Hearing loss is a major health problem that affects large populations in societies, causing loss of money, work force and a decrease in quality of life. 10 million people in the US have permanent, irreversible hearing loss due to noise and trauma alone. Hearing loss is the most common chronic problem after arthritis and hypertension. The most common hearing loss is age-related hearing loss or presbycusis, followed by noise-induced hearing loss. There are not many epidemiological studies that have examined hearing loss by populations, etiology or risk factors.
In an epidemiological study published by Cruickshanks et al., they screened hearing loss with audiometry and tympanometry in a population aged 48-92 years with hearing loss25. According to this study, the prevalence of hearing loss in the given age group was reported as 45.9%. The prevalence of hearing loss increases with increasing age and is more common in males. The incidence of hearing loss under the age of 18 is reported as 17/1000. As a result of a better understanding of the molecular and cellular pathophysiology underlying many different causes of hearing loss, their frequency, risk factors and which populations they affect, a much better treatment and rehabilitation will be offered to patients.
Hearing loss occurs due to many reasons. There is insufficient epidemiological data on most of them. In this article, the frequency, risk factors and etiologies of some common hearing losses are discussed in the light of epidemiological data. The etiologies of hearing loss are shown below.
Causes of conductive hearing loss:
Conductive hearing loss, located between the mouth of the external ear canal and the hairy cells of the cochlea, is basically the inhibition of the transmission of auditory stimuli to the cochlear receptor cells.
Pathologies originating from the external ear canal
plug
foreign body
Congenital aplasia or atresia
exocytosis
tumors
osteoma
cysts
Otitis externa
Middle ear pathologies
Acute otitis media and otitis media with effusion
Chronic otitis media and cholesteatoma
Tympanosclerosis
middle ear trauma
Bone chain anomalies
otosclerosis
tumors
Past middle ear operations
Causes of sensorineural hearing loss:
Sensorineural hearing loss is due to defects either in the sensory end organ of the cochlea or in the neural conduction pathway that extends to the central nervous system. This defect occurs either during the inner ear sensory organ’s conversion of acoustic energy into electrical energy or during the transmission of neural impulses to the centre.
Presbycusis
Noise-induced hearing loss
ototoxicity
Sudden idiopathic hearing loss
autoimmune inner ear disease
Meniere’s disease
Congenital sensorineural hearing loss
Trauma
syphilis
Meningitis
multiple sclerosis
Migraine
Diabetes Mellitus
Paget’s Disease
Conductive hearing loss
Outer ear pathologies
Plug: Probably the most common cause of conductive hearing loss. In the ear examination findings made by Düzce University Faculty of Medicine in a school, earwax was found to be the most common pathology (detected in 39.4% of children)45.
Foreign Body: Although it can be seen mostly in children and in the external ear canal, foreign body publications that can be visualized in the middle ear are also encountered in the literature46.
ECA Aplasia and ECA Stenosis: Considering their embryological development, these two deformities, which are usually seen together, rarely include inner ear deformity. In our country, M.Kebapçı et al.’s article on “HRCT findings in Congenital Aural Atresia” supports this47. Microtia is seen at a frequency of 0.03% live birth. Half of these patients have a related syndrome55. It is more common in males and in the right ear.
DHF Exostosis: This pathology, which is defined as the formation of bone protrusions towards the DHF canal, especially seen in swimmers, is one of the causes of conductive hearing loss. In a prevalence study conducted in 300 surfboard users in Australia, 90 male and 10 female surfers found significant enough (2/3 or more of DKY) occluded exostosis. It has been reported that one out of every two male surfers (more than 20 years) and three out of seven female surfers who swim regularly (over 20 years) develop exostosis, which over time causes an obstruction in the DKY channel48.
DHF Tumors: Ca with squamous h is a rare disease of the external auditory canal, as reported in a study conducted in the Netherlands, with a 5-year survival rate of 35% to 65%50. Another article from Australia supports this survey. It was stated here that DHF and temporal bone malignancy were not common, and a 5-year survival rate of 54% was reported in a series of 59 patients treated at the Prince’s Hospital of Wales between 1974 and 1995. These tumors are usually seen between the ages of 40-60.
Osteomas: They are rare benign tumors. It is usually found incidentally and does not cause symptoms49.
Cysts: Cysts that can cause conductive hearing loss may rarely be encountered in the external ear canal.
