Causes Sensorineural hearing loss

1 causes

1.1 genetic
1.2 congenital
1.3 presbycusis
1.4 acquired

1.4.1 noise
1.4.2 disease or disorder
1.4.3 ototoxic , neurotoxic drugs , chemicals
1.4.4 head trauma
1.4.5 perinatal conditions
1.4.6 iodine deficiency / hypothyroidism
1.4.7 brain stroke

causes

sensorineural hearing loss may genetic or acquired (i.e. consequence of disease, noise, trauma, etc.). people may have hearing loss birth (congenital) or hearing loss may come on later. many cases related old age (age-related).

genetic

hearing loss can inherited. more 40 genes have been identified cause deafness. there 300 syndromes related hearing loss, , each syndrome may have causative genes.

recessive, dominant, x-linked or mitochondrial genetic mutations can affect structure or metabolism of inner ear. may single point mutations whereas others due chromosomal abnormalities. genetic causes give rise late onset hearing loss. mitochondrial mutations can cause snhl i.e. m.1555a>g makes individual sensitive ototoxic effects of aminoglycoside antibiotics.

both dominant , recessive genes exist can cause mild profound impairment. x-linked recessive genes hearing loss occur , these passed unaffected mothers onto sons have hearing loss. daughters unaffected carriers because second x chromosome provide second normal copy of gene, whereas shorter y chromosome not. dominant , recessive hearing impairment can syndromic or nonsyndromic. recent gene mapping has identified dozens of nonsyndromic dominant (dfna#) , recessive (dfnb#) forms of deafness.

the common cause of recessive genetic congenital hearing impairment in developed countries dfnb1, known connexin 26 deafness or gjb2-related deafness.
the common syndromic forms of hearing impairment include (dominant) stickler syndrome , waardenburg syndrome, , (recessive) pendred syndrome , usher syndrome.
mitochondrial mutations causing deafness rare:mt-tl1 mutations cause midd (maternally inherited deafness , diabetes) , other conditions may include deafness part of picture.
tmprss3 gene identified association both congenital , childhood onset autosomal recessive deafness. gene expressed in fetal cochlea , many other tissues, , thought involved in development , maintenance of inner ear or contents of perilymph , endolymph. identified tumor associated gene overexpressed in ovarian tumors.
charcot–marie–tooth disease inherited neurological disorder delayed onset can affect ears other organs. hearing loss in condition ansd (auditory neuropathy spectrum disorder)a neural cause of hearing loss.
muckle–wells syndrome, rare inherited autoinflammatory disorder, can lead hearing loss.
autoimmune disease: although rare, possible autoimmune processes target cochlea specifically, without symptoms affecting other organs. granulomatosis polyangiitis, autoimmune condition, may precipitate hearing loss.

congenital

infections:

congenital rubella syndrome, crs, results transplacental transmission of rubella (german measles) virus during pregnancy. crs has been controlled universal vaccination (mmr or mmrv vaccine).
human cytomegalovirus (hcmv) transmission developing fetus during pregnancy (congenital infection) common infectious cause of congenital hearing loss. hcmv congenital infection can lead sensorineural hearing loss may identified shortly after birth although many affected children have no hearing loss until later. classically hearing loss progressive on first decade , possibly later. worldwide, hcmv congenital infection impacts between 0.5 , 2% of live births, sensorineural hearing loss estimated occur in 10 20% of infected newborns. thus, estimated 7,000,000 people alive today have suffered hearing loss attributed hcmv congenital disease. majority of cases not have recognisable hearing loss @ birth develop in first decade of life.
toxoplasmosis, parasitic disease affecting 23% of population in u.s. can cause sensorineural deafness fetus in utero.


hypoplastic auditory nerves or abnormalities of cochlea

presbycusis

normal progressive age-related loss of hearing acuity or sensitivity starting age 18, affecting high frequencies, , men more women. such losses may not become apparent until later in life. presbycusis far dominant cause of sensorineural hearing loss. hearing loss accumulates age caused factors other normal aging, such noise-induced hearing loss, not presbycusis, although differentiating individual effects of multiple causes of hearing loss can difficult. 1 in 3 persons have significant hearing loss age 65; age 75, 1 in two. age-related hearing loss neither preventable nor reversible.

