Common Inner Ear Pathologies Flashcards
How may a sensory-neural HI arise?
Can arise from deficits in the:
- Cochlear
- Auditory nerve
- Centrally
Common disorders include:
- Presbyacusis
- Dead regions
- Hidden hearing loss
- Noise induced hearing loss
- Non-organic hearing loss
- Vestibular schwannoma and other lesions
What is the cause of presbyacusis?
Caused by loss of hair cells (hair cells are post-mitotic)
Three systems in the inner ear are susceptible to age related decline:
- Stria vascularis: lowers endo-cochlear potential
- Outer hair cells: loss of cochlear amplification, reduction in basilar membrane vibration
- Inner hair cells: loss of sensitivity to basilar membrane vibration
These systems can be effected alone or in combination
What does “voltage starved” mean for an individual with presbyacusis and what may their audiogram look like?
- When there is a degradation of stria vascularis, the flow of potassium ions into the hair cells is negatively impacted
- This will show up in a flat or gently sloping loss
What does a typical audiogram look like for an individual with presbyacusis?
- Flat loss in the low frequencies
- Gently sloping loss in the high frequencies above 1KHz
Why might we see a notched pattern in males with presbyacusis?
- This can be due to noise exposure effects
- After screening for NIHL, there is little gender difference
What other relevant factors are there that can contribute to presbyacusis?
- Noise exposure
- Ototoxicity
- Age
- Genetics
Presbyacusis accumulates due to these factors, not linearly .
What would a presbyacusis sensory loss look like on an audiogram?
- Steeper than a metabolic loss (reduction in endo-cochlear potential)
- Moderate to profound deafness
What happens when hair cells in presbyacusis?
- Atypical function: reduced cell size of shape, stereocilla damage or loss, fragmented pattern
- Apoptosis: “active” or controlled cell death
- Necrosis: “passive” via energy deprivation
What is cochlear loss associated with?
- Loss of sensitivity
- Abnormally steep growth in loudness with level
- Reduction in frequency selectivity
If cochlear loss resulted in loss of sensitivity alone, we would be able to just amplify the regions of loss. However, because of loudness growth and reduced frequency selectivity, it becomes more complicated.
What is the effect of loss of absolute sensitivity?
- Quiet parts of speech becomes inaudible
- Difficulty hearing quieter sounds first (voiceless sounds, fricatives, plosive bursts - p, k, t)
- Reduction in fricative contrasts
What is the effect of abnormal loudness growth?
- The cochlear has a compressive non-linearity
- In low level sounds, there is high amplificiation. In high level sounds there is little amplification, often only the passive movement of the BM
- For those with presbyacusis, they lose this compression. Therefore, loudness grows much more rapidly.
- Therefore HA’s need compression
What is the effect of reduced frequency selectivity?
- Damage to OHCs results in a loss to the sharp tuning of the auditory filters
- The result is a much wider and broader auditory filter and difficulty separating similar sounds.
- Especially difficult to understand speech in noise but not in quiet
What is a dead region?
- A type of sensory-neural hearing loss that effects the IHCs
- Associated with SNHL greater the 55dB HL
- Expect poor speech discrimination
- Difficult to identify exact dead regions due to off frequency listening. However, the TEN test can identify these regions.
What is a “hidden hearing loss”?
A change in hearing ability that doesn’t lead to an increase in pure tone thresholds
What are the first steps you should take in a suspected hidden hearing loss?
- Test the extended high frequencies
- Identify what their baseline is (e.g., their baseline may be -10 and they are now 20. Whilst still normal, it is still a loss of hearing)
What is thought to cause hidden hearing loss?
- Attached to each neuron in the inner ear are complements of neurons
- A complement is like a collection of many different neurons
- Each of these neurons are a narrow dynamic range that has a different level of excitation (some respond to low level sounds, medium and high)
- It is thought that a hidden hearing loss occurs when the medium and higher level responding neurons are damaged, but not the low levels.
What would an audiogram look like for someone experiencing ototoxicity?
Steeply sloping hearing loss in the high frequencies.