Otitis Externa: In Thailand, the prevalence of ear diseases was examined in 980 elderly population aged 60-96 years, and otitis externa (4.3%) was reported as the second most common pathology after earwax (8%). In another study, the incidence of otitis externa was reported at a rate of 4/1000 per year57.
Middle ear pathologies:
Acute otitis media with effusion: It is one of the most common diseases of the ear. In a study conducted in the south of the United States, 84% of the children participating in the study had at least one otitis media attack, 50% had 3 or more otitis media attacks, and 25% had 6 or more otitis media attacks26. In the Greater Boston Otitis Media study, 93% of children had at least one otitis media attack, and 74% had at least 3 or more otitis media attacks27. It is seen that the prevalence has been increasing gradually in the USA in recent years. The highest prevalence is observed in the first 2 years of age, and the incidence of otitis media decreases with increasing age.
The incidence of otitis media increases in winter months due to being more crowded in crowded environments, regardless of climate.
The risk factors for otitis media identified by Teele can be listed as male gender, early otitis media attack, bottle feeding and having a relative with otitis media attack28. Later, Pulander, Karma, and Sipil also cited allergy, socioeconomic status, previous viral infections, mother’s smoking, and parents’ having otitis media attacks as risk factors. Low birth weight is not a risk factor. Breast milk, on the other hand, plays a protective role only during the period it is taken, other than that, it does not provide any protection for later periods.
Risk factors for acute otitis media and otitis media with effusion have been studied together. Because these two diseases symbolize two different periods of the disease called otitis media. In addition, different studies have shown that these two diseases have the same risk factors.
The prevalence of secretory otitis media in preschool and school-age children was investigated in a study conducted by S. Inanli et al. While the overall prevalence of SOM was 9% in 539 children included in the study, this rate was 13.6% in the 3-6 age group and 7% in the 6-9 age group. A comprehensive study conducted in Denmark examined the epidemiology of otitis media with effusion and investigated the prevalence of otitis media with effusion as evidenced by tympanometric examination. According to the results, the incidence of Type B or Type C2 tympanometry in 1-year-old babies was found to be 24%33. However, the age group in which tympanometry is most frequently encountered as Type B is 2-4 years old. The prevalence of otitis media with effusion, as evidenced by thymoanometry, begins to decline after the age of 6-7 years.
Historically, otitis media has been viewed as a disease related to eustachian tube function. Basically, the Eustachian tube has 3 important functions, which are aeration of the middle ear, cleaning and protection from infection. While it was mentioned in previous studies that the occluded Eustachian tube predisposes to infection in acute otitis media etiology, it is mentioned in recent studies that acute otitis media is primarily due to bacterial infection and eustachian dysfunction occurs secondary to this. In the etiology of acute otitis media, the same pathogens are universally seen as causative agents. The most common causative agent is S.pneumonia and it is seen due to H.influenza and B.catarrhalis, respectively. Eustachian dysfunction is at the center of the pathophysiology in otitis media with effusion. However, eustachian dysfunction occurs secondary to an inflammatory condition rather than a primary problem.
Chronic otitis media and Cholesteatoma: The prevalence of COM was reported as 39 per 100 000 people in a study conducted in Israel53. It is accepted that the disease is associated with genetic structure and socioeconomic level. The true prevalence of cholesteatoma is unknown. Chronic otitis media with cholesteatoma is seen in 4.2/100000 people and chronic otitis media without cholesteatoma is seen in 13.8/100000 people40. In some studies, it has been reported that chronic otitis media with cholesteatoma is seen at a rate of 3/100,000 in children and 12.6/100,000 in adults42. The theories of intussusception, epithelial invasion, basal cell hyperplasia and squamous metaplasia have separately found supporters in the etiology of cholesteatoma. Biofilms have been discussed in the etiology of chronic otitis media without cholesteatoma in recent years.
