Download ComD 3700 Basic Audiology Lesson 15 Inner Ear Disorders

ComD 3700 Basic Audiology
Lesson 15
Inner Ear Disorders
Highlighted information refers to a change between the audio
recording (using 10th edition) and the 11th edition of the textbook
1. COMD 3700 for Distance Education. This is lesson 15 on inner ear
disorders. This lesson will cover pages 293-321 in Chapter 11 of your
textbook. Again, the textbook is very effective in the teaching of
hearing disorders. You can read from the chapters and gain a great
deal of information. Therefore, there will be more reading for you to
do and less listening for you to do in this lesson. I will briefly review
some of the disorders. But the majority of the information will be
gained from the chapter readings in your text.
2. Because most of you have taken an anatomy and physiology of
hearing course, we will not be discussing details of the anatomy or
development of the inner ear in this course. However, it is
recommended that you to review pages 280-293 to ensure that you
have a good understanding of the anatomy of the inner ear.
3. The inner ear consists of the oval window, round window, the
cochlea and the superior, inferior and horizontal semicircular canals.
4. Conditions that affect the inner ear will result in a sensorineural
hearing loss. SNHL is caused by damage or a disorder of the inner
ear, or of the auditory nerve (nerve fibers) going from the inner ear to
the brain stem. Older terms for SNHL were nerve loss or perceptive
loss. Again, you should be able to recognize this on an audiogram.
5. Inner ear disorders may be organized into three orders or classes.
They are: prenatal, perinatal and postnatal. They don't have to be, but
this is the organization that many texts take and this is the
organization we will pursue. Prenatal refers to something that is
existing or occurring before birth. Perinatal causes of hearing loss are
those that occur during the process of birth itself. Postnatal causes of
hearing loss occur after birth. These can occur at any point in the
lifespan.
As we start this discussion on inner ear disorders, you have to
understand there are a multitude of orders we're not going to address
in this class. In fact, in the graduate curriculum in audiology there
are a number of classes almost entirely dedicated to hearing
disorders. So we're just scratching the surface, trying to give ourselves
the opportunity to be exposed to some of the common disorders and
the types of hearing losses that result. Unfortunately with inner ear
disorders there isn’t any way to “see” what is happening. So these
won’t be very exciting slides. But maybe some of you didn’t like seeing
all the outer and middle ear disorders, so you may be relieved!
6. We will begin by reviewing some of the prenatal causes of hearing
loss. Some prenatal causes are genetically related. There are multiple
genetic disorders. You could spend an entire semester talking about
genetic factors that cause hearing loss. At this time it is enough to say
there are multiple genetic disorders and interactions with multiple
causes and multiple effects. Many times these result in syndromes
with their own characteristics.
Rh incompatibility is a prenatal factor that can cause hearing loss.
This is a factor more prevalent in the past than today because the way
we can deal with and anticipate this. The problem with Rh
incompatibility was the molecule known as the Rh factor was present
in the fetal blood but absent in the maternal blood. This caused the
mother's body to perceive the fetus as a foreign body and tend to
build antibodies against the fetus. Antibodies begin to increase in the
mother until red blood cells in the fetus were damaged prior to
effective treatment for the Rh factor. Each successive pregnancy was
more and more susceptible to the antibodies built up by the mother.
With successive pregnancies, the antibodies became more and more
effective. It's less of a problem today than in the past with maternal
immunizations and fetal blood transfusions. An interesting fact you
might want to know is that the Rh is because the research into the
cause and treatment of this disorder was done with the Rhesus
monkeys and so you have the Rh in Rhesus taken as the factor.
7. Another prenatal cause is acquired immune deficiency syndrome
(AIDS) and the human immunodeficiency virus (HIV) found in those
with AIDS. Mothers with HIV have a 50% chance of delivering a baby
with the disease. HIV can have an affect on the cochlea. Viral
infections are also more likely to occur in a newborn if the mother
suffered from a disease that causes deficiency in her immune system.
A major cause of prenatal sensorineural hearing loss is
cytomegalovirus, also known as CMV. This is a harmless virus that
doesn't affect the mother to a great degree. It belongs to the herpes
group. However, when the fetus is infected, a variety of physical
difficulties can be present including sensorineural hearing loss. The
fetus can be infected with CMV prenatally, perinatally or postnatally.
8. Now we will discuss perinatal causes of hearing loss. A common
cause of damage is anoxia. This is the lack of oxygen during birth for
the fetus. This can result in multiple physical and mental disorders
including sensorineural hearing loss.
