Bilateral hearing loss

Bilateral hearing loss is a hearing impairment in both the left and right ears, which is accompanied by a deterioration in the detection and understanding of sounds. Depending on the extent and etiology of the problem, the patient loses the ability to hear individual speech parts, which negatively affects the intelligibility of speech - spoken or whispered. Bilateral hearing loss may occur suddenly or grow gradually, may be the result of disorders of the hearing apparatus itself, and may affect different segments of the hearing range.

Epidemiology

At least 6% of the world's population - almost 300 million people - have some form of hearing impairment or no hearing at all. According to statistics provided by the World Health Organization, the number of people in the world who have a hearing impairment exceeding 40 dB, regardless of the origin of the impairment, is estimated at about 360 million people, and more than one million of them are children.

One child per thousand newborns has bilateral total deafness. In addition, during the first three years of life, two or three more children will develop hearing loss. 13-15% of people in the 45-65 age group and 30% of the elderly have unilateral or bilateral hearing loss.

According to information provided by the American Academy of Audiologists, more than 660,000 babies are born each year with some degree of hearing loss. This figure tends to increase with age, and by the age of 9 the number of children with hearing loss doubles.

According to World Health Organization projections, there is a persistent trend of worsening global hearing loss every year.

Preterm infants are more likely to have hearing loss. Among children screened for GJB2 mutations, the genetic origin of hearing loss was confirmed in 70% of cases. [1]

Causes of the bilateral hearing loss

The main causes of bilateral hearing loss are hereditary (genetic, hereditary) and external factors. Depending on the origin, hearing loss can be congenital or acquired.

Molecular genetics research has provided experts with a wealth of information regarding the etiology of bilateral hearing loss. It is proved that genotype failures are the cause of this pathology in 70% of children with congenital and early (pre-speech) form of the disorder. In most cases, however, it is a non-syndromic problem. More than a hundred genes are involved in the coding of regulatory, membrane and structural proteins of the inner ear. Mutations in these genes lead to a malfunction of the organ of Corti and the development of bilateral peripheral hearing loss.

The most common causes are mutations of the GJB2 gene. Deletion 35delG, which has a heterozygous carrier frequency of about 3-5% in a healthy population, can be considered the most frequently detected problem. This form of congenital pathology occurs in about half of babies with persistent bilateral hearing loss.

The GJB2 gene is involved in encoding the production of the protein connexin 26, which is a structural subunit of the connexin pathways responsible for K+ ion stability in the cochlea. The outcome of changes in this gene is the formation of congenital bilateral nonsyndromic non-syndromic sensorineural severe hearing loss and complete hearing loss.

Syndromes associated with congenital hearing loss include Pendred syndrome, Usher type IIA, Waardenburg syndrome, Branhio-oto-renal syndrome, and others.

The most common non-hereditary cause of congenital bilateral hearing loss is cytomegalovirus, found in a total of 1% of newborn infants and one in four premature infants. In 10% of newborns with cytomegalovirus infection, a nonspecific clinical picture is present, and 50% of children have sensorineural hearing loss. In half of the cases, this disorder is characterized by an increasing course with progressive dynamics: often unilateral pathology is gradually transformed into bilateral.

To date, other intrauterine infectious diseases have rarely been considered as causes of congenital hearing loss. There is also no convincing evidence for the involvement of herpesvirus infection in the development of congenital hearing loss.

Pathologic conditions that contribute to hearing loss include:

• hypoxia;
• hyperbilirubinemia.

The causes of acquired bilateral hearing loss are diverse. Among them: meningitis, viral infections, taking ototoxic medications (diuretics, aminoglycosides, etc.), head injuries (fractures of the skull base or temporal bones), neurodegenerative pathologies. [2]

Risk factors

The pathomorphological basis of bilateral sensorineural hearing loss is a quantitative lack of functioning neural components at different stages of the auditory analyzer, from the peripheral zones - the spiral organ - to the central area represented by the auditory cortex of the cerebral temporal lobe.

The main factor in the appearance of bilateral hearing loss up to complete hearing loss is damage to the receptors that belong to the sensitive elements of the cochlea. The initial pathomorphofunctional basis for the development of the disorder lies in the dystrophic process affecting the hair cells. If a timely response is made, the problem is recognized and treatment is initiated, the process may be reversible.

