Editing Sensorineural hearing loss (section)

==Causes==
Sensorineural hearing loss may be genetic or acquired (i.e. as a consequence of disease, noise, trauma, etc.). People may have a hearing loss from birth ([[congenital]]) or the hearing loss may come on later. Many cases are related to old age (age-related).{{citation needed|date=February 2023}}

===Genetic===
Hearing loss can be inherited. More than 40 genes have been implicated in the cause of deafness.<ref>{{Cite journal |vauthors=Matsunaga T |date=December 2009 |title=Value of genetic testing in the otological approach for sensorineural hearing loss |journal=The Keio Journal of Medicine |volume=58 |issue=4 |pages=216–22 |doi=10.2302/kjm.58.216 |pmid=20037285 |doi-access=free}}</ref>  There are 300 syndromes with related hearing loss, and each syndrome may have causative genes.{{citation needed|date=February 2023}}

[[Recessive]], [[Dominant gene|dominant]], [[X-linked]], or [[Mitochondrial gene|mitochondrial]] genetic mutations can affect the structure or metabolism of the inner ear. Some may be [[Point mutation|single point mutations]], whereas others are due to [[chromosomal abnormalities]]. Some genetic causes give rise to a late onset hearing loss. Mitochondrial mutations can cause SNHL i.e. m.1555A>G, which makes the individual sensitive to the ototoxic effects of [[aminoglycoside antibiotics]].{{cn|date=December 2024}}
* The most common cause of recessive genetic congenital hearing impairment in developed countries is [[DFNB1]], also known as Connexin 26 deafness or [[GJB2]]-related deafness.
* The most common syndromic forms of hearing impairment include (dominant) [[Stickler syndrome]] and [[Waardenburg syndrome]], and (recessive) [[Pendred syndrome]] and [[Usher syndrome]].
* Mitochondrial mutations causing deafness are rare: [[MT-TL1]] mutations cause [[MIDD]] (Maternally inherited deafness and diabetes) and other conditions which may include deafness as part of the picture.
* [[TMPRSS3]] gene was identified by its association with both congenital and childhood onset autosomal recessive deafness. This gene is expressed in fetal cochleae and many other tissues, and is thought to be involved in the development and maintenance of the [[inner ear]] or the contents of the [[perilymph]] and [[endolymph]]. It was also identified as a tumor associated gene that is overexpressed in [[ovarian tumor]]s.
* [[Charcot–Marie–Tooth disease]]<ref name="Papadakis 2003">{{Cite journal |vauthors=Papadakis CE, Hajiioannou JK, Kyrmizakis DE, Bizakis JG |date=May 2003 |title=Bilateral sudden sensorineural hearing loss caused by Charcot-Marie-Tooth disease |journal=The Journal of Laryngology and Otology |volume=117 |issue=5 |pages=399–401 |doi=10.1258/002221503321626465 |pmid=12803792}}</ref> an inherited neurological disorder with delayed onset that can affect the ears as well as other organs. The hearing loss in this condition is often ANSD (auditory neuropathy spectrum disorder) a neural cause of hearing loss. 
* [[Muckle–Wells syndrome]], a rare inherited [[autoinflammatory]] disorder, can lead to hearing loss.
* [[Autoimmune disease]]: although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. [[Granulomatosis with polyangiitis]], an autoimmune condition, may precipitate hearing loss.

