Pediatric Audiology 101 (Subtitle: Why mild hearing loss can still cause speech problems)

Disclaimer #1: I am not a doctor.  This is my best estimation of pediatric audiology 101.  I had it checked by an audiologist, so that I don't grossly mislead you, but I don't profess to be a hearing expert.

Disclaimer #2: I am also not a real blogger.  I wrote this in Word, and it took me a few days to get it as simple as possible, but I had font issues with copying & pasting it.  Sorry that some parts have abrupt font changes.  I don't know enough html coding to fix it.

Over the past few weeks, I’ve learned a lot about ears, hearing, and data analysis.  Now I’m going to share it all, so saddle up for some scientific good times J

The Ear

First things first, here’s a brief education in Pediatric Audiology.  I present to you: the ear.

As you can see, the ear has three zones---outer, middle, and inner.  Sound waves travel into the outer ear and cause the ear drum to vibrate, which causes the “three ear bones” to vibrate.  Those vibrations then travel through the cohlea (the snail-shaped thing in the inner ear) and the cells in the cochlea send information through the auditory nerve to the brain, which tells you what you are hearing. 

There are 2 families of causes of hearing loss. The first is conductive, meaning that the sound does not get properly "conducted"  from the outer ear all the way to the nerve in the back of the ear system, due to a myriad of issues that could arise anywhere along the pathway.  (This is common in children who might have fluid in the middle ear, ear infections, etc). The second source of hearing loss is sensorineural, meaning the the sound can be conducted through the system properly, but there is a disruption along the neural pathway. 

Since Maya had clean, properly fitted, functioning ear tubes (which were checked immediately prior to the ABR), we are expecting her loss to be sensorineural and *not* conductive.  Additional tests that will be done on July 5 will (hopefully) rule out a conductive component.   (It’s possible that there could be a combination of sensorineural and conductive components, but that will likely leave me with more questions, so I’m hoping that things will be simple.  Ha ha ha.)

So that’s the anatomical side of hearing loss.  Now, let’s look at some data. (Note: the data that I am about to show you is not Maya’s.  It is made up.  Although I share a lot, I don’t feel right about sharing her medical data---that should be her choice.  When I asked her if I could post her data online, she was noncommittal.  So I made up some data and my super audiologist friend created this audiogram based on it, for illustrative purposes).

The Audiogram

I present to you:  an audiogram.

The numbers across the top, from 125 to 8000, represent pitch (or Frequency) of sound, going from low pitches (left)  to very high pitches (right). The numbers along the side, from -10 to 120, represent hearing level in Decibels, going from very soft sounds (at the top) to very loud sounds (towards the bottom).   

The goal of hearing testing is to figure out the softest level  that a child can detect each of the different pitches (so if your data line was right up near the top, you would have great hearing . . . if you were at the bottom, profound hearing loss.)

Here’s the same audiogram with some color coding to make it easier to see the zones.  The green zone is where children with “normal” hearing would show up.  Yellow is “mild hearing loss.”  Red is “moderate hearing loss”.  The lines represent the child’s approximate hearing (X= her left ear, O= her right ear).

So the quietest sound this child can hear would be around 40 decibels, while the quietest sound that children with normal hearing could hear would be anywhere between 20 (for some kids) and -10 (for the supersonic hearing kids) decibels.  You can see on the audiogram that this child has mild hearing loss in the mid-frequencies (1000 Hz) and moderate loss as the frequencies increase (2000-4000Hz).

The other color-coded zone on the audiogram is that blue/grey “speech banana”.  The speech banana is represents the volumes and pitches of average conversational speech (if you want to get more technical, it represents the average conversational pitches and volumes of 2 people with normal hearing talking at about 5-7 feet apart).   

Here, the child’s hearing thresholds are within the speech banana. That suggests that she has access to the sounds necessary to develop spoken language.  A child with this type of hearing loss could still responds well when spoken to, even from another room, like Maya does.   However, this speech may sound much softer to her, and if there is background noise it would become difficult for her to hear and understand conversational speech.

But here’s what’s really interesting.  Maya’s hearing loss follows a loosely similar pattern to this made-up data, in that her hearing loss is slightly more pronounced at high frequencies.  When we heard that her impairment was more significant at higher pitches, we thought “Well, what’s high pitched?  Dog whistles, microwaves beeping?”  What we didn’t know what that every speech sound has its own frequency.   Check out the letters on the audiogram . . . you can see that the j-m-d sounds are low pitched, p-h-g are in the middle, and f-s-th are high pitched. 

The configuration of this child’s hearing loss would suggest that she's getting the high frequency consonants f,s, th, etc. inconsistently, or missing them entirely.  So, even a child with mild hearing loss can have speech issues, because they just can't hear certain letters.  (That might be an overenthusiatic use of bold/underlining, but it was a big lightbulb moment to me.)  The letters in the 1000-2000 range would probably be inconsistent or unclear as well.  And why is there no data below 1000 Hz?  That’s because the background noise in the operating room makes it impossible to test low frequency sounds.  (And this is why more testing is usually necessary after a sedated ABR, to gather data on the lower frequencies and to check on that whole conduction thing I mentioned before).

So, Back to Maya

We’ve always thought that Maya could hear well, because of her responses (“What does an H say?”  “Hhhhhaa”).  However, our apartment doesn’t have a lot of background noise (like school will) and kids with hearing impairment are apparently highly adaptable and skilled at compensating.   The knowledge that she is hearing impaired is certainly making us re-think the times when she “stops paying attention.”  Did she just decide to suddenly ignore us, or is it that she just couldn’t hear/understand the last set of directions? 

 I’m also rethinking some of her oral-motor issues.   If I say, “Maya, say ‘dada’” and she replies “Baba!” is that because she couldn’t get her mouth organized enough to say “dada” or because she misheard me? 

Who knows.  But you can bet your bottom dollar that I’ll be taking some good before-hearing-aids/after-hearing-aids observations and videos for comparison’s sake.

The Take-Home Message

I’ve done a lot of reflecting on the roles of parents, doctors, and various clinicians in diagnosing hearing loss.  Especially in terms of the advocacy, vigilance, and thoroughness that all of the players have to bring to the table.  If I had to sum it all up in one sentence, I would say this:   “If at first you don’t succeed (in getting clear audiological data), try, try again.”

Also applicable, the good old “When you assume (that your child hears normally because she understands and responds to you most of the time) you make an ass out of u and me."

(Well, not me.  Just you.)

Jokes aside, the big picture thing that I’ve learned is that hearing loss can be very tricky, because young kids are highly adaptable and learn to how to work around their weaknesses.  So, if you have a child with speech delays, do your best to get clear audiological data.

Even if you think that your kid can hear. 

Really!

I almost cancelled the ABR when I realized a few days beforehand that I can stand in the kitchen and say “What does a ‘B’ say?” and Maya can respond from the living room “Ba!”.  I thought, surely, if she can hear that I said B (instead of D or P) from a room away, without seeing my lips move, then her hearing must be fine.   But it’s not.

Make sure that you are working with an ENT that you trust, and explore the possibility of hearing impairment.    Every time our ENT said “Oh, has it been 6 months?  Let’s get her in for the behavioral hearing eval again.” I would roll my eyes and dread the appointment---which typically ended with a breakdown (on Maya’s part) and frustration (at spending our time in another appointment that yielded not much information).   But thank goodness we all stuck with it.