acquired
noise

most people living in modern society suffer degree of progressive sensorineural (i.e. permanent) noise-induced hearing loss (nihl) resulting overloading , damaging sensory or neural apparatus of hearing in inner ear. nihl typically drop-out or notch centered @ 4000 hz. both intensity (spl) , duration of exposure, , repetitive exposure unsafe levels of noise contribute cochlear damage results in hearing loss. louder noise is, shorter safe amount of exposure is. nihl can either permanent or temporary, called threshold shift. unsafe levels of noise can little 70 db (about twice loud normal conversation) if there prolonged (24-hour) or continuous exposure. 125 db (loud rock concert ~120 db) pain level; sounds above level cause instant , permanent ear damage.

noise , ageing primary causes of presbycusis, or age-related hearing loss, common kind of hearing loss in industrial society.

noise-related causes of hearing loss divided extrinsic (nosocusis) , intrinsic (sociocusis) causes: in auditory system, extrinsic component (nosocusis) includes hearing loss due otologic disease, hazardous noise exposure, acoustic trauma, , ototoxic agents. intrinsic component (sociocusis) indicates wear-and-tear effects of exposure everyday sounds of normal living. people live in nonindustrialized regions avoid both nosocusis , sociocusis , demonstrate excellent hearing old age.

the dangers of environmental , occupational noise exposure recognized. numerous national , international organizations have established standards safe levels of exposure noise in industry, environment, military, transportation, agriculture, mining , other areas. sound intensity or sound pressure level (spl) measured in decibels (db). reference,

an increase of 6 db represents doubling of spl, or energy of sound wave, , therefore propensity cause ear damage. because our ears hear logarithmically, not linearly, takes increase of 10 db produce sound perceived twice loud. ear damage due noise proportional sound intensity (spl), not perceived loudness, s misleading rely on our subjective perception of loudness indication of risk hearing, i.e., can underestimate danger.

while standards differ moderately in levels of intensity , duration of exposure considered safe, guidelines can derived.

the safe amount of exposure reduced factor of 2 every exchange rate (3 db niosh standard or 5 db osha standard) increase in spl. example, safe daily exposure amount @ 85 db (90 db osha) 8 hours, while safe exposure @ 94 db(a) (nightclub level) 1 hours. noise trauma can cause reversible hearing loss, called temporary threshold shift. typically occurs in individuals exposed gunfire or firecrackers, , hear ringing in ears after event (tinnitus).

ambient environmental noise — populations living near airports, railyards , train stations, freeways , industrial areas exposed levels of noise typically in 65 75 dba range. if lifestyles include significant outdoor or open window conditions, these exposures on time can degrade hearing. u.s. dept. of housing , urban development sets standards noise impact in residential , commercial construction zones. hud’s noise standards may found in 24 cfr part 51, subpart b. environmental noise above 65 db defines noise-impacted area.
personal audio electronics, such ipods (ipods reaching 115 decibels or higher), can produce powerful enough sound cause significant nihl.
repeated exposure loud noise (90-95 db or more) can cause progressive hearing loss. sound levels @ places live or dance music performed typically range 95 db 104 db.
acoustic trauma — exposure single event of extremely loud noise (such explosions) can cause temporary or permanent hearing loss. typical source of acoustic trauma too-loud music concert.
workplace noise — osha standards 1910.95 general industry occupational noise exposure, , 1926.52 construction industry occupational noise exposure identify level of 90 db(a) 8 hour exposure level necessary protect workers hearing loss.

disease or disorder

inflammatory

suppurative labyrinthitis or otitis interna (inflammation of inner ear)


diabetes mellitus

a recent study found hearing loss twice common in people diabetes in don t have disease. also, of 86 million adults in u.s. have prediabetes, rate of hearing loss 30 percent higher in normal blood glucose. has not been established how diabetes related hearing loss. possible high blood glucose levels associated diabetes cause damage small blood vessels in inner ear, similar way in diabetes can damage eyes , kidneys. similar studies have shown possible link between hearing loss , neuropathy (nerve damage).
tumor

