ABR: An Illustration of Auditory

Dysfunction through Clinical Cases,

Presented in Partnership with Rush
University
Amy K. Winston, AuD, Robin B. Stoner, AuD
November 18, 2013

Amy Winston: Today, Dr. Stoner and I will highlight some auditory brainstem
response (ABR) cases that we have seen here at Rush. We have a diverse
patient population and we see both classic and complex cases. Through an
illustration of a few cases, we hope to reinforce what we know and understand
about the auditory pathway and ABR testing. Our learning objectives today are
to discuss the characteristics of a normal click-evoked ABR relative to the
waveform neural generator sites, to discuss how observed changes in the click-
evoked ABR waveform can assist in characterizing the nature and degree of
identified hearing loss, and finally, to explain the effects of disruptions at
specific points along the auditory pathway on the ABR waveform.

Before we begin to discuss cases, we wanted to review what the ABR is, what it
is not, the neural generators sites, and the standard waveform characteristics.
Since its inception in the late 1960s, the ABR has been an invaluable diagnostic
tool for audiologists. As an objective test, it allows us to gain information about
the integrity of the auditory system, and provides an estimation of hearing
sensitivity for patients who are unable to give us reliable subjective
information. This would include infants and young children, but also difficult-to-
test older children and even some adults. We should all be clear that ABR is not
a direct test of hearing; it is a test of synchronous neural function. However, it
can be used to estimate hearing sensitivity, which is how we will be talking
about it today.

Click Stimulus
There are different stimuli that we can use with the ABR, the most basic being
the broadband click stimulus. The click is not frequency specific. It is thought
to be generated in the cochlea in the 2000 to 4000 Hz range. We also can use

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frequency-specific tone bursts, most commonly 500, 1000, 2000, and 4000 Hz
stimuli. These are very brief stimuli that trigger a rapid, synchronous neural
onset. The click tends to be a little more efficient than the tone burst stimuli,
simply because of its construction. The tone burst can give us a good response,
but we get a classic waveform morphology with the click stimulus.

As we go through the presentation, Dr. Stoner and I will be focusing on

responses to click stimuli; we did that for a few reasons. The first reason is
because of the classic ABR response we can elicit. In addition, there are an
abundance of normative data that have been developed using the click. Finally,
the majority of cases we will present today were started as follow-up testing to
newborn hearing screenings. The automated ABR systems use a click stimulus
in their protocol, so we will typically begin our testing with a click stimulus as
well, and then proceed with tone burst stimuli as needed from there.
Fortunately for us, all of these stimuli can be conducted both by air and by bone
conduction to allow for a full investigation of the auditory system.

There are five primary ABR waveform components, waves I through V. We have
been able to establish the neural generator sites for these specific wave
components. Wave I is generated from the distal portion of cranial nerve VIII
where it exits the cochlea. When looking at the waveform, we are then able to
follow the pathway up through the lower brainstem. Through replicated
research studies, we have a good understanding of when these waveforms
should occur post-stimulus onset, known as absolute wave latencies. We also
have a good understanding of when these waves should occur relative to one
another, known as interwave latencies. Understanding the neural generator
sites, latencies and interwave latencies provides a good benchmark against
which to measure change, which is what we will be doing today.

Neural Generators
As I mentioned, wave I is initiated at the peripheral or distal portion of cranial
nerve VIII; it should occur at approximately 1.5 msec for a click. As we move
along cranial nerve VIII, wave II is thought to originate from the more proximal
portion of that nerve at about 2.5 msec. Wave III is generated at the level of the
cochlear nucleus and should occur at approximately 3.5 msec. Wave IV is
generated in the region of the superior olivary complex/lateral lemniscus at 4.5
msec. Finally, wave V is generated in the region of the lateral lemniscus/inferior
colliculus around 5.5 msec.

Robin Stoner: When we are conducting the ABR, we are looking for predictable
changes in the waveform in response to changes in the auditory stimulus, which
may include intensity or polarity. This will provide diagnostically significant
information about the presence and type of hearing loss. Some of the waveform
characteristics may include the presence or absence of wave V using air- or

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bone-conducted stimuli, latency measures or changes in the waveform in
response to polarity changes, as well as the waveform morphology and the
amplitude.

