Brief overview
- Causes and risk factors: gene defects, effects on the baby during pregnancy or birth, ear infections, certain medications
- Symptoms: Non-responsiveness to sounds, in children lack of speech development.
- Diagnostics: ear mirroring, Weber and Rinne test, sound threshold audiometry, speech audiometry, brainstem audiometry, etc.
- Treatment: aids such as hearing aids for hearing loss, inner ear prosthesis (cochlear implant) for deafness
- Course and prognosis: deafness cannot be reversed; consequential damage of deafness can be contained by treatment
- Prevention: avoidance of alcohol, nicotine, drugs and medication during pregnancy reduces risk of deafness in the child
What is deafness?
Deaf people are not necessarily also mute. However, there are deaf-mute people just as there are people who are deaf and blind. With them the communication is strongly limited.
Anatomy and physiology of the ear
The ear can be divided into three sections: Outer ear, middle ear and inner ear.
The outer ear consists of the pinna and the external auditory canal, through which the sound waves reach the middle ear (air conduction).
The transition to the middle ear is formed by the eardrum, which is directly connected to the so-called malleus. The malleus, together with two other tiny bones, incus (anvil) and stapes (stirrup), form the so-called auditory ossicles. They conduct sound from the eardrum via the middle ear to the inner ear, where auditory perception is located.
Sound is registered in the cochlea, transmitted to the brain via the auditory nerve and processed there. Each stage of hearing perception and processing is susceptible to interference, which in severe cases leads to deafness.
Hearing impaired or deaf?
Hearing loss is defined as impaired auditory perception, while deafness is defined as the complete loss of auditory perception. The distinction can be determined objectively with a hearing test called a tone threshold audiometry: This determines the hearing loss in the so-called main speech area. The main speech range is the frequency range in which most human speech occurs. A hearing loss of 100 decibels or more in the main speech range meets the definition of deafness.
What are the causes of deafness?
A sound conduction disorder is when sound arriving via the external auditory canal is not transmitted normally via the middle ear to the inner ear. The cause is usually damage to the sound-amplifying ossicles in the middle ear. Such a disorder is congenital in some people; in others, it develops during life.
Although a sound conduction disorder is a possible cause of hearing loss, it cannot be the sole cause of deafness. This is because sound can be perceived even without being transmitted through the air (air conduction), since a small part of it also reaches the inner ear via the bones of the skull (bone conduction).
Psychogenic hearing impairment: In rare cases, psychiatric disorders lead to deafness. Psychological stress disturbs the hearing sensation in some people – even without detectable damage to the ears. Objective hearing examinations can be used to assess whether or not acoustic signals are still reaching the patient’s brain.
Congenital deafness
There are genetically determined hearing disorders. One indication of this is the frequent occurrence of deafness in the family. Triggers of genetic deafness are malformations of the inner ear or brain.
In addition, there is a risk that infections of the mother during pregnancy, for example with rubella, will impair normal development of hearing in the unborn child and thus lead to impaired hearing sensation and even deafness.
Oxygen deficiency and brain hemorrhage during birth also cause deafness in some children. For example, premature infants, who often suffer from oxygen deprivation shortly after birth due to inadequate lung maturity, have an increased risk of hearing loss.
Studies have shown that a developmental delay in auditory pathway maturation can also lead to hearing loss. In this case, hearing often improves during the first year of life. Sometimes, however, profound hearing loss or deafness persists.
Acquired deafness
The most common cause of acquired deafness is a prolonged infection of the ear. In severe cases, this damages both the middle ear (sound conduction) and the inner ear (sound sensation). Infections of the meninges (meningitis) or brain (encephalitis) also sometimes result in deafness.
Other causes of acquired deafness are tumors, noise damage, circulatory disorders, a hearing loss or chronic diseases of the ear such as otosclerosis. More rarely, industrial pollutants (for example, carbon monoxide) and injuries also lead to deafness.
How does deafness manifest itself?
A distinction is made between unilateral and bilateral deafness. Some people are deaf from birth. In other cases, deafness develops gradually or arises suddenly, for example, as a result of an accident.
Unilateral deafness
In unilateral deafness, hearing is not completely impaired, but it is usually significantly impaired. Other people often notice that the affected person reacts with delay or not at all to sounds such as a sudden loud bang.
Bilateral deafness
In bilateral deafness, the hearing sensation is completely lost and therefore communication through acoustic information exchange such as speech is not possible. For this reason, speech development is severely impaired in deaf children, especially if the deafness has existed since birth. The suspicion of bilateral deafness in young children arises when they obviously do not respond to sounds.
Due to the close coupling of the senses of balance and hearing, attacks of dizziness and nausea also occur in deafness.
How is deafness diagnosed?
The ear, nose and throat (ENT) specialist is the right person to diagnose deafness. During the interview to take the medical history (anamnesis), the doctor will primarily ask about the reason for suspecting deafness, risk factors for hearing disorders and previous abnormalities.
- The child often does not respond when spoken to or called.
- Instructions are not followed correctly.
- Often follows up with “How?” or “What?”.
- Language development is not age appropriate.
- Intelligibility of speech is impeded by poor articulation.
- When watching TV or listening to music, the child sets particularly high volume levels.