Another perinatal cause is toxemia. This is an accumulation of toxic
substances in the maternal blood. The toxic substances begin to
accumulate and cross the placenta and cause damage to the fetus.
Maternal toxic substances in the blood may reduce the passage of
oxygen across the placenta and cause anoxia in the fetus.
Prematurity of the baby is another perinatal cause of hearing loss.
The preterm infant with an immature auditory system is at higher
risk of auditory damage. Environmental noise, hypoxia, fluctuations
in blood pressure, ototoxic drugs and neonatal infections are common
problems in the NICU. The average incidence of hearing loss in the
preterm infant population is 2% to 6%. This is a picture of my son
who was born 2 months premature. In this picture he is 2 weeks old
and weighs about 3.5 pounds. As you can see he was placed in an
incubator. If any of you have been in a Neonatal Intensive Care Unit,
you may have noticed that it is a very noisy environment due to all of
the machines to monitor the infants. In addition to the motor
operating the incubators, there is constant beeping from the
machines. So, prematurity itself can cause hearing loss, but the noise
that premature infants are exposed to can also cause hearing loss. As
you can imagine, as an audiologist, I was very relieved when my son
passed his newborn hearing test. Unfortunately it was one of the last
tests performed prior to leaving the hospital, so I had to wait 1 month
before I found out he had normal hearing.
9. The rest of the disorders that we will discuss all occur postnatal, or
after birth. Some occur in childhood, while others occur in adulthood.
One cause, which occurs most often in childhood, is otitis media.
When we discussed otitis media in the last lesson, I stated that it
caused conductive hearing loss, which it does. However, if left
untreated, the bacteria can travel from the middle ear to the inner ear
and cause a mixed hearing loss. Sometimes it may cause total
deafness, as in the case of bacterial meningitis. Other problems that
occur after the child is born are diseases such as labyrinthitis and
barotrauma. These are problems that can cause different types of
hearing loss. With labyrinthitis, it usually causes a sensorineural
disorder. Barotrauma can cause conductive hearing losses but can
disturb the balance of fluids and pressures in the inner ear and cause
sensorineural hearing loss as well. Ototoxic drugs or agents can be a
problem. The mycin family is particularly suspect in terms of
sensorineural hearing loss. Many of the mycin drugs are known to
cause sensorineural hearing loss. However, not all mycin drugs cause
sensorineural hearing loss. Your physician knows which mycin drugs
will potentially toxic and which will not. So if you have a drug with the
name mycin in the name, don't panic, but I would ask your physician
or pharmacist to be assured that those drugs are not ototoxic. There
are other specific drugs that are ototoxic, such as quinine drugs.
These were mostly used in the past. But it did have ototoxic effects.
Use of aspirin over long periods of time can be ototoxic. Nicotine has
been shown to be ototoxic as well as a variety of other substances. All
of these result in damage to the inner ear, and most always we're
talking the cochlea. It could be other parts of the neural system, but
mostly it's the cochlea.
10. A common postnatal cause of SNHL is noise. Noise exposure can
cause a temporary hearing loss. This is known as a temporary
threshold shift. You may have experienced this after shooting a gun or
attending a concert. Noise exposure can also cause irreversible
hearing losses. This is referred to as a permanent threshold shift. As a
person moves through life, if they're constantly exposed to intense or
loud noises, over a period of time, their pure tone audiogram, the
threshold will show some hearing loss. In the initial stages, the
hearing losses won't be seen the next day. But over time, that
temporary shift in threshold will be seen as a permanent shift and the
audiogram will not recover to normal. Noise induced hearing loss
usually comes through long periods of exposure to intense sound.
Noise induced hearing loss affects males more than females. This is
not as true as it used to be. When males were out in the industrial
world, they had more exposure to loud noises, so it would affect males
more than females. With females more and more in the workplace,
the difference between males and females has lessened somewhat. In
addition, we are now seeing an increase in noise induced hearing loss
in teenagers. A recent national study found that a stunning number of
teens have lost a little bit of their hearing — nearly one in five — and
the problem has increased substantially in recent years. This is very
likely due to listening to loud music through the ear buds of digital
music players (IPod, mp3 players). Some young people turn their
digital players up to levels that would exceed federal workplace
exposure limits. In the next slide I’ll review the safe amount of time to
listen to your IPod. In another study of about 200 New York college
students, more than half listened to music at 85 decibels or louder.
