neuromas, stroke, etc. (1)

In the remaining 90% of cases of sudden sensorineural hearing loss, the cause is typically unknown and thus diagnosed as idiopathic (cause unknown) hearing loss. The two most commonly suspected causes of idiopathic hearing loss are viral attacks to the inner ear and vascular problems (blood clots) in the tiny arteries in the inner ear. (1)

Is Sudden Sensorineural Hearing Loss Permanent?

Whether sudden sensorineural hearing loss proves to be permanent or temporary hinges on several factors. The most important factor is the severity of the sudden loss. Milder losses tend to be temporary, while more severe losses tend to be permanent. And between these two is an intermediate condition where some, but not all, hearing comes back. This is more common with moderate to severe sudden hearing losses.

One study revealed that normal or complete recovery occurred in 45% of the people with sudden hearing loss. Another study showed that 65% of the people recovered to functional hearing levels spontaneously and independently of any type of medical treatment. (1)

This is good news. It means that for a good number of people who experience sudden sensorineural hearing loss, their hearing will come back whether they have any treatment or not. Unfortunately, for other people, no hearing comes back in spite of any treatment given. For them, their sudden sensorineural hearing loss is permanent. For the rest, conventional treatment may improve the chances of their hearing coming back.

I say hearing “may” come back with treatment. You see, it is hard to tell whether the current conventional treatment causes hearing to return, or whether hearing, in such cases, would have returned by itself without any treatment.

The typical conventional treatment for sudden sensorineural hearing loss is taking a course of corticosteroids—typically Prednisone, Prednisolone, Betamethasone or Dexamethasone. If your doctor suspects a viral or vascular cause to the SSHL, he may include anti-viral drugs and vasodilators in addition to corticosteroids. Even so, “the efficacy of the corticosteroid treatment approach is fiercely disputed,” (1) since, according to one study, the hearing in patients who had received corticosteroids did not recover better than non-treated patients. (1)

Another triple-blinded, placebo-controlled, clinical trial “demonstrated that corticosteroids given in customary dosages did not influence hearing recovery.” (1) No doubt that is why some doctors refuse to prescribe corticosteroids for sudden hearing loss. They just do not believe it helps—either your hearing will come back on its own to some degree or other, or it won’t.

This is where constraint-induced sound therapy comes in. Studies show it can help more hearing come back than would otherwise occur without this new treatment. (1)

Since CIST can be used along with other treatments, if you feel that taking corticosteroids may help, you can take them along with CIST and cover more of your bases. However, the latest research seem to indicate that it is the CIST treatment alone that gives the increased hearing recovery, not concurrently taking corticosteroid drugs. (2)

Sudden Sensorineural Hearing Loss Causes Changes in the Brain

Besides the obvious changes to structures in the inner ear (e.g. ultimately death to hair cells among other things), sudden sensorineural hearing loss in one ear can (and does) cause changes in the brain itself. You see, our brains are plastic. This means they can grow and change to meet new conditions.

Researchers have recently discovered that one result of sudden sensorineural hearing loss is that it causes changes in neural activity in the central auditory system in our brains. This, in turn, results in physical changes in the auditory cortex (where sound signals are processed) due to the neural plasticity of our brains. (1)

One study demonstrated that our brains begin to reorganize the auditory cortex within a few days of sudden hearing loss. Now get this. The degree of cortical reorganization correlated negatively with the recovery rate from the sudden hearing loss. (1) In other words, the more our auditory cortex reorganizes, the less likely we are to recover from sudden hearing loss.

Therefore, it appears that preventing the auditory cortex from reorganizing itself may be one of the keys to successfully treating sudden sensorineural hearing loss. And this brings us to constraint-induced sound therapy.

What Is Constraint-Induced Sound Therapy?

