Conductive hearing loss

Hearing impairment associated with problems with the passage of sounds through the outer and middle ear is defined in otology as conductive or conductive hearing loss.

Epidemiology

According to WHO statistics, more than 5% of the world's population - 432 million adults and 34 million children - have a hearing loss of 35 decibels (dB) or less.

According to the U.S. Centers for Disease Control and Prevention (CDC), the prevalence of hearing loss is twice as high as diabetes or cancer, and nearly 16% of U.S. Adults report hearing problems.

One in 15 schoolchildren out of 100 has some degree of hearing loss. In the United States, three children per thousand are born with hearing loss in one or both ears each year. [1]

Causes of the conductive hearing loss

Conductive hearing loss can be temporary (transient) or permanent - depending on the cause. [2] And this type of hearing loss can lead to this type of hearing loss:

• wax plugs in the external auditory canal;
• infection in the ear canal otitis externa;
• Acquired stenosis (narrowing) of the external ear canal after surgery or radiation therapy;
• exostoses of the external auditory canal, which can potentially cause its closure;
• accumulation of fluid in the middle ear; [3]
• inflammatory diseases of the middle ear - exudative middle otitis media, chronic suppurative middle otitis media;
• Eardrum perforation (caused by trauma, ear infections or barotrauma - sudden change in atmospheric pressure);
• Thickening of the tympanic membrane or scarring of its tissue - tympanosclerosis;
• blockage of the auditory (eustachian) tube, which can result from tubo-otitis;
• otosclerosis; [4]
• neoplasms in the middle ear - tumors or cholesteatoma;
• A rupture of the chain of auditory ossicles (ossicula auditus) of the middle ear caused by severe trauma to the skull;
• immobility of the auditory ossicles due to trauma, infection, cholesteatoma or retracted eardrum.

In childhood, frequent ear infections are a particularly common cause of temporary hearing loss, but the other causes and risk factors mentioned above for impaired passage of sounds through the outer and middle ear also apply fully to children. In addition, conductive hearing loss in a child can result from:

• foreign bodies in the external ear canal (children may put small objects in their ears);
• Hypertrophy of the pharyngeal tonsil - adenoids;
• hypertrophy of the tubal tonsil (tonsilla tubaria) located in the eustachian tube.

Conductive hearing loss can also be the result of congenital ear development anomalies. This is an underdevelopment of the auricles - microtia, particularly in Goldenhar, Townes-Brocks, Konigsmark, Treacher Collins syndromes.

In Treacher Collins syndrome and Crouzon syndrome there is atresia (blockage) of the external auditory canal.

Congenital anomalies of the auditory ossicles leading to conductive hearing loss in children include, first of all, immobility of the stapes - stapedial ankylosis (including in combination with other defects), which is noted in Klippel-Feil syndromes, Wilderwank syndrome, Rubinstein-Taybi syndrome (otopalatodigital syndrome) and other genetically determined diseases.

Also read - Hearing loss in a child

If conductive hearing loss is combined with sensorineural hearing loss, due to damage to the inner ear or auditory nerve, it is called a mixed hearing loss.

Pathogenesis

Sounds, i.e. Sound waves in the range from 16 Hz to 20 kHz perceived by the human ear, must pass through the external ear canal and middle ear (where the tympanic cavity, auditory ossicles and eustachian tube are located) to the cochlea, the sound-receiving part of the inner ear. It is there that the mechanical vibrations caused by sound waves are converted into nerve signals that are transmitted to the auditory cortex of the temporal lobe of the brain by the neurons of the prevertebral-cochlear nerve.

And the pathogenesis of conductive hearing loss is due to the fact that the penetration of sound into the inner ear through the external ear canal and/or middle ear is impeded or blocked.

For example, an earwax plug prevents the normal passage of sound through the external ear canal.

The mechanism of hearing loss in exudative otitis media is explained by a decrease in the mobility of the tympanic membrane and the chain of auditory ossicles middle ear (malleus, incus and stapes). Hearing acuity decreases due to destruction of the chain of these ossicles as the size of the cholesteatoma increases.

And in the case of otosclerosis, the normal transmission of sound wave vibrations to the inner ear is impaired due to the fusion of the stapes in the middle ear with the surrounding bony structures. [5]

Symptoms of the conductive hearing loss

The first signs of conductive hearing loss begin to be experienced when the general volume of sounds becomes difficult, as all sounds seem faint or muffled. And in order to hear better, the volume of the TV is increased or the speaker is interrupted. And this is a clear indicator of hearing loss.