As stated earlier, the ABR is not a true test of hearing, but it can help to
estimate the degree of hearing loss by finding the lowest intensity level where
wave V is present and replicable. Latency information and results from bone-
conducted stimuli can help to provide insight to the nature of the hearing loss.
Finally, auditory neuropathy spectrum disorder can be confirmed or ruled out by
looking at the polarity effects on the waveform.

Case Studies
The cases that we present today show expected ABR findings with both normal
and abnormal auditory function at various anatomical points along the auditory
pathway. They illustrate how outer, middle, and inner ear dysfunction as well as
auditory neuropathy and brainstem dysfunction influence the characteristics of
the click-evoked ABR.

Case #1: Normal Auditory Function

This first patient was a three-year-old male who was first seen in our outpatient
clinic for an audiological evaluation. During the case history, his parents stated
that their son only responded to certain sounds and had a limited expressive
vocabulary. Their primary concern was for his speech and language
development. In addition, they mentioned that a psychological evaluation
completed one month prior indicated that the patient may have a mild degree of
autism. His parents reported that the pregnancy and birth histories were
essentially normal. His mother said that she had a C-section because his heart
rate dropped, but there were no other complications. In addition, his parents
denied a history of ear infections and there was no family history of hearing loss.

The audiological evaluation was completed with two testers and limited results
were obtained. We completed behavioral audiometry using visual reinforcement
audiometry (VRA); the patient was not developmentally appropriate for
conditioned play audiometry even though he was three years old. We obtained a
minimal response level at 30 dB at 2000 Hz in the sound field, and a speech
awareness threshold (SAT) was obtained at 0 dB. These two values were not in
good agreement and were not what we would expect for a three-year-old.
Tympanometry was also completed and the results were normal. The patient
did not tolerate otoacoustic emissions (OAE) testing. Based on all of this and
his history, a sedated ABR was scheduled.

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Our first item of business was to run a high-intensity, air-conducted click
stimulus and then change the polarity. A robust waveform was noted, and no
inversion of the waveform was observed when the polarity was changed. At the
high intensity level, the absolute and interwave latencies were within normal
limits. A reproducible Wave V was noted down to 20 dB nHL in both ears. The
waveforms are shown in Figure 1.

Figure 1. Case #1 ABR results.

At 80 dB nHL, we see nice waves I, III, and V. They are at the expected
latencies. We also see at 80 dB that we used a rarefaction click and a
condensation click. When we changed the polarity, our waveform was still
intact. There was no inversion of the waveform. In addition, we see a well-
formed wave V at 20 dB. Finally, the 0 dB run shows no identifiable waveforms,
which is what we would expect. Furthermore, it confirms that the 20 dB run and
the 80 dB run were true responses.

Case #1 Discussion
Let’s discuss these findings. We have ruled out auditory neuropathy spectrum
disorder because the waveform did not invert when the polarity was changed,
and auditory function to the level of the brainstem is normal as noted by the
normal latency values and the fact that wave V was intact at 20 dB nHL. We

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know this this to be true for at least a portion of the frequency range of the click
stimulus. Keep in mind that the click stimulus is between 2000 and 4000 Hz.

The click was just our starting point. We wanted to know more about this
patient’s hearing, so tone burst testing was completed. We used 500, 1000,
2000, and 4000 Hz tone burst stimuli and the results using these stimuli were
also normal. Our overall interpretation was a normal ABR study.

The latency-intensity data for this ABR are shown in Figure 2. We would expect
to see normal absolute latencies for waves I, III, and V as well as normal
interwave latencies. Wave V latency was noted in the normal range, which is
the gray shaded area, for 80, 60, 40, and 20 dB nHL (Figure 2, top). The other
latency-intensity functions shown are the I-V interwave latency, as well as wave
I and wave III absolute latencies. We know that it is normal for waves I and III
to disappear as we decrease intensity.

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Figure 2. Normative data for Case #1, from top to bottom: wave V latency, wave
I latency, wave III latency, wave I-V interwave latency.

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Now that you know what normal auditory function looks like, let’s look at a few
cases of auditory dysfunction, starting with a case of conductive hearing loss.

