Wednesday, August 26, 2015

Is it Hyperacussis or Recruitment?: When Say What? and Don't Yell! Go Hand In Hand

Hyperacussis or recruitment? Which one affects Meniere's patients?

They are 2 completely different things yet similar enough to be confused for one another.

www.hyperacusis.org defines hyperacusis as:

 A reduction of normal tolerance for everyday sounds. 
It is also defined as a collapse of the normal
range of tolerance for sounds that is present 
in otherwise normally functioning ears.

What this means is that normal everyday sounds at the normal everyday volume seem excruciatingly loud. As with Meniere's disease, there is no absolute known cause.  Again from hyperacusis.org:


 It can initially affect only one ear but generally speaking, within a short time, the condition is almost always bilateral. It can be mild or severe. Often, people who have hyperacusis also have tinnitus, or phantom noises in their auditory system (ringing, buzzing, chirping, humming, or beating).  Research has shown that about half of all people who have tinnitus, also have reduced tolerance for moderate or loud sounds, known as hyperacusis. No one is quite sure how many people in the world suffer from hyperacusis without tinnitus.   
Adults and children can develop hyperacusis: certain birth conditions are associated with hyperacusis, including Williams Syndrome and autism.  Since the auditory system connects the outer organs of hearing with the central nervous system, through a complex series of neural pathways, that literally pass through or coordinate with many diverse areas of the brain, there are endless possibilities for dysfunction that may contribute to hyperacusis.

In other words, the understanding of the mechanism of hyperacusis is often extremely challenging and it is yet impossible to specifically locate a single structural change that is responsible for hyperacusis.  There is no objective test for hyperacusis.  

It is a safe bet that during a vertigo attack what we suffer from is hyperacusis, the acute intolerance to sound.

Recruitment is a bit different.

www.hearinglink.org defines it like this:

Recruitment is a large increase in the sensation of loudness with only a slight increase in the actual intensity of a sound.  Even though quiet sounds cannot be heard due to the presence of hearing loss, louder sounds may quickly become uncomfortable to the listener as they increase in volume.  Recruitment is commonly associated with a sensorineural hearing loss and does not vary with emotions. 

Here is how it has been explained to me.

Inside your cochlea are thousands of microscopic hair cells. These cells are aligned in rows for each frequency. As you hear sounds, the first row of hair cells start to vibrate, or bend. As the sound continues to grow louder, the next rows begin to vibrate or bend. This continues until the loudest sounds are engaging all of the rows of hair cells.

When your hair cells become damaged, it is the ones that react to the quietest sounds that get damaged first, hence the reason you can't hear soft noises. As your hearing progressively gets worse, more and more hair cells along the line become damaged.

Now, when you have recruitment, what happens is that the damaged hair cells attempt to "recruit" neighboring hair cells to hear for them in the damaged frequency, as well as it's own, overloading the recruited hair cells. What else happens is that when all the hair cells at a certain volume are damaged, the sounds at that decibel level are skipped. You don't hear them at all. So when a sound reaches the level that you can hear them it gives you the startle effect. But you don't hear it at a soft level, you hear it at the actual volume that it is presented, which may be extremely loud.

For example, if your hearing is damaged to a level of 70 dB, which is a bit on the high side of normal conversation, you won't hear anyone whispering, but when they talk to you it will seem loud because you are missing all the soft sounds. Or if your hearing is in the profound hearing loss range of 90dB, the first thing you may hear is a horn honk, but not the car that it came from.

This also creates a problem when trying to fit a person with hearing aids.  The usable hearing you have between the softest sound you hear, and the loudest you can tolerate is called your Dynamic Range.  The narrower that dynamic range, the less benefit you are going to get from hearing aids because they have to be set at a level you can hear, but stop at a level you can tolerate.  If your hearing is at 80dB and the loudest they will set them is 120dB, you are not going to hear as well as someone who has hearing loss at 50dB.  The hearing aids can't make you hear something you are unable to, and it is almost impossible to compress all of the sounds into a very narrow range.

It is also known that a person with no hearing loss cannot have recruitment, so their sensitivity has to be hyperacusis.

As hearing loss associated with Meniere's disease advances, it is very likely that we suffer from recruitment on a daily basis. I know I did.

So, which is it, hyperacusis or recruitment?

Probably both.

'Til next time

Dennis

Just a guy trying to live with an invisible, potentially debilitating illness


2 comments:

  1. Thank you for this excellent post explaining the difference between Hyperacusis and Recruitment. It was really helpful since I also have to add in phonophobia with my migraines so it gets so confusing! Totally bookmarking this to link in the future.

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    1. You are so welcome. Feel free to use my posts, just credit me. I would think migraine sufferers would also fall into the hyperacusis group.

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