CAPD: Making Informed, Evidence-Based Clinical Decisions


Hello, I’m Gail Chermak. I’m going to speak with you today
about central auditory processing disorder, making informed evidence-based
clinical decisions. My financial disclosures consist of the following. I’m Professor and Chair, Speech
and Hearing Sciences, the Elson S. Floyd College of Medicine, Washington State
University, Health Sciences, Spokane, Washington. I receive royalties from Plural
Publishing, financial compensation from ASHA for this presentation and past
online presentations. I have no nonfinancial disclosures. The recommended practices for diagnosis and
intervention for central auditory processing disorder are dynamic, undergoing
review and refinement as new research emerges. These practices have been developed by consensus
groups, with careful consideration of the merits of various positions surrounding
points of disagreement. Nonetheless, a number of controversial assertions
and practices continue to appear in the literature. In this course, I would like to present my
perspective on a number of these issues, highlighting the current state of the evidence
supporting my viewpoint. I would
also like to provide information that will assist clinicians in making informed,
evidence-based clinical decisions. The gap between research and clinical practice
continues to shrink appears the need for evidence to substantiate clinical
decisions becomes more necessary. Well spoken by our prior president, Gail Richard. In fact, this
statement underlies an article that we published last spring in the hearing review
in which we argued science to support clinical practice positions. I’m going to cover these six topics in this
session today: Definition, nature and causes of CAPD, ICD-10 and the gold standard;
differential diagnosis, minimizing confounds; efficient test batteries for diagnosis
of CAPD; efficacy of auditory interventions; and future research needs. Central auditory processing disorder is a
disorder of the central auditory nervous system. Deficits in the perceptual processing of auditory
stimuli in the central nervous system and in the underlying neurobiological
activity that gives rise to the electrophysiological auditory potentials. The predominant deficits
characterizing CAPD manifest in the auditory modality. Central auditory processing disorder affects
perceptual and neural processes underlying sound localization and lateralization,
auditory discrimination, auditory pattern recognition, temporal processing,
auditory performance with competing or degraded acoustic signals, and
others, for example, spatial processing or spatial release from masking. There are many functional deficits or behavioral
manifestations associated with CAPD. Perhaps the most characteristic being the
difficulty understanding spoken language in competing message or noise
backgrounds, in reverberant acoustic environments, or when rapidly presented. As you can see, in the last slide and in this
slide, there are many, many behaviors that are seen in individuals with CAPD. These difficulties are not definitively
diagnostic of CAPD, as you can tell from the behaviors listed. These deficits,
difficulties, can be seen in individuals with a variety of problems, from central
hearing loss to peripheral hearing loss, language processing issues, attention
deficit issues and so on. CAPD affects individuals across the life span. It’s due to benign
neuromorphological anomalies, neuromaturational delays, or acquired
neurological brain damage, suffered from head injuries, strokes, tumors and the
like. CAPD is also seen within the context of cognitive
syndromes, certain types of dementia, psychiatric disorders, or age-related
changes to the central nervous system of the and it is diagnosed
on the basis of a battery of tests with documented sensitivity in patients with confirmed
neurological lesions of the central auditory nervous system. It is not diagnosed on the basis of parental
or other informant’s report or questionnaires. This slide displays some of the common neuroanatomical
and neurophysiological sources of abnormal processing
or delayed immature processing. Interhemispheric transfer deficits, which
in children likely due to developmental delay in myelination, lack of
appropriate hemispheric lateralization, atypical hemispheric asymmetries,
imprecise synchrony of neural firing, decreased central inhibition, probably
others, and in older adults loss of myelin integrity, neural slowing, decreased
brain connectivity and so on. I would like to elaborate a bit on the causes
of CAPD in children. Primary
causes, neurodevelopmental and acquired. Under neurodevelopmental, we
find maturational lag, likely due to delayed myelination and possibly auditory
deprivation, seen in about 20-30% of the cases. Neuromorphological errors,
seen in 60-70%. These are underlying benign, diffuse neuroanatomic
or neuromorphological abnormalities such as polymicrogyria,
in which we have misshaped smaller cells, or heterotopias,
where we have cells that are normal but they are in the wrong places in the brain. And then we have a very small
fraction of children with CAPD who have acquired CAPD due to some type of
neurological disorder. That’s 5-10% of the population. Although we tend to think
about neurological disorders as a cause of CAPD in adults, we also see it,
although in a small percentage, 5-10%, in children, and in a 2011 article, Frank
Musiek and I described some of the acquired pathologies seen in the central
nervous systems of children, as displayed on this slide. What about the causes of CAPD in adults? Of course the adult could have a
neurodevelopmental disorder since childhood, which was either diagnosed or
perhaps not, or they could experience an acquired disorder due to a