Case #2: Conductive Hearing Loss

Amy Winston: This next case is of a three-week-old female. She was seen for
an unsedated ABR after failing her newborn hearing screening bilaterally. We
know that she was born at 36 weeks and that mom’s health was compromised
during pregnancy by prenatal diabetes. Medical history for the patient was
significant for a number of things including bilateral microtia, and left external
auditory canal atresia and stenosis of the right external auditory canal. So upon
visual inspection, we already know that she has certain issues that will
contribute to a conductive hearing loss. This patient did have a CT scan prior to
arriving at our clinic, which confirmed that there was no left external auditory
canal. It also showed other unexpected findings that were very helpful to us
during our testing. Ossicular chain malformation was noted in both ears, and it
appeared that the malleus and the incus were fused on both sides. This
presented additional concerns for obvious reasons, and led us to a continued
hypothesis for conductive hearing loss in both ears.

Before we started the ABR, we completed tympanometry using a 1000 Hz probe

due to her age, as well as OAEs. The results for tympanometry were grossly
abnormal for the right ear and we were unable to test the left ear due to the
aural atresia. Distortion-product (DP)OAEs were absent in the right ear and
could not be tested in the left ear. This is what we anticipated for the right
ear. Based on the CT findings of ossicular chain malformation, the patient’s
abnormal tympanometry and absent OAE results were expected.

We started the ABR testing in the right ear. The patient did have a stenotic ear
canal, but it was open. We began with an air-conduction rarefaction click and
found that waves I, III, and V were present at our starting intensity of 80 dB
nHL. Following protocol, we changed the stimulus polarity to condensation.
We did not see an inversion of the high-intensity waveform, ruling out auditory
neuropathy spectrum disorder. We did note that the absolute latencies of
waves I, III, and V were prolonged at this high intensity, meaning that the timing
at which each waveform component was present was later than normal. The
interwave latencies, however, were retained, and fell within normal limits.
Wave V remained intact and replicable down to 70 dB nHL with the click
stimulus. We proceeded to test with a 500 Hz tone burst stimulus and found
that wave V was intact and replicable down to 60 dB nHL.

Figure 3 shows the right air conduction click results. It looks as if she has a
bifurcated wave I at 80 dB nHL. Absolute latencies are pushed out, but the
relative interwave latencies were retained within normal limits. Wave V was

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replicable at 70 dB nHL but disappeared at 60 dB nHL. Choosing this as wave V
threshold was relatively easy in this case.

Figure 3. Case #2 right-ear click ABR results.

We know about the right ear, but what about the left ear? Our goal is always to
get ear-specific information. Remember that the left ear has no external
auditory canal, so testing under insert earphones is not feasible. We moved on
to perform unmasked bone conduction testing with the oscillator behind the left
ear. We started with a click stimulus, and found that wave V was present and
replicable down to 30 dB nHL (Figure 4), which is considered to be within normal
limits in our clinic. Bone conduction testing with a 500 Hz tone burst stimulus
showed wave V present and replicable down to 25 dB nHL, which is considered
normal as well.

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Figure 4. Case #2 left-ear unmasked bone conduction ABR results using a click
stimulus.

The left ear was unmasked, but let me clarify how we know this was a left-ear
response. The bones of the skull in young children have not completely ossified,
and there are additional cartilaginous components within the skull. Because
the fontanels have not closed at this age, that alters the normal interaural
attenuation for bone conduction; it increases it. Research indicates that
unmasked bone conduction testing on a child this age can be done. You can get
ear-specific information if you look for certain characteristics of the waveform.
Most notably, we are looking for wave latencies that are within normal limits.
We found that to be true in this case, which supported our belief that we were
looking a response from the left ear, even though it was an unmasked bone
conduction response.

Another component that I wanted to note on the bone conduction waveform

(Figure 4) is the robust wave I on the high-intensity run, although it is not
marked. This lends further support that this is a left-ear response. If it were a
response from the contralateral ear, we would be less likely to have such a
robust wave I. Bone conduction responses were present and replicable down to
30 dB nHL, which is, again, within normal limits for our clinic.