The concept of constraint-induced sound therapy is intriguing. The basic premise is that if you suffer a sudden sensorineural hearing loss in one ear, your brain reorganizes itself—what the researchers call “maladaptive auditory cortex reorganization”—to pay more attention to the signals coming from the better (or normally-hearing) ear. This makes total sense. For example, if you have a sudden hearing loss in one ear, you naturally and automatically switch to paying more attention to the sounds your better ear hears. (2) In short, you listen more with your better ear.

What happens next is that this new listening behavior increases the neural activity corresponding to your better ear. At the same time, your brain reduces neural connections between your bad ear and the auditory cortex. (2)

Thus, if hearing later comes back to the affected ear (either spontaneously or via amplification such as wearing a hearing aid), your brain may have already learned to largely ignore sound signals from your bad ear. The result is that your bad ear becomes a “second-class citizen” and is more or less ignored.

Constraint-induced sound therapy tries to prevent this maladaptive auditory cortex reorganization, induced by “non-use”, from happening. The obvious way to prevent this reorganization is to make your brain hear about the same from both ears. You can do this by blocking (constraining) sounds from the good ear, while at the same time stimulating output (enhancing sounds) from the bad ear.

The result is that from your brain’s perspective, both ears are now hearing more or less equally. Therefore, no auditory cortex reorganization is necessary, and thus does not take place.

In order to make this happen, since one ear has suffered a sudden hearing loss, you either have to quickly “correct” this hearing loss in the bad ear, or you have to temporarily “damage” the good ear so it hears at roughly the same level as the bad ear. In actual fact, CIST takes both of these approaches at the same time. Here is how it does this.

First, CIST constrains the hearing of your good ear by using an ear plug. This could simply be a foam ear protector that has a protection rating of 30 dB or so. This brings the hearing of your good ear down by roughly 30 dB. This is the “constraint-induced” part of constraint-induced sound therapy.

At the same time, you listen to music that has been specifically boosted for lost volume by frequency. Thus, your bad ear now has louder music to listen to. This “forces” you to pay auditory attention to, and listen to, music intensively via your affected ear. (2) This is the “sound therapy” part of CIST. By doing this, both ears are sending more or less equal signals to your brain. The result is that your brain sees no need to do any auditory cortex reorganization, or if any takes place, it is minimal.

As a result, as hearing returns to your bad ear over the next few days and weeks, your brain continues to process these sound signals equally with the sound signals received from your good ear.

Not only does auditory cortex reorganization not take place (a good thing in this case), but something else wonderful happens. The damaged ear recovers even more hearing than it would otherwise have done if CIST was not used.

Here is why they think this happens. “Several studies have reported that sound stimulation dilates blood vessels and increases red blood cell velocity in the cochlea.” (1) Thus, listening to music likely improves the circulation in your cochlea which, in turn, increases oxygen levels. “By supplying more oxygen and substances necessary for restoration and for removing toxic substances, the increased blood flow may support the recovery of damaged cochlear tissues.” (1)

Constraint-Induced Sound Therapy Guidelines

In order for constraint-induced sound therapy to be successful, you need to follow certain guidelines. Among them are:

1. Confirm that you have suffered a sudden sensorineural hearing loss of at least 30 dB at three or more adjacent frequencies.

2. Confirm that your hearing loss is of unknown (idiopathic) origin and thus is not caused by the conditions listed under a previous heading “Causes of Sudden Sensorineural Hearing Loss”. If the cause results in permanent hearing loss (as is generally the case with the above conditions), CIST is basically a waste of time since hearing isn’t coming back. However, if the cause may result in temporary hearing loss, then by all means try CIST and see if it helps.

Note: ototoxic drugs can cause either permanent or temporary hearing loss (or a combination of both), so if you have sudden hearing loss in one ear caused by the side effects of taking any ototoxic drugs, you have even odds that taking the CIST treatment will help more of your hearing to return.

3. Confirm that the hearing level difference between your ears averaged across 500, 1,000 and 2,000 Hz is less than 50 dB based on an air-conduction pure-tone audiogram.

