Tinnitus

Tinnitus /ˈtɪnɪtəs/ or /tɪˈntəs/; from the Latin word tinnītus meaning “ringing” is the perception of sound within the human ear (ringing of the ears) when no actual sound is present. Despite the origin of the name, “ringing” is only one of many sounds the person may perceive.

Tinnitus is not a disease, but a condition that can result from a wide range of underlying causes. The most common cause is noise-induced hearing loss. Other causes include: neurological damage (multiple sclerosis), ear infectionsoxidative stress,[1] emotional stress,[2] foreign objects in the ear, nasal allergies that prevent (or induce) fluid drain, wax build-up, and exposure to loud sounds. Withdrawal from benzodiazepines may cause tinnitus as well. Tinnitus may be an accompaniment of sensorineural hearing loss or congenital hearing loss, or it may be observed as a side effect of certain medications (ototoxic tinnitus).

Tinnitus is usually a subjective phenomenon, such that it cannot be objectively measured. The condition is often rated clinically on a simple scale from “slight” to “catastrophic” according to the difficulties it imposes, such as interference with sleep, quiet activities, and normal daily activities.[3]

If there is an underlying cause, treating it may lead to improvements.[4] Otherwise typically management involves talk therapy.[5] As of 2013, there are no effective medications.[4] It is common, affecting about 10-15% of people.[5] Most however tolerate it well with it being only a significant problem in 1-2% of people.

Subjective tinnitus can have many possible causes, but most commonly results from otologic disorders – the same conditions that cause hearing loss. The most common cause is noise-induced hearing loss, resulting from exposure to excessive or loud noises. Tinnitus, along with sudden onset hearing loss, may have no obvious external cause. Ototoxic drugs can cause subjective tinnitus either secondary to hearing loss or without hearing loss and may increase the damage done by exposure to loud noise, even at doses that are not in themselves ototoxic.[28]

Subjective tinnitus is also a side effect of some medications, such as aspirin, and may also result from an abnormally low level of serotonin activity. It is also a classical side effect of quinidine, a Class IA anti-arrhythmic. Over 260 medications have been reported to cause tinnitus as a side effect.[29] In many cases, however, no underlying physical cause can be identified.

Tinnitus can also occur due to the discontinuation of therapeutic doses of benzodiazepines. It can sometimes be a protracted symptom of benzodiazepine withdrawal and may persist for many months.[30][31]

Causes of subjective tinnitus include:[32]

Pathophysiology

One of the possible mechanisms relies on otoacoustic emissions. The inner ear contains thousands of minute inner hair cells with stereocilia which vibrate in response to sound waves, and outer hair cells which convert neural signals into tension on the vibrating basement membrane. The sensing cells are connected with the vibratory cells through a neural feedback loop, whose gain is regulated by the brain. This loop is normally adjusted just below onset of self-oscillation, which gives the ear spectacular sensitivity and selectivity. If something changes, it is easy for the delicate adjustment to cross the barrier of oscillation, and tinnitus results. Exposure to excessive sound kills hair cells, and studies have shown as hair cells are lost, different neurons are activated, activating auditory parts of the brain and giving the perception of sound.[citation needed]

Another possible mechanism underlying tinnitus is damage to the receptor cells. Although receptor cells can be regenerated from the adjacent supporting Deiters cells after injury in birds, reptiles, and amphibians, in mammals it is believed they can be produced only during embryogenesis. Although mammalian Deiters cells reproduce and position themselves appropriately for regeneration, they have not been observed to transdifferentiate into receptor cells except in tissue culture experiments.[36][37] Therefore, if these hairs become damaged, through prolonged exposure to excessive sound levels, for instance, then deafness to certain frequencies results. In tinnitus, they may relay information that an externally audible sound is present at a certain frequency when it is not.