Significant factors in the formation of bilateral hearing loss include:

• Infections of various etiologies, including viral (epidparotitis, influenza, tick-borne encephalitis, measles and others), microbial (diphtheria, typhoid, spinal epidmeningitis, scarlatina or syphilis).
• Intoxications: industrial, domestic, medication, including those caused by taking ototoxic drugs (aminoglycosides, diuretics, chemopreparations, non-steroidal anti-inflammatory drugs).
• Diseases of the circulatory system (hypertension, IBS, cerebral circulatory disorders, blood clotting disorders, etc.).
• Degenerative-dystrophic processes of the spinal column (spondylolisthesis with signs of "vertebral artery syndrome", spondylosis, uncovertebral arthrosis of the cervical vertebrae).
• Hereditary predisposition, genetic monogenic diseases.
• Unfavorable environmental influences, including regular exposure to high noise levels.

Congenital bilateral hearing loss in children is detected immediately after the child is born. The problem arises due to an unfavorable gestation process, or due to birth complications, or due to genetic factors. In order to rule out congenital hearing loss in the infant, a hearing test is performed while the baby is still in the maternity hospital. The procedure is called hearing screening. If the necessary equipment is not available at the maternity hospital, the mother is advised to visit another specialized clinic or medical facility where such a test can be performed (if hearing loss is suspected).

In general, bilateral hearing loss can occur at any age. In many cases, this process is associated with natural age-related changes and old age, but often the "culprits" are the above-mentioned provoking factors. [3]

Pathogenesis

Every sound has some effect on the hearing organ, and the degree of this effect depends on the loudness and strength of the sound, which is defined in dB (decibels).

If a person has normal hearing, he or she can distinguish sounds within a fairly wide range that starts at 0 decibels. The range of comfortable sound is usually no higher than 85 decibels. Louder sounds cause discomfort, and rumbling sounds exceeding 120 decibels can cause damage and rupture of the eardrums.

Depending on the sound height, the number of oscillations of the sound wave is determined. This value is measured in Hz (hertz). The higher the hertz value, the higher the tone. The human hearing organ distinguishes sounds with frequencies between 16 and 20 thousand Hz. Frequencies below 16 Hz are infrasounds, and frequencies above 20 thousand Hz are ultrasounds.

The best sound perception in humans is between 500 and 10 thousand Hz. Hearing also deteriorates slightly with age, which is due to natural causes.

In hearing loss, the auditory function is partially impaired and the ability to recognize and interpret sounds is impaired. Depending on the degree of pathology, the patient loses the ability to hear certain elements of the speech signal, which negatively affects speech intelligibility.

In patients with sensorineural hearing loss, the sound-receptive mechanism is affected: the inner ear, the precaudal nerve or the brain's auditory centers. Initially, the outer hair cells are damaged, which impairs the perception of soft sounds. As a result, the patient perceives sounds that are actually loud to be soft.

The development of conductive hearing loss is due to disturbances in sound transmission or problems in the middle ear or ear canals. The causes are often tumors, otitis media, developmental defects, wax plugs, otosclerosis, and trauma to the auditory ossicles.

In mixed hearing loss, it is a combination of sensorineural and conductive causes of pathology.

In patients with auditory neuropathy, the auditory nerve endings are mostly intact, so they retain the ability to fully perceive sound. However, as nerve impulses travel to the brain structures, sound information is altered and distorted. [4]

Symptoms of the bilateral hearing loss

The main manifestations of bilateral hearing loss are hearing loss in both ears and tinnitus. Sometimes there are complaints of dizziness, nausea.

There is a marked change in the perception of spoken speech and whispering, which corresponds to the degree of the pathologic process.

The first signs of a problem are often manifested by tinnitus - intermittent, gradually increasing or constant. The noise may be high-frequency (ringing, murmuring, squeaking) or low-frequency (humming). Reaction from the cochleovestibular mechanism includes dizziness, sometimes with nausea (vomiting), symptoms of impaired balance: motor coordination suffers, there is a shaky gait and unsteadiness, the risk of falling during sudden movements increases.

Long-term increasing bilateral hearing loss often provokes further psycho-emotional disorders: patients report a deterioration of mood, frequent irritability, anxiety, poor sleep. The aggravation of pathology gradually leads to minimization of social ties, loss of ability to work.

In elderly patients, bilateral hearing loss is often combined with memory and thinking disorders, hallucinatory delusional syndromes.

Acute bilateral hearing loss usually manifests itself suddenly; hearing may deteriorate over a period of several hours, often during nighttime rest, without any precursors. Sometimes the acute deterioration of hearing function is slower, over a period of about 4 days. If the process drags on for several weeks, we speak of a subacute pathological process.