That's about as loud as a hair dryer or a vacuum cleaner. With this
type of hearing loss symptoms include: SNHL, tinnitus (ringing in the
ears) and difficulty discriminating or understanding speech. Often
times audiometric testing will reveal an increased hearing loss at
4000 Hz. This is known as a “noise notch”. This has to do with the
location of the 4000 Hz region of the basilar membrane and the way
the noise reacts in the cochlea. There is no treatment for noise
induced hearing loss other than ear protection and avoiding loud
noises. Once you have had years of being exposed to loud noises, you
go through a permanent hearing threshold shift and you have then
have a permanent hearing loss.
Industrial audiologists work with companies to protect employees
from intense noises. They can test the environment for the amount of
noise present. This informs the employer, and they should require the
employees to protect themselves from noise induced hearing loss.
11. As I mentioned, this is a table created based on research by Figor
and Portnuff in 2006. This is a guide to the maximum iPod listening
time per day. To be safe, no one should listen to the volume at louder
than 50% of the possible volume. IPod’s have a volume control setting
that can set the volume limit. Set the volume limit on your iPod to
50% in order to avoid hearing loss, regardless of how long you listen
to it every day.
12. OSHA, the Occupation Safety and Health Administration, has
recommended guidelines indicating how long an individual can be
exposed to a certain level of noise. The maximum exposure is 85 dB of
environmental noise, or noise in the work environment over an 8
hour day. As the level of noise increases, the amount of time that the
employee can work in the environment decreases. So if the level of
noise is 90 dB, they can only work in that environment for 4 hours.
Every time the sound level increases 5 dB the time they can spend in
the environment is cut in half. There are fines imposed on employers
who allow their workers to remain in a loud environment longer than
the guidelines allow. But there are no regulations to force people to
limit their noise exposure during recreational activities. So many
individuals with hobbies that involve motorboats, motorbikes,
racecars, shooting guns, or music may also experience NIHL.
13. A cause of sudden unilateral (one ear) hearing loss is Meniere's
disease. It is sometimes called endolymphatic hydrops because
there's an excess of endolymph fluid. So you get abnormal pressure in
the endolymphatic system. As pressure builds up in the cochlear duct,
hair cells become affected. Hair cells begin to die, and they are
damaged. This causes noise in the ear (tinnitus) and hearing loss.
Also the vestibular mechanics will become involved. I’m referring to
the vestibules and the semicircular canals. This causes vertigo
(dizziness). This is a disorder of the entire inner ear, not just the
cochlea. So, the infamous triad to identify Meniere’s disease is
vertigo, fluctuating sensorineural hearing loss and a roaring tinnitus.
In most patients with regular SNHL you will not see fluctuations. We
see sensorineural hearing loss, but it usually gradually gets worse and
it is not fluctuating. If this occurs where the hearing may improve for
a few days or weeks and then get worse and then suddenly drop or
improve again, this is associated with this Meniere's disease. Also, the
tinnitus with Meniere’s disease is not a high-pitched ringing type but
more a low-pitched roaring. This disease is named after Prosper
Meniere, a French physician, who lived between 1799 and 1862. He
called this disease a labyrinthine storm. I like this term a lot. It is kind
of like a storm but then you add lightning and rain. Here, you have
vertigo and fluctuating sensorineural hearing loss and tinnitus. It's a
lot like a storm in the inner ear.
14. With Meniere's disease, the onset of symptoms are described as:
fullness in the ear--but not like wax in the ear canal. There is the
sensation of fullness, but it's caused in the cochlea; low frequency
roaring tinnitus; hearing loss, great difficulty in speech
discrimination--this is one of the great difficulties and violent vertigo.
In half of the cases the onset of Meniere's is between 40-60 years of
age. Meniere’s is characterized by attacks followed by periods of
remission. So during a Meniere’s attack a patient will have roaring,
dizziness, hearing loss. It can really affect them and they may have to
take it easy for a while. Then after a period of hours, days, weeks, it
subsides. They will have a period of remission that varies from days to
weeks to years.
15. The diagnosis for Meniere’s is made by the combination of
symptoms. As I mentioned, the patient will have a fluctuating
unilateral sensorineural hearing loss. That's a unique condition. It's
rare to have a flat, fluctuating, unilateral and sensorineural hearing
loss. Usually hearing loss in sensorineural hearing loss is not flat, it's
worse in the higher frequencies. One really distinguishing factor I've
seen in my career is not only is the sensorineural hearing loss flat, but
it seems more severe in the low frequencies than the mid or high
frequencies. That's just the opposite of most other sensorineural
hearing losses. The roaring tinnitus rather than the high pitches or
clicking that others report is also rare. So if you have hearing loss and
a dizzy patient at the same time, you're putting together a good
argument for Meniere's disease. This is true especially if they have
excessively poor speech discrimination. After testing, you look at the
discrimination scores on the audiogram. For example, if you have a
mild to moderate hearing loss, but the speech discrimination is 4050%. This is out of proportion with the hearing loss. So, along with
the other symptoms you would begin to suspect Meniere’s disease.
