Prognostic Predicament: Don`t Take the Audiogram at Face Value

to an ongoing series
that challenges the
audiologist to identify
a diagnosis for a case
study based on a
listing and explanation
of the nonaudiology
and audiology test
battery. It is important
to recognize that
a hearing loss or a
vestibular issue may
be a manifestation of a
systemic illness. Being
part of the diagnostic
and treatment “team”
is a crucial role of the
audiologist. Securing
the definitive diagnosis
is rewarding for
the audiologist and
enhances patient
hearing and balance
health care and, often,
quality of life.
—Hillary Snapp,
CSI Reference Guide: Visit and
search keywords “CSI
Reference Guide.”
Predicament: Don’t
Take the Audiogram
at Face Value
By Sarah Sydlowski
Case History
A 45-year-old male was referred for
a cochlear implant (CI) evaluation.
Audiologic history included the
ƒƒ 15-year history of progressive
bilateral hearing loss
ƒƒ Perceived his right ear to be worse
than his left ear
ƒƒ Bilateral, ringing tinnitus that
was a 6/10 on a Tinnitus Distress
ƒƒ 13-year use of bilateral behindthe-ear hearing aids that were
approximately three years old
ƒƒ Poor word recognition ability,
even in aided condition
ƒƒ Poor speech perception in noisy
environments and group settings
ƒƒ Reliance on visual cues for communication purposes
ƒƒ Occasional imbalance, but no true
ƒƒ Denied family history of hearing
loss, significant noise exposure, middle-ear disorder, aural
pressure or fullness, or other
otologic complaints.
Audiometric Findings
Otoscopic examination revealed
clear ear canals and intact tympanic
membranes bilaterally. Audiometric
evaluation (FIGURE 1) revealed moderate sensorineural hearing loss
through 500 Hz dropping to profound
at 1000 Hz and above. Word recognition was 0 percent at 25 dB SL in the
right ear and 10 percent in the left
ear (patient could not tolerate higher
presentation levels). Tympanometry
indicated normal middle ear pressure, mobility, and volume bilaterally.
Acoustic reflexes were absent in
the ipsilateral and contralateral
conditions for all frequencies tested.
Review of previous audiograms over
10 years revealed bilateral, asymmetric (right worse than left), sloping,
progressive sensorineural hearing
loss (SNHL) with gradual decline in
word recognition.
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The patient’s hearing aids were
evaluated using real ear measures
and were found to meet prescribed
targets as closely as possible, given
the degree of hearing loss. Aided
testing was then completed in a
sound booth with speech materials
presented at 60 dBA from 0° azimuth.
Results are summarized in TABLE 1.
Does the patient report and
audiometric findings assist
you in making a differential
diagnosis? Does the etiology of
the patient’s hearing loss matter
when considering cochlear implant
Consider the Facts
ƒƒ Progressive bilateral, asymmetric sensorineural hearing loss,
tinnitus, and imbalance (no true
ƒƒ Audiometric results more severe
than hearing loss that could be
attributed to his limited history of
noise exposure or aging
ƒƒ No family history of hearing loss
that would suggest a genetic
ƒƒ Very poor word recognition
despite history of consistent hearing aid use
ƒƒ Limited demonstrated benefit from hearing aids on aided
speech-perception measures
The patient meets FDA criteria
for cochlear implantation and his
audiometric evaluation seems
relatively unremarkable, although
some asymmetry was noted, and
we do not know the etiology of the
hearing loss. Should we proceed
with cochlear implantation? Is
there other information that might
be relevant?
Other Medical History
Upon further questioning, the patient
revealed that he had sustained a
head injury in a motor vehicle at four
years of age. He did not lose consciousness, but the report suggests it
was a significant injury. He reported
a history of headaches beginning at
age eight that were noted to occur
three to four times per year. Around
age 22, he began having more severe
headaches along with tingling in his
TABLE 1. Preoperative Aided Speech-Recognition
Results in the Sound Booth with Speech
Materials Presented at 60 dBA from 0° Azimuth
CNC Words
+10 SNR
Note: CNC = consonant-nucleus-consonant; SNR = signal-to-noise ratio.
FIGURE 1. Results from audiometric evaluation
revealing bilateral moderate sensorineural
hearing loss through 500 Hz dropping to
asymmetric profound hearing loss from 1000 to
8000 Hz.
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extremities. He also developed gait
and coordination problems with a
tendency to stumble. He began to
notice bilateral hearing loss and tinnitus in his late twenties, which has
steadily progressed. Most recently,
he has noticed urinary incontinence.
