What is Asymmetric Nerve Hearing Loss

Given my last blog article regarding an ENT who got sued for not doing an MRI after audiogram showing an asymmetric hearing loss, the question that should be on everybody's mind is what IS asymmetric nerve hearing loss on a hearing test?

I am sad to report that there is no clear consensus on what is asymmetric nerve hearing loss.

First of all, at its most basic definition, asymmetric nerve hearing loss is when hearing is worse in one ear when compared with the opposite ear due to nerve damage.

Technically, hearing should decrease equally on both sides over time, but when one side gets worse faster than the other, it can cause concern because:

1) A tumor can be pressing against the nerve causing it to slowly fail faster than the other ear's nerve which is not compressed.
2) There is a loud noise history with asymmetric exposure to the ears. One example is hunting with a rifle where the left ear would repetitively get noise-induced damage from the gunshot in a right-handed shooter.
3) Bad luck

The conflict is at what point is an asymmetry considered significant enough to warrant a workup which may include an MRI scan of the head and/or auditory brainstem response (ABR)? Also, for a given patient history, a physician/patient may elect to recheck hearing bi-annually to monitor for asymmetric progression rather than pursue workup immediately (further studies being pursued only if asymmetry progresses over time).

Is asymmetry defined as 1 decibel difference between ears? Is it 50 decibel difference?

Even if the decibel difference is agreed upon, than over what frequencies? All of them or just a few of the frequencies?

So for the purposes of a "medically" significant asymmetric nerve hearing loss, the definition must define not only HOW big the difference in hearing loss is present between ears but also at what frequencies.

In one paper, it is 15 decibels at just 3000 Hz.

In another paper, it is 20 decibels at any two adjoining frequencies (or 15 decibels at two adjoining frequencies between 2000 and 8000 Hz).

Get this... even when criteria is defined, one study found substantial disagreement among five expert judges on what hearing tests they considered showed asymmetry.

Even insurance companies are jumping into the fray in what they considered significant enough to warrant covering the MRI scan. At one point when I ordered an MRI scan of the head for what I thought was a significant asymmetry found in one patient's hearing test, the insurance company denied the test citing "that there needed to be other neurological deficits PLUS the asymmetry seen on hearing test before MRI scan would be authorized".

I personally pursue further workup using the 20 decibel difference at two adjoining frequencies OR 30 decibel at one frequency.

Assuming medically significant asymmetric hearing loss has been defined and is present...

What are the chances of something bad going on (i.e., tumor) when an MRI scan of the head is ordered for asymmetry found on hearing test?

Less than 10% (depending on study, can be as low as 1-4%).

Given such a low positive yield on testing, why even pursue a MRI scan?

Because of defensive medicine to avoid being named in a lawsuit if the affected patient just happens to be within that 10% found to have an acoustic neuroma.

Indeed, in one study, 40% of ENTs stated medico-legal concerns factored into their decision to get an MRI scan of the head.

People DO Suffer Hearing Loss After a Loud Concert

Almost everybody at some point in their lives have attended a loud concert or loud nightclub.

Almost everybody will also recall a temporary reduction in their hearing with or without ringing afterwards for a short period of time.

This phenomenon is called temporary threshold shift (TTS) whereby the affected person has a temporary hearing loss that may last hours to days due to temporary damage of the outer hair cells of the cochlea.

If loud nose exposure happens enough times, permanent hearing loss can occur.

For some, permanent hearing loss may occur after attending numerous loud concerts whereas in other more "susceptible" individuals, it can happen after a single loud concert.

It doesn't even have to be a loud music concert. ANY loud noise exposure can do including shooting guns, listening to a portable music player like the iPod, fireworks, playing in an orchestra/band, etc.

However, loud concerts are of particular interest given how many individuals are exposed all at once and provided a unique research opportunity which was presented on May 21, 2012 at the American Otologic Society Meeting in Los Angeles.

The researchers (led by Dr. Jennifer Derebery of the House Ear Institute) essentially took hearing test before and after the concert of 29 teenagers.

72% suffered objective hearing loss after the concert though only 53% reported subjective hearing loss. 25% reported new onset tinnitus after the concert.

Of note, hearing ear plugs were offered to the study subjects, but only 3 accepted them.

Adult researchers who sat with the teenagers under investigation measured sound levels throughout the concert. During the 26 songs played during the three hour concert, sound levels ranged from 82 to 110 decibels with an average of 98.5 decibels. The mean level was greater than 100 decibels for 10 of the 26 songs.

As a reference, ear pain occurs at 125dB. Jet engine noise is at 140dB. Sustained loud noise exposure of 90-95dB can result in permanent hearing loss.

OSHA (Office of Safety and Health Administration) mandates workers to never be exposed to sound levels of 100dB for more than 2 hours per day (no more than 4 hours per day at 95dB).

Clearly something more needs to be done to protect teenagers' hearing, especially given how few accepted hearing ear plugs. A fundamental cultural shift would most likely have to occur with encouragement from not only the musicians but also parents and teachers...

OR, the music volume at concerts should be turned down... No boos please.


Reference:
Teenagers Hear Worse After Attending Concert. LiveScience 5/21/12

Head MRI and CT Scans Explained!

@ENTHouse brought to my attention a FANTASTIC website that literally identifies and goes through all anatomic structures on every slice of a CT or MRI scan of the head.

Sinus cavities, blood vessels, nerves, bone, suture lines, etc...

Wish I thought of doing it first...

It may be a bit confusing for a layperson, but if you have a copy of your CT/MRI scan and wonder where the maxillary sinus or optic nerve is located on your scan, check this website out and you probably can figure it out!

headneckbrainspine.com

Check it out!