===Congenital===
* Infections:{{citation needed|date=February 2023}}
** [[Congenital rubella syndrome]], CRS, results from transplacental transmission of the [[rubella virus]] during pregnancy. CRS has been controlled by universal vaccination ([[MMR vaccine|MMR]] or [[MMRV vaccine]]).
** [[Cytomegalovirus]] (CMV) infection is the most common cause of progressive sensorineural hearing loss in children. It is a common viral infection contracted by contact with infected bodily fluids such as saliva or urine and easily transmitted in nurseries and thus from toddlers to expectant mothers. CMV infection during pregnancy can affect the developing foetus and lead to learning difficulties as well as hearing loss.
** [[Toxoplasmosis]], a parasitic disease affecting 23% of the population in the U.S., can cause sensorineural deafness to the fetus in utero.
* [[Hypoplasia|Hypoplastic]] auditory nerves or abnormalities of the cochlea. Abnormal development of the inner ear can occur in some genetic syndromes such as LAMM syndrome (labyrinthine aplasia, microtia and microdontia), [[Pendred syndrome]], [[branchio-oto-renal syndrome]], [[CHARGE syndrome]]{{cn|date=December 2024}}
* [[GATA2 deficiency]], a grouping of several disorders caused by common defect, viz., familial or sporadic [[Mutation#By effect on function|inactivating mutation]]s in one of the two parental ''[[GATA2]]'' [[gene]]s. These [[autosomal dominant]] mutations cause a reduction, i.e. a [[haploinsufficiency]], in the cellular levels of the gene's product, [[GATA2]]. The GATA2 [[protein]] is a [[transcription factor]] critical for the [[Embryogenesis|embryonic development]], maintenance, and functionality of [[blood|blood-forming]], [[Lymphatic system|lympathic-forming]], and other tissue-forming [[stem cell]]s. In consequence of these mutations, cellular levels of GATA2 are deficient and individuals develop over time hematological, immunological, lymphatic, and/or other disorders. GATA2 deficiency-induced abnormalities in the lymphatic system are proposed to be responsible for a failure in generating the [[perilymphatic space]] around the inner ear's [[semicircular canals]], which in turn underlies the development of sensorineural hearing loss.<ref name="pmid28179280">{{Cite journal |vauthors=Crispino JD, Horwitz MS |date=April 2017 |title=GATA factor mutations in hematologic disease |journal=Blood |volume=129 |issue=15 |pages=2103–2110 |doi=10.1182/blood-2016-09-687889 |pmc=5391620 |pmid=28179280}}</ref><ref name="pmid28643018">{{Cite journal |vauthors=Hirabayashi S, Wlodarski MW, Kozyra E, Niemeyer CM |date=August 2017 |title=Heterogeneity of GATA2-related myeloid neoplasms |journal=International Journal of Hematology |volume=106 |issue=2 |pages=175–182 |doi=10.1007/s12185-017-2285-2 |pmid=28643018 |doi-access=free}}</ref>

===Presbycusis===
{{main|Presbycusis}}
Progressive age-related loss of hearing acuity or sensitivity can start as early as age 18, primarily affecting the high frequencies, and men more than women.<ref>{{Cite journal |vauthors=Mills JH, Going JA |date=April 1982 |title=Review of environmental factors affecting hearing |journal=Environmental Health Perspectives |volume=44 |pages=119–27 |doi=10.1289/ehp.8244119 |pmc=1568958 |pmid=7044773|bibcode=1982EnvHP..44..119M }}</ref> Such losses may not become apparent until much later in life. [[Presbycusis]] is by far the dominant cause of sensorineural hearing loss in industrialized societies. A study conducted in Sudan, with a population free from loud noise exposures, found significantly less cases of hearing loss when compared with age-matched cases from  an industrialized country.<ref>{{Cite journal |last1=Rosen |first1=S. |last2=Bergman |first2=M. |last3=Plester |first3=D. |last4=El-Mofty |first4=A. |last5=Satti |first5=M. H. |date=September 1962 |title=Presbycusis study of a relatively noise-free population in the Sudan |journal=The Annals of Otology, Rhinology, and Laryngology |volume=71 |issue=3 |pages=727–743 |doi=10.1177/000348946207100313 |issn=0003-4894 |pmid=13974856 |s2cid=30150198}}</ref>    Similar findings were reported by a study conducted of a population from Easter island, which reported worse hearing among those that spent time in industrialized countries when compared with those that never left the island.<ref>{{Cite journal |last1=Goycoolea |first1=M. V. |last2=Goycoolea |first2=H. G. |last3=Farfan |first3=C. R. |last4=Rodriguez |first4=L. G. |last5=Martinez |first5=G. C. |last6=Vidal |first6=R. |date=December 1986 |title=Effect of life in industrialized societies on hearing in natives of Easter Island |journal=The Laryngoscope |volume=96 |issue=12 |pages=1391–1396 |doi=10.1288/00005537-198612000-00015 |issn=0023-852X |pmid=3784745 |s2cid=23022009}}</ref>   Researchers have argued that factors other than differences in noise exposure, such as genetic make up, might also have contributed to the findings.<ref>{{Cite book |last=Salawati |first=Liza |url=http://jurnal.unsyiah.ac.id/JKS/article/view/2744 |title=Noise-Induced Hearing Loss |date=2012 |work=Jurnal Kedokteran Syiah Kuala |isbn=978-1-4419-9522-3 |editor-last=Le Prell |editor-first=Colleen G. |series=Springer Handbook of Auditory Research |volume=40 |pages=45–49 |language=en-gb |format=<!-- Submitted manuscript --> |doi=10.1007/978-1-4419-9523-0 |editor-last2=Henderson |editor-first2=Donald |editor-last3=Fay |editor-first3=Richard R. |editor-last4=Popper |editor-first4=Arthur N. |issue=1 |s2cid=6752992}}</ref>   Hearing loss that worsens with age but is caused by factors other than normal aging, such as noise-induced hearing loss, is not presbycusis, although differentiating the individual effects of multiple causes of hearing loss can be difficult. One in three persons have significant hearing loss by age 65; by age 75, one in two. Age-related hearing loss is neither preventable nor reversible.{{cn|date=December 2024}}

