Classification and etiology of deafness I. According to the time of occurrence of deafness, congenital deafness and acquired deafness, prelingual deafness and postlingual deafness are classified.
(i) Congenital deafness: Hearing impairment that exists at birth or shortly after birth and is caused by embryonic or perinatal deafness-causing factors, and its etiology can be classified into two categories: hereditary deafness or non-hereditary deafness.
(ii) Acquired deafness: deafness due to disease or accidental injury after birth.
(c) Prelingual deafness: Those who are severely congenitally deaf or lost their hearing in infancy, due to the inability to receive speech signals through speech communication, moreover, without their own speech feedback, resulting in speech development disorder is called prelingual deafness, and eventually most of them become mute due to deafness.
(4) Post-speech deafness: Those who lose their hearing after the formation of speech are called post-speech deafness. Post-lingual deafness is a condition in which the speech function often deteriorates gradually over time.
Classification according to the nature of the lesion
(a) Conductive deafness: Hearing loss caused by lesions in the outer ear and middle ear that prevent sound waves from reaching the inner ear. For example, cerumen embolism, otitis media, eustachian tube lesion and otosclerosis.
(B) Sensorineural deafness: Organic lesions of the inner ear, auditory nerve or auditory center can prevent the perception and analysis of sound or affect the transmission of sound information, resulting in hearing loss or hearing loss called sensorineural deafness.
Depending on the cause of the hearing impairment, sensorineural deafness can be divided into 3 categories.
1. Hereditary deafness: hearing impairment caused by defects in the development of the auditory organs secondary to genetic defects such as genetic or chromosomal abnormalities. These include congenital hereditary deafness and acquired congenital hereditary deafness.
2. Non-inherited congenital deafness: It refers to hearing impairment caused by maternal factors or delivery factors during pregnancy. Viral infections, birth injuries and nuclear jaundice are the main causes of congenital deafness, and fetal deafness can also be caused by syphilis, AIDS or ototoxic drugs applied during pregnancy. Non-inherited congenital deafness is often bilateral and severe or profound deafness.
3. Non-hereditary acquired sensorineural deafness: The incidence accounts for more than 90% of clinically diagnosed sensorineural deafness.
Common disorders include.
(1) Drug deafness: deafness caused by the application of certain ototoxic drug treatments or exposure to other chemical toxicants. There are no less than 100 known ototoxic drugs, including aminoglycoside antibiotics such as streptomycin, gentamicin, kanamycin and neomycin, antineoplastic drugs such as cisplatin and vincristine, loop diuretics such as furosemide (tachyphylaxis) and etanercept (diuretic acid), salicylates and quinine and chloroquine antimalarials such as quinine and chloroquine. In addition, chemical substances such as copper, phosphorus, arsenic, benzene, carbon monoxide, carbon disulfide, and carbon tetrachloride may enter the inner ear through the blood circulation, cerebrospinal fluid, or cochlear membrane, causing damage to the auditory organs and causing toxic deafness.
(2) Age-related deafness: Hearing loss due to gradual aging and degeneration of the auditory system with age is called age-related deafness. The age of appearance and the rate of development of senile deafness varies from person to person and is related to genetic factors and to a large extent to the exposure of the organism to various harmful factors in the internal and external environment. The clinical features of senile deafness are bilaterally symmetrical sensorineural deafness proceeding slowly from high frequencies to speech frequencies, which may be accompanied by high-pitched tinnitus, mostly with loudness reverberation, and speech recognition rate inconsistent with pure tone audiometry results.
(3) Sudden deafness: A severe sensorineural deafness of unknown etiology that occurs instantaneously. Its onset is currently thought to be associated with viral infection, vagal edema, vascular lesions and rupture of the vagal window membrane.
(4) Infectious deafness: sensorineural deafness caused by or complicated by various infectious factors. Some of the more common clinical deafness-causing infections include epidemic meningomyelitis, mumps, influenza, ear herpes zoster, typhus, scarlet fever, AIDS, rubella, chicken pox, and syphilis.
(5) Noise deafness: hearing impairment caused by acute or chronic strong acoustic stimulation that damages the auditory organs.
(6) Traumatic deafness: Broadly speaking, all mechanical traumas that cause damage to the auditory system and hearing loss are considered traumatic deafness, including blast deafness, noise deafness, temporal bone trauma, and surgical trauma. These mechanical injuries cause disturbances in the internal environment of the inner ear and irreversible damage to the auditory receptors leading to deafness.
(7) Systemic disease-related deafness: Certain systemic diseases such as hypertension and atherosclerosis, diabetes, hypothyroidism, hyperlipidemia, renal failure, systemic lupus erythematosus, erythroblastosis, leukemia, sickle cell anemia, multiple sclerosis, and polyarteritis nodosa can cause damage to the inner ear and lead to sensorineural deafness.
(8) Metabolic disorders of certain essential elements: It is currently believed that metabolic disorders of essential elements such as iodine, iron, zinc and magnesium are associated with sensorineural deafness and tinnitus.
(9) Autoimmune sensorineural deafness: Sensorineural deafness manifested by damage to the inner ear caused by the reaction of inner ear tissues to specific antigens or autoimmune diseases. Testing for antibodies specific to the inner ear tissue can help in the diagnosis.
(10) Central deafness: It refers to hearing loss due to lesions from the cochlear nucleus to the cerebral cortex and is associated with various lesions in and around the brainstem auditory pathway and auditory cortex, such as multiple cerebral infarction and multiple sclerosis.
(11) Auditory neuropathy: A specific type of sensorineural deafness in which the lesion is located in the auditory nerve.
(12) Tumor: Auditory neuroma and other cerebellopontine horn tumors can lead to sensorineural deafness, mostly due to nerve conduction disorders caused by tumor compression.
(13) Functional deafness: without organic changes in the auditory system, the patient complains of not being able to hear sounds while the objectively observed hearing is normal, including pseudo-deafness, hysterical deafness and neurosis.
(3) Mixed deafness: the presence of simultaneous lesions in the transmitral and sensorineural bodies. Such as long-term chronic suppurative otitis media, advanced otosclerosis, and blast deafness.
C. Classification according to the degree of deafness
The degree of deafness is classified according to the average of the hearing threshold of speech frequencies measured by pure tone audiometry.
Classification of deafness The average speech frequency pure-tone hearing threshold is classified into 5 levels according to WHO 1980 deafness classification criteria.
Mild deafness: listening to general conversation at close range without difficulty, with pure tone and speech hearing thresholds of 26 to 40 dB on audiometry.
Moderate deafness: difficulty in listening to speech at close range, hearing threshold of 41~55dB
Moderate or severe deafness: difficulty hearing loud speech at close range, hearing threshold 56～70dB.
Severe deafness: Hearing by shouting loudly in the ear, hearing threshold 71～91dB.
Very severe deafness (total deafness): can’t hear loud shouting in the ear, pure tone audiometry hearing threshold over 91dB