4. You need to begin this treatment within 5 days of your sudden hearing loss—the sooner the better. Studies have reported that the shorter the delay between the sudden hearing loss and beginning treatment leads to better return of hearing. (2) If you wait too long, you probably won’t have positive results to show for all your effort.

5. Choose music you like, but it must cover a wide frequency range from at least 125 to 8,000 Hz. I’d also suggest you select music that does not have wide swings in volume to make it easier on your ear if you happen to also have hyperacusis as a result of you SSHL.

In the study being quoted, they used classical music, but admit they do not know what kind of music is best for CIST. They state that “listening to music is much less distressing than listening to pure tones or noise.” They also emphasize that “the enjoyment of a stimulus is an important factor in the initiation of cortical reorganization”. (1) Therefore, for best results, it seems wise to choose music you particularly enjoy.

6. Confirm that you can comfortably listen to music with your affected ear. This might not be possible if you also now have severe hyperacusis.

7. Caution: Do not turn the volume up too high such that you cause acoustic trauma. This could happen if you turn the volume up too much to compensate for your hearing loss—e.g., turning up one frequency on the equalizer too high to try to compensate for your hearing loss at that frequency. This is especially important since you will be listening to music at this level for a minimum of six hours each day. (2) Therefore, set the volume at a comfortable listening level for your damaged ear.

8. Check that you are not hearing any music in your plugged (good) ear via cross-over hearing. If you can hear the music in your better ear, then this treatment probably won’t help you as much as it otherwise would have since your brain will generally listen to your good ear instead of your bad ear.

Even so, constraint-induced sound therapy may still prove to be efficacious to some degree even if your sudden hearing loss is worse than a 50 dB average because of the enriched acoustic environment effect, even if some degree of cross-over hearing occurs. (1)

Cross-over hearing is the hearing you get in your better ear when a loud sound is applied to your worse ear. The loud sound vibrates your skull and thus transmits this signal to your better ear via bone conduction where you hear it, albeit at a lower volume—about 30 dB or so lower—because of attenuation of the sound via bone conduction.

Thus, if your better ear hears the CIST sound at a higher level than your bad ear hears it, then negative auditory cortex reorganization can still take place. That’s the reason they excluded people with more severe sudden hearing losses (hearing loss greater than 50 dB) in this study.

An exception to this 50 dB rule could occur if you already had hearing loss in both ears. Then the 50 dB would apply to the maximum difference in hearing between both ears. For example, if your better ear had a 30 dB loss, then this technique should still work even though your worse ear had up to an 80 dB loss since your better ear’s response to bone conduction signals will also be reduced by 30 dB.

Furthermore, this study assumed you only had sudden hearing loss in one ear and normal hearing in the opposite ear. But theoretically, the above exception should apply if you had sudden hearing loss in both ears, but the loss was worse in one ear than the other—as long as the difference between them was 50 dB or less.

9. During active treatment you want to be in a safe environment since your better ear is now plugged and you are listening to music with your worse ear. Essentially you now have a significant hearing loss or are functionally deaf. As a result, you likely will not hear the everyday sounds you normally would hear. Since you were a hearing person, you relied on such audible sounds to keep yourself out of “trouble”. Now that you cannot hear them, you may inadvertently put yourself in the way of harm and have more accidents.

10. You can use the CIST treatment along with any medications you are taking. It works whether you are taking any drugs or not.

Constraint-Induced Sound Therapy Treatment

You can do your own CIST treatment if you are so inclined, or if you can’t find a professional that is knowledgeable about it.

All you need is:

1. A foam ear protector (or ear plug)
2. Headphones that fit over your ears (like earmuffs)
3. Portable music sound source (MP3 player, iPod, iPhone, smart phone, etc.)
4. Portable equalizer/amplifier (Speech-Adjust-A-Tone, etc.)
5. Some hours of recorded music

In order to effectively use CIST, you need to plug your better hearing ear so that your brain has to actively use the affected ear to hear.

