Neurosensory hearing loss

Neurosensory hearing loss is one of the variations of deterioration (up to complete loss) of auditory function, which is caused by damage to any parts of the sound-perceptive mechanism of the hearing analyzer - from the sensory area of the cochlea to the neural apparatus. Other names of the pathology: sensorineural or perceptual tohaukhost, cochlear neuropathy. The problem is considered quite common, and treatment and prognosis depend on the severity of the pathological process, the degree of damage and localization of the focus of the violation. [1]

Epidemiology

At least 6% of the world's population (about 280 million people) have some kind of hearing problem or no hearing at all. According to WHO statistics, the number of people on the planet with hearing impairments above 40 dB in the hearing ear, with different origins of the disease, is estimated at 360 million people. In the post-Soviet countries this figure is at least 13 million people, and among them more than one million are children.

One baby per thousand newborns is born with a hearing impairment. In addition, up to three more babies are born with hearing loss during the first few years of life. Neurosensory hearing loss occurs in 14% of people aged 45-65 years, and in 30% of older people (over 65 years).

According to American audiological statistics, more than 600,000 newborns are born each year with some kind of hearing impairment (over 40 dB). This figure increases with age, and by the age of nine, it doubles. The World Health Organization's forecasts are not encouraging: in the future, the number of people with sensorineural hearing loss is expected to increase by about 30%. [2]

Causes of the sensorineural hearing loss

The most common etiologic prerequisites for the occurrence of sensorineural loss of auditory function are considered to be:

• Infectious processes:
  • viral pathologies (influenza, epidparotitis, tick-borne encephalitis, measles);
  • microbial pathologies (scarlatina, cerebrospinal epidmeningitis, diphtheria, syphilis, typhus, etc.).
• Intoxications:
  • acute poisonings (household, industrial);
  • medication toxic effects of ototoxic drugs (aminoglycoside antibiotics, diuretics, chemopreparations, non-steroidal anti-inflammatory drugs, etc.).
• Pathologies of the circulatory system:
  • Diseases of the cardiovascular system (hypertension, ischemic heart disease);
  • disorders of blood circulation in the brain, rheological pathologies of blood, etc.
• Degenerative and dystrophic processes in the spinal column (spondylosis and spondylolisthesis, _C1-C4 uncovertebral arthrosis).
• Genetic monogenic disorders, hereditary predisposition to the negative influence of environmental factors.

Risk factors

The main risk factors are considered to be:

• Having relatives with a hearing impairment;
• working in unfavorable noise conditions (high industrial noise);
• treatment with ototoxic drugs;
• Infectious pathologies (epidparotitis, meningitis, influenza infection, measles, etc.);
• somatic pathologies.

Neurosensory hearing loss can occur in almost any person at any age. The pathology can occur in different variations and can be provoked by various causes, and can be the result of functional disorders in various ear structures. The most common factors in the development of sensorineural hearing loss in old age are problems with the auditory nerve and inner ear. The root cause may be hereditary predisposition, as well as some infectious pathologies, taking certain medications, head injuries, "wear and tear" of the auditory mechanism due to prolonged exposure to noise. [3] Increase the risk of pathology development in elderly people:

• ischemic heart disease;
• diabetes;
• otitis media, meningitis, and other conditions affecting the auditory organs.

We will consider the peculiarities of the formation of neurosensory loss of auditory function in childhood separately.

Pathogenesis

The pathomorphological basis for the development of neurosensory loss of auditory function is considered to be a quantitative deficiency of functioning neural components at different stages of the auditory analyzer - in particular, from the periphery (cochlea) to the central part (auditory cortex of the temporal lobe of the brain). The basic morphofunctional prerequisite for the formation of a sensorineural disorder is damage to the sensory receptors of the spiral structure. Initial damage in the form of dystrophic processes in hair cells can be treated and recovered if timely medical care is provided. [4]

In general, sensorineural hearing loss is a multifactorial condition that can develop under the influence of vascular, infectious, traumatic, metabolic, hereditary, age-related, or immune pathology. Vascular disorders accompany hypertension, neurocirculatory dystonia, stroke states, atherosclerosis, osteochondrosis of the cervical spine, hemopathology. It should be noted that the internal auditory arterial vessel is not equipped with anastomoses, so any hemodynamic disturbances can cause oxygen deficiency in hair cells and deterioration of their function, up to death. This also occurs during fetal development, when the problem is provoked by hypoxia during pregnancy or childbirth. [5]