neurological lesion or a compromise of the central auditory nervous system,
including neoplasms, neurodegenerative processes like multiple sclerosis or
Alzheimer’s, head trauma, impaired cerebral circulation as a result of a stroke,
let’s not forget changes in the central auditory nervous system, a type of
presbycusis due to aging, noise exposure, and neurotoxic chemicals or heavy
metal exposure. In fact, from the 7th decade of life and beyond,
central auditory function, as measured by behavioral
tests, declines more than pure tone sensitivity or outer hair cell function. In fact, some have suggested that
CAPD may be a precursor of cognitive impairment. I would like to spend a few minutes talking
about the ICD-10 and the gold standard. Some have challenged the veracity of CAPD
as a diagnostic entity, claiming that it is ill-defined and poorly understood. While there is some disagreement
between the professional associations in the U.S. and European associations, the
two major sets of guidelines published by professional associations in the U.S.,
ASHA and AAA, present consistent evidence-based positions and
recommendations. Moreover, CAPD is listed in the ICD-10 under
ear diseases, code H93.25, for both acquired and congenital
CAPD, which confirms the physiological nature of this disorder and
supports the medical necessity for care. Some have argued that there is no gold standard
CAPD diagnostic test battery. Consistent with medical terminology, which
defines gold standard as a method or procedure that is widely recognized as
the best available, it’s my position that while there might not be a universally accepted
gold standard, we have a considerable body of research demonstrating
the efficiency of individual central auditory tests and central auditory
test batteries based on performance of individuals with confirmed central auditory
nervous system lesions, including such lesions in children. Consider, for example, Musiek, et al. and
Weihing, et al., who reported similar performance on multiple central auditory tests
in a group of patients with confirmed neurological lesions of the CANS
and a group of children with CAPD diagnosed on the basis of an efficient behavioral
test battery remitted by AAA and ASHA, respectively. Boscariol and colleagues have demonstrated
that children with known CANS lesions present central
auditory behavioral test performance patterns and brain imaging similar
to those seen in adults with known central auditory nervous system lesions
and similar to those seen in children with developmental CAPD, that is,
a child who shows no identifiable lesion of the CANS and no apparent prenatal
or perinatal disease, injury or exposure-related explanation for the CAPD
as well. Let’s spend a few minutes talking about differential
diagnosis, the importance of minimizing confounds. The potential for language and cognitive confounds
are seen with any task that requires cooperation and behavioral response
on the part of the individual being tested. All auditory tasks from pure tone detection
to spoken language processing are influenced by higher order,
non-modality-specific factors such as attention, memory, motivation and decision
processes. Why is it important to minimize confounds? We need to reduce the risk of
false-positive diagnosis. Pediatric CAPD is often comorbid with other
disorders that can influence central auditory processing
test results. Remember, the
audiologist’s role is not just to determine which central auditory processing tests
are failed and how many, but whether the negative influence of comorbidities
can be ruled out. This figure, taken from Sharma, et al., in
2009, demonstrates the likelihood that a child with central auditory processing disorder
is going to present with other disorders. You can see that 47% of their sample experience
auditory processing disorder and comorbid reading disorder and
language impairment. There are means to minimize confounds. We can design tasks, as we have, that
inherently require minimal cognitive and/or language skills. We can select tests
commensurate with the patient’s abilities, so for example, if a patient has
memory issues, select tests with low memory load, for example, gap detection or
dichotic digits. If an individual has a peripheral hearing
loss, select tests that are less influenced by hearing level, such as
the frequency and duration patterns test and the dichotic digits test. Use nonverbal or simple speech stimuli, for
example, again, frequency or duration patterns, gap detection and dichotic
digits. In addition to selecting particular tests,
we can also minimize confounds using intra-test measures to control in part for
non-auditory factors, asking the question are performance deficits on our central auditory
processing tests due to acoustic manipulations or lack of familiarity
with the language and/or significantly reduced memory or attention? So we can compare between ears,
and I will show you an example of that in the next slide. We can monitor or
measure performance-intensity functions, what happens to performance as we
increase intensity. We can compare the humming versus the labeling
response in frequency pattern or duration pattern tests. We can check performance in
nonmanipulated conditions, looking at monaural versus dichotic performance
or non-filtered versus filtered speech performance. And we can examine tasks
that differ in the demands placed on auditory processing but that differ
minimally in the demands placed on cognitive abilities, as is done in the LiSN,
listening in spatialized noise test. As you can see in this slide, adapted from
a figure in Bellis, et al., 2011, the performance across three different groups
on dichotic digits shows a very different intra-aural outcome. For children diagnosed with central auditory
