Tinnitus affects up to about a quarter of older adults. The precise form ranges from whistling, humming, clicking, whining, rumbling, and even musical hallucinations. This can be intrusive and distracting causing depression, anxiety and sleep difficulties. It also can interfere with hearing. 

Current treatment is limited to removing any possible build-up of wax or changing medication which may be contributing. Ultimately, many people are advised (and helped) simply to live with it. 

A Connection?

A connection between the two conditions has been known for some time. It is known, for example, if people have hearing loss at particular frequencies, a whine from tinnitus is frequently at the same pitch.¹ Interestingly, it is also possible to trigger temporary tinnitus by wearing heavy duty earplugs for several days to mimic hearing loss. 

The connection is somewhat paradoxical with one being the inability to hear noise that is physically present, and the other the ability to hear noises which are not physically present. However, a theory known as ‘central gain theory’ suggests that a loss of input from the ears causes the brain to compensate by becoming more sensitive. 

However, a problem with this theory is that up to a quarter of people with tinnitus have normal hearing test results.  An answer to this may now be known. 

Soundwaves pass through the eardrum reaching fluid inside the cochlea.  Cells with tiny hairs within this fluid are buffeted turning soundwaves into electrical impulses which travel along nerves to the brain. Such hair cells gradually die off as people get older especially ones registering high-frequency sounds. It has also been assumed that loud noise damages the hearing by killing the same hair cells. 

A New Theory? 

However, a theory, considered by Sharon Kujawa and Charles Liberman from the Harvard Medical School dating to 2009 following work on mice, found that the nerve fibres that carry signals from the hair cells to the brain are more vulnerable to noise damage than hair cells are. 

It was also found that there are at least three different types of nerve fibres processing sounds at different volumes: quiet, intermediate and loud. It is the fibres processing loud noise which are most susceptible to damage. 

Such findings have been replicated on a number of different animals. 

This may provide an explanation as to why it is common for older people to have difficulties understanding speech in noisy (loud) surroundings such as pubs and restaurants. It may be that the nerve fibres responding to quiet sounds are fine but that those responding to louder sounds are damaged. 

This may also explain why some people with tinnitus have good hearing according to an audiogram. An audiogram only measures the quietest sound that people can hear, and not their ability to hear louder sound². 

Further research from University College in London found that people with tinnitus but normal results on hearing tests had lower activity in the nerves leading from the ear to the brain compared to those without tinnitus but with normal hearing.  This supports the idea that the brain is getting less input from the damaged nerve fibres and so responds by generating phantom sounds of tinnitus. 

This research also proposed a condition of having hearing problems only in noisy environments called ‘hidden hearing loss’, a term which has gained some traction. Further studies have confirmed this finding in larger groups of people. 

Accordingly, the evidence that noise exposure can affect cochlear nerves to cause hidden hearing loss, even before it kills hair cells is beginning to be taken more seriously. However, it is unknown how common this form of hearing loss is. 

Treatment 

As to treatment, reversing damage caused by hair cells was considered to be a formidable challenge. However, repairing cochlear nerve fibres is considered to be more achievable. Natural signalling molecules called neurotrophins can coax fibres and synapses to regrow. In one experiment with animals, synapse growth was possible to the extent at this gave the animals superior hearing to normal. 

A French firm called Cilcare has several drugs in the works which can trigger production of multiple neurotrophins, and is due to start a trial next year for people considered to have hidden hearing loss, with or without tinnitus. 

Of course, such an approach may take some time to become available in the clinic. 

Tinnitus 

There is another approach being undertaken in relation to tinnitus specifically. 

The cochlear nucleus also receives inputs from other parts of the body, including from touch neurons from the face, jaw and neck.  It is thought that this may be to suppress sounds caused by body movements such as chewing.  It may be why some people are able to change the pitch/ loudness of their tinnitus by moving their jaw or neck. 

Two companies are producing devices aiming to reduce tinnitus symptoms by providing sounds alongside electrical stimulation of touch neurons.  The theory is that over time this will reduce overactivity of the auditory circuits within the cochlear nucleus. 

In one trial there was a reduction of loudness of tinnitus with electrodes placed on the jaw or neck, and in another with stimulation to the tongue. 

Conclusion 

This interesting article does show that there are some future treatments that may ameliorate symptoms for both hearing loss and tinnitus.  It does appear that such treatment may improve symptoms, but not remove symptoms entirely.   

It does not seem that there will be any immediate impact on NIHL cases. 

However, in time, these potential treatments may increase the chances of individuals being able to live with and ‘make peace’ with their problems.  If trials are successful, then it will be interesting to see if such treatment will start to appear on Schedules of Loss in the future.