Symptoms that are consistent with this type of hearing loss include

• ringing or tinnitus (tinnitus);
• ear stuffiness;
• one ear hears better than the other;
• A feeling of pressure in one or both ears;
• seems to make your own voice sound louder or different;
• If there is an infection in the ear, a foul odor from the ear canal;
• pain in one or both ears.

There are four degrees of conductive hearing loss:

• 1 degree (mild): the volume level of perceived sounds 26-40 dB (at a distance of three meters a person can hear normal speech well, and whispering - not further than two meters away);
• 2 degrees (moderate): loudness level 41-55 dB (a person can hear ordinary speech well at a distance of no more than two meters from himself, and whispering - if the speaker stands next to and whispers in his ear);
• 3 degrees (severe): loudness at 56-70 dB, a person can hear normal speech only at a distance of no more than one meter and cannot hear whispers at all;
• Grade 4 (deep): perceived sounds (if shouted near the ear) with a volume of ˃ 71 dB.

Complete deafness is defined as a perceived loudness level of ˃90dB.

Besides the fact that conductive hearing loss can be temporary and permanent, a distinction is made between its forms or types:

• acute conductive hearing loss (acute otitis media, acute perforation of the tympanic membrane or traumatic rupture of the auditory ossicle chain);
• chronic conductive hearing loss (due to chronic otitis media, stenosis and exostosis of the external auditory canal, neoplasms in the middle ear, tympanosclerosis, etc.).
• unilateral left-sided or right-sided conductive hearing loss;
• bilateral or bilateral conductive hearing loss (in cases of otosclerosis, microtia, atresia of the external auditory canal, congenital anomalies of the auditory ossicles).

Complications and consequences

In adults, conductive hearing loss negatively affects the ability to communicate with others and quality of life, and can lead to increased anxiety and prolonged depression.

In children, besides psychological discomfort, it can cause speech delays and a decrease in overall cognitive level.

Diagnostics of the conductive hearing loss

Diagnosis of conductive hearing loss is based on history taking and a complete otolaryngologic examination, during which bilateral otoscopy is performed to identify the most obvious causes of hearing loss (foreign bodies, earwax, infections, perforation of the tympanic membrane, presence of exudate in the ear).

Instrumental diagnosis utilizes techniques such as:

• audiometry - determination of the hearing threshold, i.e. Audiometric characterization of conductive hearing loss or audiogram, which graphically depicts the patient's hearing level; [6]
• Weber chamber tests in conductive hearing loss - to determine the side of the lesion and the nature of the impairment of sound conduction (air or bone); [7]
• tympanometry (acoustic impedanceometry); [8]

To detect neoplasms and congenital malformations, ear and temporal bone x-rays and/or CT scans of the temporal bones of the skull are used.

The findings of all examinations are recorded on a special medical form, often defined as a hearing passport.

To distinguish conductive hearing loss from sensorineural hearing loss and to identify the true etiology of hearing loss, differential diagnosis is performed. [9]

Read more:

• Ear examination
• Hearing test
• Diagnosis of hearing loss in children

Treatment of the conductive hearing loss

Treatment of conductive hearing loss focuses on treating the etiologically related disease.

In case of earwax accumulation, wax plug removal, foreign bodies are also removed from the ear. [10]

Medications used for ear inflammation, read:

• Treatment of chronic otitis media
• Antibiotics for otitis media
• Drops for otitis media

Surgical treatment is required if tumors or cholesteatoma are present - they are removed.

When hearing loss is caused by abnormalities in the structures of the middle ear, surgery is also performed. For example, ossiculoplasty is performed to reconstruct the middle ear ossicle chain; stapedectomy; auriculoplasty is performed in cases of congenital microtia in children.

More information in the material - Ear Abnormalities - Treatment

For many patients with chronic conductive hearing loss, a hearing aid is necessary to hear better, more information in the publication - Hearing aids.

Prevention

Prevention of hearing loss is particularly important in childhood, as about 60% of cases of conductive hearing loss in children are due to preventable causes. It is therefore important to detect and treat common ear diseases and prevention of adenoids in children.

Forecast

What is the prognosis for people with conductive hearing loss? It depends on the causes, some of which are chronic. [11]