deafness

Deafness: description

Deafness or the often synonymously used term Deafness describes the complete loss of hearing. The cause may be the entire path between sound perception in the ear and the processing of the acoustic stimuli in the brain. As a result, there are also forms of deafness in which the person concerned can record sounds with his ear but can not process them and thus understand them.

Deafness may be one-sided or bilateral, congenital or acquired. In some cases, it is only temporary (for example in the context of infections of the ear), in other cases permanently.

Anatomy and physiology of the ear

The ear has three parts: outer ear, middle ear and inner ear.

The outer ear consists of the auricle and the external auditory canal, through which the sound waves enter the middle ear (air line).

The transition to the middle ear is formed by the eardrum, which is directly connected to the so-called hammer (Malleus). The hammer forms together with two other tiny bones (anvil = incus and stapes = stapes) the so-called ossicles. They direct the sound from the eardrum over the middle ear into the inner ear, where the hearing perception sits.

The inner ear and middle ear are mostly located in the temporal bone, part of the bony skull. From the auditory ossicles, the sound is transmitted via the so-called oval window into the liquid-filled cochlea. However, the sound can bypass this path via the eardrum and also enter the cochlea via the cranial bone (bone conduction). In the cochlea, the sound is registered and passed over the auditory nerve into the brain, processed first in the lateral brain and then sent to higher processing centers. Any stage of listening and processing can be disturbed and lead to deafness.

Distinction between deafness and deafness

Deafness refers to impaired hearing, deafness to complete loss of hearing. The distinction can be determined objectively with a hearing test (threshold audiometry): Here, the hearing loss is detected in the so-called main speech area. The main language area is the frequency area in which predominantly human speech takes place. It is between 250 and 4000 hertz (Hz). Frequencies in the main speech domain are perceived particularly well by the human ear, which is why a hearing loss in this area particularly serious.

The extent of hearing impairment is determined as hearing loss (expressed in decibels = dB) compared to normal hearing. There are slight (20 to 40 dB), moderate (from 40 dB) and severe (from 60 dB) hearing impairments. Residual hearing describes a hearing loss between 90 and 100 dB. From a hearing loss of 100 dB in the main speech range, the definition of deafness is fulfilled.

frequency

About two out of every thousand children are deaf in their ears from birth. A congenital unilateral deafness occurs in less than a child of a thousand. In newborns with risk factors (premature birth, for example), the risk of deafness is increased approximately tenfold. According to the Deaf Federation in Germany about 80,000 people are deaf. About 140,000 people have such a severe hearing loss that they need a sign language interpreter.

Deafness: symptoms

One distinguishes one-sided and bilateral deafness. Some people are deaf by birth. In other cases, the deafness develops creeping or arises suddenly (for example, by an accident).

One-sided deafness

In one-sided deafness the hearing is not perfect, but usually considerably limited. Often, other people notice that the person responds late or not at all to sounds (such as a sudden loud bang). Since hearing is severely impaired overall, people with unilateral deafness often ask questions in a conversation because they often can not fully absorb the information of the conversation. In addition, people who are deaf in one ear, often very loud (sometimes with poor articulation) and make the sound of radio and television strikingly loud. Most such behaviors are the first indications of deafness or one-sided deafness.

People with unilateral deafness also find it harder to determine the direction from which a sound is coming. This impaired ability to locate the direction of noise sources can be problematic in everyday life, for example, when crossing a road. Also, people with one-sided deafness often have trouble eliminating background noise, which makes it harder for them to follow a conversation when there is a high level of noise in the background (such as music or other conversations). Social interaction can be permanently disrupted due to the difficult communication with the environment.

Bilateral deafness

In the case of bilateral deafness, the hearing sensation has completely failed and therefore communication via an acoustic information exchange such as the language is not possible. For this reason, language development is severely disturbed in deaf children, especially if the deafness has existed since birth. The suspicion of bilateral deafness in young children arises when they are obviously not responding to sounds.

Bilateral deafness, which occurs in the context of genetic diseases, is often accompanied by other abnormalities, such as malformations of the eyes, bones, kidneys or skin. Due to the close coupling of balance and hearing, dizziness can also cause dizziness and nausea.

Deafness: causes and risk factors

There are a variety of causes of deafness. Roughly speaking, the cause can be both in the ear (especially at the sound sensation in the inner ear) and at the other stations of the auditory pathway in the brain. A combination of several causes is possible. Overall deafness may be due to a conductive or abnormal sound disorder or psychogenic hearing impairment:

From one Conductive hearing loss One speaks when the sound arriving via the external auditory canal is not passed on normally via the middle ear to the inner ear. The cause of this is usually a damage to the sound-enhancing ossicles in the middle ear. Although a conductive problem may be a cause of deafness, it is the only cause of deafness. Because even without the transmission of sound through the air (air line), the perception of sound is possible because this reaches the inner ear to a small extent, even over the skull bone (bone conduction). A conductive conduction may be innate or acquired.