You can get foam ear protectors from any drugstore. Get ones that have a protection rating for around 30 dB or so. To insert the foam ear protector properly in your good ear, simply roll the ear protector between your thumb and index finger to compress it, then quickly insert it into your ear canal as deeply as you can. The foam expands to give a good seal and you should notice right away that you can’t hear as well as you used to in that ear.

Wear this ear protector in your better ear all day for about 10 days or so. Take it out at night of course.

For this treatment, you want to wear ear-muff type headphones that fit over your ears. The sound on your good ear side is switched off so you only hear the music in your affected ear. (Some headphones have a balance control so you can send all the sound to one ear only; some headphones have separate volume controls for each headphone so you can turn the volume all the way down on one side; or you can modify the headphones by cutting the wire to one side or modifying the wiring in the plug).

Place the silent (disabled) headphone over your good ear—the one with the ear protector in it—to give added sound proofing. Place the headphone with the music in it over your affected ear.

Listen to music for a minimum of 6 hours a day via the headphones. Now you “have” to use your bad ear (the one that had the sudden hearing loss). in order to hear. Concentrate on listening via your affected ear. You don’t have to listen to the music for six hours straight. You can break it up into several sessions throughout the day. When you are not listening to the music, you can take the headphones off.

To get maximum benefit from the music, you need to adjust the music yourself so that it sounds natural and comfortable to you (or at least as near to normal as you can make it). Since you have typically lost more hearing in some frequencies than others, this results in distorted sound. Consequently, you need an equalizer to increase the volume of those frequencies that were involved in your sudden hearing loss in order to make the music sound natural again. Doing this results in an increase of sound energy in the frequency regions affected by your sudden hearing loss as well as a decrease of sound energy in any unaffected frequencies. (1)

Typically equalizers have 6 frequency bands that you can adjust separately.

Some audio devices have built-in equalizers that enable you to do this. If your MP3 player, iPod or iPhone, etc. allows you to do this, great. If not, you can purchase a small portable equalizer to do this and feed the audio from your sound source into the equalizer.

If you need more volume than your audio device can put out, add in an headphone amplifier to the mix. You would hook them up in series in this order:

Audio device (e.g. MP3 player)  –>  Equalizer  –>  Headphone amplifier  –>  Headphone

If you don’t know where to get an equalizer and/or headphone amplifier, the Speech Adjust-A-Tone contains both in one portable unit. It has plenty of volume—even for the worst hearing losses. You can purchase the Speech Adjust-A-Tone here. (The model HGA-Tp is all you need.)

If you are using the Speech Adjust-A-Tone, plug your audio device (MP3 player, smart phone, etc.) into it using a standard audio patch cord, and plug your headphones into the Speech Adjust-A-Tone. The hookup would look like this.

Audio device (e.g. MP3 player)  –> Equalizer/Headphone amplifier  –>  Headphone

How Long Does It Take for Constraint-Induced Sound Therapy to Work?

You are likely now wondering how long it takes for constraint-induced sound therapy to do its job. Or put another way, “How long do I need to continue the CIST treatment?

The answer is, continue CIST treatment until:

1. Your hearing recovers completely (returns to its previous level) This might happen in less than two weeks.
2. Your hearing recovers to normal (that is, 25 dB or better) Again, this might only take a couple of weeks, but it could be longer.
3. Your hearing has reached a plateau and has stopped recovering.

A rule of thumb is that your hearing will either have fully recovered, returned to normal or reached a plateau by about the end of 30 days since your sudden hearing loss. Thus, you normally would not need to continue CIST treatment longer than about 30 days.

The one exception is that is if your hearing is still improving at the end of 30 days, then continue on with the CIST treatment as long as your hearing continues to improve, which might be for another week or two or possibly longer.