Subsequent to the presentation of
these neurologic symptoms, he had
several spinal taps, which revealed
blood products in the cerebrospinal
fluid (CSF) and consistently elevated
pressure. The patient’s medical history is somewhat unusual and should
trigger the clinician to suggest
further medical evaluation to determine the possibility of an associated
etiology. Medical evaluation led to
magnetic resonance imaging (MRI)
with results consistent with superficial siderosis of the central nervous
system (SSCN).
Does this diagnosis influence the
patient’s candidacy for cochlear
SSCN is an extremely rare neurotologic disorder involving chronic
hemorrhaging into the subarachnoid
space and subsequent deposition
of hemosiderin (an iron-protein)
onto susceptible neural structures
including the brainstem, cerebellum,
and CNVIII (Tomlinson and Walton,
1964; Parnes and Weaver, 1992; Kale
et al, 2003; Vibert el al, 2004). This
hemorrhaging typically occurs due
to the presence of dural tears around
the brain or spinal cord (Parnes
and Weaver, 1992; Cohen-Gadol et
al, 2006) resulting from vascular
malformations, tumor growth or
resection, or trauma (Tomlinson and
Walton, 1964; Dhooge et al, 2002). As
red blood cells circulate within the
cerebrospinal fluid and degenerate
(Takasaki et al, 2000; Dhooge et al,
2002), hemosiderin is produced. Glial
iron clearance mechanisms cannot
keep up with the iron influx, and
exposed structures essentially rust,
causing cell death and neuronal
In the current case, the nonspecific findings of bilateral, progressive
sensorineural hearing loss, tinnitus,
and imbalance alone are inadequate
to pinpoint an etiology. However, the
presence of SNHL exceeding hearing
loss that could be attributed to aging,
observation of ataxia, history of head
trauma, and eventually confirmation
of hemosiderin staining on MRI, all
point to classic presentation of superficial siderosis of the central nervous
system (SSCN).
The cardinal feature of SSCN is
hearing loss (95 percent) (Fearnley et
al, 1995); however, a variety of neurological signs and symptoms may be
present to varying degrees, including
but not limited to gait ataxia, widebased gait, dizziness/imbalance,
dementia, anosmia, neurogenic
bladder (including incontinence,
voiding difficulty, or urgency), bowel
incontinence, aniscoria, dysarthria,
spasticity, tinnitus, diplopia, headaches, seizures, hydrocephalus,
hypogeusia, memory loss, cognitive
decline, seizures, extra-ocular motor
palsies, neck pain, back pain, nystagmus, and dysphagia (Parnes and
Weaver, 1992; Fearnley et al, 1995;
Kale et al, 2003).
Hearing loss resulting from SSCN
is probably retrocochlear in nature
(Yamana et al, 2001; Ushio et al, 2006)
due to the largely glial myelination
of CNVIII and the diffuse exposure of
the cochlear nucleus to CSF circulating through the fourth ventricle.
However, several studies have
demonstrated that peripheral auditory structures may also be impacted,
although how they become affected
is unclear (Irving and Graham, 1996;
Takasaki et al, 2000; Yamana et al,
2001; Weekamp et al, 2003; Vibert et
al, 2004; Hathaway et al, 2006; Kim
et al, 2006; Sydlowski et al, 2013).
Possible mechanisms include interruption of cochlear vasculature due
to thickening of CNVIII (Yamana et al,
2001), hair cell degeneration secondary to deafferentation of CNVIII
(Prasher et al, 1995), or circulation
of hemosiderin within the cochlea
via a patent cochlear aqueduct
(Wlodyka, 1978) or internal auditory
canal (Holden and Schuknecht, 1968).
Regardless of site(s) of lesion, hearing
loss is usually bilateral, asymmetric,
progressive, sloping SNHL (Sydlowski
et al, 2013). Word recognition varies
but tends to be disproportionately
poor (Sydlowski et al, 2011) and progressively worsens. There has been
some speculation that individuals
with intra-axial brainstem lesions
or lesions at the level of the cerebellopontine angle may have better
speech recognition ability than those
with extra-axially located lesions
(Mobley et al, 2002), but further
research is necessary.
SSCN is difficult to diagnose
because of variable and nonspecific
symptoms that often present decades
after initial onset of the disorder
(Fearnley et al, 1995; Offenbacher et
al, 1996). Although otologic symptoms such as hearing loss, tinnitus,
and imbalance are frequently among
the first and most commonly
reported symptoms (Sydlowski et al,
2013), many patients exhibit a very
long asymptomatic phase (months
to many years) after bleeding begins.