At a Sensorineural hearing loss is the sound transmission to the inner ear intact. There, however, the incoming acoustic signals are usually not registered (sensory hearing impairment). In rarer cases, the signals are registered in the inner ear, but then not forwarded to the brain and perceived there – either due to a disturbance of the auditory nerve (neural hearing impairment) or the central hearing (central hearing impairment). A sensory disturbance may also be innate or acquired.

Psychogenic hearing disorder: In rare cases, psychiatric disorders can lead to deafness. Mental stress can lead to a disturbed sense of hearing without detectable damage to the ears. With objective hearing examinations, which are not dependent on the cooperation of the patient, one can estimate whether or not acoustic signals arrive in the brain of the patient.

Congenital deafness

There is Genetic hearing disorders, An indication of this may be the increased occurrence of deafness in the family. The causes of genetic deafness are malformations of the inner ear or the brain. For example, the so-called Down syndrome (trisomy 21) can bring about genetic deafness.

Besides, too infections During pregnancy (for example, rubella) the mother may impair the normal development of hearing in the unborn child, resulting in a disturbed sense of hearing, including deafness. In addition, certain increase drugs, but also drugs (especially alcohol and nicotine) during pregnancy, the risk of hearing loss in the child. Known examples of ear-damaging (ototoxic) drugs are thalidomide and various antibiotics from the group of aminoglycosides, macrolides and glycopeptides.

lack of oxygen and Cerebral hemorrhage during childbirth can also lead to deafness. For example, premature infants, who often suffer from oxygen deprivation shortly after birth due to poor lung maturity, are at increased risk of hearing impairment. An increased risk of deafness is also borne by newborns who have been in the incubator (incubator) for more than two days.

Recent studies have shown that even one Developmental delay of the Hörbahnreifung can lead to deafness. In this case, hearing often improves during the first year of life. Sometimes, however, a pronounced deafness or deafness persists.

Acquired numbness

The most common cause of acquired deafness is a severe or prolonged one Infection of the ear, This can severely damage both the middle ear (sound conduction) and the inner ear (sound sensation). Also infections of the meninges (meningitis) or the brain (encephalitis) can cause deafness: Deafness caused by meningitis can lead to ossification of the cochlea. In encephalitis, neural pathways in the brain that are responsible for passing on the auditory information from the inner ear can be damaged. Similarly, the receiving site for this information in the brain (auditory cortex) can be damaged by encephalitis and thus cause a deafness.

drugs Not only can the unborn child be harmed during pregnancy, but occasionally they can also cause hearing loss or deafness later in life. Doctors say that these drugs have an ototoxic (ear damaging) effect. In addition to certain anticancer drugs (chemotherapeutics), these include certain dehydrating agents (diuretics) and a whole range of antibiotics. But the common pain and fever acetylsalicylic acid has been shown to have an ototoxic effect. However, it is significantly lower than the aforementioned drugs.

Another major cause of acquired deafness are tumors, The most common tumor leading to hearing loss is the so-called acoustic neuroma. This is a benign tumor originating from the envelope of the auditory nerve (cochlear nerve). The auditory nerve itself runs in a narrow bony canal. Through the proliferating tumor of the nerve in the bony boundary is increasingly depressed, whereby the signal conduction between the inner ear and brain is disturbed or even interrupted. The result is a mostly one-sided and typically slowly progressing deafness. In principle, even tumors in the brain itself can lead to deafness. Not to be underestimated are also ear damage due to noise exposure, Other causes of acquired deafness are Circulatory disorders, one Sudden Hearing Loss or chronic diseases of the ear such as the so-called otosclerosis. Rarer also lead industrial pollutants (for example, carbon monoxide) and injury to deafness.

Deafness: examinations and diagnosis

Studies suggest that parents tend to over-estimate their children’s hearing on suspicion of hearing loss or deafness. However, any suspicion of deafness must be taken seriously, especially in childhood. The Otolaryngologist (ENT) is the right person to contact in this case. In the discussion about the collection of the medical history (medical history) the physician will ask above all for the reason for the suspicion, risk factors for hearing disturbances and past abnormalities.

According to the American Speech Language Hearing Association (ASHA), the following abnormalities in children are serious because they may indicate hearing impairment or deafness:

• The child often does not respond to speech or calls.
• Instructions are not followed correctly.
• Often people ask with “how” or “what”.
• The language development is not age appropriate.
• The intelligibility of the language is hampered by a poor articulation.
• When watching TV or listening to music, the child sets particularly high volumes.