processing disorder, there is a clear right ear advantage or left ear deficit. For
the normal children, there is little, if any, advantage. Both ears perform
essentially the same. And for the children diagnosed with attention
deficit hyperactivity disorder, there is some slight
right ear advantage, but it’s not nearly as large as that seen in the children with
central auditory processing disorder. Another important way that we can minimize,
if not isolate confounds is through multidisciplinary evaluations. Each team member contributes to the differential
diagnosis of the patient’s disorders, identifying disorders in a variety of areas that
might be contributing to the profile and might be potentially problematic for our
test battery as it might be for other members of the disciplinary team. And of course when cognitive or language processing
deficits are suspected or confirmed, the audiologist is not at all convinced
that she or he has isolated those other deficits, the audiologist should
then considerate use of auditory evoked potentials rather than relying on behavioral
auditory tests, which nonetheless those AEP’s or auditory evoked
potentials would still be interpreted within the context of a multidisciplinary
evaluation. Next I would like to talk about the efficient
test batteries for diagnosis of CAPD. Based upon a lot of published research, we
have concluded, based on sensitivity and specificity data, that these
four tests, gaps-in-noise, either frequency pattern or duration pattern test,
dichotic digits, and masking level difference, are the four most efficient tests
for diagnosis of CAPD in adults. In
addition, of course, case history, very necessary component of the test battery,
and any pertinent medical or neurological reports. Here you see a table reproduced from a chapter
we wrote in 2015, the reference is in your reference list, in which
we identified the different tests that would contribute information to differential
diagnosis with particular reference to a level of the central auditory nervous
system or the peripheral auditory nervous system. We included a similar table in a recent article
in the ASHA Leader. This time,
however, we added some of the evoked potential information in terms of their
contributions to differential information relative to various levels across the
auditory system. Again a reference in your list. What you see here above the blue line are
some of the data we have pulled from various publications demonstrating the
sensitivity and specificity to various levels of lesion, cortical and otherwise,
and then you see below that some of the other measures like low pass filtered speech
which seems to have less sensitivity even to brainstem and temporal lobe lesions. Many ask the question: How many tests do I
need to administer to diagnose CAPD? We examine that in a couple of publications,
and as you can see in this adapted figure, two tests probably gives us
the best compromise between sensitivity and specificity, at least for
the tests we were using in these two studies. If you add more tests, you certainly improve
your specificity, but you lose your sensitivity and therefore you compromise overall
efficiency, and if you use one test that is particularly sensitive to CAPD,
you will get 100% sensitivity, but you’re going to have a lot of overreferrals. You’re not going to have very good
specificity. You’re going to overdiagnose individuals who
don’t have the disorder. So the best compromise seems to be two tests. And in adults those two tests seem to be dichotic
digits and frequency patterns. So showing you again the slide that I showed
just a few moments back, while we have four tests that have very good efficiency
with adults for the diagnosis of CAPD, we found in our work that the dichotic
digits and the patterns test were the most sensitive. Does that mean that you — I should say the
most sensitive and specific, forming the best compromise
for efficiency. Does that mean you
should never bother with the gaps-in-noise or the masking level difference? I
would suggest that if you are able to administer more than two tests, more than
the patterns and the digits test, by all means do because you will collect more
information in particular using masking level differences and even the
gaps-in-noise, you’re going to obtain more information related to the brainstem
because if you go back to the two tables that I referenced earlier, you’ll find
that dichotic digits gives you much more information about the cortex and the
corpus callosum and the duration patterns similarly, much more information
about the cortex and the corpus callosum. So if you want to look a little lower
down in the central auditory nervous system, masking level differences and
gaps-in-noise will give you more information at those lower levels. Moreover, if
you have more information, meaning you’ve tested more of the auditory
processes underlying central auditory processing, you have more information
that will help you moving forward with a treatment plan. And as noted before, there are times when
auditory evoked potentials become absolutely essential. They’re always of interest, but they’re not
always essential to the diagnosis, the clinical diagnosis,
but here I’m sharing with you a slide that Frank Musiek compiled representing sensitivity
and specificity data for MLR and ABR, and you see again that these are very
impressive data, sensitivity, specificity, and therefore overall efficiency. What about the efficient behavioral test battery
for children? You’ll see some
definite overlap between that for adults and that for children. In fact, the slide is
identical, the recommendation is identical except that we have substituted
