Tinnitus is a relatively common complaint affecting both individuals with normal hearing & a hearing loss. The severity of the hearing loss is not necessarily related to the perceived severity of the tinnitus. However, many people who report hearing loss do report tinnitus. Noise exposure is a common cause of hearing loss and tinnitus.
Tinnitus iscommonly described as a “ringing”, “buzzing” or “humming” signal & can last from a few seconds to hours. In some cases it is described as constant. Tinnitus can be perceived as being monaural (single ear) or bilateral (both ears), and it can change in intensity & frequency.
Tinnitus is an internal signal without any corresponding external acoustic activity. It is a subjective perception and as such will be experienced by individual patients in different ways, and with varying emotion or distress from non-problematic to severe.
It is suggested that 80% of persons experiencing constant tinnitus habituate to this naturally and as such tinnitus does not cause them a problem. The remaining 20% do not naturally habituate and will report varying degrees of complaint.
WHY IS TINNITUS PROBLEMATIC?
Stimuli that warn of potential danger or discomfort are assigned highest priority by the auditory and limbic system in the brain. Therefore, any presenting “important” or “ threatening” stimuli is not ignored. The importance of a certain sound depends on the initial association with that sound, in the same way a certain song can invoke a particular emotional reaction or make you remember a particular event, or how you may attend to your name being called when walking down the street, but dont attend to a car going past. The loudness of a signal is secondary to its significance, thus tinnitus doesn’t have to be loud to cause anxiety or interruption, this is determined more by a person’s association of the tinnitus signal to a particular event.
THE PHYSIOLOGY OF TINNITUS
Inner and outer hair cells are tonotopically organised in the organ of corti within the inner ear apparatus. Typically outer hair cell (OHC) loss is related to tinnitus. Approximately 0.5% of OHCs disappear each year, however up to 30% of human outer hair cells can be destroyed without causing an effect on the audiogram or inducing a recognisable hearing loss, as long as the OHC loss is spread across all the OHCs and the damage is not restricted to one area. For this reason hearing can be preserved until 60-70years of age.
Damage to outer hair cells is believed to be related to tinnitus, however because damage can occur without an effect on hearing, a person can have tinnitus and relatively normal hearing.
Inner hair cells are better protected within the anatomy and therefore more difficult to damage. However, just 10% destruction of IHC’s will induce speech discrimination difficulty.
THE NERVOUS SYSTEM & TINNITUS
The autonomic nervous system controls our glands, respiratory, circulatory, digestive, urogenital and hormonal systems. There are two mutually antagonistic components, the sympathetic and parasympathetic nervous systems. Activation of the sympathetic system prepares our body for action.
In the case of a person with problematic tinnitus, the sympathetic nervous system is activated. Depending upon the perceived severity of the tinnitus the sympathetic system is over-stimulated which may lead to anxiety, sleep difficulties and panic attacks. Such an effect can suppress the ability of the patient to enjoy life.
DIET AND TINNITUS
It has recently been suggested that diet has no effect on the perception of tinnitus, except moderate alcohol consumption which may induce non-spontaneous tinnitus. In the case of tinnitus perceived by the Meniere’s patient a reduced salt, caffeine and alcohol intake can assist with fluid retention issues and result in reduced tinnitus perception. However, diet may present as an aggravator of tinnitus, but is uncommonly related to the cause.
MEDICATION AND TINNITUS
Some medications can induce tinnitus or worsen any existing tinnitus, however in general reduction in the dose of such medication (under practitioners instruction) will usually reverse the effect. It is usually high doses of medications , usually presented intraveniously and in life threatening situations, that cause damage to the auditory system and thus the symptom of tinnitus can arise.
TINNITUS AND REDUCED NOISE TOLERANCE
Often patients who describe tinnitus also have a reduced sound tolerance. Reduced amplification by wax, earplugs, otosclerosis or other hearing loss etc, will induce the ears automatic gain, and this can have the effect of increasing the sensitivity of the auditory system, which in turn will increase a person’s perception of tinnitus.
It is suggested that 60% of tinnitus patients also have reduced sound tolerance, and 30% require treatment for hyperacusis. Hyperacusis or reduced sound tolerance can co-exist with misophonia, which is described as an increased awareness of external sounds &/or somatosounds (internal physiological sounds) which are usually habituated. Such internal physiological sounds (such as chewing and swallowing) can then attract a very strong emotional reaction, for example intolerance to the sound of chewing or eating. In extreme cases a person can be diagnosed with phonophobia, or an actual fear of a particular sound.
TINNITUS RETRAINING THERAPY (TRT)
Tinnitus Retraining Therapy (TRT) is based on the neurophysiological model of tinnitus which was first described by Jastreboff in 1990 (Jastreboff, 1990). There are two main components to TRT – councelling & sound therapy.
Tinnitus Retraining Therapy (TRT) is a treatment, not a cure. TRT works above the level of the cause of the tinnitus to remove the connection between the tinnitus and the reaction of a patient to their tinnitus. TRT re-classifies tinnitus to a neutral or a non-threatening stimuli, and as such the patient begins to accept the tinnitus, and the signal ceases to induce negative reactions.
Hearing aids and/or sound generators may be used as part of the treatment. Hearing aids are required only in the case of hearing loss, while sound generators may be used in conjunction with hearing aids or alone. Sound generators are generally only required for the duration of treatment (12-18months), following treatment the patient will no longer need to wear ear level sound generators but may choose to use them intermittently if required. Improvement is dependent upon initial perception of the severity of the tinnitus. TRT will take between 9-18months and patients typically attend appointments every 3 months after the initial assessment. Patient’s tend to report gradual improvement over this period of treatment, but generally patients will describe a significant improvement after 12weeks.
Neuro physiological mode of tinnitus (Jastreboff, 1990)