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LESSON 214

What is tinnitus?

Why does tinnitus happen, and why does it bother some people so much? In this lesson we cover subjective and objective tinnitus, the role of hearing loss and increased central gain, the effect of attention and emotional networks, and the prevalence of tinnitus and its impact on daily life.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will learn what tinnitus is, its types, and the mechanisms that explain how it arises.
We will also discuss why some people are strongly affected by tinnitus while others are hardly bothered at all.
Tinnitus is the perception of sound in the ear or head when there is no external sound source.
In everyday language it is often called ringing in the ears, but in the clinic we use the term tinnitus.
People describe the sound in different ways, such as ringing, buzzing, humming, hissing or crackling.
Tinnitus is not a disease in itself, but a symptom of a change in the auditory system.
So a detailed audiological and medical evaluation is needed to understand the underlying cause.
Most people with tinnitus also have a measurable hearing loss.
On the other hand, noticing a brief, faint ringing in a very quiet room is common and is not a problem in itself.
Subjective tinnitus is tinnitus heard only by the person themselves.
Most tinnitus seen in the clinic is of this type.
There is no real sound in the ear; the perception comes from changes in neural activity in the auditory pathways.
Objective tinnitus, by contrast, is the perception of a sound actually produced in the body.
This sound can sometimes be heard by the examiner with a stethoscope or with a microphone in the ear canal.
Causes include vascular flow sounds and rhythmic contractions of the middle ear muscles.
Objective tinnitus is rare and often needs further evaluation; we will go into detail in the next lesson.
Tinnitus may be perceived in one ear, in both ears or in the middle of the head.
The sound may be tonal, like a whistle at a single pitch, or noise-like, like a rustle.
Tinnitus that beats in time with the pulse is called pulsatile tinnitus; this type deserves special attention.
By duration, recent-onset and persistent tinnitus are distinguished; the American guideline calls tinnitus lasting over 6 months persistent.
Clinically, perhaps the most important distinction is whether the tinnitus bothers the person.
Tinnitus of the same loudness may go unnoticed by one person yet clearly disturb another's sleep and daily life.
A large meta-analysis found the prevalence of tinnitus in adults to be about 14 percent.
The proportion of adults for whom tinnitus is severely bothersome is about 2 percent.
The prevalence of tinnitus increases with age and with hearing loss.
But it can also occur in children and young people; temporary tinnitus after loud music is especially common.
Bothersome tinnitus most often affects falling asleep, attention and concentration.
Anxiety and depressive symptoms often occur with tinnitus and can feed each other.
Tinnitus is also often accompanied by excessive sensitivity to everyday sounds; this is called hyperacusis.
The strongest risk factor for tinnitus is hearing loss; age-related and noise-induced hearing loss are the most common examples.
Exposure to loud noise at work or in leisure settings is an important cause of persistent tinnitus.
Ototoxic drugs, such as some aminoglycoside antibiotics, cisplatin and high-dose salicylates, can also cause tinnitus.
Tinnitus is a common symptom of ear disorders such as Meniere's disease and otosclerosis.
In some people, jaw or neck movements can change the loudness of tinnitus; this is called somatic tinnitus.
Stress and anxiety usually do less to start tinnitus than to make it feel more bothersome.
The most common starting point of subjective tinnitus is damage in the cochlea.
Noise, age or ototoxic drugs usually affect the outer hair cells first.
The inner hair cells and their nerve fibers can also be damaged.
As a result, neural input to the brain from certain frequency regions decreases.
Interestingly, tinnitus often arises from the brain's response to this reduced input.
This is why tinnitus can persist even after the auditory nerve is cut: the perception arises in the central auditory pathways, not the ear.
Outer hair cell damage shows on the audiogram as threshold loss, but nerve fiber loss may not always affect thresholds.
When input from the cochlea decreases, the central auditory system tries to compensate.
Neurons increase their sensitivity; this process is called increased central gain.
In centers such as the cochlear nucleus and inferior colliculus, spontaneous neural activity increases even without sound.
This increased and more synchronized activity can be perceived as a sound in the auditory cortex.
In addition, the cortical map representing the frequency region with reduced input can reorganize.
This is why the pitch of tinnitus is often close to the frequency region of the hearing loss.
The process is compared to phantom limb pain after losing an arm; tinnitus is a kind of phantom auditory perception.
In this example, both ears show a clear notch around 4000 Hz with partial recovery at 8000 Hz.
The low and mid frequencies are largely within the normal range.
This shape is a pattern often seen in noise-induced hearing loss.
When tinnitus pitch is matched in such a person, it is often found near 4000 Hz, where the loss is.
This is a clinical observation that supports the view that tinnitus is linked to the frequency region with reduced input.
But the pitch does not always match the deepest point of the loss; it may also lie near the edge of the loss or elsewhere.
Some people have tinnitus even though their standard audiogram is normal.
Some of them may have a loss at frequencies above 8000 Hz, which the standard audiogram does not measure.
Another possibility is the loss of connections between hair cells and nerve fibers, called cochlear synaptopathy.
This is also called hidden hearing loss; its role in humans is still being researched.
In some people, somatic input from the jaw or neck clearly changes the loudness of tinnitus.
A normal audiogram does not mean the tinnitus is not real; it only shows that the mechanism may be different.
The best-known model of why tinnitus bothers some people so much is the neurophysiological model proposed by Jastreboff in 1990.
According to this model, the tinnitus signal does not stay in the auditory pathways but interacts with other brain networks.
The limbic system, which regulates emotion, and the autonomic nervous system, which drives the stress response, are central to this.
If tinnitus is perceived as a threat, the brain directs more attention to it and the signal becomes more prominent.
As anxiety rises, attention rises, and as attention rises, tinnitus feels more bothersome; this creates a vicious circle.
Conversely, when the signal is learned to be harmless, the brain gets used to it; this is called habituation.
So the loudness of tinnitus and how much it bothers the person do not always go hand in hand.
A tip from the field: do a full audiological evaluation for everyone who complains of tinnitus.
Along with pure tone and speech tests, tympanometry and acoustic reflex findings also contribute to the evaluation.
Tinnitus that is unilateral, pulsatile or that starts with a sudden hearing loss needs medical assessment.
Time matters in sudden hearing loss; these people should be referred without waiting.
Explaining in plain language that tinnitus is common, and how it arises, is also an important step in reducing anxiety.
In this lesson we learned that tinnitus is mostly subjective, while objective tinnitus is rare.
Tinnitus affects about 14 percent of adults, and hearing loss is its strongest risk factor.
When input from the cochlea decreases, increased central gain can lead to the perception of sound without sound.
How bothersome tinnitus becomes is largely determined by attention and emotional networks.
Test yourself: in tinnitus, increased central gain is mainly a response to what?
The correct answer is A: reduced neural input from the cochlea to the brain.
The central auditory pathways increase their sensitivity to offset reduced input, which raises spontaneous activity.
In the next lesson we will examine pulsatile and one-sided tinnitus, the situations that call for referral.
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