Current Issues in Pediatric Audiology - Vanderbilt Audiology's Journal Club

Editor’s Note: This text course is an edited transcript of a live seminar. Download supplemental course materials.

Dr. Gus Mueller:  Our presenter today is Dr. Anne Marie Tharpe.  She is Professor and Chair at the Department of Hearing and Speech Sciences, Vanderbilt University School of Medicine.  You may know Dr. Tharpe not only from Vanderbilt, but also for the work that she has done in the area of pediatric audiology over the years.  Perhaps you have the Comprehensive Handbook of Pediatric Audiology textbook, which she completed a few years ago with Richard Seewald (2010).  It has become one of the main texts for teaching pediatric audiology and is an excellent resource. 

This year marks the 30^th anniversary of the seminal publication that Dr. Tharpe authored along with Dr. Fred Bess (1984) entitled, Unilateral Hearing Impairment in Children.  The publication of that article was the first bit of evidence showing that unilateral hearing loss can have quite an impact on many aspects of a child’s life.

In addition to her academic and research accomplishments, Dr. Tharpe is the Chair of the Department of and Hearing and Speech Sciences.  There are 9 different clinics at Vandy, 5 of which are on the main campus, and 2 preschools – one for children with hearing loss and one for children with autism.  We have about 20 research labs.  There are 41 full-time faculty in the department, 16 or 17 of which are audiologists.  There are about 130 staff people, of which 32 are clinical audiologists.  We see about 84,000 patient visits a year.  Dr. Tharpe is in charge of all that, and she does an excellent job.  With that, I will turn it over to our speaker today, Dr. Anne Marie Tharpe.

Dr. Anne Marie Tharpe:  Thank you, Gus.  It’s a pleasure to be here today.   As you’ve mentioned, my passion has always been in pediatric audiology, and my research has focused on applied clinical issues.  Today I’m going to review three interesting articles from the past year that have a direct clinical application to pediatric audiology, although there are many more that were worthy of consideration.

Article 1: Subjective Fatigue in Children with Hearing Loss: Some Preliminary Findings

The first article I’ll review is by Ben Hornsby and colleagues (2013), here at Vanderbilt.  Fatigue has become a hot topic in audiology today.  We have finally gotten beyond simple speech perception advantages with hearing aids, and now we are starting to look at functional health advantages and implications.  I would like to also point out that Fred Bess began looking at functional health measures in the elderly including fatigue and stress when he was conducting the Charge Project in the 1980s.  That was the first time I became aware of this issue.  Dr. Bess later looked at the impact of minimal hearing loss on stress and other functional health status. 

I want to provide you with some background information before getting into the Hornsby (2013) study.  Bess, Dodd-Murphy and Parker (1998) did some work on minimal, permanent hearing loss in children.  The takeaway was that children with minimal losses reported less energy than children with normal hearing.  That was of great interest to those of us who had an interest in minimal bilateral loss as well as unilateral loss. 

I want to explain the concept of effort and how it contributes to fatigue.  We assume a commonly held hypothesis of limited effort capacity, which means that we have only so much effort available to us.  Think about effort being contained in a bucket.  There is a limited capacity.  If we have two tasks to perform, one of which is a difficult listening task, we are going to use most of that effort in the bucket for the listening task, which only leaves a little effort for a secondary task.  Many people have used a paradigm of dual-task performance that is based on this concept of limited effort capacity. 

In a prior study (Hicks & Tharpe, 2002), we looked at listening in the presence of background noise as a primary task.  As a secondary task, we asked children to push a button when they saw a light come on.  The light would come on randomly in front of them.  The children’s primary task was to repeat a word that they heard and the secondary task was pushing a button when the light came on.  The premise here was that if the majority of effort was being used to listen, then children with hearing loss would have a longer reaction time in pushing the button when the light came on than children with normal hearing, because most of their effort was already being allocated towards listening.  This is what we found to be true. 

