Sensorineural hearing loss - Causes and pathogenesis

Hearing impairments can be acquired or congenital.

[ 1 ]

Acquired causes of sensorineural hearing loss

Numerous clinical observations and scientific studies have proven the role of:

• infectious diseases (flu and acute respiratory viral infections, infectious mumps, syphilis, etc.);
• vascular disorders (hypertension, vertebrobasilar dyscirculation, cerebral atherosclerosis);
• stressful situations;
• ototoxic effects of industrial and household substances, a number of drugs (aminoglycoside antibiotics, some antimalarial and diuretic drugs, salicylates, etc.);
• injuries (mechanical and acoustic, barotrauma).

About 30% of sensorineural hearing loss and deafness are of infectious origin. Viral infections are in first place - flu, mumps, measles, rubella, herpes, followed by epidemic cerebrospinal meningitis, syphilis, scarlet fever and typhus. Pathology of the hearing organ in infectious diseases is localized mainly in the receptor of the inner ear or the spiral ganglion of the cochlea.

Vascular-rheological disorders can also lead to the development of hearing loss. Changes in vascular tone due to direct or reflex irritation of the sympathetic nerve endings of large arteries (internal carotid, vertebral), as well as circulatory disorders in the vertebrobaeilar basin lead to circulatory disorders in the arterial system of the labyrinth, the formation of thrombi, hemorrhages in the endo- and perilymphatic spaces.

One of the most important causes of sensorineural hearing loss is still intoxication, it takes 10-15% in the structure of causes of sensorineural hearing loss. Among them, the first place is occupied by ototoxic drugs: aminoglycoside antibiotics (kanamycin, neomycin, monomycin, gentamicin, amikacin, streptomycin), cytostatics (cyclophosphamide, cisplatin, etc.), antiarrhythmic drugs; tricyclic antidepressants; diuretics (furosemide, etc.). Under the influence of ototoxic antibiotics, pathological changes occur in the receptor apparatus of the cochlea and blood vessels.

In some cases, hearing loss is caused by trauma. Mechanical trauma can lead to a fracture of the skull base with a crack in the pyramid of the temporal bone, often accompanied by damage to the auditory root of the VIII cranial nerve. Possible causes are barotrauma (average pressure above 400 mm Hg), a fracture of the base of the stapes with the formation of a perilymphatic fistula. Acoustic and vibration trauma at the level of maximum permissible parameters leads to damage to receptors in the cochlea. The combination of both factors produces an adverse effect 25 times more often than the effects of noise and vibration separately. High-frequency impulse noise of high intensity usually causes irreversible sensorineural hearing loss.

Hearing loss due to physiological aging is called presbycusis. Usually, age-related hearing changes, if they are not combined with hearing loss of other origin, are characterized by symmetry in both ears. Presbycusis is a multifaceted and versatile process that affects all levels of the auditory system, caused by biological processes of aging and influenced by the social environment. Today, different authors distinguish several types of presbycusis based on the topic of damage to the organ of hearing: sensory, metabolic, presbycusis as a result of damage to auditory neurons, cochlear, cortical.

Other causes of sensorineural hearing loss include neurinoma of the VIII cranial nerve, Paget's disease, sickle cell anemia, hypoparathyroidism, allergy, local and general irradiation with radioactive substances. The meteorological factor plays a significant role: a connection can be traced between sudden sensorineural hearing loss and weather conditions, between fluctuations in the spectrum of atmospheric electromagnetic waves, the passage of cyclones in the form of a warm front of low pressure and the frequency of pathology development. It has been established that acute sensorineural hearing loss most often occurs in the second month of each season (January, April, July, October).

[ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ]

Congenital causes of sensorineural hearing loss

Among congenital sensorineural hearing impairments, hereditary causes and pathology during childbirth are distinguished. Pathology during childbirth, as a rule, means fetal hypoxia, leading to damage to the central nervous system and the organ of hearing. Hereditary causes are varied. Non-syndromic hearing damage is not associated with visible anomalies of the outer ear or with other diseases, but it can be associated with anomalies of the middle and / or inner ear. Syndromic hearing damage is associated with congenital malformations of the ear or other organs. More than 400 genetic syndromes including hearing loss have been described. Syndromic hearing damage accounts for up to 30% of pre-speech deafness, but its contribution to all cases of deafness is relatively small, since the incidence of post-speech hearing loss is significantly higher. Syndromic hearing loss is presented according to the types of inheritance. The most common types are presented below.

Autosomal dominant syndromic hearing impairment

Waardenburg syndrome is the most common form of autosomal dominant syndromic hearing loss. It involves varying degrees of sensorineural hearing loss and pigmentary abnormalities of the skin, hair (white streak), and eyes (heterochromia iridis). Branchio-oto-renal syndrome involves conductive, sensorineural, or mixed hearing loss associated with bronchial cystic clefts or fistulas, congenital malformations of the external ear including preauricular puncta, and renal anomalies. Stickler syndrome is a symptom complex of progressive sensorineural hearing loss, cleft palate, and spondyloepiphyseal dysplasia with eventual osteoarthritis. Neurofibromatosis type II (NF2) is associated with a rare, potentially treatable type of deafness. The marker for NF2 is hearing loss secondary to bilateral vestibular neuromas.

[ 8 ], [ 9 ], [ 10 ], [ 11 ], [ 12 ], [ 13 ], [ 14 ], [ 15 ]

Autosomal recessive syndromic hearing impairment

Usher syndrome is the most common form of autosomal recessive syndromic hearing loss. It involves damage to two major sensory systems.

Individuals with this disorder are born with sensorineural hearing loss, later developing retinitis pigmentosa. Pendred syndrome is characterized by congenital severe sensorineural hearing loss and euthyroid goiter. Jervell-Lange-Nielsen syndrome involves congenital deafness and prolonged QT interval on the electrocardiogram. Biotinidase deficiency is caused by a deficiency of biotin, a water-soluble B-complex vitamin. Because mammals cannot synthesize biotin, they must obtain it from dietary sources and endogenous free biotin turnover. If this deficiency is not recognized and corrected by daily biotin supplementation, affected individuals develop neurologic signs and sensorineural hearing loss. Refsum disease involves severe progressive sensorineural hearing loss and retinitis pigmentosa, caused by abnormalities in phytanic acid metabolism.

[ 16 ], [ 17 ], [ 18 ], [ 19 ], [ 20 ]

X-linked syndromic hearing impairment

Alport syndrome includes progressive sensorineural hearing loss of varying severity, progressive glomerulonephritis leading to end-stage renal disease, and various ocular manifestations.

Pathogenesis of sensorineural hearing loss

In the development of acquired sensorineural hearing loss, a number of successive stages are distinguished: ischemia, circulatory disorders, death (due to intoxication) of sensitive cells of the inner ear and nerve elements of the auditory analyzer pathway. Congenital genetic disorders are the cause of congenital sensorineural hearing loss.