low-redundancy speech for masking level difference. And I’m going to talk
more about low-redundancy speech as we move through the next few slides,
but keep in mind that here we have four very efficient tests, some more efficient
than others, and again, I’ll come back to that, but also note that the case history
is an essential component of the behavioral test battery with children. Here is a figure from our 2015 study in which
we compared the failure rates across a number of tests in our battery, and
you’ll find that the children with CAPD failed in large numbers all of the tests
in the battery. You’ll also notice,
however, that the children who were normally processing, the NP’s, actually
failed the low pass filtered speech test with a fairly high rate of failure. In fact, we can’t be sure that the children’s
difficulties on low pass filtered speech was reflecting an auditory processing
issue. It may have also reflected
their knowledge of the language and specifically comprehension of single
words when sentence context is absent. The two-test combination that showed
the next highest failure rates among children with CAPD and did not include low
pass filtered speech was competing speech and frequency patterns. However,
if one wishes to include a dichotic measure that has a lower linguistic load than
competing speech and potentially might have a bit less sensitivity but much
higher specificity, then we recommend substituting dichotic digits,
notwithstanding the slightly lower failure rate of the dichotic digit frequency
pattern battery relative to the competing speech frequency pattern battery. I would also like to share with you some data
again compiled by Frank Musiek, showing some of the sensitivity data for children
with various types of disorders and typically-developing children, again pointing
out that electrophysiological measures are useful in the evaluation of children
as well as adults. So we come back to the slide I showed you
a few slides back, the efficient behavioral test battery in children, this
time highlighting the patterns test and the dichotic digits as our go-to test battery
with children we feel provides the best compromise between sensitivity and specificity
and therefore most efficient. Again, as I said with adults, this is not
to suggest that you should never use any other tests in the battery. The gaps-in-noise and low-redundancy speech
may be quite useful. Gaps-in-noise can provide some information
not only about detection, but also provide information about
brainstem function and low-redundancy speech, while it is linguistically
loaded, does provide a more functional measure of auditory closure, for
example, and so that could be very directly translatable, results on that test
could be very directly translatable to an intervention goal. Now that we’ve covered diagnosis, let’s talk
a little bit about the efficacy of auditory interventions. Some have criticized auditory training as
ineffective because it does not improve language or reading skills. However, reading and language processing
are influenced by many variables, some of which are far removed from the
auditory domain. The purpose of auditory training is to improve
auditory processes, not to improve language or reading
skills. Moreover, true auditory interventions utilize
auditory training exercises. Behavioral tasks that are auditory-based and
aim to strengthen the basic sensory processing of auditory stimuli at
the level of the central auditory nervous system of the language, metacognitive and
cognitively interventions are not auditory interventions. A number of computer-based auditory training
programs that have been suggested for treatment of
CAPD are language-loaded. For
example, Earobics, Fast ForWord, and they are not truly auditory interventions. Auditory training, as a bottom-up strategy,
aims to improve sensory processing of individuals with auditory skills deficits,
with the expectation that such improvement is likely to benefit real-life
listening situations. Improvement in
areas not directly related to the targeted auditory deficit, for example, reading
and spelling, may occur but is not the primary goal of auditory training. Several recent studies have provided behavioral
and electrophysiological evidence that auditory training improves auditory
processing skills of children with CAPD or auditory-based learning problems. Here you see a table taken from a 2015 publication
in which we summarize the evidence available at that time supporting
the efficacy of auditory training. I’m
going to focus on two studies, one which was conducted after this publication,
a 2016 study, as well as spend a moment on the Cameron and Dillon 2011 study
that’s shown in this slide. Both of these studies present level 2 evidence. So Loo, et al., in 2016 conducted a nonrandomized
experimental but controlled study in which they trained children diagnosed
with CAPD, as per ASHA criteria, in several speech-in-noise tasks and in dichotic
listening tasks. They reported
better speech recognition in noise on all conditions of the can LISN-S test, as well
as in functional listening, measured by the CHAPS questionnaire, and in the use
of language as measured by the CELF. Similar improvements were not seen in
children with CAPD who did not undergo training. The LiSN and Learn, an auditory training program
specifically developed to improve binaural spatial skills and speech
recognition in noise, was shown to be effective in improving binaural processing
as measured by the LISN-S test. Enhancements to self-reported ratings on listening
skills were also reported, and the children with spatial processing disorder
who did not undergo training or underwent another training program, in this
case Earobics, did not demonstrate the same benefits, highlighting the importance