====Noise====
{{main|Noise-induced hearing loss}}
Most people living in modern society have some degree of progressive sensorineural (i.e. permanent) noise-induced hearing loss (NIHL) resulting from overloading and damaging the sensory or neural apparatus of hearing in the inner ear.{{Citation needed|date=October 2022}} NIHL is typically a drop-out or notch centered at 4000&nbsp;Hz. Both intensity (SPL) and duration of exposure, and repetitive exposure to unsafe levels of noise contribute to cochlear damage that results in hearing loss. The louder the noise is, the shorter the safe amount of exposure is. NIHL can be either permanent or temporary, called a threshold shift. Unsafe levels of noise can be as little as 70&nbsp;dB (about twice as loud as normal conversation) if there is prolonged (24-hour) or continuous exposure. 125&nbsp;dB (a loud rock concert is ~120&nbsp;dB) is the pain level; sounds above this level cause instant and permanent ear damage.{{citation needed|date=February 2023}}

Noise and ageing are the primary causes of [[presbycusis]], or age-related hearing loss, the most common kind of hearing loss in industrial society.<ref>{{Cite journal |vauthors=Gates GA, Mills JH |date=September 2005 |title=Presbycusis |journal=Lancet |volume=366 |issue=9491 |pages=1111–20 |doi=10.1016/S0140-6736(05)67423-5 |pmid=16182900 |quote=Presbycusis (or presbyacusis) is a general term that refers to hearing loss in the elderly and, as such, represents the contributions of a lifetime of insults to the auditory system. Of these, ageing and noise damage are the chief factors, plus genetic susceptibility, otological disorders, and exposures to ototoxic agents.}}</ref>