Case #2 Discussion

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Let’s discuss what we know, starting with the right ear. We found prolonged
absolute wave latencies, but interwave latencies within normal limits. These
two components are indicative of a conductive hearing loss. Remember that we
found the click response down to 70 dB nHL and the 500 Hz tone burst stimulus
down to 60 dB nHL. We can estimate that there is at least a moderate hearing
loss across those test frequencies. It is most likely conductive, based on what
we see in the characteristics of the ABR waveform response and what we know
about the patient history as well.

In normal hearing individuals, we see the latency of wave V shift out later as the
stimulus intensity is decreased; that is essentially what is happening with a
conductive hearing loss, just at higher intensities than would be expected. The
beauty of the middle ear system is that it gives us a natural boost in intensity of
about 60 dB to help overcome the impedance mismatch that occurs as sound
waves are traveling quickly and efficiently through the air to the fluid-filled
cochlea, which is not an acoustic-friendly environment. The middle ear
structures provide a boost in intensity to transfer sound from air to fluid. When
we have a middle ear dysfunction, in this case, ossicular chain fusion, it reduces
the efficiency of the middle ear transfer function. It reduces the intensity of the
stimulus that ultimately reaches the cochlea. Seeing those latencies shifted
with a conductive hearing loss makes perfect sense and is exactly what we
would anticipate seeing.

In the left ear, because of the characteristics of the unmasked bone conduction
response, we do believe that we are seeing normal cochlear function across 500
Hz and some portion of the 2000 to 4000 Hz range. Knowing that this patient
has an absent external auditory canal and ossicular chain malformation, we
would anticipate a maximum conductive hearing loss in the left ear. Having a
normal cochlear reserve would allow her to take advantage of bone-conducted
stimuli. She was ultimately fit with a bone-anchored hearing aid (Baha) soft-
band device at an outside facility. Moving forward, the goal is to try to obtain as
much diagnostic auditory information as possible from the right cochlea.

To summarize, characteristic ABR findings for conductive hearing loss include

prolonged absolute latencies. You can see a classic pattern on the normative
data graph where all the responses for absolute wave latencies are shifted
above the shaded area (Figure 5, top). You will also see interwave latencies
within normal limits (Figure 5, bottom). Your bone conduction results should
also be within normal limits, which would reflect a normal cochlear reserve.
The degree of loss would clearly be reflected by the air conduction wave V
threshold, which we would anticipate would be elevated.

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Figure 5. Case #2 latency-intensity function (top) and interwave latency data for
the right ear (bottom).

Case #3: Sensory Hearing Loss

Robin Stoner: Our next patient was a nine-month-old female who failed the
newborn hearing screening and was referred to us from an outside facility. Her
mother accompanied her to the appointment and stated that she felt the patient
could hear and was babbling. The mother did not have any concern about the
child’s overall development, and we think that is part of the reason that it took
so long for this family to follow up. In addition, her mother reported an
unremarkable full-term pregnancy, and there were no complications associated
with the patient’s birth. A family history of hearing loss was denied, as was a
patient history of ear infections. There were essentially no risk factors for
hearing loss identified from the case history. It is our clinic’s policy to perform
an audiological evaluation with two testers in our outpatient clinic before
proceeding to the sedated ABR.

During this patient’s audiological evaluation, we were able to obtain an SAT in

both ears using insert earphones. The SAT was 30 dBHL for the right ear and 50
dBHL for the left ear; we would expect to see an SAT around 10 to 15 dB for a
nine-month-old. We attempted tonal stimuli but could not obtain any responses
due to patient fatigue. We were able to complete tympanometry and acoustic
reflex screening using a 1000 Hz ipsilateral stimulus; the reflex was intact in
both ears. We tried OAEs, but the patient was too noisy. Based on these

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results and the patient’s history, we decided to proceed with the sedated ABR.
We obtained responses for both ears, but I am going to concentrate mostly on
the findings from the right ear.

Once again, we started with a high-intensity, air-conducted click stimulus, and

we changed the polarity from rarefaction to condensation. A beautiful
waveform was noted at 80 dB nHL (Figure 6). There was no inversion when the
polarity was changed. Returning back to the rarefaction click stimulus, we
were able to track wave V down to 50 dB nHL; no response was observed below
that. We found normal absolute and interwave latencies using the high-intensity
click stimulus. The wave V latency was slightly prolonged as the intensity
decreased. No response was noted at the output limits (55 dB nHL) of the bone
conduction oscillator.