of auditory interventions that are deficit-specific. Most of the published auditory training protocols
lead to improved auditory function following a schedule of 15 to 45
minutes of training, two to seven times a week, for a period of two to three months. Post-training benefits have been
demonstrated to persist after 3 to 36 months of the end of the training program. However, maintenance of these been facilities
over longer time periods has not been investigated. The evidence reviewed here demonstrates that
auditory training is an effective treatment for central auditory processing
deficits. Clinicians and researchers
might disagree as to the quantity of evidence needed to support the
acceptance of scientific results; however, none should confuse any perceived
concern about quantity of evidence with the demonstrated positive outcomes
of that evidence. I would like to mention research needs in
four areas, one reflected in this slide, which will just speak about in a minute, well
defined research participants, and three other areas, differential diagnosis,
electrophysiological measures, and tests to diagnose children at younger ages. Participants diagnosed with CAPD, not
simply suspected of based on a parental reported or a questionnaire, are the
kinds of participants we need in our studies. A recent European consensus on
APD reached by professionals in 17 European countries noted that the two
primary reasons why debate around CAPD lingers are, one, failure by critics to
employ the currently available auditory processing test batteries with
demonstrated efficiency, which then leads them to draw conclusions regarding
CAPD based on characteristics of individuals who are not diagnosed with CAPD
and are so-called suspected of presenting CAPD. We’ve already discussed comorbidities and
confounds. I would like to draw
your attention to a new acronym on the block, HHL, which stands for hidden
hearing loss. Hidden hearing loss refers to individuals
who have difficulty understanding speech-in-noise despite normal
audiograms. It might sound
familiar to you because that is an earmark of central auditory processing
disorder as well. However, the term “hidden hearing loss” really
refers to a peripheral neural issue at the synapse between
the inner hair cells and the affarent fibers, and I have to say that at
this point in time there is limited evidence that hidden hearing loss underlies
this perceptual deficit of difficulty understanding speech-in-noise despite normal
audiograms in individuals, humans. There is a bit of research done on animals,
but we do not yet know whether hidden hearing loss or this deficit
that is seen in the affarent fiber inner hair cell ribbon synapse communication really
underlies any of these individuals we are seeing with the difficulty understanding
speech despite a normal audiogram. In fact, the research suggests so far that
you would have to lose 80 to 90% of the synapses with the inner hair
cells before behavioral shifts would begin to show. I would also like to draw your attention to
the future in terms of the use of electrophysiological paradigms, hybrid approaches,
perhaps where psychophysical tests were injected into electrophysiological
paradigms, for example, recording auditory evoked potentials
in response to stimuli used in behavioral tests, or while an individual concurrently
performs a behavioral central auditory test. These types of hybrid approaches would provide
more objective information and might in fact be
more sensitive than comparable behavioral indices, and they would reflect
the integrity of both neural substrate underlying behavioral tasks and the pathways
responsible for generating the auditory evoked potentials. And such hybrid approaches might provide
objective measures of which patients might benefit from particular training and
of treatment efficiency and efficacy. I would also add brain imaging work,
which although very expensive at this point and not used clinically for the
diagnosis of CAPD could at some point be a useful tool to identify some of the
underlying issues that we see manifested in our behavioral tasks. And the fourth area for future research focus
is thrown here as a challenge. Tests and procedures are needed to enable
early diagnosis of CAPD in children 7 years and younger to maximize the efficacy
of intervention. To do so,
however, is going to require research to find measures of sufficient challenge to
the central auditory nervous system that can still be completed by young
children without such variability that makes it impossible to establish reasonable
cutoff norms. In the meantime, we and others have recommended
a number of informal interventions for children who
are at risk but have not yet been diagnosed with CAPD. My presentation is part of the upcoming ASHA
audiology online conference on central auditory processing disorder. This conference examines the complexities
of CAPD including how to select evidence-based measures for evaluation and
diagnosis and how to interpret results accurately. We’ll also explore useful and
specific recommendations for intervention to improve auditory processing and
achieve functional outcomes. You’ll learn from both audiology and
speech-language pathology perspectives and also get up to speed on the
measures used by other professionals to examine potential comorbid deficits in
psychosocial, educational and neurocognitive areas of individuals with CAPD. You can learn more at the URL on this slide. I would like to thank everyone for your attention
and to let you know that I will take your comments and I will answer your
questions during the live text chat session. Thank you again for your attention and your
participation.

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