What are the types and causes of hearing loss?
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What are the types and causes of hearing loss?
Deafness is divided into conductive deafness, sensorineural deafness, mixed deafness, and central deafness. The causes of these four types of deafness are different.
1. Causes of conductive deafness
(1) Congenital malformations are common, including malformations of the outer ear and middle ear, such as congenital external auditory canal atresia or tympanic membrane, ossicles, Cochlear window and vestibular window are underdeveloped.
(2) Acquired obstruction of the external auditory canal, such as cerumen embolism, bone warts, foreign bodies, tumors, inflammation, etc. Purulent or non-purulent inflammation of the middle ear causes obstruction of the sound transmission mechanism of the middle ear, or ear trauma causes damage to the ossicular chain, benign or malignant tumors of the middle ear, or otosclerosis, etc.
2. Causes of sensorineural deafness
(1) Congenital hearing loss is often caused by underdevelopment of the auditory nerve in the inner ear, or caused by viral infection during pregnancy or taking ototoxic drugs , or injuries during childbirth, etc. Deafness caused by congenital inner ear malformations is sensorineural deafness. Inner ear malformations are divided into five categories based on inner ear X-ray tomography and embryogenesis, namely labyrinth absence, common cavity malformation, cochlear agenesis, cochlear hypoplasia and incomplete septation. In addition, large vestibular aqueduct syndrome is also a common congenital inner ear malformation that leads to sensorineural deafness.
Congenital deafness in sensorineural deafness can also include non-hereditary and hereditary causes. Deafness caused by viral infection during pregnancy, taking ototoxic drugs, or injury during childbirth is non-genetic deafness. Non-hereditary conditions include the use of ototoxic drugs during pregnancy, viral infections, syphilis, and bacterial infections during pregnancy, neonatal hypoxia, birth trauma, and neonatal hyperbilirubinemia. In addition, non-hereditary conditions include noise exposure and head trauma during delivery. , radiation exposure, etc. Hereditary deafness is caused by changes in genetic genes. The incidence rate of non-hereditary and hereditary deafness is 50% each. 70% of patients with hereditary deafness have no other symptoms besides deafness. This type of deafness is non-hereditary deafness. Syndromic deafness. Hereditary deafness includes autosomal negative, autosomal dominant, X-linked, Y-linked, mitochondrial (maternal) inheritance, etc.
At present, it is known that many genes are related to non-syndromic deafness. Mutations in one or several of these genes, or mutations at different sites in a gene, can cause deaf. However, deafness genes and their mutation sites are different among people of different races, or even in people from different regions of the same race. Relevant research in my country shows that GJB2, SLC26A4, and mitochondrial genes (A1555G and C1494T mutations) are the three most common genes that cause most of the hereditary deafness in China. Genetic testing of these few genes can identify 40% of the deaf people. % of genetic causes, combined with family history analysis and investigationThe body can diagnose more than 95% of hereditary deafness. Screening and detection of deafness genes provide the possibility to prevent congenital sensorineural deafness and reduce its incidence.
(2) Acquired
① Deafness caused by infectious diseases: various acute infectious diseases, bacterial or viral infections, such as Japanese encephalitis , mumps, purulent meningitis, measles, scarlet fever, influenza, herpes zoster, typhoid fever, etc. can damage the inner ear and cause sensorineural deafness of varying severity.
②Drug poisoning deafness: more common in aminoglycoside antibiotics, such as gentamicin, kanamycin, polymyxin, dihydrostreptomycin, neomycin, etc., and other drugs such as quinine , salicylic acid, cisplatin, etc. can all cause sensorineural deafness, and ear drug poisoning is closely related to the susceptibility of the body. Toxic deafness caused by drug poisoning is bilateral, often accompanied by tinnitus, and vestibular function may also be damaged. Long-term dripping of such drugs in the middle ear may also penetrate into the inner ear through the cochlear window membrane, so attention should be paid.
(3) Presbycusis is mostly caused by vascular sclerosis and bone hyperplasia, which leads to insufficient blood supply and degenerative lesions, leading to hearing loss.
(4) Traumatic deafness, craniocerebral trauma and temporal bone fracture damage the inner ear structure, causing inner ear bleeding, or inner ear damage caused by strong concussion, which can lead to sensorineural deafness, sometimes accompanied by tinnitus and vertigo. . Those with mild symptoms can recover. Inadvertently damaging the structures of the inner ear during ear surgery can also cause deafness.