Chronic bilateral hearing loss develops over several months (usually at least 1-2 months). [5]

Stages

Bilateral hearing loss can be caused by a variety of factors and differs depending on the stage of the disease process. This is important, above all, for determining the therapeutic tactics. For example, bilateral hearing loss in the 2nd degree can still be treated with medication, whereas later degrees require implantation or the use of a hearing aid.

Within auditory dysfunction there are four degrees of hearing loss, the main characteristics of which are summarized in the table below:

	Speech perception (distance in meters)	Whisper perception (distance in meters)	Hearing threshold (in dB)
1 degree of hearing loss	6 to 7	1 to 3.	25 to 40
Hearing loss grade 2	4	1	41 to 55
Hearing loss grade 3	1	-	56 to 70
Hearing loss grade 4	Less than 1	-	71 to 90

Grade 1 bilateral hearing loss is a hearing impairment in which there is a loss of receptivity to sounds between 26 and 40 decibels. In relative silence from a distance of a few meters, the patient can hear and distinguish individual words normally. However, in noisy conditions, speech cannot be clearly discerned; whispers are difficult to distinguish at a distance of more than two meters. This degree of pathology often successfully succumbs to drug therapy, but ignoring the problem contributes to further progression of hearing loss.

Bilateral hearing loss of the 2nd degree already includes the inability to hear spoken language. The person picks up individual sounds, but it is difficult to understand speech in general. In addition, tinnitus may be bothersome. Depending on the pathogenetic mechanism, there are separate types of bilateral hearing loss of the 2nd degree:

• Conductive hearing loss is caused by an obstruction at the level of the left and right outer ear. This problem is often unilateral, but it can also be bilateral, for example, in the case of wax plugs, damage to the auditory ossicles or eardrums.
• Bilateral sensorineural hearing loss (another name - sensorineural) - is associated with a decrease in the pain threshold for sound perception. A person indicates the appearance of painful sensations when the sound exceeds the threshold of permeability. This occurs against the background of diseases of the auditory nerve, Meniere's disease, autoimmune processes. Most often, bilateral sensorineural hearing loss is the result of infectious pathologies, including measles and meningitis, as well as intoxication - for example, with mercury or lead compounds.
• Bilateral mixed hearing loss is caused by several factors at the same time. The pathology is characterized by a complex course and almost always requires the use of additional hearing aids.

Bilateral hearing loss of the 3rd degree belongs to serious pathologies, the patient's quality of life suffers, additional dangers appear - in particular, a person may not be able to hear the sound of approaching vehicles, warning shouts and so on. The main reason for the development of pathology of the 3rd degree is incorrect treatment or its absence in the early stages of hearing loss.

Bilateral hearing loss of the 4th degree is a hearing loss in both ears with insensitivity to sounds in the range of 71-90 decibels. The patient cannot hear whispered speech at all, and can distinguish conversation, but with difficulty, from a distance of no more than 1 meter.

Sensorineural hearing loss of 4th degree especially often results in complete deafness. The patient does not perceive sounds at a distance of less than one meter satisfactorily, he cannot hear whispered speech at all. [6]

Complications and consequences

Partial hearing loss can always be transformed into total deafness. In the beginning, the patient stops hearing a certain sound range, but continues to perceive sounds of other frequencies and volumes. If hearing is lost completely or almost completely, deafness is said to develop.

This complication is particularly threatening to patients with third-degree hearing loss and above:

• if a person stops hearing whispers and perceives a conversation from a distance of no more than 1 meter;
• if the ability to hear sounds below 75-90 decibels is lost.

A typical feature of deafness is a complete loss of speech perception ability.

Hearing ability is an integral part of a normal life. If a person begins to hear poorly, he or she soon becomes isolated from society, which adversely affects the quality of life and psycho-emotional state. Children's bilateral hearing loss is considered particularly dangerous in this respect, as it leads to delayed speech development, making further social adaptation much more difficult. [7]

Diagnostics of the bilateral hearing loss

Typical complaints in acute sensorineural bilateral hearing loss include:

Sudden bilateral hearing loss or deterioration (most often the patient complains of problems with speech intelligibility and high-frequency sound perception);

If bilateral hearing loss is associated with trauma, circulatory disorders in the labyrinth artery or intoxication, then simultaneously with the deterioration of hearing there is subjective noise of different heights, sometimes - vestibular and autonomic disorders such as dizziness and nausea, increased heart rate and blood pressure fluctuations, increased sweating and ataxia.

