Tinnitus but No Detectable Hearing Loss? You May Still Have Hearing Loss.
The development of tinnitus has a strong association with hearing loss. The association is so strong that many researchers believe that hearing loss is the most common cause of tinnitus – the evidence is very strong on this point.
However, some individuals have “normal” audiograms that have no detectable hearing loss on them, yet they still have tinnitus. These individuals typically also do not have any identifiable cause for their tinnitus.
It’s a puzzle, particularly given that most of the models we have to explain the development of tinnitus start with noise induced hearing loss.
But what if people with normal audiograms had undetectable hearing loss?
Audiograms measure the “bottom” or “low” threshold of hearing by playing very quiet tones and then increasing the volume until they are detected.
However, audiograms assume that hearing loss occurs in an upwards, step wise fashion.
It turns out that there are different neurons that detect sound at a high volume threshold – and these are not tested in an audiogram.
Overexposure to intense sound can cause temporary or permanent hearing loss. Postexposure recovery of threshold sensitivity has been assumed to indicate reversal of damage to delicate mechano-sensory and neural structures of the inner ear and no persistent or delayed consequences for auditory function.
Here, we show, using cochlear functional assays and confocal imaging of the inner ear in mouse, that acoustic overexposures causing moderate, but completely reversible, threshold elevation leave cochlear sensory cells intact, but cause acute loss of afferent nerve terminals and delayed degeneration of the cochlear nerve.
Results suggest that noise-induced damage to the ear has progressive consequences that are considerably more widespread than are revealed by conventional threshold testing. This primary neurodegeneration should add to difficulties hearing in noisy environments, and could contribute to tinnitus, hyperacusis, and other perceptual anomalies commonly associated with inner ear damage.
Translated, this means:
- You can have a normal audiogram and damage to your auditory perception. This is why people with normal audiograms may have developed tinnitus – they may have undetected damage to their auditory system.
Science continues to change our understanding of tinnitus at a rapid rate.