Subjects & Methods

Hornsby and colleagues asked, “What is the effect of hearing loss on subjective reports of fatigue in school-aged children?”  They had 10 children with hearing loss and 10 age-matched peers with normal hearing (Hornsby, et al., 2013).  They used subjective ratings quantified by the PedsQL Multidimensional Fatigue Scale.  This is a well-standardized, widely- used scale.  All children had normal nonverbal intelligence, and the children with hearing loss had poorer language abilities than those with normal hearing, as would be expected.  They were age-matched within plus-or-minus six months.  The children with hearing loss varied widely in terms of their hearing losses.  There were five who used hearing aids, four with cochlear implants, and one who had a unilateral hearing loss. 

As I mentioned, they used the PedsQL Fatigue Scale.  It queried areas of general fatigue (e.g., “I feel tired”), sleep and rest fatigue (e.g., “I rest a lot”), cognitive fatigue, and then there is a composite score. 

Results

They found that children with hearing loss demonstrated or reported more fatigue than their normal-hearing counterparts on all portions of that scale.  It is interesting to note that the fatigue scores reported in this study indicated more fatigue experienced by children with hearing loss than children with other chronic conditions, such as cancer, rheumatoid arthritis, diabetes, and obesity (Varni, Burwinkle, Katz, Meeske, & Dickinson, 2002; Varni, Burwinkle, & Szer, 2004; Varni, Limbers, Bryant, & Wilson, 2009; Varni, Limbers, Bryant, & Wilson, 2010).  In fact, the study might have even underestimated the impact of hearing loss on fatigue because the PedsQL does not include items for speech processing and listening effort.  I think it is important to consider that more work needs to be done. 

We also know that fatigue can be caused by additional mental effort, and that can lead to increased stress and tension.  In adults, this fatigue has resulted in an increased rate of sick leave (Kramer, Kapteyn, & Houtgast, 2006) and is also associated with attentional and concentration issues, slow mental processing, and impaired decision-making (van der Linden, Frese, & Meijman, 2003).  Certainly, those of us who are interested in pediatric audiology would all be concerned about fatigue being a mitigating factor in poor academic performance of children with hearing loss. 

I also want to mention that Hornsby (2013) had another study that I did not include in this review.  He examined speech-processing-related fatigue and was specifically looking at whether or not hearing aids would mitigate the impact of fatigue.  We have not seen this work done in children, but in adults, he found that the use of hearing aids decreased listening effort.  I think that is a very exciting finding.  Again, it takes us away from only thinking about the impact of hearing loss on speech perception and focuses more globally on what might be going beyond the ears of children with hearing loss. 

Article 2: Predictors of Hearing Aid Use Time in Children with Mild-to-Severe Hearing Loss

The next study that I would like review is by Walker and colleagues (2013); I was intrigued by the title right away.  As a pediatric audiologist, one of our primary goals for children with hearing loss is to ensure full-time hearing aid use.  We typically define full-time use in children as wearing hearing aids during all waking hours, with the exception of bathing or swimming.  I was interested in what kind of documentation might be used in this particular study.  The researchers asked, “What are the predictors of hearing aid use time in children with hearing loss, and what are the challenges?”  As most of you know, we are now screening more than 95% of babies at birth (Russ, Hanna, DesGeorges, & Forsman, 2010).  That is good news but we hope that the process does not stop there.  Identification is not helpful unless it leads to early intervention. 

Although we have a significant loss-to-follow-up rate (Russ, et al., 2010), we do expect that early diagnosis of hearing loss will lead to early intervention, likely hearing aid fitting in most cases.  It is also assumed that children who can achieve consistent full-time use of hearing aids will have better outcomes than children who do not.  Although we accept this on faith, we have not seen this topic specifically addressed in the literature, in terms of the wear time of hearing aids with children. 

There is some evidence that Mary Pat Moeller and colleagues brought forth in 2009 showing that hearing aid use is inconsistent early in life and becomes more consistent with age.  It is also likely that some situations for wearing hearing aids are more challenging than others; these can also vary by age. 