{{citation needed|date=November 2015}} The dangers of environmental and occupational noise exposure are widely recognized. Numerous national and international organizations have established standards for safe levels of exposure to noise in industry, the environment, military, transportation, agriculture, mining and other areas.<ref group="Note">A few prominent ones are American National Standards Institute (ANSI), International Organization for Standardization (ISO), Deutsches Institut für Normung (DIN), Swedish Standards Institute (SSI), Canadian Standards Association (CSA), British Standards Institute (BSI), Austrian Standards International(ÖNORM), and in the United States, Environmental Protection Agency (EPA), Occupational Safety and Health Administration (OSHA) and numerous state agencies, and Department of Defense (DOD) among others.</ref> Sound intensity or sound pressure level (SPL) is measured in decibels (dB). For reference:
{| class="wikitable"
|+
!db Level
!Example
|-
|45&nbsp;dB
|Ambient noise level around the home
|-
|60&nbsp;dB
|Quiet office
|-
|60–65&nbsp;dB
|Normal conversation
|-
|70&nbsp;dB
|City street noise at {{Convert|25|ft|m|abbr=on}} or average TV audio
|-
|80&nbsp;dB
|Noisy office
|-
|95–104&nbsp;dB
|Nightclub dance floor
|-
|120&nbsp;dB
|Close by thunder or a loud rock concert
|-
|150–160&nbsp;dB
|Gunshot from a handheld gun
|}
An increase of 6&nbsp;dB represents a doubling of the SPL, or energy of the sound wave, and therefore its propensity to cause ear damage. Because human ears hear logarithmically, not linearly, it takes an increase of 10&nbsp;dB to produce a sound that is perceived to be twice as loud. Ear damage due to noise is proportional to sound intensity, not perceived loudness, so it is misleading to rely on subjective perception of loudness as an indication of the risk to hearing, i.e. it can significantly underestimate the danger.{{cn|date=December 2024}}

While the standards differ moderately in levels of intensity and duration of exposure considered safe, some guidelines can be derived.<ref group="Note">The various standards quantify nose exposure with a set of specified measures, usually with respect to a reference exposure time of 8 hours, a typical working day. The measures include, a weighting scale (usually A) with a sample time, a threshold value in dB, a criterion sound pressure level in dB with an exposure time usually in hours, and an exchange rate in dB. A weighted SPL is denoted dB(X) where X is a weighting scale, usually A, but sometimes C. (A) refers to [[A-weighting]] of SPL, which is an adjustment to measured SPL to compensate for the frequency response of the human ear, which is less sensitive to low frequencies. The criterion level is the average sound pressure level permitted over the exposure time. The threshold sound pressure level is the level above which sound will be integrated into the average. The sample time (fast, slow or impulse) is the rate of sampling&nbsp;— a slow sample time is 1 second; a fast sample time is 1/8 second, and impulse sample time is 35 milliseconds. The effect of a slower sample time means that very short duration sounds may not be fully sampled (or even sampled at all in rare cases), so the noise exposure may be underestimated. The exchange rate is the amount by which the permitted sound level may increase if the exposure time is halved.</ref>

The safe amount of exposure is reduced by a factor of 2 for every exchange rate (3&nbsp;dB for NIOSH standard or 5&nbsp;dB for [[Occupational Safety and Health Administration|OSHA]] standard) increase in SPL. For example, the safe daily exposure amount at 85&nbsp;dB (90&nbsp;dB for OSHA) is 8 hours, while the safe exposure at 94&nbsp;dB(A) (nightclub level) is only 1 hour. Noise trauma can also cause a reversible hearing loss, called a temporary threshold shift. This typically occurs in individuals who are exposed to gunfire or firecrackers, and hear ringing in their ears after the event ([[tinnitus]]).{{cn|date=December 2024}}
* '''Ambient environmental noise''': Populations living near airports, railyards and train stations, freeways and industrial areas are exposed to levels of noise typically in the 65 to 75 dBA range. If lifestyles include significant outdoor or open window conditions, these exposures over time can degrade hearing. [[United States Department of Housing and Urban Development|U.S. Dept. of Housing and Urban Development]] sets standards for noise impact in residential and commercial construction zones. HUD's noise standards may be found in 24 CFR Part 51, Subpart B. Environmental noise above 65&nbsp;dB defines a noise-impacted area.
* '''Personal audio electronics''': Personal audio equipment such as [[Apple iPod|iPods]] (iPods often reach 115 decibels or higher), can produce powerful enough sound to cause significant NIHL.<ref name="def1">{{Cite web |title=Sound Output Levels of the iPod and Other MP3 Players: Is There Potential Risk to Hearing? |url=http://www.hearingconservation.org/docs/virtualPressRoom/portnuff.htm |archive-url=https://web.archive.org/web/20071030124816/http://www.hearingconservation.org/docs/virtualPressRoom/portnuff.htm |archive-date=October 30, 2007 |access-date=2007-11-20}}</ref>
* '''Acoustic trauma:''' Exposure to a single event of extremely loud noise (such as explosions) can also cause temporary or permanent hearing loss. A typical source of acoustic trauma is a too-loud music concert.
* '''Workplace noise:''' The OSHA standards 1910.95 General Industry Occupational Noise Exposure and 1926.52 Construction Industry Occupational Noise Exposure identify the level of 90&nbsp;dB(A) for 8 hour exposure as the level necessary to protect workers from hearing loss.