Tympanosclerosis: It occurs secondary to trauma or as a complication of otitis media. In most patients, these calcified hyaline plaques do not cause hearing loss or cause very mild, clinically insignificant hearing loss. The cause of hearing loss in tympanosclerosis is fixation in the bone chain. The incidence of tympanosclerosis in chronic otitis media has been reported as 9-38%. In a study by Kinney, tympanosclerosis was found in 20% of 1495 patients who were operated for chronic otitis media3. In a study published by Daly, an average incidence of tympanosclerosis was reported in 10% of children aged 5-15 years at a 4-year follow-up1. Hussl and Mueller reported in their study that tympanosclerosis is a frequent complication of otitis media with chronic effusion2. In this study, they found tympanosclerosis in 19.7% of the eardrums 6-8 years after the ventilation tubes placed for otitis media with effusion. They also reported that tympanosclerosis was observed after frequently recurrent acute otitis media. Tos and Stangerup found more tympanosclerosis in the ears with a ventilation tube (59%) than in the contralateral ears with only myringotomy (13%)5. Magat et al. reported the incidence of tympanosclerosis as 23.6% in a study they conducted on 1274 patients who had a tympanostomy tube inserted4.
Ear trauma: Conductive hearing loss as a result of ear traumas can be seen as a result of perforation of the tympanic membrane, hemotympanum or ossicular dislocation, which may occur after a blunt trauma. In addition, sensorineural hearing loss can be seen in inner ear damage due to temporal bone fractures. The etiology of hearing loss due to all ear traumas is examined under this title. In the past, 75% of motor vehicle accidents were accompanied by head trauma. In recent years, this rate has decreased after the introduction of helmets and seat belts.
If the trauma is large enough to cause fracture of the skull bones, a temporal bone fracture is seen in 14-22% of patients6,7. In the largest series ever published for temporal bone fractures, 31% of all temporal bone fractures are due to motor vehicle accidents8. Temporal bone fractures are usually seen in men (3:1) and in young and middle-aged adults. It has been reported that 8-29% of temporal bone fractures are bilateral. In the past, temporal bone fractures were classified as longitudinal or transverse, but since most fractures are oblique or mixed, this classification has been replaced by a new classification as fractures that involve the otic capsule or those that do not8,9. According to the old classification, longitudinal fractures are seen in 70-90% and transverse fractures in 10-30%. According to the new classification, 2.5-5.8% of fractures have been reported as involving the otic capsule8,10.
Most of the fractures involving the otic capsule were found in the longitudinal plane10. Although almost all of the fractures involving the otic capsule result in sensorineural hearing loss, there are also publications reporting that it does not always happen. Fractures that do not involve the otic muscle usually result in conductive or mixed hearing loss8. Hemotympanum or bloody otorrhea is seen in almost all temporal bone fractures. Traumatic tympanic membrane perforations usually heal spontaneously and do not require immediate intervention. As a result of the studies, the prevalence of traumatic tympanic membrane perforation has been reported as 1.4-8.6/100000 per year. Temporal bone fractures usually rupture the tympanic membrane around the notch of the rivinus. In these fractures, 20% of the ossicular chain detachment is observed11. The most common pathology is incudostapedial joint separation12. Conductive hearing loss after temporal bone traumas heals spontaneously at a rate of 80% without any intervention13. If conductive hearing loss does not improve, there is probably bone chain pathology.
Bone chain anomalies: It is the ossicle stapes, the development of which is the latest in the middle ear ossicles and the most malformation is seen. The development of other ossicles is rapid.
Otosclerosis: It is a hereditary disorder that shows autosomal dominant inheritance characteristics with variable penetrance rates. 2/3 of the patients are women. Although hearing loss usually begins in the late 10s and early 20s, the onset of hearing loss may be delayed until the age of 40 in some patients. The youngest otosclerosis patient diagnosed surgically is 6 years old. It may worsen with pregnancy and estrogen use. The prevalence of otosclerosis differs according to races. In the Caucasian race, it is seen at a rate of 7.3% in men and 10.3% in women44. Stapes is observed as fixed in only 12.3% of patients diagnosed with otosclerosis histopathologically. In 70% of the patients, the disease is seen bilaterally. The frequency of onset of the disease, which is known to worsen during pregnancy, has been reported between 10-17%. In a study in which it was shown as the most common cause of hereditary hearing loss in adults, it was found in 2% of the selected population with hearing loss65.
Tumors: There are many rare primary benign and malignant tumors involving the middle ear. Some of them gain importance as they are more common problems. Rhabdomyosarcoma is the most common tumor of the middle ear and mastoid region in children. Paragangliomas are the most common temporal bone tumors after acoustic neuroma.