These indications can also be applied to affected adults, although the articulation is relatively normal in adults who have not been deaf since childhood.

After the medical history, various examinations and tests follow to clarify the suspicion of deafness. The different (partly child-appropriate) hearing tests usually only allow a combination of hearing loss. Exact examination of hearing and speech comprehension also serves to determine the degree of hearing impairment or disability (in adults).

Ear reflection (otoscopy)

First, the doctor will examine the affected person’s ear with an otoscope (magnifier with integrated light source). He can already determine whether the eardrum is intact and whether there is possibly an effusion in the middle ear. But this can only be a statement about the anatomy are made. About the function of the ear, this investigation provides limited information.

Weaver and gutter test

Two simple tests (Weber and Rinne test) can provide important information on the type and location of the hearing impairment. The doctor makes a tuning fork to vibrate and puts the end of the tuning fork at different points in the area of ​​the head:

At the Test according to Weber The doctor places the tuning fork on the patient’s center of the head and asks if the patient hears the sound better in one ear than the other. Usually the hearing is the same on both ears. If, however, the patient hears the sound louder on one side (lateralization), this can either point to a conductive or sensory disturbance: If the patient hears the sound louder on the affected ear, this indicates a conductive problem. For example, in the case of middle ear inflammation, the sound is to a certain extent reflected by the inflammation and therefore perceived louder by the diseased ear. On the other hand, if the patient hears the sound louder on the healthy side, this indicates a sensation of sound sensation in the diseased ear.

In addition to the Weber test, the Rinne Test carried out. In this test, the tuning fork is placed on the bone behind the ear (mastoid) until the tone is no longer audible. Then the most still swinging tuning fork is held in front of the ear. In normal hearing, the sound is perceived again because the air duct is better than the bone conduction.

Listening tests: Subjective methodsSubjective methods of a hearing test require the cooperation of the patient. They make it possible to check the entire path of the listening process.

Basically, the sound can be transmitted both via the air line through the ear canal and through the bone (bone conduction) and then perceived in the inner ear. The ear is designed to absorb sound mainly via the air line. If the structures of the outer and middle ear required for air conduction are damaged, the person concerned can still register the sound that enters the inner ear via the bone in the inner ear. For this reason, in many examinations either normal headphones as a source of sound or special headphones that transmit the sound to the bones behind the ear can be used.

The classic hearing test is called by physicians as audiometry. In the Tonschwellenaudiometrie the audibility of sounds via headphones or bone conduction headphones is used to determine the frequency-dependent threshold of hearing. The hearing threshold is expressed in decibels (dB) and states how quiet a tone can be that it is just perceived by the patient. To test the hearing threshold in different pitches (frequencies), the patient is successively played a series of tones in different frequencies. Every sound gets louder and louder. The patient should press a button as soon as he hears the sound. As the sound gets louder and louder, it can be assumed that the later the patient perceives the sound and presses the button, the more impaired is the hearing.

An addition to the threshold audiometry is the Speech, Instead of sounds, patients are presented with words or sounds that they should recognize and repeat. In this way, the understanding of language can be tested. This has a particularly important role in everyday life and also helps, for example, to set hearing aids correctly. The results of the threshold audiometry are depicted in a so-called audiogram. On this, the doctor can see at which frequencies the patient has lost his hearing (indication of hearing loss in decibels). This provides the doctor with information on possible causes of hearing loss. For example, noise-induced hearing damage due to a hearing loss in the range of high tones, so for example at a frequency of 4000 hertz (Hz). A hearing loss of 100dB in the main speech area (see above under “Description”) is by definition deafness.

Especially in children, in addition to audiometry, other hearing tests are used to check the hearing. If it is not possible to wear headphones or, as in infants, it is not possible, the sound will be delivered via loudspeakers. Although this method does not allow separate ear examinations, it still provides evidence of hearing. Other special procedures for these cases include behavioral audiometry, reflex audiometry, visual conditioning, and conditioned performance audiometry.

In addition, tests such as the so-called SISI– (Short Increment Sensitivity Index) or the Fowler test Indications as to whether the cause of deafness / deafness is to be found in the sound registration in the cochlea or in the adjacent nerve tracts (auditory pathway).

Listening tests: Objective methods

The objective hearing test procedures require only very little cooperation from the patient. By examining sections of the auditory pathway, they help to determine the nature and extent of the hearing impairment. In most cases, they are also usable when subjective procedures are not possible with a patient.

