We are Learning More about “Hidden Hearing Loss.”

It may happen once or twice a week:  Someone comes into the office saying they are having difficulty hearing at times when the people with them are not having problems. They may miss the punchline of a joke, or struggle to follow a conversation at a noisy restaurant.  They are not sure if they have normal hearing or not.   We do our testing, and find that the audiogram – the gold standard test of hearing sensitivity – is normal.

Researchers from Massachusetts Eye and Ear have, for the first time, linked difficulty with speech understanding in noisy settings with evidence of a condition known as “hidden hearing loss” in people with normal hearing sensitivity. 

Hidden hearing loss refers to damage to the connections between the auditory nerve fibers and the sensory cells in the cochlea.  This damage precedes the loss of the sensory cells themselves.  Reduced connections likely contribute to problems understanding speech in noisy or reverberant environments, even when the audiogram indicates “normal” hearing.  Lost connections may also play a part in the onset of tinnitus (ringing in the ear) or hyperacusis (sensitivity to loud sounds).

We know that these difficulties do not show up on our routine tests. The researchers at Mass Eye and Ear set out to develop better measures to test for cochlear synaptopathy, that is, damage to the sensory-neural connections.

Diagnostic tests for hidden hearing loss are important to fully assess damage to the inner ear, especially damage induced by noise exposure.  This would give us a more comprehensive understanding of the basis of the problems our patients are reporting.  We can then discuss preventive strategies going forward, and offer assistive technology options such as remote microphones.  Better diagnostic tools are also important is developing future therapies to repair inner ear nerve damage. Research is being done on animals that offer hope that one day connections between sensory cells and auditory nerve fibers can be successfully restored!

This is a work in progress.  Researchers are looking at whether Speech-in-Noise testing or auditory nerve tests can pick up early inner ear damage even before there are audiometric changes.   Clear definitive answers are not here yet, but this is an exciting direction that may lead to better understanding and future solutions.

Meanwhile, protect your ears from excessive sound levels, as we are sure that noise is in part the culprit for inner ear damage, and stay tuned as we learn more.