Subjects & Methods

I should point out that the Walker et al. study (2013) was part of the larger Outcomes of Children with Hearing Loss (OCHL) study, which is a multi-site study that has been going on for a number of years; the data are now starting to come out.  They took parents of 272 children with permanent bilateral mild- to- severe hearing loss and presented a hearing aid use questionnaire, which was completed on their regular study visits over time.  Parents, using this questionnaire, would estimate the average amount of time their child used hearing aids per day during the week and also on the weekend, with the assumption that children might vary usage between weekdays when they are in school and on the weekend.  Parents also rated how often their child wore hearing aids in eight different listening environments (car, school, daycare, meal time, playing alone, book sharing, playground, and public).

Results

On average, parents reported children wore hearing aids about 10-and-a-half hours a day during the week and about 10 hours on weekends.  The longer hearing aid use time was associated with older age, poorer hearing, and higher maternal education level.  I want to stop here to say that, for most pediatric audiologists, these results are likely somewhat surprising and disappointing.  Ten hours a day seems relatively short for children, especially school-aged children. 

I also want to mention some interesting results that came out at the Sound Foundation conference in December 2013, as reported by Christine Jones.  She was using data logging to confirm wear time in hearing aids.  She reported that children, on average, were using their hearing aids six hours a day.  That is obviously even more concerning than 10-and-a-half hours a day.  I speculate that the children enrolled in this current study (Walker et al., 2013) are optimal cases.  These are families who have chosen to participate in a longitudinal study that requires some effort on their part to go in on a regular basis to have testing.  I would consider these families to probably be more motivated than average. 

Going back to Christine Jones’ (2013) study, the range of wear time was considerable, with the data logging showing that some children wear their hearing aids less than 30 minutes a day.  There were only 33% of the children in that study who wore their hearing aids greater than or equal to eight hours a day.  That is quite alarming. 

Here are the predictors that Walker (2013) found in this current study.  For every 10 dB increase in the pure-tone average (PTA) of the better hearing ear, the average hearing aid use time increased by half an hour.  This means that the greater the hearing loss, the more the children wore their hearing aids.  For every 10-month increase in age, there was also an increase in hearing aid use time by 0.71 hours.  Mothers who obtained a college degree had children with the most hearing aid use time compared to mothers with less education. 

Furthermore, only 35% of parents of infants responded that they used hearing aids in the car, compared to 78% of parents of preschoolers and school-aged children who use hearing aids in the car.  I think that is understandable and not surprising to most of us who have worked with infants and young toddlers.  We know that infants are in car seats placed in the back seat, and there is often concern about children getting their hearing aids out, throwing them out the window, swallowing them, et cetera.  It is not too surprising that infants would not be wearing their hearing aids in the car as much as older children.  I think it is also interesting to note that 58% of parents of infants reported that they always wear hearing aids at daycare, compared to 79% of preschoolers and 76% of school-aged children who wear hearing aids at daycare.  Again, this is likely a concern about damage to or loss of the hearing aids, and now we have some concrete evidence to support some of the suspicions that many of us have had over the years. 

In terms of the relationship between hearing levels and the use of hearing aids in public and at school, children who had greater hearing loss showed more consistent hearing aid use in public and at school.  It is speculated that this is likely because children (or the parents of those children) who have hearing losses better than 50 dB feel that they can get along without hearing aids, and that it is not as important as for those children with more significant losses. 

The authors presented an open-ended question about the challenges of consistent hearing aid use in relation to age.  The child’s state was considered one of the most important and significant challenges to hearing aid use.  In other words, if a child was fussy, crying, and tearing off the hearing aid, that was an important factor related to keeping a hearing aid on a child.  That was more important for those children who were very young, in the birth to two-year age range. 

Parental Estimates of Average Hearing Aid Use

A second study was also completed (Walker et al., 2013).  For this study, the researchers examined the accuracy of parental estimates of average hearing aid use time for their children.  They compared these reports to objective data logging measures.  It is important to note that the parents were unaware that the data logging feature of the hearing aid was being used.  They found 84% of parents overestimated their child’s hearing aid use time.  This might relate back to what I was saying about the report from Christine Jones (2013) who, through data logging, found less hearing aid use than in this current parental report.  They found that only 16% either underestimated or were accurate in their estimations of hearing aid use.  The parents reported about 10-and-a-half hours a day of use, and the data logging indicated about 8 hours a day of use.  The older the child was, the smaller the expected difference would be between the parents’ estimates and data logging.