This prolonged separation of onset of
disorder and development of symptoms coupled with fairly “typical”
sloping SNHL makes suspicion of
SSCN based solely on audiometric
battery unlikely. SSCN is ultimately
identified by hypointensity surrounding affected structures on
gradient echo T2-weighted (T2*) MRI
images (Parnes and Weaver, 1992;
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Padberg and Hoogenraad, 2000; Ushio
et al, 2006).
Awareness of this esoteric disorder is important for audiologists
for several reasons. First, SSCN is a
perfect example of the importance of
integrating audiologic and medical
histories. In this case, the patient’s
reported history of head trauma
and constellation of neurological
complaints, coupled with worsethan-expected hearing loss without
another identifiable etiology, should
prompt recommendation for medical
(ideally neurologic) evaluation if the
diagnosis of SSCN has not already
been made, even though the hearing
loss was essentially unremarkable
except for high frequency asymmetry.
Second, a diagnosis of SSCN
introduces a very different prognosis for patients than more common
presbycusis, although pure tone
thresholds may look similar. Because
the presence of hemosiderin in
the subarachnoid space results in
progressive destruction, locating and
ablating the source of the hemorrhage is a priority. Methods described
in the literature have included
surgical ablation of the bleeding
source and iron chelation therapy
(Miliaras et al, 2005). Avoidance
of anticoagulant and antiplatelet
medications, including aspirin, has
been suggested to slow bleeding into
the subarachnoid space (Dodson
et al, 2004). However, the source of
bleeding is usually microscopic and
is only found in 50 percent of cases.
Even if bleeding ceases, once neural
structures are encrusted with hemosiderin, symptoms may continue to
progress (Cohen-Gadol et al, 2006).
Because of its retrocochlear component and likelihood of progression,
clinicians should recognize that
the potential for improved speech
recognition with hearing aid and/
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or cochlear implant use may be
limited or may deteriorate over time
(Sydlowski et al, 2009). While SSCN
is not a contraindication to cochlear
implantation, research suggests outcomes may be variable (Sydlowski et
al, 2009) and appropriate counseling
regarding expectations is critical.
Finally, even in cases where
most components of the standard
audiologic battery may not appear
retrocochlear in nature, inclusion of
objective measures such as acoustic
reflexes and otoacoustic emissions
are important for diagnostic as well
as for hearing aid fitting purposes.
In cases of predominantly retrocochlear disorders such as SSCN
or auditory neuropathy spectrum
disorder (ANSD), special care must
be taken with hearing aid fitting to
avoid overamplification and damage
to cochlear structures.
Given the diagnosis of superficial
siderosis, is there any additional
audiologic testing that may be
Objective Findings
Objective measures may be valuable
for evaluating the lesion site (particularly confirming possible cochlear
involvement), although there has
been no evidence to suggest that
inclusion of objective measures in
SSCN can predict potential outcomes
following cochlear implantation. In
the current case, electrocochleography (ECochG), auditory brainstem
response (ABR), and distortion product otoacoustic emissions (DPOAEs)
evaluated for the frequencies of
2000 through 8000 Hz all resulted in
absent responses bilaterally, consistent with the degree of hearing
loss and likely cochlear involvement,
although whether or not the peripheral dysfunction is due to SSCN or
other causes cannot be determined.
Despite confirmed peripheral abnormality, the diagnosis of SSCN also
makes retrocochlear involvement
highly probable, so care was taken
when counseling the patient regarding prognosis for speech recognition
following cochlear implantation.
Key Points
ƒƒ Comprehensive case history,
including determination of etiology when possible, is essential,
particularly when considering
surgical intervention options
such as cochlear implantation.
ƒƒ Hearing loss, even symmetrical hearing loss that cannot
be explained by aging or other
factors, should trigger clinicians
to consider medical evaluation.
ƒƒ The audiogram in isolation will
frequently not tell the whole
story. Etiology and site of lesion
can alter prognosis and should
be thoroughly investigated and
incorporated into counseling.
Final Thoughts
If asked whether they are familiar
with disorders that result in hearing
loss in 95 percent of patients, most
audiologists would not hesitate to
respond in the affirmative. However,
SSCN is not well known to audiologists because of its exceptionally
rare presentation. Reviewing cases
involving complex disorders, such as
SSCN, highlights the importance of
approaching audiologic evaluation
with a broad viewpoint and reminds
audiologists of the importance of
gathering comprehensive diagnostic
information in order to accurately
identify hearing loss, develop a
reasonable prognosis, and provide
appropriate management recommendations in special populations.
Sarah Sydlowski, AuD, PhD, is audiology
director of the Hearing Implant Program
at the Cleveland Clinic in Cleveland, Ohio.
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