Figure 6. Case #3 right-ear ABR results.

Case #3 Discussion
The presence of a normal waveform at a high-intensity is consistent with the
cochlear site of lesion, and it reflects that the dysfunction within the auditory
pathway is peripheral to the generator sites of the ABR waveform. In this case,
air and bone conduction ABR results were consistent with a moderate sensory

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hearing loss for a portion of the frequency range of the click stimulus. In
addition, tone burst stimuli were utilized to estimate frequency-specific
thresholds and define the configuration of the hearing loss. The results
indicated a mild sloping to moderate sensory hearing loss. Remember that the
ABR is not a true test of hearing, but an objective measure of auditory function.

The sensory nature of this hearing loss is supported by normal absolute wave
and interwave latencies at a high intensity, an elevated wave V threshold, and
the absence of a response to the bone-conducted stimulus. This patient was
ultimately fit with binaural amplification at an outside facility. Since a hearing
loss was identified through the sedated ABR, we recommended audiologic
monitoring for this patient. Our goal now is to obtain ear- and frequency-
specific threshold information for both ears using behavioral test measures,
recognizing that it may take a few appointments to get a complete picture of her
true thresholds. She did return to the clinic two months after our sedated ABR,
and VRA was performed using insert earphones. The results at that time were
consistent with the ABR results.

In summary, sensory hearing loss is characterized by wave I falling outside the

normal latency-intensity function. Wave V latency is normal at higher
intensities, but as the intensity is decreased, it will be prolonged, showing an L-
shaped latency-intensity function (Figure 7). The interwave latencies are either
normal or shortened. When we are looking at degree of hearing loss, we are
looking at where wave V threshold falls. With sensory losses that threshold
would be elevated.

Figure 7. Latency-intensity function for sensory hearing loss.

Case #4: Auditory Neuropathy Spectrum Disorder

Amy Winston: I want to highlight an interesting case of auditory neuropathy.
There is still some debate about precisely where the site of lesion is for auditory
neuropathy, and we will discuss that as well.

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This patient was a three-month-old female when we saw her at Rush for an
unsedated ABR. She had some unfortunate social and family dynamics going on
at the time. She was brought in by her maternal grandmother, who was unable
to give us any information about the baby’s mother, who was her daughter.
There was no pregnancy history or information about the mother’s health. The
grandmother was also unable to give us any information about this baby’s father,
so we did not have a lot of background information. Thankfully, we did have
paperwork that the grandmother had brought with her from Cook County
Hospital, which is next door to us, indicating that the baby was being followed
there by a high-risk team, so we could obtain some information from the
physicians there.

We know that she failed her automated ABR newborn hearing screen bilaterally
at Cook County Hospital. Furthermore, reports indicated that the baby’s history
was significant for a G6PD deficiency. I had not heard of that before, but
through some research, I discovered that G6PD is an X-linked enzyme deficiency,
specific in the glucose 6 enzyme– phosphate dehydrogenase. Because this is an
X-linked deficiency, it occurs primarily in males, and it will be most significant in
its presentation in males; however, it can occur in females. Generally the
presentation is mild. There are rare instances, though, where additional
mutations occur and allow this deficiency to present in a more robust form. As
you will see as we go forward in this case, it may be that our patient,
unfortunately, fell into this small category of females.

G6PD deficiency causes red blood cells to break down prematurely, which
results in anemia, which can be particularly severe in newborns. Secondarily,
these patients will then develop jaundice, which we know is a red flag for
hearing loss. As the red blood cells break down, bilirubin is developed as a by-
product. With the ongoing breakdown of red blood cells, increasingly high levels
of bilirubin begin to build up in the blood. When the bilirubin levels are
extremely high, the bilirubin is able to cross the blood-brain barrier and go into
the brain tissues. The concern is that there may be additional damage within
the brain, leading to a condition called kernicterus. Kernicterus includes brain
damage, specifically to the brainstem nuclei and the cerebellum.

The auditory pathway encompasses many brainstem structures and the

cerebellum as well. The cerebellum is also a critical component in integrating
inputs to our balance system. We certainly would not be surprised to see
hearing loss and balance problems in patients with cerebellar and brainstem
damage.