Note: the sooner your hearing begins to return, the better your chances are of a more complete recovery. For example, if you already notice your hearing is coming back beginning just 2 or 3 days after your sudden hearing loss, you have a good chance of regaining all or almost all of your lost hearing. However, if you do not notice any recovery in the first two weeks or so, you have a slim chance of regaining much, if any, of your lost hearing. Typically, the hearing you have at the end of 30 days is what you will be left with in the future.

What Are the Results of Constraint-Induced Sound Therapy?

In one study, 53 participants were divided into two groups. Participants in both groups took corticosteroids (Betamethasone in this case), but one group also practiced constraint-induced sound therapy at the same time.

Here are the results. 58% of the participants in the corticosteroid only group showed normal (hearing levels greater than 25 dB) or complete (return of hearing to previous levels) recovery (18/31); 19% showed partial recovery (improvement greater than 10 dB) (6/31), 19% showed no change (6/31); and in 3% hearing got worse (1/31). (1)

However, in the group that also took the CIST, the results were dramatically better. 86% showed normal or complete recovery (19/22); 14% showed partial recovery (3/22), and 0% had no change or got worse (0/22).

This indicates that “the sound stimulation of the affected ear and the temporary artificial hearing loss induced in the intact ear were beneficial for the recovery of hearing thresholds in the affected ear.” (1) In other words, constraint-induced sound therapy works.

Looking at these data another way, at the time of the sudden hearing loss, both groups had similar degrees of hearing loss. However, by day 10 or so the group taking the CIST therapy had an average of about 8 dB more hearing come back than the other group. And after a month or two, the difference had increased to an average of about 11 dB. (2)

An average of about 11 dB may not seem like much, but when you consider that with each 10-dB increase in sound, you perceive this as being twice as loud. Ultimately, the CIST treated group’s hearing improved such that they could hear more than twice as well as the untreated group. While not perfect, that’s a considerable improvement. Thus, no matter how you look at it, the CIST treatment program seems to be an effective, inexpensive, easy and safe treatment for SSHL.

Note: in this study, all the participants had an average sudden hearing loss of less than 50 dB. This skews the results in favor of more, rather than less, hearing returning. Why? Because typically, the worse the hearing loss, the less the chance of recovery. Thus, a person who has a sudden hearing loss of say 40 dB has a much better chance of making a full or near-full recovery, as compared to a person who experiences a 90 dB sudden hearing loss.

For example, a person with a 40 dB sudden hearing loss could expect to recover all this loss or be left with a minimal loss of perhaps 10 dB as this study shows. However, a person with a 90 dB sudden hearing loss might recover 10 to 20 dB and be left with a permanent loss of 70 to 80 dB. It would be very unusual to recover all of this lost hearing.

The people in this study all fell into the former class, and none in the latter class. Therefore, the people in this study all had a higher probability of recovery in the first place.

It would be interesting to see how well CIST works for people with more severe sudden hearing losses. I think the results would not be as good just because of this greater probability of hearing not coming back, and also because of the cross-over hearing effect in trying to constrain the hearing in the better ear since much move volume would be needed to bring up the hearing in the bad ear and this would easily allow hearing cross-over.

Although they didn’t mention it in this study, it seems reasonable that if your hearing doesn’t come back to normal or near normal levels, you should get and wear a hearing aid in the affected ear if it will help you. The sooner you do this, the less chance you’ll have of negative auditory cortical reorganization.

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(1) Okamoto, Hidehiko. 2014. Constraint-induced sound therapy for sudden sensorineural hearing loss—behavioral and neurophysiological outcomes. http://www.nature.com/articles/srep03927.

(2) Sekiya, Kenichi, et. al. 2016. Neuro-rehabilitation Approach for Sudden Sensorineural Hearing Loss. https://www.jove.com/video/53264/neuro-rehabilitation-approach-for-sudden-sensorineural-hearing-loss.