====Disease or disorder====
{{Prose|section|date=January 2018}}
* [[inflammation|Inflammatory]]
** Suppurative [[labyrinthitis]] or otitis interna (inflammation of the inner ear)
* [[Diabetes mellitus]] {{main|Diabetes mellitus and deafness}} A recent study{{As of?|date=March 2025}} found that hearing loss is twice as common in people with diabetes as it is in those who do not have the disease.{{Cn|date=March 2025}} Also, of the 86 million adults in the U.S. who have prediabetes, the rate of hearing loss is 30 percent higher than in those with normal blood glucose.{{Cn|date=March 2025}} It has not been established how diabetes is related to hearing loss. It is possible that the high blood glucose levels associated with diabetes cause damage to the small blood vessels in the inner ear, similar to the way in which diabetes can damage the eyes and the kidneys. Similar studies have shown a possible link between that hearing loss and neuropathy (nerve damage).
* [[Tumor]]
** Cerebellopontine angle tumour (junction of the [[pons]] and [[cerebellum]]) – the cerebellopontine angle is the exit site of both the [[facial nerve]](CN7) and the [[vestibulocochlear nerve]](CN8). Patients with these tumors often have signs and symptoms corresponding to compression of both nerves.
*** [[Acoustic neuroma]] (vestibular schwannoma) – benign neoplasm of [[Schwann cell]]s affecting the vestibulocochlear nerve
*** [[Meningioma]] – benign tumour of the [[pia mater|pia]] and [[arachnoid mater]]
* [[Ménière's disease]] – causes sensorineural hearing loss in the low frequency range (125&nbsp;Hz to 1000&nbsp;Hz). Ménière's disease is characterized by sudden attacks of vertigo, lasting minutes to hours preceded by [[tinnitus]], aural fullness, and fluctuating hearing loss. It is relatively rare and commonly over diagnosed.
* Bacterial [[meningitis]] e.g. pneumococcal, meningococcal, haemophilus influenzae may damage the [[cochlea]] – hearing loss is one of the most common after-effects of bacterial meningitis. It has been estimated that 30% of bacterial meningitis cases result in mild to profound hearing loss. Children are most at risk: seventy percent of all bacterial meningitis occurs in young children under the age of five.
* Viral
** [[AIDS]] and [[AIDS-related complex|ARC]] patients frequently experience auditory system anomalies.
** [[Mumps]](epidemic parotitis) may result in profound sensorineural hearing loss (90 [[Decibel|dB]] or more), unilaterally (one ear) or bilaterally (both ears).
** [[Measles]] may result in [[Vestibulocochlear nerve|auditory nerve]] damage but more commonly gives a mixed (sensorineural plus conductive) hearing loss, and can be bilaterally.
** [[Ramsay Hunt syndrome type II]] (herpes zoster oticus)
* Bacterial
** [[Syphilis]] is commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf.

====Ototoxic and neurotoxic drugs and chemicals====
{{main|ototoxicity}}
Some over-the-counter as well as prescription drugs and certain industrial chemicals are ototoxic. Exposure to these can result in temporary or permanent hearing loss.

Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the [[aminoglycoside]]s (main member [[gentamicin]]). A rare mitochondrial mutation, m.1555A>G, can increase an individual's susceptibility to the ototoxic effect of aminoglycosides. Long term [[hydrocodone]] (Vicodin) abuse is known to cause rapidly progressing sensorineural hearing loss, usually without vestibular symptoms. [[Methotrexate]], a chemotherapy agent, is also known to cause hearing loss. In most cases hearing loss does not recover when the drug is stopped. Paradoxically, methotrexate is also used in the treatment of autoimmune-induced inflammatory hearing loss.{{Citation needed|date=February 2022}}

Various other medications may reversibly degrade hearing. This includes loop [[diuretic]]s, [[sildenafil]] (Viagra), high or sustained dosing of [[NSAID]]s ([[aspirin]], [[ibuprofen]], [[naproxen]], and various prescription drugs: [[celecoxib]], etc.), [[quinine]], and [[macrolide]] antibiotics ([[erythromycin]], etc.). Cytotoxic agents such as carboplatinum, used to treat malignancies can give rise to a dose dependent SNHL, as can drugs such as desferrioxamine, used for haematological disorders such as thalassaemia; patients prescribed these drugs need to have hearing monitored.{{Citation needed|date=February 2022}}

Prolonged or repeated environmental or work-related exposure to ototoxic chemicals can also result in sensorineural hearing loss. Some of these chemicals are:
* [[butyl nitrite]] – chemical used recreationally known as '[[poppers]]'
* [[carbon disulfide]] – a solvent used as a building block in many organic reactions
* [[styrene]], an industrial chemical precursor of [[polystyrene]], a plastic
* [[carbon monoxide]], a poisonous gas resulting from incomplete [[combustion]]
* heavy metals: [[tin]], [[lead]], [[manganese]], [[mercury (element)|mercury]]
* [[hexane]], an industrial solvent and one of the significant constituents of [[gasoline]]
* [[ethylbenzene]], an industrial solvent used in the production of styrene
* [[toluene]] and [[xylene]], highly poisonous petrochemical solvents. Toluene is a component of high-octane gasoline; xylene is used in the production of polyester fibers and resins.
* [[trichloroethylene]], an industrial degreasing solvent
* [[Organophosphate pesticide]]s

====Head trauma====
There can be damage either to the ear itself or to the central auditory pathways that process the information conveyed by the ears. People who sustain head injury are susceptible to hearing loss or tinnitus, either temporary or permanent. Contact sports like football (U.S. NFL), hockey and cricket have a notable incidence of head injuries (concussions). In one survey of retired NFL players, all of whom reported one or more concussions during their playing careers, 25% had hearing loss and 50% had tinnitus.{{citation needed|date=November 2015}}

====Perinatal conditions====
These are much more common in premature babies, particularly those under 1500&nbsp;g at birth. [[Premature birth]] can be associated with problems that result in sensorineural hearing loss such as anoxia or hypoxia (poor oxygen levels), jaundice, intracranial haemorrhages, meningitis. [[Fetal alcohol syndrome]] is reported to cause hearing loss in up to 64% of infants born to [[alcoholism|alcoholic]] mothers, from the [[ototoxicity|ototoxic effect]] on the developing fetus, plus malnutrition during pregnancy from the excess [[ethanol|alcohol]] intake.

====Iodine deficiency / Hypothyroidism====
[[Iodine deficiency]] and endemic [[hypothyroidism]] are associated with hearing loss.<ref>{{Cite journal |vauthors=Kochupillai N, Pandav CS, Godbole MM, Mehta M, Ahuja MM |date=1986 |title=Iodine deficiency and neonatal hypothyroidism |journal=Bulletin of the World Health Organization |volume=64 |issue=4 |pages=547–51 |pmc=2490891 |pmid=3490923}}</ref> If a pregnant mother has insufficient iodine intake during pregnancy it affects the development of the inner ear in the foetus leading to sensorineural deafness. This occurs in certain areas of the world, such as the Himalayas, where iodine is deficient in the soil and thus the diet. In these areas there is a high incidence of endemic goitre. This cause of deafness is prevented by adding iodine to salt.

====Brain stroke====
[[Brain stroke]] in a region affecting auditory function such as a [[posterior circulation infarct]] has been associated with deafness.