The history should specify the duration of the period of hearing impairment, possible factors that may cause the problem. In particular, attention should be paid to previous infectious diseases, intoxication, circulatory disorders, degenerative-dystrophic lesions of the spinal column, head or neck trauma.

The physical examination should include procedures such as:

• otoscopy;
• Assessment of hearing acuity using spoken language;
• Acumetry - whisper and spoken speech receptivity test, the tuning chamber tone test;
• Weber's test (in normal hearing function, the chamber tone sound is equally transmitted to the two ears, or is perceived sensitively in the head; in unilateral hearing loss due to a failure of the sound conducting apparatus, sound perception is carried out from the affected side, and in unilateral pathology of the sound-perceiving mechanism - from the healthy side);
• Rinne's test (the test is negative if the duration of the sound of the tuning fork on the bone is longer than in the air, indicating a lesion of the sound-conducting apparatus; if the test results are reversed, it is recognized as positive, indicating a lesion of the sound-perceiving mechanism, although the same positive result is noted in healthy people);
• Federici's test (normal and lesion of the sound-perceiving apparatus are evaluated as a positive result - i.e., the perception of sound from the gooseneck is longer; in case of lesion of the sound-conducting system, the result is considered negative).

If the patient complains of dizziness, the vestibular system is evaluated as an additional study. Such diagnostics includes:

• detection of spontaneous symptomatology;
• performing and evaluating vestibular test scores;
• other neurological exams.

Spontaneous nystagmus is defined:

• tonic upper limb abductions in the course of the palpation, finger-finger test;
• Romberg pose;
• forward gait, flank gait.

Tests in bilateral hearing loss are not characterized by specific changes, so they are prescribed only as part of general diagnostic measures.

Instrumental diagnosis is primarily represented by audiometry and tonal threshold audiometry with the determination of bone and air conduction of sound in the normal frequency range.

Other studies include:

• impedanceometry (acoustic reflexometry and tympanometry);
• oto-acoustic emission (to assess cochlear function);
• Detection and recording of short-latency auditory evoked potentials;

CT scan of temporal bones, MRI (conventional and contrast) of the internal auditory canal area, pontine-brachial angles, posterior cranial fossa - if hearing loss is asymmetric.

Differential diagnosis

Pathology	Basis for differential diagnosis	The root cause of bilateral hearing loss	Pathology exclusion criterion
Acute sensorineural hearing loss	Abrupt bilateral hearing loss, up to and including hearing loss	Neurologic infection, influenza, meningitis, barotrauma, acoustic or mechanical trauma, administration of ototoxic drugs	Audiometric test determines hearing loss in the frequency range. According to the results of ultrasound examination - possible hemodynamic disorder
Vertebrobasilar deficit syndrome, vertebral artery syndrome	Bilateral progressive hearing loss	Compression of the vertebral plexus and arterial vessel in the spinal canal, atherosclerotic changes of cerebral vessels	Ultrasound Doppler ultrasonography identifies the intraextracranial arteries of the vertebrobasilar basin
Labyrinthopathy, Meniere's syndrome.	Vertigo attacks and tinnitus, fluctuating hearing loss	Congenital deficiency of cochleovestibular mechanism, disorder of endolymphatic metabolism and ionic equilibrium of intralabyrinthine media	Typical symptoms and audiometry findings
Otosclerosis	Initial unilateral, then bilateral hearing loss with a progressive course	Hereditary osteodystrophic pathology of the bony labyrinth of the inner ear localized at the base of the stapes	An audiologic examination often reveals a "Carhartt's prong". Computed tomography reveals foci of newly formed bone tissue
Auditory neurinoma	Gradual deterioration of hearing in one ear first, pain on the affected side of the face, paresis of the withdrawing and facial nerves, problems with swallowing, articulation and phonation	Loss of a tumor-suppressor gene on the long arm of chromosome 22	MRI determines a smooth contour of the neoplasm with a peripheral band, curvature of the bridge and brainstem, "hanging drop" syndrome.

In turn, otosclerosis is differentiated with middle ear pathologies that are accompanied by conductive hearing loss. In such situations, typical diagnostic signs for each specific pathology are usually defined.

Exudative otitis exudata is manifested by increasing hearing loss, initially conductive, then mixed. The disease often starts after acute respiratory viral infection. A tympanogram is of particular diffrential diagnostic value.