Any toxic substances or infectious agents can cause the development of sensorineural hearing loss, especially in the context of renal pathologies, otitis media or immune deficiencies. [6]

The following medications have an ototoxic effect:

• Aminoglycoside antibiotics (streptomycin preparations).
• Amphomycins (Rifampicin).
• Glycopeptides (Vancomycin).
• Amphenicols (Levomycetin, Chloramphenicol).
• Macrolides (Erythromycin, Spiramycin.
• Antitumor agents (Vincristine, Cisplatin).
• Diuretics (Furosemide).
• Non-steroidal anti-inflammatory drugs (Acetylsalicylic acid, Indomethacin).
• Ephedrine preparations.
• Antimalarials (Quinine, Delagil).
• Arsenic preparations.
• Tuberculosis drugs, as well as medications containing organic dyes and toxic substances.

Symptoms of the sensorineural hearing loss

The basic clinical symptom of sensorineural hearing loss is the progressive deterioration of hearing function itself. In most cases, the problem increases gradually, but sometimes it can be characterized by rapid development. Among additional symptoms, the leading ones are:

• intra-aural murmurs;
• pain;
• a feeling of stuffiness in the ears.

Sound unintelligibility (the patient can hear relatively well, i.e. Hearing is present, but the person does not understand the speech addressed to him). Such a disorder is more characteristic of brain pathologies. There may also be signs of intolerance to loud noises and sounds to the ear, the so-called hyperacusis - unusual, painful sensitivity to the usual surrounding sounds. Such patients experience not just sound discomfort, but even additional ear pain, which is caused by damage to the inner cochlear hair cells.

In many patients, sensorineural hearing loss is accompanied by vestibular disorders such as dizziness, nausea, and vomiting. [7]

Typical symptomatology of acute auditory pathology is:

• sudden unilateral or bilateral sensorineural hearing loss, with impairment of speech intelligibility and perception of high-frequency sounds, up to complete insensitivity;
• occurrence of subjective multi-height noises in the ear, acute vestibular and autonomic dysfunction in the form of ataxia, nausea, dizziness, increased sweating, palpitations, blood pressure fluctuations, nystagmus (mainly after acute trauma, circulatory disorders in the labyrinthine arterial vessel, intoxication).

Unilateral sensorineural hearing loss is accompanied by impaired auditory function in combination with ear noise - more often constant, mostly with mixed tones.

Neurosensory hearing loss in a child

The development of pathology at the intrauterine stage can be caused by external and internal factors. The most common external causes are infectious diseases (especially during the first trimester). Neurosensory loss of auditory function in the infant can cause such pathologies as measles and rubella, viral hepatitis and herpesvirus infection, cytomegalovirus, toxoplasmosis and syphilis. Chemical intoxications are also considered equally dangerous: in particular, risk factors include:

• use of alcoholic beverages and drugs by the expectant mother;
• smoking;
• use of ototoxic medications;
• being in an environment with high radiation or heavy chemical contamination.

But the more common factors for intrauterine sensorineural hearing loss are thought to be intrinsic, genetic causes.

In addition, such a disease of newborns as bilirubin encephalopathy can be dangerous. This pathology is caused by the incompatibility of the blood Rh factors of the baby and his mother. The problem can lead to the development of toxic neuritis of the auditory nerve.

The vast majority of the factors described above result in impaired blood circulation in the inner ear in newborn children. The appearance of sensorineural hearing loss in babies 2-3 years old and older is caused by other causes, among which the leading ones are:

• meningitis and encephalitis;
• measles, influenza, and complications of viral infections;
• otitis media, maxillary sinusitis causing damage to the auditory nerve or inner ear.

Mechanical injuries can also be dangerous: head bumps, sudden loud noises (explosions). [8]

Forms

In international medicine, there is a clearly defined distribution of degrees of hearing loss:

Degrees	Average hearing threshold at 500, 1000, 2000, 4000 Hz (dB)
Grade 1 sensorineural hearing loss	26-40
Grade 2 sensorineural hearing loss	41-55
Grade 3 sensorineural hearing loss	56-70
Grade 4 sensorineural hearing loss	71-90
Total deafness	Over 90 (91 and above)

According to the clinical course, congenital and acquired sensorineural hearing loss, as well as total deafness, are usually distinguished. In turn, acquired pathology is divided into the following types:

• Sudden loss or deterioration of hearing (development of the disorder occurs within less than 12 hours).