When the bilirubin gets extremely high, the physician’s concern is to bring the
levels back down as quickly as possible. This is typically achieved by an
exchange transfusion, because that is the fastest way to clean the blood. On
our pediatric intake form, we specifically ask, not only about jaundice, but about

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exchange transfusions. This gives us an indication of the level of the bilirubin
that might have been present. In the notes that the grandmother brought, the
physician did indicate that our patient had hyperbilirubinemia to such an extent
that she did require an exchange transfusion.

Before we started the ABR, we did our initial testing, tympanometry and OAE
testing. Tympanometry with a 1000 Hz probe was normal bilaterally. We found
that DPOAEs were absent in both ears across the test frequencies. With the
concern of the hyperbilirubinemia and the exchange transfusion, now we were
seeing an indication that there was likely some outer hair cell dysfunction.
There was great concern going forward as we started the ABR.

In our traditional form, we began the ABR with a high-intensity, rarefaction click
stimulus. Per our protocol, the second run was changed to a condensation
click stimulus. When I did that, it showed a complete inversion of the
waveform. I now had a great concern that this was auditory neuropathy. I did
proceed at that point with an alternating click stimulus, which eliminated the
waveform entirely.

The waveforms for both ears for this patient are shown in Figure 8. You can see
how we separated the rarefaction click and the condensation click. Below
those waveforms is the alternating click recording, followed by a 0 dB recording,
which looks much like the alternating click run. You can see that the
rarefaction and condensation runs are essentially a mirror image of each other.

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Figure 8. Case #4 waveforms for right and left ear using rarefaction,
condensation and alternating click stimuli.

With a normal ABR, we would expect to see a cochlear microphonic prior to

wave I. We know the cochlear microphonic is generated within the cochlea, and
it will also respond to a change in stimulus polarity. We anticipate the pre-
neural cochlear microphonic to invert from rarefaction to condensation click in
any patient, but the rest of the waveform should remain intact. You might see a
slight latency shift, but you certainly should not see the inversion that we see in
this case (Figure 8). Given that the entire waveform inverted, it indicates that
this response is coming from the cochlea and does not reflect any kind of neural
response. Given this finding, we now have to recognize that we cannot get any
information about the integrity of the auditory pathway. Furthermore, it
eliminates our need pursue any decrease in intensity to see what we might find,
because we are not getting a response from the auditory system beyond the
cochlea.

Case #4 Discussion
The classic ABR finding for auditory neuropathy is the inversion of the ABR
waveform in response to a change in stimulus polarity. The site of lesion for
auditory neuropathy spectrum disorder is not definitively known. At present,

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there are two schools of thought. One theory suggests that the issue is
presynaptic, and the other suggests that it is postsynaptic.

Presynaptic problems would occur at level of the inner hair cell, specifically as
an abnormality of the inner hair cell or disruption between the connection
between the inner hair cell and the overlying tectorial membrane. It also might
be the result of difficulties in the synapse between the inner hair cell and a
dendrite of the afferent nerve fiber. All of these problems are going to occur
before this becomes a neural response, hence, “presynaptic.”

Postsynaptic issues would include abnormalities of cells on the afferent nerve

fibers, which would include dendrites, axons in the afferent nerve fiber, or even
the loss of myelin surrounding the nerve fiber, which would certainly disrupt the
transmission of the message along the auditory pathway.

In trying to isolate the cause of auditory neuropathy as presynaptic or

postsynaptic, some of the literature looks at how well some of these children
function when they receiver a cochlear implant. Children with auditory
neuropathy, in large part, do not respond well to traditional amplification. In
certain cases, some children respond more appropriately with a cochlear
implant. So why do some children with auditory neuropathy thrive with a
cochlear implant and others do not? The thought there is that perhaps those
who do very well have a presynaptic issue, which then would not prevent them
from taking full advantage of the cochlear implant. The group that does not do
quite as well may suffer from a postsynaptic lesion. These are interesting
thoughts and points that you might want to look at if you are interested in
auditory neuropathy.