These indications can also be applied to affected adults, although articulation is relatively normal in adults who have not been deaf since childhood.
After the anamnesis, various examinations and tests follow to clarify the suspicion of deafness. However, the various hearing tests usually only allow a statement about the hearing ability in combination. The detailed examination of hearing and speech comprehension also serves to determine the degree of hearing impairment or, in the case of adults, the reduction in earning capacity.
Otoscopy (ear examination)
Weber and Rinne Test
The Weber and Rinne tests provide important information about the type and location of hearing impairment. The physician makes a tuning fork vibrate and holds the end of the tuning fork at various points around the head:
In the Weber test, the doctor places the tuning fork on the center of the patient’s head and asks if the patient hears sound better in one ear than the other. Normally, hearing is the same in both ears. However, if the patient hears the sound louder on one side (lateralization), this indicates either a sound conduction or sound perception disorder.
If the patient hears the sound louder in the affected ear, this indicates a sound conduction disorder. If, on the other hand, the patient hears the sound louder on the healthy side, this indicates a sound perception disorder in the diseased ear.
Hearing tests: Subjective methods
Subjective methods of a listening test require the patient’s cooperation. In this way, the entire path of the hearing process can be checked.
Sound threshold audiometry
The classic hearing test is called audiometry by doctors. In tone threshold audiometry, the audibility of sounds through headphones or bone conduction headphones is used to determine the frequency-dependent hearing threshold. The hearing threshold is expressed in decibels. It marks the lower limit of loudness from which patients can just perceive the sound.
Speech audiometry
A complement to tone threshold audiometry is speech audiometry. Instead of tones, words or sounds are played to the patients, who have to recognize and repeat them. In this way, the understanding of speech is also tested. This is particularly important for everyday life and also helps, for example, to adjust hearing aids correctly.
Other examinations
Especially in children, other hearing tests are used in addition to audiometry to check hearing ability. If wearing headphones is refused or not possible, loudspeakers are used. Although this procedure does not allow side-separated examination of the ears, it still provides indications of hearing ability. Other specialized procedures for these cases include behavioral audiometry, reflex audiometry, visual conditioning, and conditioned play audiometry.
In addition, tests such as the Short Increment Sensitivity Index (SISI) or the Fowler test provide clues as to whether the cause of the hearing loss/deafness is to be found in the sound registration in the cochlea or in the adjacent nerve pathways (auditory pathway).
Hearing tests: objective methods
Tympanometry
Tympanometry (impedance audiometry) is a very important test that is used in every child with a suspected hearing disorder: sound waves entering the ear reach the eardrum (tympanum) through the external auditory canal. The tympanum is a thin skin that is moved by the sound waves. This movement triggers movement of the downstream auditory ossicles, initiating the cascade of sound perception.
In tympanometry, the physician inserts a probe into the ear, sealing it airtight. The probe emits a sound and continuously measures the resistance of the eardrum and thus also that of the downstream auditory ossicles. This provides information about the functionality of the middle ear.
Measurement of the stapedius reflex
Newborn screening
Since 2009, all newborns have been screened for deafness. The aim is to detect hearing disorders at an early stage by the third month of life and to initiate therapy by the sixth month of life. The following two methods are also used in this newborn screening.
One is the measurement of so-called otoacoustic emissions, a painless procedure for testing the function of the cochlea. The emissions are very quiet echoes coming from the inner ear. The outer hair cells in the inner ear emit this echo in response to an incoming sound wave.
For this purpose, the patient is fitted with headphones that emit a tone. Electrodes attached to the scalp then measure the shape of the electrical excitations and the time between the tone and the electrical response in the nerves and brain.
Further examinations in deafness
Particularly in cases of sudden deafness, the doctor looks for specific causes, such as a foreign object blocking the ear canal, severe infections and the use of certain medications.
Imaging techniques are used if the patient receives a cochlear implant or if cancer or a malformation is suspected as the cause of the deafness. Magnetic resonance imaging (MRI) or computed tomography (CT) is used to obtain detailed images of the brain or ear, respectively.
Further examinations may be required in cases of deafness, such as examinations by an ophthalmologist or neurologist. In certain cases, especially in the case of genetic causes or familial deafness, human genetic counseling is performed. Human geneticists are specialists in analyzing genetic information and diseases.
How is deafness treated?
In most cases, deafness cannot be reversed. However, there are many methods of bridging the failed areas of the complicated hearing system and in this way making hearing possible after all.
The type of treatment depends on whether there is complete deafness or some residual hearing. In the latter case, the use of hearing aids may be possible.
How does deafness progress?
Depending on the cause of a hearing impairment, it either remains the same severity or increases in severity over time. Hearing loss sometimes develops into deafness over time. It is therefore important to recognize and treat such a progressive deterioration of hearing at an early stage.
As a rule, existing deafness cannot be reversed. However, modern procedures such as the inner ear prosthesis help to avert consequential damage caused by deafness. These consequential damages of deafness include the development of impaired speech comprehension as well as developmental disorders in the emotional and psychosocial areas.
Can deafness be prevented?
Adults are well advised to take care of their hearing, for example by avoiding extreme noise and taking medications that damage hearing.