• Acute sensorineural hearing loss (development of the disorder occurs within 24-72 hours, with the pathology persisting for up to 4 weeks).
• Subacute loss of hearing function (impairment lasts for 4-12 weeks).
• Chronic sensorineural hearing loss (persists for more than 12 weeks, characterized by stability, increasing progression and fluctuation).

The course of pathology can be reversible, stable and progressive. In addition, depending on the localization, sensorineural hearing loss can be unilateral and bilateral (symmetric and asymmetric).

According to the etiologic factor, it is customary to distinguish hereditary (genetic), multifactorial (mainly hereditary) and acquired hearing loss. [9]

Complications and consequences

Most specialists do not consider sensorineural hearing impairment as a separate disease: the problem is usually a consequence or complication of another congenital or acquired pathology that has led to the appearance of disorders of the receptor mechanism of hearing.

Direct sensorineural hearing loss in childhood can lead to these adverse effects:

• inhibition of speech and mental development in the child, which is caused by a state of sensory deprivation (reduced flow of impulses to the central nervous system of the baby from the auditory organs);
• formation of individual speech defects, due to the lack of hearing and, accordingly, the inability to reproduce speech correctly;
• development of mute, characteristic mainly of congenital profound hearing loss, which is not correctable.

As an adult, the consequences are somewhat different:

• psychopathic, withdrawn;
• social isolation;
• neuroses, depressions.

Elderly patients have increased risks of progression of Alzheimer's disease, personality degeneration, and chronic depression.

Diagnostics of the sensorineural hearing loss

In the process of collecting anamnesis, the doctor specifies the time of onset of sensorineural hearing loss, the speed of symptom development, checks the symmetry of auditory function, the presence of communication problems. In addition, the presence of tinnitus, vestibular disorders, neurological symptoms is also clarified.

For hearing problems, tests are performed as part of a general clinical examination:

• general blood work;
• Biochemical blood test (cholesterol index, lipid spectrum);
• coagulogram;
• hormonal balance.

The instrumental diagnosis of sensorineural hearing loss must include otoscopy. This simple examination helps to rule out a sound conduction disorder due to obstruction, stenosis or atresia of the auditory pathway. It is also important to carefully examine the facial area for possible abnormalities in the innervation of the cranial nerves.

It is recommended to study the hemodynamic parameters of the bracheocephalic vessels (duplex, triplex scanning), as well as to perform acometry - assessment of hearing by whispered and spoken speech, and Weber's and Rinne's tuning tests.

Acumetric testing is used at the stage of ENT examination, and its result determines the need for further consultation with a surdologist.

It is mandatory to determine the hearing threshold by means of air and bone tone stimulation with an extended frequency range. Tone threshold audiometry is performed.

Above-threshold testing is recommended to evaluate for loudness perception hearing loss. Impedance testing (acoustic reflexometry and tympanometry) is also performed to identify or rule out middle ear disorders and conductive hearing loss. If endolymphatic hydrops is suspected, electrocochleography is indicated.

Some patients undergo magnetic resonance imaging or computed tomography, including with contrast agent injection: the area of internal auditory tracts, pontocerebellar angles, posterior cranial fossa are examined. Additionally may be recommended:

• radiographic examination of the cervical spinal column, with functional load;
• magnetic resonance imaging of the brain;
• contrast enhancement for detection of acoustic neurinoma.

Differential diagnosis

As part of the differentiation of hearing impairment, other specialists are additionally involved in the diagnosis: general practitioner, neurologist.

It is mandatory to exclude the presence of other forms of pathology, which are usually accompanied by loss of auditory function:

• labyrinthopathies (the result of chronic purulent inflammatory process in the middle ear, or radical middle ear surgery, or labyrinthitis);
• pathologies of the inner ear as a consequence of infection;
• toxic lesions;
• neurinoma of the VIII nerve;
• cerebral circulatory disorders in the area of the vertebro-basillary basin;
• MS;
• neoplasms in the brain;
• head and spinal injuries;
• diabetes;
• chronic renal failure;
• blocked by a sulfur plug;
• low thyroid function, etc.