cerebellopontine angle tumour (junction of pons , cerebellum) - cerebellopontine angle exit site of both facial nerve(cn7) , vestibulocochlear nerve(cn8). patients these tumors have signs , symptoms corresponding compression of both nerves.
acoustic neuroma (vestibular schwannoma) - benign neoplasm of schwann cells affecting vestibulocochlear nerve
meningioma - benign tumour of pia , arachnoid mater


ménière s disease - causes sensorineural hearing loss in low frequency range (125 hz 1000 hz). ménière s disease characterized sudden attacks of vertigo, lasting minutes hours preceded tinnitus, aural fullness, , fluctuating hearing loss.
pneumococcal meningitis may damage cochlea - hearing loss 1 of common after-effects of meningitis. has been estimated 30% of meningitis cases result in mild severe hearing loss. children @ risk: seventy percent of bacterial meningitis occurs in young children under age of five.
viral

aids , arc patients experience auditory system anomalies.
mumps(epidemic parotitis) may result in profound sensorineural hearing loss (90 db or more), unilaterally (one ear) or bilaterally (both ears).
measles may result in auditory nerve damage more commonly gives conductive hearing loss or rarely, bilaterally.
ramsay hunt syndrome type ii (herpes zoster oticus)


bacterial

syphilis commonly transmitted pregnant women fetuses, , third of infected children become deaf.



ototoxic , neurotoxic drugs , chemicals

some over-the-counter prescription drugs , industrial chemicals ototoxic. exposure these can result in temporary or permanent hearing loss.

some medications cause irreversible damage ear, , limited in use reason. important group aminoglycosides (main member gentamicin). rare mitochondrial mutation, m.1555a>g, can increase individual s susceptibility ototoxic effect of aminoglycosides. long term hydrocodone (vicodin) abuse known cause rapidly progressing sensorineural hearing loss, without vestibular symptoms. methotrexate, chemotherapy agent, known cause hearing loss. in cases hearing loss not recover when drug stopped. paradoxically, methotrexate used in treatment of autoimmune-induced inflammatory hearing loss.

various other medications may reversibly degrade hearing. includes loop diuretics, sildenafil (viagra), high or sustained dosing of nsaids (aspirin, ibuprofen, naproxen, , various prescription drugs: celecoxib, etc.), quinine, , macrolide antibiotics (erythromycin, etc.).

prolonged or repeated environmental or work-related exposure ototoxic chemicals can result in sensorineural hearing loss. of these chemicals are:

butyl nitrite - chemical used recreationally known poppers
carbon disulfide - solvent used building block in many organic reactions
styrene, industrial chemical precursor of polystyrene, plastic
carbon monoxide, poisonous gas resulting incomplete combustion
heavy metals: tin, lead, manganese, mercury
hexane, industrial solvent , 1 of significant constituents of gasoline
ethylbenzene, industrial solvent used in production of styrene
toluene , xylene, highly poisonous petrochemical solvents. toluene component of high-octane gasolne; xylene used in production of polyester fibers , resins.
trichloroethylene, industrial degreasing solvent
organophosphate pesticides

head trauma

there can damage either ear or central auditory pathways process information conveyed ears. people sustain head injury susceptible hearing loss or tinnitus, either temporary or permanent. contact sports football (u.s. nfl), hockey , cricket have notable incidence of head injuries (concussions). in 1 survey of retired nfl players, of whom reported 1 or more concussions during playing careers, 25% had hearing loss , 50% had tinnitus.

perinatal conditions

these more common in premature babies, particularly under 1500 g @ birth. premature birth can associated problems result in sensorineural hearing loss such anoxia or hypoxia(poor oxygen levels), jaundice, intracranial haemorrhages, meningitis. fetal alcohol syndrome reported cause hearing loss in 64% of infants born alcoholic mothers, ototoxic effect on developing fetus, plus malnutrition during pregnancy excess alcohol intake.

iodine deficiency / hypothyroidism

iodine deficiency , endemic hypothyroidism associated hearing loss. if pregnant mother has insufficient iodine intake during pregnancy affects development of inner ear in foetus leading sensorineural deafness. occurs in areas of world, such himalayas, iodine deficient in soil , diet. in these areas there high incidence of endemic goitre. cause of deafness prevented adding iodine salt.

brain stroke

brain stroke in region affecting auditory function such posterior circulation infarct has been associated deafness.