Sensorineural hearing loss:
Presbycusis: It is hearing loss associated with old age for which an etiology cannot be determined. Usually, hearing loss is sensorineural and concentrated at high frequencies. It is very difficult to carry out epidemiological studies on this subject, especially it is almost impossible to exclude noise-induced hearing loss from the study groups. It is the most common cause of hearing loss. It is seen at a rate of 30% in the population over 65 years of age14. It increases to 50% in the population over 75 years old. Hearing loss due to old age is more serious in male patients. In a study conducted in Korea, the prevalence of presbycusis was found to be 37.8% in the population over 65 years of age without risk factors64.
Noise-induced hearing loss: It is one of the most common causes of hearing loss. Noise-induced hearing loss was found to be 20% in 30,000 Hungarians studied between 1966 and 197115. In the United States, 30 million people are exposed to noise, and 10 million of them have hearing loss16.
Ototoxicity: Ototoxicity includes chemical agents or drugs that cause temporary or permanent inner ear dysfunction. Many chemicals can cause this damage. Here, epidemiological data on some common substances will be mentioned. Aminoglycosides are antibiotics that have been used for many years to treat serious infections. Ototoxicity due to aminoglycosides is seen at a rate of 20% in total when all agents are considered17. The toxic effects of these agents appear days or weeks after use. Aminoglycosides primarily affect high frequencies, and speech frequencies are also affected if use continues. Aminoglycosides interact with the inner ear and cause toxicity especially in outer hair cells after the formation of free oxygen radicals.
Cisplatin is a potent antineoplastic agent used in the treatment of many malignant tumors. In a study, permanent hearing loss was found in 20% of patients given cisplatin for testicular cancer, and the incidence of hearing loss was found to be 50% in patients receiving high-dose cisplatin18. We see cisplatin ototoxicity more frequently in pediatric patients. Ototoxicity was observed with a rate of 6% in a study with furasemide19. Ototoxicity caused by furosemide is directly proportional to its free fraction in plasma. Salicylates also cause hearing loss. The amount of free salicylate in the plasma causes an increase in the threshold potential in the sensorial cells of the inner ear, and the depth of hearing loss increases as the free amount increases20. It has been reported in 20% of patients using Quinine-induced hearing loss used in the treatment of malaria. Macrolide antibiotics and Vancomycin are also some of the ototoxic antibiotics.
Sudden idiopathic hearing loss: Its average incidence varies between 1/5000 and 1/20000 people per year. Although it can be seen at any age, it is most common between the ages of 50-60. The male female ratio does not differ. The probability of simultaneous bilateral occurrence is very low. Although viral infections, vascular occlusion, autoimmunity and intracochlear membrane ruptures are blamed in the etiology, they are most commonly seen as idiopathic. 28% of patients with sudden hearing loss describe a viral URI in the last 1 month. Vascular causes have also been studied in etiology, but in fact very few patients have been truly vascular aetiology.
Autoimmune inner ear disease: Primary autoimmune inner ear disease is a rare condition. Since there is no definitive diagnosis method, its true incidence is not known. However, it is a rarer disease than sudden hearing loss with an incidence of 1/5000-1/20000 per year. Ear involvement in multisystemic autoimmune diseases is rare except for Wegener’s granulomatosis and Cogan’s disease. Ear involvement is seen in 30-50% of patients with a diagnosis of Wegener’s granulomatosis.
Meniere’s disease: The incidence of Meniere’s disease has been reported differently in many studies. It was determined as 157/100000 in England, 46/100000 in Sweden and 7.5/100000 in France. Meniere’s disease generally affects the Caucasian race and is somewhat more common in women. The disease, which is usually unilateral, can be bilateral more rarely.
Congenital sensorineural hearing loss: The incidence of congenital sensorineural hearing loss was found to be 1-3/1000 live births. The proportion of people with profound congenital sensorineural hearing loss is 1/1000 live births. Connely et al. found the frequency of hearing loss in newborns as 1/811 in the population without risk factors and as 1/75 in the population with risk factors58. While 30% of this is due to syndromic sensorineural hearing loss, 70% is non-syndromic hearing loss. 18% of non-syndromic hearing losses show autosomal dominant, 80% autosomal recessive and 2% X-linked or mitochondrial inheritance. In an epidemiological study conducted among children with hearing loss in Istanbul and Zonguldak in Turkey, 62.9% of hearing loss was found to be of genetic origin59. In this study, it was emphasized that congenital hearing loss is much more common in developing countries than in developed countries.
Although over 200 syndromes are associated with congenital hearing loss, the epidemiological data of the relatively more common ones are listed below.