Going back to our patient, hyperbilirubinemia is certainly a risk factor for hearing
loss, but it is a major risk factor for auditory neuropathy, specifically. Our
patient was a little bit different than the classic case of auditory neuropathy
because her OAEs were absent. For the majority of cases involving auditory
neuropathy, the literature suggests that OAEs are most often present,
particularly when children are very young. The fact that we did not have
DPOAEs in this case suggests that there was likely outer hair cell dysfunction
and possibly a sensory loss in addition to the auditory neuropathy. I mentioned
that our patient underwent an exchange transfusion, so there is a concern of
kernicterus and the accompanying brain damage that could possibly occur. The
high-risk team involved in this patient’s care had not yet completed all their
evaluations, but concern was expressed about some possible brain damage.

There were some different thoughts when it came to recommendations and a

future treatment plan. One recommendation was to proceed with the rest of her
comprehensive evaluations, and in the future, we could consider cochlear

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implantation. Some literature suggests that patients who develop auditory
neuropathy secondary to hyperbilirubinemia will recover some neural function.
In these instances, an ABR at a later date will show recovery and look like a
normal ABR waveform. Obviously the global issue we face is the timing of
implantation – is it urgent or do we watch and wait? There is a bit of a tug of war
at times with some of these patients. We would recommend, and we did
recommend, additional ABR testing going forward. We do not assume from the
first test that auditory neuropathy will be permanent. We want to evaluate her
in another six to twelve months and repeat the ABR.

Case #5: Brainstem Dysfunction

Robin Stoner: This is a case of brainstem dysfunction in a two-month-old
female. She arrived to our outpatient clinic via medical transport from her long-
term care facility. She was accompanied by her nurse and respiratory
therapist. We generally do not see medically involved cases at such a young
age in our outpatient clinic, which caught my attention. Her mother was not at
the appointment, but from the electronic medical record and the physician’s
referral, we knew that the patient did not pass the newborn hearing screening,
which was the reason for the appointment. We also knew that she was born at
38 weeks with a normal birth weight. The patient’s mother was under the care
of a high-risk fetal neonatal center as well. Her medical history was quite
involved and included myelomeningocele, Chiari II malformation, perinatal
intraventricular hemorrhage, ventriculoperitoneal (VP) shunt, gastrostomy tube
(G-tube) and central apnea. An MRI of the brain was completed during her stay
in the neonatal intensive care unit (NICU) at Rush. It revealed no recognizable
fourth ventricle, although it appeared to show a remnant of the upper cervical
cord. A physician’s note also indicated that the cerebellar tissue was herniated
into the upper cervical spinal canal, and the cerebellar tissue appeared to wrap
around the medulla and the upper cervical cord. In addition, the patient had
central apnea, which required long-term ventilation and tracheostomy.

Using an air-conducted click stimulus at a high intensity, we observed a clearly

identifiable wave I. There was no inversion of wave I when the stimulus polarity
was changed. The absolute latency of wave I was within normal limits at all of
the tested intensities. Wave I remained intact down to 20 dB nHL for both
ears. However, waves II through V were completely absent at all intensities for
both ears. Waveforms are shown in Figure 9.

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Figure 9. Case #5 right-ear ABR results.

Right away, we can see a very robust wave I at all intensities, with no inversion
present at 80 dB nHL. We can also see that there is nothing identifiable after
wave I. I wanted to do a 0 dB run to rule out artifact or external noise, and we
saw a flat line, meaning that the wave I responses were, in fact, neural
responses. It is interesting to note also that, generally, wave V appears at
lower intensities and all the earlier waveforms disappear; in this case, we had a
robust wave I down to threshold. Figure 10 shows the latency-intensity function
for wave I. At the high intensity, it falls within that normal shaded region, and it
shifts appropriately as we decrease the intensity.

Figure 10. Latency-intensity function for wave I of Case #5.

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The patient was still asleep, so we performed 1000 Hz tympanometry. The
tracings were grossly normal, meaning that we saw a nice peak. With the 1000
Hz probe tone, you are not looking at the standard values associated with the
classifications of Type A, B, C, et cetera. If the tracing is flat, then we know it
could be consistent with middle ear dysfunction. However, when we see a nice
peak tracing with a child this young, it is either normal middle ear function or
possibly some effect from the ear canal. We were able to perform TEOAEs and
DPOAEs, and they remained intact in both ears, confirming normal middle ear
function from the tympanometry as well.

