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Acquired hearing loss is often accompanied by tinnitus. Tinnitus is an auditory perception (such as a whistling or hissing) without an external stimulus. This perception can be very debilitating and nearly 50% of all adult visits to otolaryngologists relate to tinnitus!
Some are simply internal sounds (caused by blood flow, jaw motion…) transmitted to the ear, but many are caused by a problem in the inner ear (cochlea), which makes treatment particularly difficult.
Numerous hypotheses have been suggested about the link between tinnitus and inner ear (cochlear) pathology. Recent research has focussed on a mechanism that could explain the origin of a large number of tinnitus cases: the disruption of the connections (known as synapses) between the sensory cells and the auditory nerve, which causes the auditory nerve fibres to be automatically activated with repetitive signals.
These signals are perceived by the auditory brain as a whistling noise which is almost non-stop! In many cases the cell eventually dies and a hearing loss occurs. Excessive noise (traumatic sound) is without doubt one of the major factors that can cause this disruption, but vascular problems or ageing can also be the cause.
Example: tinnitus onset after a traumatic sound
The traumatic sound (a very intense noise) damages the connection between the hair cell and the auditory nerve.
The auditory nerve fibre, missing the normal input from its partner, starts to self-excite, sending non-stop messages to the brain which are perceived as a whistling noise: this is tinnitus.
Note: it is possible, in experimental animals, to block abnormal activity in the auditory nerve and to stop tinnitus.
A pharmacological treatment, based on a local application (through the eardrum) of active molecules could therefore soon be available.
Internal sounds passed to the ear
Also called 'objective tinnitus', this type of tinnitus is particular as it is sound generated by the body and perceived by the ear of the sufferer.
This tinnitus generally has a characteristic sound, which can be like a pulse and in-time with the heartbeat, like a watch ticking, or a cracking sound. Very rarely, it can be perceived as a continuous whistling sound.Objective tinnitus often arises from an abnormality in the blood vessels that pass by the inner ear, abnormal rhythmical muscle contractions, or problems with jaw movement.
The cause of most objective tinnitus cases can be precisely determined, and may, in many cases, be relieved by medical intervention.
The term “central tinnitus” is often misused, as it is obviously the brain that perceives the cochlear tinnitus! However, when used properly, the term “central” refers to tinnitus which has its roots in the brain itself, which represents only a tiny proportion of cases. We’ll not talk about the rare cases of auditory hallucinations, which are more related to neurology than hearing.
That said, the best therapy for tinnitus often involves accepting that it is present. We know, for example, that the perception of tinnitus varies greatly between sufferers, and that in each individual, tinnitus perception increases with increases in anxiety. This means that relaxation techniques and diverting attention away from the tinnitus can help (see “ treatments”).