Applications

Why is this important?  I think most of us can come up with many reasons why this would be important for an audiologist to know.  One reason could be for counseling parents about hearing aid use.  We can tell them that we know there are certain challenges for keeping aids on and one of them is that their very young children get fussy -- and they are not alone.  All parents find that it is difficult keeping the hearing aids on a young child, but the important thing is that things get better.  As children get older, their state is better controlled, they are not as fussy, and it will be easier to keep the hearing aids in.  I think that that is an important message for counseling purposes. 

For me, this raises another interesting issue, and that is the use of data logging to monitor how much hearing aids are used.  I have been in several discussions with pediatric audiologists at meetings talking about whether or not we should notify parents that we can look at how many hours their child is using hearing aids or not.  Is that going to put pressure on parents?  Will it make them feel that big brother is watching?  Is it going to, for some parents, make them turn on the hearing aids and set them on the dresser to fool their audiologists? Or is it better for us to have that information and knowledge, and then use the knowledge of how much a child is using his or her hearing aids to help us in counseling that family?  It would be an indication to us that perhaps we need to spend more time with the family when we see data logging that suggests the family is having a difficult time keeping the hearing aids in. 

The other point I would like to make is on counseling for parents of children with milder losses.  This study (Walker et al., 2013) verified that less hearing loss resulted in less hearing aid use time.  This is something that also came up in Mary Pat Moeller’s 2009 study as well.  Parents of children with milder losses do not see the benefits as dramatically as parents of children with more severe hearing losses.  This is where I think providing families with simulations of mild hearing loss can be particularly useful, because it is hard for them to see the benefits of hearing aid use with their own eyes.

Article 3: The Future Role of Genetic Screening to Detect Newborns at Risk of Childhood-Onset Hearing Loss

The next study that I would like to cover discusses the role of genetic screening for hearing loss in infancy (Phillips, Bitner-Glindzicz, Lench, Steel, Langford et al., 2013).  I would like to start by first saying that I am not a geneticist, nor do I conduct genetic research, but as a pediatric audiologist, I am very interested in this concept, as I am sure you are as well.  Interest has been growing in genetic screening for hearing loss over the last decade, and as we learn more and more about genetics and genetic hearing loss, more and more interest in screening is expressed.   I am going to describe an expert consensus statement out of England.  Let me provide a bit of background before we get into the details of what this paper discussed. 

We know that hearing loss is the most common birth defect in developed countries.  Permanent hearing loss of greater than moderate degree occurs in about 1.6 per 1,000 live births.  These are data out of England, but are similar in the United States.  At least two-thirds of these losses have a genetic cause, and about 70% of those genetically- caused losses are non-syndromic. 

Discussion

This group of experts asked, “What is the future potential of genetic screening to detect newborns at risk of childhood hearing loss?”  I see this as very similar to the way that we approached newborn hearing screening back in the early 1990s.  We had a group of experts come together as the National Institutes of Health (NIH) Consensus Group in March of 1993 to discuss the future of newborn hearing screening in this country.  That is a very similar approach to what was taken here.  In England, as I mentioned, they have a rate of about 1.6 per 1,000 births with permanent hearing loss, and about 3.5 per 1,000 children at school-age.  That is a big increase between the newborn period and entry into school.  It is not clear if these children were those with very mild losses who were passed on a newborn hearing screening, whether or not they were true false negatives, or whether they had acquired late-onset, progressive losses because of genetic predisposition for hearing loss.  That is what set the stage for these individuals to start considering genetic screening for hearing loss. 