The mechanisms of subjective tinnitus are often obscure. While it is not surprising that direct trauma to the inner ear can cause tinnitus, other apparent causes (e.g., temporomandibular joint dysfunction and dental disorders) are difficult to explain. Research has proposed there are two distinct categories of subjective tinnitus: otic tinnitus, caused by disorders of the inner ear or the acoustic nerve, and somatic tinnitus, caused by disorders outside the ear and nerve, but still within the head or neck. It is further hypothesized somatic tinnitus may be due to “central crosstalk” within the brain, as certain head and neck nerves enter the brain near regions known to be involved in hearing.[38]

It may be caused by increased neural activity in the auditory brainstem where the brain processes sounds, causing some auditory nerve cells to become overexcited. The basis of this theory is most people with tinnitus also have hearing loss,[9] and the frequencies they cannot hear are similar to the subjective frequencies of their tinnitus.[10] Models of hearing loss and the brain support the idea a homeostatic response of central dorsal cochlear nucleus neurons could result in them being hyperactive in a compensation process to the loss of hearing input.[11]

Diagnosis

The basis of quantitatively measuring tinnitus relies on the brain’s tendency to select out only the loudest sounds heard. Based on this tendency, the amplitude of a patient’s tinnitus can be measured by playing sample sounds of known amplitude and asking the patient which they hear. The volume of the tinnitus will always be equal to or less than that of the sample noises heard by the patient. This method works very well to gauge objective tinnitus (see above). For example: if a patient has a pulsatile paraganglioma in their ear, they will not be able to hear the blood flow through the tumor when the sample noise is 5 decibels louder than the noise produced by the blood. As sound amplitude is gradually decreased, the tinnitus will become audible, and the level at which it does so provides an estimate of the amplitude of the objective tinnitus.

Objective tinnitus, however, is quite uncommon. Often patients with pulsatile tumors will report other coexistent sounds, distinct from the pulsatile noise, that will persist even after their tumor has been removed. This is generally subjective tinnitus, which, unlike the objective form, cannot be tested by comparative methods. However, pulsatile tinnitus can be a symptom of intracranial vascular abnormalities, and should be evaluated for bruits by a medical professional with auscultation over the neck, eyes, and ears. If the exam reveals a bruit, imaging studies such astranscranial doppler (TCD) or magnetic resonance angiography (MRA) should be performed.[39]

Severity[edit]

Assessment of psychological processes related to tinnitus involves measurement of tinnitus severity and distress (i.e. nature and extent of tinnitus-related problems), measured subjectively by validated self-report tinnitus questionnaires.[19] However, wide variability, inconsistencies and lack of consensus regarding assessment methodology is evidenced in the literature, limiting comparison of treatment effectiveness.[40] Developed to guide diagnosis or classify severity, most tinnitus questionnaires have also been shown to be treatment-sensitive outcome measures.[41]

Auditory evoked response

Tinnitus is the description of a noise inside a person’s head in the absence of auditory stimulation. The noise can be described in many different ways, but the most common description of the tinnitus is a pure tone sound. Tinnitus affects one third of adults at some time in their lives, whereas ten to fifteen percent are disturbed enough to seek medical evaluation.[42]

Tinnitus can be classified as either subjective or objective. Objective tinnitus can be detected by other people and is usually caused by myoclonus or a vascular condition. Subjective tinnitus can only be heard by the affected person and is caused by otology, neurology, infection, or drugs.[43] A frequent cause of subjective tinnitus is noise exposure which damages hair cells in the inner ear causing tinnitus. Tinnitus can be associated with many emotions. It is best illustrated by Jastreboff’s Neurophysiological model.[44]

Tinnitus can be evaluated with most auditory evoked potentials; however results may be inconsistent. Results must be compared to age and hearing matched control subjects to be reliable. This inconsistently reported may be due to many reasons: differences in the origin of the tinnitus, ABR recording methods, and selection criteria of control groups. Since research shows conflicting evidence, more research on the relationship between tinnitus and auditory evoked potentials should be carried out before these measurements are used clinically.

Differential diagnosis

Other potential sources of the sounds normally associated with tinnitus should be ruled out. For instance, two recognized sources of very-high-pitched sounds might be electromagnetic fields common in modern wiring and various sound signal transmissions. A common and often misdiagnosed condition that mimics tinnitus is radio frequency (RF) hearing, in which subjects have been tested and found to hear high-pitched transmission frequencies that sound similar to tinnitus.[45]

Prevention

Tinnitus and hearing loss can be permanent conditions.

