Aided cortical testing – considerations for patients with auditory neuropathy spectrum disorder

This video will explore the clinical utility of the aided cortical tests for patients with auditory neuropathy spectrum disorder (ANSD). Patients with ANSD are challenging to manage due to the discrepancy between their ABR results and actual hearing thresholds. The aided cortical test can be used in the unaided state to help inform decisions regarding amplification, cochlear implantation referral and validation of any hearing aids provided to this complex group.

You can read the full transcript below.

ABR

There has been a lot of interest in the clinical application of cortical testing for patients with Auditory Neuropathy Spectrum Disorder, also known as ANSD.

This is generally because cortical testing provides information about where the sounds are detected at the furthest part of the auditory pathway, the cortex.

The pathophysiology of Auditory Neuropathy Spectrum Disorder relates to the connection between the cochlea and the neural pathway and is typically identified using auditory brainstem response testing.

The issue with ABR testing is that although it can help in the identification of ANSD, the results don't tend to correlate with behavioral testing or how well the patient can actually hear in the real world.

ABR results in cases of ANSD can show absent morphologies at maximum presentation levels, which can look like severe to profound hearing loss.

However, it is known that behavioral testing can and does often show much better thresholds.

The problem with relying on behavioral thresholds to understand the degree of hearing loss, and therefore the best method of intervention, is that for children it may be several years after their diagnosis as an infant before reliable behavioral thresholds can be obtained, and accurate amplification can be provided.

This can lead to the child missing out on receiving vital auditory information during those early years of crucial speech and language development.

ALR/CAEP

There is evidence that cortical auditory evoked potentials, also known as the auditory late response, are less affected by ANSD than ABRs, as they are less reliant on timing to elicit responses.

Threshold cortical testing can be useful for older children and adults with ANSD in order to establish frequency-specific threshold information.

However, this is not recommended for infants and younger children, due to the immature cortex and resulting lack of robust waveform morphology.

This is further exacerbated by challenges in reducing the patient noise sufficiently to record the small amplitude responses around threshold.

Instead, for this patient group, there has been more attention given to cortical testing using speech-like stimuli, which are presented via the sound field.

This is an example of using the aided cortical test, but in the unaided condition.

The results obtained can help inform decisions about earlier provision of hearing aid amplification than was traditionally possible, and also onward referral for cochlear implantation.

Research on assessing ANSD

Rance et al. in 2002 compared two cohorts of children, one with ANSD and one with sensorineural loss [1].

They performed speech testing and unaided cortical testing using a speech like stimulus and a tonal stimulus.

Amongst a range of findings, of the 18 children with ANSD, cortical responses were recordable in 50% of the cases.

The findings of this study confirm that cortical waveforms can be recorded in ANSD patients, but also raise a note of caution regarding the interpretation of non-responses.

As is the case for any children undergoing cortical testing, it is important to remain mindful that an absent response does not always indicate that the patient cannot hear the presented stimulus.

In this paper by Pearce et al., a case study was presented of an infant diagnosed with ANSD who then went on to have unaided cortical testing performed using speech stimuli in order to help guide decisions regarding whether amplification was warranted [2].

This child had absent ABR responses to 500 Hz and 2 kHz at the maximum testable levels, but present DPOAEs across the full tested frequency range.

The parents reported that the child was responsive to sounds around the home, such as familiar voices and the stereo.

Unaided cortical testing showed repeatable responses to all three stimuli at a level of 65 dB SPL.

It is worth highlighting the relatively poor frequency specificity of the stimuli used.

Based on the results obtained and the parental reporting, it was possible to exclude a severe hearing loss.

However, a mild to moderate loss was still possible.

As a result, it was decided to proceed with amplification using an audiogram that would not cause cochlear damage even if the thresholds were found to be normal.

This patient's unaided cortical testing was performed at 7 weeks corrected age, allowing for hearing aid fitting shortly after.

In contrast, reliable behavioral thresholds via visual reinforcement audiometry could not be obtained until two and a half years of age.

Typically, behavioral testing can be performed reliably at a much younger age than this, however it is not uncommon to see a delay in obtaining results in ANSD cases.

Furthermore, this child was born at 28 weeks gestation age.

Prematurity and ANSD are often seen together and a degree of developmental delay can result, leading to delays in being able to perform behavioral testing.

A paper published by Punch et al. in 2016 summarized the Australian Hearing protocol for fitting hearing aids to infants diagnosed with hearing loss, which were the guidelines followed in the previous study [3].

These guidelines specifically highlight that in cases of ANSD, any decision to provide hearing aids and the estimated audiogram levels used should be based on all of the available clinical information, including behavioral testing, parental reporting, for example through the use of the validated PEACH questionnaire, and unaided cortical testing results.

In addition to providing useful information regarding the decision to aid, the Australian Hearing protocol also advises on the use of aided cortical testing for those patients with ANSD who have been fitted with hearing aids.

This can add valuable information regarding decisions surrounding consideration for cochlear implantation, which many ANSD patients are deemed suitable for.

Managing ANSD patients

Patients with ANSD continue to be challenging to diagnose and manage.

Cortical testing in both the unaided and aided condition, using speech-like stimuli, can provide useful information in both the decision-making process relating to amplification and the validation of amplification provided.

Caution must be used when interpreting non-responses, as there are scenarios where cortical responses may not be present, but the stimuli may in fact be audible.

It is essential to adopt a test-battery approach, whereby multiple sources of information and test results are used to corroborate each other and inform the most suitable management for each individual patient.

References

[1] Rance, G., Cone-Wesson, B., Wunderlich, J., & Dowell, R. (2002). Speech perception and cortical event related potentials in children with auditory neuropathy. Ear and hearing, 23(3), 239–253.

[2] Pearce, W., Golding, M., & Dillon, H. (2007). Cortical auditory evoked potentials in the assessment of auditory neuropathy: two case studies. Journal of the American Academy of Audiology, 18(5), 380–390.

[3] Punch, S., Van Dun, B., King, A., Carter, L., & Pearce, W. (2016). Clinical Experience of Using Cortical Auditory Evoked Potentials in the Treatment of Infant Hearing Loss in Australia. Seminars in hearing, 37(1), 36–52.