This was an expert-led discussion of current and future developments in genetic technology to understand what the knowledge base is of genetic hearing loss and the viability of genetic screening.  They concluded that technology would yield it possible to have an entire genome sequenced within 10 years.  It is interesting though that there is little commercial interest in developing genetic assays for hearing loss compared to other conditions.  This is likely because there are no commercially produced therapeutic interventions that could be linked.  We end up with “what now?” and “where do we go from here?”  There is also a great need to standardize the interpretation of genetic tests across geneticists.  There is large variance in terms of interpretation, how geneticists approach such information, and how they use it.  There is a need for algorithms that can guide the counseling and the interpretation of these genetic tests before they are widely used. 

They also concluded that genetics cannot be reliably used in a screening capacity for hearing loss until we know more about the genes involved and the clinical significance.  We do not know if an asymptomatic newborn with a mutation in the gene will experience hearing loss or not.  Hearing loss is genetically very heterogeneous, and it involves mutations in many genes.  It is not possible to predict the risk of developing the hearing loss by assessing a single or even a selection of genes that are currently identified. 

For example, we know that the most frequent causative gene is GJB2.  GJB2 has at least 300 mutations.  In order to assay this, we would have to have measures that would search for 300 different mutations on just one gene.  I think you can imagine the load that would be required for doing a thorough screening for hearing loss.  There have been about 70 genes for nonsyndromic hearing loss identified to date.  It is anticipated that more than 500 genes, some with hundreds of mutations per gene, are likely to be involved in causing hearing loss.  Furthermore, some of these mutations could require interactions among genes.  Identifying one gene mutation does not necessarily mean that hearing loss will be expressed. 

We also know that current methods of DNA analysis require two to five milliliters of blood, and this is simply unacceptable for a newborn screen.  This will improve over time, and the hope is that the heel prick obtained in nurseries for screening for other conditions will be sufficient for a DNA analysis, but at this point in time, that is not the case.  Additionally, whole genome sequencing would require extensive data processing and storage requirements.  The cost is rather remarkable.

Another issue, that reminds me of some of the debates that we had around universal newborn hearing screening in the 1990s, involves incidental findings.  What about the impact on the families of these results?  For example, if a whole genome is sequenced, what about all the other mutations not related to hearing loss that become available and could give rise to future diseases and conditions?  What is our ethical and moral obligation to report what is seen even beyond what was screened for?  This paper recommended that we be cautious in moving forward with genetic screening for hearing loss and that we consider testing all newborns and children with known hearing loss so that we can help to determine the etiology, as it can improve our knowledge of genetic causes of hearing loss.  However, genetically screening newborns universally, certainly at this time, is not justified. 

They did provide a lot of good information about what considerations should be made as we approach and consider genetic screening for hearing loss.  I think it would be an interesting article for all of us to read.  They also discussed the notion that in the next 10 years, it is likely that genetic screening will be much more widespread.  It is also likely that we will not just be screening for hearing loss but for many genetic indicators of chronic disease.   With newborn hearing screening, we went out on our own as a field to screen for hearing using auditory brainstem response (ABR) and otoacoustic emissions (OAE).  In the case of genetic screening, we will need to partner with our medical colleagues from other areas, because screening for genetic hearing loss will be but one part of a global screening process for children. 

I found this article to be fascinating, and it got me thinking about all kinds of changes that could be implemented with newborn hearing screening.  In other words, we now have the potential for a better mousetrap, if you will.  We have all been concerned about the number of children that we miss, especially those with milder losses through newborn screening, and the fact that we do not have an additional mandated screening until children enter school.  That is a long period of time in which we are missing hearing losses, many of which are genetically based.  I find this to be an intriguing topic and one that should be garnering the attention of anyone who has interest in pediatric audiology. 

Those are the articles that I wanted to cover with you today, and at this time we’ll take questions. 

Questions and Answers

You mentioned subjective fatigue in the Hornsby (2013) study.  Did they measure objective fatigue in that study also?  I also know that you have been involved in studies where you measure objective fatigue.  Could you talk about how that is done? 

The Hornsby et al. (2013) study was simply on the subjective fatigue measures.  This is part of a larger study that this Vanderbilt group is doing where they are objectively measuring fatigue.  However, he did not report it here.  Those results are still being analyzed, but I expect them to be out relatively soon. 