(5) Sudden deafness is a sensorineural hearing loss that occurs suddenly and has no known cause. At present, it is believed that acute inner ear microcirculation disorder and viral infection are common causes of this disease.
(6) Blast deafness is an acute injury to the hearing caused by a sudden strong pressure wave and strong impulse noise. The eardrum and cochlea are the most vulnerable parts of the hearing aid. When a person is exposed to noise above 90dB, cochlear damage can occur. If the intensity exceeds 120dB, it can cause permanent deafness.
(7) Noise-induced deafness is a slowly progressive sensorineural hearing loss caused by long-term exposure to noise stimulation above 85dB. The main symptoms are tinnitus and deafness, and pure tone audiometry shows 4000Hz valley-shaped notch or high-frequency attenuation type.
(8) Auditory neuropathy Auditory neuropathy is a disease with relatively special clinical manifestations. The main audiological features include absence or severe abnormality of auditory brainstem response, normal otoacoustic emission, and stapedius muscle reflex. disappear or the threshold increases, and pure tone audiograms mostly show low-frequency hearing threshold loss. The patient's main complaint is poor speech resolution and the inability to communicate normally with others. The significant differences between auditory neuropathy and general sensorineural deafness are attracting more and more attention. However, the cause, pathogenesis and outcome of the disease are still unclear.
(9) Autoimmune autoimmune sensorineural hearing loss is a sensorineural hearing loss caused by damage to inner ear tissue caused by autoimmune disorders. This hearing loss can progressIt is linear and fluctuating, and can affect one or both ears. If it is bilateral, the hearing loss is mostly asymmetrical. Clinically, patients with autoimmune sensorineural deafness can have a variety of audiograms, such as low-frequency type, high-frequency type, flat type, bell-type, etc., but the low-frequency type is the most common. It may be related to the fact that the immune reactive damage of the inner ear first starts at the cochlear apex and the middle part of the cochlea, showing the typical characteristics of cochlear deafness, which is also a characteristic of clinical audiology.
(10) Meniere's disease Meniere's disease is an inner ear disease of unknown cause with hydrocele in the membranous labyrinth as its main pathological feature. The course of the disease is variable, with episodic vertigo, fluctuating deafness and tinnitus as its main symptoms. The cause of Meniere's disease is unknown, but it may be related to congenital inner ear abnormalities, autonomic nerve dysfunction, viral infection, allergies, endocrine disorders, salt and water metabolism disorders, etc. At present, it is generally believed that obstruction of endolymphatic reflux or malabsorption is the main cause of disease, such as endolymphatic stenosis or blockage; autonomic nerve dysfunction can cause spasm of small blood vessels in the inner ear, leading to labyrinth microcirculation disorder, tissue hypoxia, and endolymph biochemical properties. Change, osmotic pressure increases and causes membranous labyrinth hydrops. The pathological change of this disease is membranous labyrinth hydrops, which mainly involves the cochlear duct and saccule. Compression and stimulation of the cochlea can produce cochlear symptoms such as tinnitus and deafness, and compression and stimulation of the vestibular end apparatus can produce vestibular symptoms such as vertigo. Typical symptoms are episodic vertigo, fluctuating deafness, tinnitus and ear fullness.
3. Causes of mixed deafness
There are lesions in both the sound transmission and sensor structures. Such as long-term chronic suppurative otitis media, advanced otosclerosis, etc.
4. The cause of central deafness
The lesions of central deafness are located in the brainstem and brain, involving the cochlear nerve nucleus and its central conduction pathway, and the auditory cortex center Causes central deafness. It can be mainly divided into the following two types:
(1) Brainstem central deafness involves the cochlear nerve nucleus, resulting in one-sided deafness, which is mild; if it involves the cochlear nerve nucleus on one side and the crossing fibers on the opposite side, it will cause hearing loss. Bilateral deafness, with partial sound deafness being the most common, is common in pontine and medulla oblongata lesions.
(2) Cortical deafness Cortical deafness makes it difficult to distinguish the distance and nature of sounds. Sometimes, although general hearing is not damaged, the aesthetic ability of language is reduced. Because the fibers of the cochlear nerve nucleus on one side project to the auditory cortex on both sides, damage to one side of the auditory cortex or damage to one side of the conductive pathway produces unilateral or bilateral hearing loss.