Prolonged exposure to sound or noise levels as low as 70 dB can result in damage to hearing (see noise health effects). This can lead to tinnitus. Ear plugs can help with prevention.

Avoidance of potentially ototoxicity medicines. Ototoxicity of multiple medicines can have a cumulative effect, and can increase the damage done by noise. If ototoxic medications must be administered, close attention by the physician to prescription details, such as dose and dosage interval, can reduce the damage done.[46]

Management

If there is an underlying cause, treating it may lead to improvements.[4] Otherwise the primary treatment for tinnitus is talk therapy[5] and sound therapy with there being little support for medications.[4]

Psychological

The best supported treatment for tinnitus is a type of counseling called cognitive behavioral therapy (CBT) which can be delivered via the internet or in person.[5][47] It decreases the amount of stress those with tinnitus feel.[48] These benefits appear to be independent of any effect on depression or anxiety in an individual.[47] Relaxation techniques may also be useful.[4] A program has been developed by the United States Department of Veterans Affairs.

Tinnitus retraining therapy (TRT) is a form of habituation therapy designed to help people who suffer from tinnitus. TRT uses counselling to explain to the patient how a combination of tinnitus retraining and sound enrichment can end their negative reaction to the tinnitus sound, and then reduce their perception of it. Numerous other methods have been suggested for the treatment of tinnitus, two key components directly follow from the neurophysiological model of tinnitus. One of these principles include counselling aimed at reclassification of tinnitus to a category of neutral signals, while the other includes sound therapy which is aimed at weakening tinnitus related neuronal activity.[1]

Frequently, noise generators are used in TRT to provide a background noise level.[2]

A great advantage to this type of therapy is that there are no side effects.[3] Another benefit is that with this type of treatment, the individual may eventually only have to go back for a check up only once every six months, and consultations can even sometimes be performed over the phone.[3]

Another study that was conducted for Tinnitus retraining therapy showed that there are actually a number of different therapies that can be used to help to habituate to tinnitus. These techniques include: hearing aids that can provide a partial masking effect for the condition and group therapy sessions that can help ease the anxiety associated with Tinnitus.[4]

In terms of the most powerful drugs that induce tinnitus, these include cisplatin, quinine, and salicylate (aspirin). An administration of salicylate in high doses will always induce tinnitus.[5]

A basic understanding of the Jastreboff model, the Heller and Bergman experiment, and how sound is perceived in the auditory cortex via the subconscious auditory neuronal networks are helpful starting points for someone wishing to begin working with TRT.[6] Two components that are essential are (1) counselling and (2) sound therapy. Counselling tries to reclassify tinnitus to a category of neutral signals and sound therapy attempts to weaken the tinnitus related neural activity.[7] The use of a portable music player as a control instrument in TRT has produced successful results in recent analysis, offering patients a more cost-efficient treatment.[8]

The psychological basis for TRT stems from the fact that the brain exhibits a high level of plasticity. In turn, this allows it to adjust to any sensory signals as long as they do not lead to negative effects. Using this knowledge the TRT works by interfering with the neural activity causing the tinnitus at its source, in order to prevent spreading to other nervous systems such as the limbic and autonomic nervous systems.

 

What causes tinnitus?

It has been proposed that tinnitus is caused by mechanisms that generates abnormal neural activity, specifically one mechanism called discordant damage (dysfunction) of outer and inner hair cell.[10]

Not everyone who experiences tinnitus suffers from it. However, some of the problems caused by tinnitus include annoyance, anxiety, panic, sleep, and concentration disturbances. Despite the fact that there haven’t been any recent studies which concluded in its optimal treatment, tinnitus retraining therapy has been regarded as effective in treating Hyperacusis.[11]

Results from a review of Tinnitus Retraining Therapy trials indicate that it may be a more effective treatment than tinnitus masking, however, this review was based on only a single trial, other trials were excluded because they were using a modified version of TRT.[12]


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