In the study that I did with Hicks (2002), we objectively measured fatigue.  We did this through the use of salivary cortisol levels, and that is a common way to measure fatigue.  In our study, we took salivary cortisol levels early in the school day for each child, and then later in the school day for each child.  We looked at whether or not there were significant differences in the cortisol levels, which are indicators of fatigue, for the children with hearing loss versus their normal hearing counterparts.  In that particular study, we did not find significant differences.  We think that that was probably due to methodological limitations, because it is very critical what time of day you take the measurements and how the time relates to when a child eats and other factors.  The cortisol can be affected by diet.  In any case, we did not find between-group differences. 

The Vanderbilt team has a new approach to how they are measuring salivary cortisol in the current study.  I am very interested to see if they improved that technique such that they could measure fatigue effects.  One of the complicating features of using cortisol is that you get increased cortisol levels with stress and decreased cortisol with fatigue.  If one assumes that children get stressed when they cannot hear and perform in a classroom, you could have some interactions that could mitigate the findings.  It is complicated, but also very interesting, and I am optimistic that Ben and his colleagues will be able to reveal something from their cortisol findings. 

Dr. Mueller:  It is certainly an interesting area.  I know these types of measures are going a step further with adults to evaluate if these types of things can be used to measure the benefit of given hearing aid features.  Do you have less fatigue when noise reduction is turned on?  Do you have less fatigue when you are using directional microphone technology?  Do you have less fatigue when you are fitted to a prescriptive method rather than some other way?  I am guessing with both children and adults that we are going to be seeing a lot of things in this area down the road.

Do you think hearing aid wear time would go down again in the teen years?

Dr. Tharpe: Absolutely.  I would venture to guess that when teenagers get to school, a lot of those hearing aids go right into their backpacks.    Again, I think the issue would be how significant the hearing loss is and whether or not the teenager thought they could get by without the hearing aid.  I expect an interaction between age and degree of hearing loss. 

Have you developed a protocol for counseling families on data logging and hearing aid use?

We have not.  I would be interested to know if anyone else has developed a protocol.  Right now we are approaching this on an individual basis.  For the most part, I would say that we do not tell our families that we are checking their data logging when we check hearing aids.  We just say we are checking the features of the hearing aid.  We are also very cognizant of trying to build trusting relationships with our families, and we do not want them to feel that we are scolding them when we find that they have not been using the hearing aids.  We would like to know that we have accurate information from the data logging and that it could raise a red flag for certain families who may need some more support in hearing aid use.  Data logging allows us the opportunity to identify those families. 

Should we be sharing with the family that as the child gets older, it may be easier to deal with the use of the hearing aids?  I am concerned that perhaps parents will relax and wait for the child to grow up before implementing consistent hearing aid use.

I think that is a wonderful point.  We always are walking a fine line of trying to reassure families without making them feel that it is not a big deal.  I think that we should let families know that they are not alone.  I think that is the message more than anything else, and that we expect things to get better over time as the child grows.  At the same time, we need to talk about how critical it is that we increase the hours that children are wearing their hearing aids.  I think we should be talking about the importance of those early years in developing speech, language and communication skills as opposed to talking about increasing wear time by a certain amount each day.  The families are much more concerned about communicating with their children than they are with how many hours the children wear their hearing aids.  We need to make that connection for them in our discussions.

Are there standard recommendations for children diagnosed with hearing loss to go to other specialties besides otolaryngology (ENT)?

Yes, there are.  The JCIH (2007, 2013) provide specific guidelines about medical management and intervention. Recommendations can include ophthalmology, genetic counseling, and depending on the results of the etiologic evaluations, we would make referrals to cardiology or to nephrology to test kidney function, et cetera.  I hope it goes without saying that all children with hearing loss will be referred to their state early intervention system. 

References

Bess, F. H., Dodd-Murphy, J., Parker, R. A. (1998). Children with minimal sensorineural hearing loss: prevalence, educational performance, and functional status. Ear and Hearing, 19(5), 339-354.

