Hidden Hearing Loss Flashcards
What is hidden hearing loss?
AKA cochlear neuropathy
Used to describe a peripheral hearing loss that is not evident on a conventional threshold audiogram
What are the clinical findings with HHL?
- Normal behavioral audiogram
- Reduced suprathreshold amplitude on CAP and ABR
- Normal otoacoustic emissions
What are the possible presenting symptoms of HHL? (Kujawa & Liberman, 2009; Furman et al., 2013; Liberman et al., 2016; Wan & Corfas, 2017)
- speech understanding difficulties in noise
- Temporal processing deficits in noise
- Tinnitus and/or hyperacusis
What are the limitations of the current test battery for detecting hidden hearing loss?
The hearing loss does not appear on the behavioral threshold audiogram and OAEs are also normal
Need a measure that is sensitive to changes in the neural synapses and spiral ganglion neurons
What clinical technologies might be promising for detecting HHL?
- Click-evoked EcochG–> evaluates difference between the waveforms created by hair cells (Summating Potential [SP]) and cochlear neurons (Action Potential [AP]) (Liberman et al., 2016). assesses cochlear function
- ABR–> latency of wave V can be used to diagnose HHL and synaptic changes (Mehraei et al., 2016)
- Ultra-high frequency testing–> shown to correlate with SP/AP ratio (Liberman et al., 2016)
- Word Recognition and Questionnaires–> quantify communication difficulties patient is experiencing
What recommendations would you make to an individual diagnosed with this kind of disorder?
- Hearing protection to prevent further damage
- Hearing aids may be helpful depending on their amount of difficulty (but they have normal hearing)
- Neurotrophic factors delivered directly to the round window to help with synapse regeneration (Liberman et al., 2016)
- Continue to monitor hearing to make sure that it doesn’t get worse
Describe the Kujawa & Liberman (2009) article
- one of first descriptions of HHL
- Used CBA/CaJ mice which aren’t susceptible to age-related hearing loss
- DPOAE, ABR, CAP–> all 3 b/c characterizes the entire path up to the brainstem
- At 16 weeks, exposed to 100 dB SPL for 2 hours resulting in 40-50 dB TTS, elevated ABR and CAP thresholds, and slightly elevated DPOAEs
What are the findings of Kujawa & Liberman, 2009?
- After a period of time, thresholds and DPOAEs recovered however suprathreshold ABR and CAP thresholds were still elevated,
- Recovery of hair cell function, but irreversible damage to the afferent nerve terminals
- Noted a delay in degeneration of spiral ganglion neurons
- Histological analysis showed hair cells were intact despite the loss of afferent nerve terminals
What are the clinical implications of Kujawa et al., 2009?
- Shows that clinical tests such as audiogram and DPOAEs are not enough to adequately capture synaptic changes occurring as a result of noise damage
- No such thing as TTS because there is irreversible damage to the nerve synapses
- Noise exposure is “more dangerous than has been assumed” because it isn’t always detected on an audiogram
What was the hypothesis of the Furman et al., 2013 article?
Cochlear neuropathy (AKA HHL) targets auditory nerve fibers with low spontaneous rates.
Neurons with high thresholds and low spontaneous rates are responsible for contributing to our ability to understand speech in background noise
Describe the methods used in Furman et al., 2013
- Used guinea pigs
- Exposed to 2 hours of 106 dB noise resulting in 40-50 dB TTS, elevated DPOAEs, and reduced ABR amplitude
What did Furman et al., 2013 find?
- 2 weeks following exposure, DPOAEs and ABR thresholds recovered but suprathreshold ABR remained reduced
- 2 weeks following exposure, single fiber recordings were normal in the remaining fibers, but population statistics showed a selective loss of low and medium spontaneous rate neurons
- Recovery of hair cell function but permanent damage to neural fibers; selective loss of low spontaneous rate neurons
- Histological analysis showed no hair cell loss
What does it mean that there is recovery in the ABR?
High rate neurons required for the ABR are not targeted by the damage
What are the clinical implications of Furman et al., 2013?
Behavioral audiogram is not enough to capture early changes associated with noise-induced hearing loss and that the low spontaneous rate neurons needed for speech understanding in noise are targeted.
Describe the Liberman et al., 2016 article
- Recruited college students wth normal hearing and split into low-risk and high-risk group based on noise exposure history
All participants completed:
- questionnaires
- behavioral audiometry (250-16,000 Hz)
- DPOAEs
- click-evoked EcochG looking at SP/AP ratio
- WR in quiet, noise, reverberation, and using time compressed stimuli