BRANCHIO-OTO-RENAL SYNDROME: It shows autosomal dominant inheritance. Its prevalence is 1/40000 newborns. It constitutes 2% of children with profound hearing loss. The mutation is in the EYA-1 gene.
NEUROFIBROMATOSIS TYPE 2: It shows autosomal dominant inheritance. Its prevalence is 1/40000 to 1/90000 births34. There is a mutation in the gene encoding the merlin protein on chromosome 22.
STICKLER SYNDROME: It shows autosomal dominant inheritance. Its prevalence is 1/10000 births35. It occurs due to mutations in COL2A1, COL2A2 or CO11A1 genes. These genes encode collagen type 2 or type 11.
WAARDENBURG SYNDROME: It shows autosomal dominant inheritance. Its prevalence varies between 1/10000 and 1/20000. Type 1 Waardenburg syndrome is caused by mutations in the PAX3 gene, Type 2 MITF gene, Type 3 PAX3 gene and Type 4 Waardenburg Syndrome as a result of mutations in EDN3, EDNRB and SOX10 genes.
TREACHER-COLLINS SYNDROME: It shows autosomal dominant inheritance. It is caused by a mutation in the TCOF gene, which encodes the treacle protein.
PENDRED SYNDROME: It shows autosomal recessive inheritance. The syndrome is the most common cause of congenital hearing loss. Its prevalence is 1/10000 people. It accounts for 10% of hereditary deafness cases39. It occurs as a result of SLL26A4 gene mutation.
USHER SYNDROME: It shows autosomal recessive inheritance. Its prevalence varies between 1/20000 and 1/25000 people. It constitutes 5% of hereditary hearing losses. It is the cause of 50% of both deaf and blind people in the society. It represents a heterogeneous group with the most frequent mutations in the MYO2A and USH2A genes.
ALPORT SYNDROME: It shows X-linked inheritance. It occurs as a result of COL4A5 gene mutation. This gene mutation occurs once in 1/5000 births.
Non-syndromic hearing loss is a group of diseases that occur due to many gene mutations and that hearing loss is not accompanied by other anomalies.
DFNB1 MUTATION: It is the most common mutation seen in non-syndromic hereditary hearing loss. It shows autosomal recessive trait. It occurs as a result of the GJB’ gene mutation encoding Connxin 26. It constitutes 50% of autosomal recessive hearing loss36. Although the carrier rate varies according to races, the average incidence of mutation is around 3%.
Meningitis: Meningitis is a common disease in developing countries. The most common neurological sequelae of meningitis is hearing loss. In a study from Ethiopia, the frequency of hearing loss was reported as 25% in children discharged after meningitis60. In a study conducted in the Netherlands in 628 patients with non-Hib meningitis, the frequency of hearing loss was found to be 7%62. This shows that hearing loss sequelae occur more frequently due to low socioeconomic status.
Cystic Fibrosis: In an epidemiological study conducted among patients followed for cystic fibrosis in Spain, the prevalence of hearing loss was found to be 28.56%63. It was also emphasized that the use of ototoxic antibiotics would increase this rate.
Syphilis: Congenital or acquired syphilis has been associated with sensorineural hearing loss. Hearing loss has been reported with a frequency of 17% in congenital syphilis, 25% in late latent syphilis, and 80% in symptomatic neurosyphilis21.
Multiple sclerosis: Sensorineural hearing loss is seen in 4% to 10% of multiple sclerosis patients22,23. It can be bilateral, unilateral, sudden onset or slow onset. It is more common in women, and the age of 20-30 is the most common period.
Migraine: Some audiovestibular complaints may accompany the symptoms in migraine patients. Especially in the basilar migraine subtype, the incidence of bilateral hearing loss was found to be 46%, and the incidence of unilateral hearing loss was found to be 34%24.
Diabetes Mellitus: Although an increased incidence of hearing loss is expected in patients with Diabetes Mellitus due to the increased risk of vascular pathology, no evidence has been obtained proving this to be the case.
Paget’s Disease: Paget’s disease is a common disease affecting 3% of the 40-year-old population and 11% of the 80-year-old population. Hearing loss is seen in 5%-44% of Paget’s disease and is usually sensorineural or mixed type56.
Behçet’s Disease: Behçet’s Disease, which is a relatively common disease in Turkey, can cause hearing loss. In a study conducted in Turkey, the frequency of hearing loss in Behçet’s Disease was found to be 55%, and most of this loss is related to high frequencies61.
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