In patients with previous trauma (predominantly traumatic brain injury), bilateral hearing loss may be associated with rupture of the auditory ossicle chain. [8]

Treatment of the bilateral hearing loss

In the initial stages of bilateral hearing loss, treatment is performed on an outpatient basis under the supervision of an otolaryngologist.

Non-medicamentous influences include interventions such as:

• a gentle auditory regimen;
• diet table #10 or #15;
• hyperbaric oxygenation.

Glucocorticosteroid drugs are prescribed according to individual indications. It is important to take into account all existing comorbidities of the patient, possible contraindications and side effects. Prednisolone or dexamethasone is taken orally in a descending scheme.

Surgical treatment is indicated if there is no effect of conservative approaches in sensorineural hearing loss, if the effect of air conduction hearing aid is insufficient.

In the initial stages of bilateral hearing loss (including 2nd degree pathology), treatment includes special techniques and apparatus complexes. It is possible to use:

Drug therapy, physical therapy, and electrical stimulation of the auditory nerve;

Surgical intervention if hearing loss is associated with damage to the tympanic membrane or auditory ossicles (tympanoplasty or myringoplasty).

One of the most common techniques is reflexology with the use of special needles or laser beam. Acupuncture course includes 10 sessions with possible repetition after 4 weeks.

Hyperbaric oxygenation (oxygen therapy) has a positive effect: the patient inhales a special air mixture saturated with oxygen. The procedure improves microcirculation in capillaries and accelerates the recovery of hearing function.

With bilateral hearing loss of 3 and 4 degrees, irreversible changes in the hearing organs occur, so drug treatment at this stage is ineffective. However, it is important to stop the pathological process and prevent its further progression.

Often patients are recommended the use of hearing devices, which are:

• clip-on or pocket (fixed to clothing, with a special insert insert inserted into the ear);
• Behind-the-ear (placed behind the ear and not as visible as handheld devices);
• in-the-ear (custom-made, more commonly used in children).

In conductive bilateral hearing loss it is important to completely eliminate all existing infectious foci in the body: sanitize the oral cavity, treat chronic otitis media and sinusitis, etc. For this purpose, the patient is prescribed antibiotic therapy, antihistamines and anti-inflammatory (often - hormonal) drugs. If there is a need for surgical intervention, it is prescribed only after the complete elimination of all foci of infection.

For sensorineural hearing loss, your doctor may prescribe the following groups of medicines:

• antibacterial or antiviral drugs (depending on the etiology of the disease);
• diuretics (if it is necessary to remove swelling);
• multivitamins;
• hormones;
• anticoagulants;
• immunomodulators.

Even after treatment is complete, all patients should have regular check-ups and monitor their hearing function. If necessary, the doctor will adjust prescriptions and provide additional recommendations.

Prevention

The basic preventive rule is to avoid the emergence of dangerous situations and the negative impact of risk factors. It is necessary to seek medical help in a timely manner, identify and treat pathologies of the upper respiratory tract, using the recommendations and prescriptions of the attending physician. It is important to take into account the fact that it is often self-treatment, including ototoxic drugs, leads to a steady worsening of hearing loss and the development of multiple complications.

People who are systematically exposed to high noise or strong vibrations are at high risk of developing bilateral hearing loss. To prevent deterioration of hearing function in such situations, it is important to observe safety precautions and use hearing protection (special headphones, earplugs). In some cases, people who are prone to hearing loss may be advised to change jobs.

Quite often the problem can be avoided by preventing infectious pathologies in the body, because some infections can provoke the appearance of deafness.

Specialists insist that you should visit a doctor as soon as the first suspicious symptoms appear. This significantly increases the chances of successful treatment of the disease and restoration of lost function.

Additional preventive measures:

• avoiding bad habits (cigarettes and alcohol);
• avoidance of stress and psycho-emotional overstrain.

These simple measures can help maintain normal hearing function for years to come.

Forecast

If untreated, bilateral hearing loss tends to progress until complete deafness occurs. How rapid this process will be depends on the nature of the pathology and the individual characteristics of the patient's body. Bilateral hearing loss associated with such factors has a less optimistic prognosis:

• old age;
• genetic predisposition;
• frequent infectious and inflammatory pathologies of the ENT organs;
• regular noise exposure;
• head trauma.

Regardless of the degree of the pathological process, all patients should see a doctor for regular check-ups. Bilateral hearing loss is reversible only at the initial stage of development, and the problem should be monitored and measures taken to prevent further aggravation of the disorder.