Case #5 Discussion
Let’s tie her history into the ABR, tympanometry, and OAE results.
Myelomeningocele is neural tube defect and the most common type of spina
bifida. It is a condition in which the back bone and the spinal canal do not close
before birth (Foster, Kolaski, & Riley, 2012). Chiari II malformation is a
congenital malformation of the brain that is nearly always associated with
myelomeningocele. Significant manifestations of Chiari II malformation include
structural changes to the pons and the fourth ventricle, and downward
displacement of the medulla, fourth ventricle and cerebellum into the cervical
spinal canal (Incesu, Khosla, & Aiello, 2011). The automated ABR used for
newborn hearing screenings looks for wave V, not wave I, so we know why she
referred on the hearing screening in the NICU. Recall that wave I corresponds to
activity from the peripheral portion of the VIIIth cranial nerve. In addition to
that, OAE results were consistent with normal outer hair cell function and
support the ABR results.

Neurologic evaluations are typically conducted with patients like this to

determine the status of nerve-related functions below the defect. The
diagnostic ABR allows us to look at the entire waveform, and we are able
interpret which waves are present or absent. This ABR did reveal a clearly
identifiable wave I only. The ABR results for this patient indicate that the
generator sites for wave I are functioning normally, but things start to go awry
as early as the proximal portion of cranial nerve VIII. Recall that the patient’s
history included no recognizable fourth ventricle on the MRI study; the fourth
ventricle is located within the pons or in the upper part of the medulla. The
superior olivary complex, lateral lemniscus and the inferior colliculus are also
located in the pons. The generator sites for waves IV and V are located in the
pons. Our ABR findings are consistent with the patient’s MRI findings, which
indicated no fourth ventricle.

What do you do when you get a case like this? My first thought was to go to the
literature, and my second thought was to tell all my audiology friends. Hall
(1992) notes that gross ABR abnormalities, like the ones we saw on this patient,
are usually found in patients with mesencephalic/pontine or lower central

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nervous system clinical signs. In terms of recommendations and treatment, she
was not a traditional candidate for a cochlear implant or a brainstem implant.
We recommended that she follow up with the referring physician, who was her
pediatrician, and we would hope that she is under the care of a neurologist and
that she is also enrolled in early intervention.

What could be a possible communication mode for a patient with such as

compromised central system? At this point, we may not know that answer.
She was only two months old and we did not know if any other sensory systems
had been evaluated. A referral to ophthalmology was recommended. Pending
the outcome of other sensory evaluations, we recommended investigating the
use of visual or tactile communication strategies.

Questions and Answers

With the Case #5, would you assume that that there is no use of auditory
information with the central pathology?

Honestly, we do not know. Because of her age, it is difficult to predict what is

going to happen or what information she can utilize. Further evaluation,
including ABR, would be in order. To date, we have not seen her back.

What is the time allotted for testing sedated and unsedated ABR?

In our clinic, our natural-sleep ABRs are scheduled for two hours. By the time
the baby is fed, burped and changed, it takes a good chunk of time before we
even complete testing, which can take all of the two hours. The sedated ABRs
are a bit different. We schedule those for an entire morning. They are
performed in our pediatric intensive care unit (PICU). We have a whole
anesthesiology team and a nurse who is assigned to us as well. We have the
patient come in early in the morning, because with sedation, they cannot eat or
drink anything prior to the testing, so the earlier, the better. They come in early
and are usually released about noon.

How do you describe ABR results to parents if the ABR is not a true test of
hearing?

We try to give parents some understanding about what we are doing and what
the test measures. The ABR does give an estimation of the sensitivity of sound
based on responses from a good portion of the auditory system. However, we
do use the term “estimated hearing loss” when counseling on results that are
consistent with hearing loss. We use normative data to make those

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estimations, but it is not a precise threshold like what we obtain with subjective
testing.

References
Foster, M. R., Kolaski, K., & Riley III, L. H. (2012). Spina Bifida. Retrieved from
http://emedicine.medscape.com/article/311113-overview

Hall III, J. W. (1992). The handbook of auditory evoked responses. San Diego,
CA: Singuluar Publishing.

Incesu, L., Khosla, A., & Aiello, M. R. (2011). Imaging in Chiari II malformation.
Retrieved from http://emedicine.medscape.com/article/406975-overview

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