The treatment for this disease include diuretics. This is used as an
attempt to lower the body fluids. One of the successful treatments for
a person with moderate to severe Meniere's disease is shunting. The
physician will enter the endolymphatic duct and put a small tube or
shunt in there and take it to a part of the anatomy where the fluid can
be absorbed. It has a little valve there, a valving mechanism. When
the fluid builds up, it's shunted off the endolymphatic network and
provides some relief. It may be recommended that they surgically
getting rid of the labyrinth. It's a radical procedure. If the other
treatments don't work and the patient is inflicted with terrible
tinnitus that is so annoying the person can't sleep or function, an
attempt might be made to sever the eighth nerve or destroy the
labyrinth. Of course the person ends up with a profound hearing loss.
This is a radical case and not done on a routine basis.
16. Presbycusis is the most common cause of hearing loss. This is
hearing loss resulting from, or associated with, increasing age. It's
usually due to the effect of infections, toxins and trauma throughout a
person's lifetime. It usually progresses gradually due to changes in
cell function, in the structure of cells, and the number of cells. All of
this adds up to a progressive sensorineural hearing loss. This is an
example of a typical audiogram you would expect to see due to
presbycusis. The patient will hear better in the low frequencies and
then gradually drop to a moderate to severe HL in the higher
frequencies.
17. The aging process affects auditory areas other than the cochlea.
The tympanic membrane, ossicular chain, cochlear windows, and the
central auditory nervous system or higher auditory pathways are all
affected by aging.
Schuknecht in 1993 proposed four different categories for
presbycusis. Number one, he talked about sensory presbycusis. This
is focusing on the cochlea, on the hair cells, the sensory organs of
hearing. As we get older, the hair cells and sensory organs become
less sensitive in the hearing process. Then he talks about neural
presbycusis. This is focused on the eighth nerve, the nerve pathway
through the brainstem and on up into the cortex. As we get older, the
neural system is less affective in passing on information. This applies
to the hearing network also. Then he talks about strial presbycusis.
The stria vascularis provides nutrients to different structures within
the cochlea and within the inner ear system. Therefore, as we get
older, there are fewer nutrients produced. The structures aren't as
nourished and don't function as well. The last is cochlear conductive.
Usually when we say conductive, our minds go to our middle ear.
We're talking here about the movement of the structures in the
cochlea, the movement of the basilar and Reissner’s membranes.
Those structures, their mechanics are slowed through aging. They
don't move as effectively as when we're younger. These four
conditions contribute to presbycusis. They are all different, but
overlapping causes.
18. So, just to review the characteristics of presbycusis, the person
usually has a bilateral sensorineural hearing loss. Both ears age at the
same time usually. There's an absence of auditory recruitment in pure
presbycusis. There is also a gradual progress in bilateral sensory
neural hearing loss. It gets worse and worse over time. Most patients
with a SNHL find that a properly fit hearing instrument is their
principal or sole means to improve hearing. Often, speech reading
(lip-reading) and auditory training combine visual and auditory clues
for a more successful fitting. This slide shows the various types of
amplification. Hopefully you can see how they look in the ear as well
as outside of the ear. Hearing instruments all have digital circuitry
and many include additional features such as dual microphones and
Bluetooth capabilities to help the patient in certain situations.
19. Here is a chart that is located in your textbook. Although we did
not cover all of these causes of hearing loss, you should be familiar
with them. You will need to be able to identify the age of onset as well
as identifying information regarding the disorder.
20. In conclusion, I just want to say thank you for enduring to the end
of this course. I know for many of you that are studying to become a
SLP, this may not have been the most exciting course. Hopefully
those of you who are interested in audiology haven’t changed your
mind! This course can be difficult because it covers so many topics
that are new and foreign to most of you. But I promise that once you
are involved in audiology more and are able to work with patients, in
becomes so much more exciting. Audiology is an evolving and
growing profession that I hope some of you will consider. I know I’m
glad I did! Thank you again for being a part of this course and I wish
you the best in your future education.