Bess, F. H., & Tharpe, A. M. (1984). Unilateral hearing impairment in children. Pediatrics, 74(2), 206-216.

Hicks, C. B., & Tharpe, A. M. (2002). Listening effort and fatigue in school-age children with and without hearing loss. Journal of Speech, Language, and Hearing Research, 45(3), 573-584.

Hornsby, B. W. Y. (2013). The effects of hearing aid use on listening effort and mental fatigue associated with sustained speech processing demands. Ear and Hearing, 34(5), 523-534. doi: 10.1097/AUD.0b013e31828003d8.

Hornsby, B. W. Y., Werfel, K., Camarata, S. & Bess, F. H. (2013). Subjective fatigue in children with hearing loss: Some preliminary findings. American Journal of Audiology, 23(1), 129-134. doi: 10.1044/1059-0889(2013/13-0017).

JCIH (2007, 2013)

Jones, C. (2013, December). What do we know about the fitting and daily life usage of hearing instruments in pediatrics? Session presented at the 6^th International Pediatric Audiology Conference, A Sound Foundation through Early Amplification, Chicago, IL.

Kramer, S. E., Kapteyn, T. S., & Houtgast, T. (2006). Occupational performance: comparing normally-hearing and hearing-impaired employees using the Amsterdam Checklist for Hearing and Work. International Journal of Audiology, 45(9), 503-512.

Moeller, M. P., Hoover, B., Peterson, B., & Stelmchowicz, P. (2009). Consistency of hearing aid use in infants with early-identified hearing loss. American Journal of Audiology, 18(1), 14-23. doi: 10.1044/1059-0889(2008/08-0010).

Phillips, L. L., Bitner-Glindzicz, M., Lench, N., Steel, K. P., Langford, C., Dawson, S. J., et al. (2013). The future role of genetic screening to detect newborns at risk of childhood-onset hearing loss. International Journal of Audiology, 52(2), 124-133.

Russ, S. A., Hanna, D., DesGeorges, J., & Forsman, I. (2010). Improving follow up to newborn hearing screening: a learning-collaborative experience. Pediatrics, 126(Suppl 1), S59-S69. doi: 10.1542/peds.2010-0354K.

Seewald, R., & Tharpe, A. M. (2010). Comprehensive handbook of pediatric audiology. San Diego, CA: Plural Publishing.

Van der Linden, D., Frese, M., & Meijman, T. F. (2003). Mental fatigue and the control of cognitive processes: effects on perseveration and planning. Acta Psychologica, 11(3), 45-65.

Varni, J. W., Burwinkle, T. M., Katz, E. R., Meeske, K., & Dickinson, P. (2002). The PedsQL in pediatric cancer: reliability and validity of the Pediatric Quality of Life Inventory Generic Core Scales, Multidimensional Fatigue Scale, and Cancer Module.  Cancer, 94(7), 2090-2106.

Varni, J. W., Burwinkle, T. M., & Szer, I. S. (2004). The PedsQL multidimensional fatigue scale in pediatric rheumatology: reliability and validity. The Journal of Rheumatology, 31(12), 2494-2500.

Varni, J. W., Limbers, C. A., Bryant, W. P., Wilson, D. P. (2009). The PedsQL multidimensional fatigue scale in type 1 diabetes: feasibility, reliability, and validity. Pediatric Diabetes, 10(5), 321-328. doi: 10.1111/j.1399-5448.2008.00482.x.

Varni, J. W., Limbers, C. A., Bryant, W. P., Wilson, D. P. (2010). The PedsQL multidimensional fatigue scale in pediatric obesity: feasibility, reliability and validity. International Journal of Pediatric Obesity, 5(1), 34-42. doi: 10.3109/17477160903111706.

Walker, E. A., Spratford, M., Moeller, M. P., Oleson, J., Ou, H., Rousch, P., et al. (2013). Predictors of hearing aid use time in children with mild-to-severe hearing loss. Language, Speech, and Hearing Services in Schools, 44(1), 73-88. doi: 10.1044/0161-1461(2012/12-0005).