The Tympanometry (Impendance audiometry) is a very important exam that should be used on any child suspected of hearing impairment: 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 a movement of the downstream auditory ossicles, which sets the cascade of sound perception in motion. In tympanometry, the doctor introduces a probe into the ear and seals it airtight. The probe emits a sound and can continuously measure the resistance of the eardrum and thus also of the downstream auditory ossicles. Thus, the functionality of the middle ear can be tested.

Of the Stapediusreflex is a reaction to loud sound. The so-called stapedius is a muscle that can tilt the third ossicle by contracting so that the sound from the eardrum is transmitted in a lesser way in the inner ear. This muscle protects the inner ear from high volume. When measuring the stapedius reflex, the reflex threshold is determined, ie the volume value at which the reflex is triggered. This study can determine if the ossicles in the middle ear are normally mobile.

Since 2009, all newborns are being examined for deafness. The goal is to diagnose hearing impairment early by the third month of life and initiate therapy until the sixth month of life. The two following methods are also used in this newborn screening used.

On the one hand, this includes the measurement of so-called otoacoustic emissions – a painless procedure for functional testing of the cochlea. The emissions are very quiet echoes that come from the inner ear. The outer hair cells in the inner ear send out this echo in response to an incoming sound wave. It is not possible to perceive this echo itself. But you can register it with high sensitivity microphones. These microphones are inserted into the ear and seal it airtight. They have integrated a sound source from which sounds are emitted to trigger an echo from the inner ear.

The second method is the so-called brainstem (for example, BERA). It examines the nerve and brain areas responsible for hearing. With the help of the measured on the scalp electrical impulses can be estimated whether the sound is registered not only in the inner ear, but also passed through the connected nerve pathways and processed in the brain. The patient is put on a headphone, which emits a sound. The scalp-mounted electrodes measure both the shape of the electrical excitations and the time between tone and electrical response in the nerve and brain.

Further examinations for deafness

Especially in the case of sudden deafness, special causes such as a foreign body clogging the ear canal, severe infections and the use of certain medications must be sought.

Imaging procedures are used if the patient is to receive a cochlear implant (planning the procedure) or if there is a suspicion of a cancer or a malformation as the cause of deafness. Magnetic resonance imaging (MRI) or computed tomography (CT) is used to detail the brain or ear.

blood tests are usually not revealing of suspected deafness. They are only helpful in certain cases, for example for the clarification of infections or for signs of a metabolic disease. Sometimes, deafness or deafness is the result of repeated ear, nose and throat disease due to increased susceptibility to infection. A blood test can help here to find an explanation.

You may need further examinations for deafness, such as Examinations at the ophthalmologist or neurologist, In certain cases, especially with genetic causes or familial deafness one can human genetic counseling be performed. Human geneticists are specialists in the analysis of genetic information and diseases. In the case of severe genetic diseases, they can also provide help for having children for deaf parents.

In children close to the hearing tests Speech and development tests An intact hearing is the basic condition for normal speech development. Deafness that has been present since birth or early childhood should be treated as soon as possible. Otherwise, the development of language development problems often can not be resolved completely. Deafness that occurs after childhood usually does not affect speech.

Deafness: treatment

In most cases deafness can not be reversed. However, there are many methods to bridge the unusual areas of the complicated hearing system and still make listening possible.

The treatment measures depend on whether there is complete deafness or if there is still some residual hearing. In the latter case, the use of hearing aids may be possible. With complete deafness, especially if it is bilateral, hearing aids would not make sense. Instead, surgery can be helpful in giving the person a Inner ear prosthesis (also called the cochlear implant) is used. This should be used as early as possible in children with deafness as soon as possible to create the best possible conditions for language acquisition. After the procedure, rehabilitation measures are important, especially intensive listening and speaking training.

In addition to the supply of hearing aids or a cochlear implant implants should be specifically promoted. In particular, children benefit from using techniques like that lipreading and the Sign language learn early. As a rule, this also makes sense for the people in the immediate environment of the person concerned.

Deafness: disease course and prognosis

Depending on the cause of a hearing disorder, it may either remain the same in magnitude or increase in severity over time. Thus, a hearing loss may develop into deafness. Such progressive hearing loss should therefore be recognized and treated early – sometimes suitable measures can prevent deafness. Especially the hearing of children should – as it is often difficult to assess – be tested at the slightest suspicion of hearing impairment by listening tests.

An existing deafness can not usually be reversed. However, modern methods such as the inner ear prosthesis can make a decisive contribution to averting consequential damage to deafness. To these consequential damages the deafness include the development of a disturbed speech understanding and developmental disorders in the emotional and psychosocial area.