Conductive and sensorineural hearing loss can also be distinguished. In the latter case, the patient loses the ability to detect sounds with a certain frequency: as a result, he or she "loses" certain tones of voices, specific exclamations and noises from the speech heard. In conductive hearing loss, there is a general decrease in loudness and a deterioration in sound clarity (like a decrease in the volume of sounds against a background of increased general noise). In the course of diagnosis, it is important to realize that both conductive and sensorineural disorders can develop simultaneously, and in such a situation it is said about a mixed hearing loss. [10]

Treatment of the sensorineural hearing loss

In acute sensorineural hearing loss, the patient is referred to the otolaryngology department for inpatient treatment, with recommendations for auditory rest.

Infusion glucocorticosteroid agents are administered - in particular, Dexamethasone with saline solution (in an amount of 4-24 mg, according to the individual scheme).

To improve microcirculation and rheological properties of blood, Pentoxifylline 300 mg or Vinpocetine 50 mg with 500 ml of isotonic sodium chloride solution (slow injection for 2.5 hours) for up to 10 days.

Intravenous infusions of antihypoxants and antioxidants (ethylmethylhydroxypyridine succinate 5% in 4 ml with 16 ml of isotonic sodium chloride solution) for up to 10 days are recommended. Upon completion of infusion measures, the patient is transferred to tablet preparations, among which are:

• vasoactive agents;
• nootropics;
• antioxidant, antihypoxant agents.

Treatment of concomitant somatic pathologies, correction of chronic disorders is mandatory. Courses of drugs optimizing cerebral and labyrinthine blood circulation, improving tissue and cellular metabolic processes are indicated.

Physiotherapeutic procedures are indicated - in particular, transcranial stimulation with acoustic loading. Physiotherapy enhances the effect of drug therapy. Its essence lies in the effect of alternating current on the cerebral cortex, resulting in the production of endogenous endorphins that optimize the work of receptors of the hearing analyzer. Electrical stimulation allows to restore the functionality of hair structures and nerve fibers affected during the pathological process. The purpose of acoustic loading is to "break" the pathological circuit in the cerebral cortex, reducing the severity of noise accompanying hearing loss.

Among other physiotherapeutic procedures, endaural electro-, phonophoresis and electrical stimulation, as well as reflexology, magnetic and laser therapy are actively used.

If necessary, a hearing aid and implants are recommended, due to the frequent ineffectiveness of drug therapy (especially in hereditary, ototoxic and postmeningitis sensorineural hearing loss). [11]

Prevention

Preventive measures to prevent the development of sensorineural hearing loss are as follows:

• Special protective earplugs should be worn when in noisy environments.
• After prolonged exposure to noisy environments, the auditory organs should be given a rest: it is advisable to end the day in peace and quiet.
• Listening to loud music, including headphones, is strongly discouraged.
• You should not add unnecessary noise - in particular, turn on the TV or radio just "for background".
• Frequent visits to clubs and discos with loud music are not recommended.
• It is advisable to visit a specialist regularly for hearing tests. For example, people who are at risk of developing sensorineural hearing loss should consult an otolaryngologist annually.

Among other recommendations:

• Any colds, runny nose, maxillary sinusitis, otitis media, laryngitis, tonsillitis should be treated in a timely manner. Any of these diseases can lead to the development of sensorineural hearing loss.
• You should not self-medicate and take medications without first consulting your doctor. Many medications have toxic effects on the hearing organs, and taking them incorrectly and without reasoning can result in permanent hearing loss.
• During swimming and diving, it is advisable to protect the ears from water entering them.
• It is important to keep an eye on your own health, and if the first symptoms of hearing loss appear, you should seek medical attention without delay.

Forecast

Neurosensory hearing loss is extremely difficult to correct, so a relatively favorable prognosis can be said only in relation to the early acute form of the pathology. The outcome of the painful condition depends on many factors, including the age category of the patient, the presence of vestibular disorders, the degree of hearing loss, audiometric parameters, and the timeliness of the beginning of therapeutic measures.

The life prognosis is favorable, i.e. There is no threat to the patient's life. Unfortunately, the transformation of unsatisfactory hearing function into complete deafness is quite likely. To prevent the development of such consequences, it is recommended, if conservative treatment is ineffective, to perform hearing aids and choose a suitable hearing aid. [12]

Cochlear implantation is performed for patients with long-standing sensorineural hearing loss, and cochlear implantation is indicated for cochlear defects. [13]

Chronic sensorineural hearing loss of the latter degrees is an indication for disability.