Causes Hearing loss

1 causes

1.1 age
1.2 noise
1.3 genetic
1.4 perinatal problems
1.5 disorders
1.6 medications
1.7 chemicals
1.8 physical trauma

causes

hearing loss has multiple causes, including ageing, genetics, perinatal problems , acquired causes noise , disease. kinds of hearing loss cause may classified of unknown cause.

age

there progressive loss of ability hear high frequencies aging known presbycusis. men, can start 25 , women @ 30. although genetically variable normal concomitant of ageing , distinct hearing losses caused noise exposure, toxins or disease agents. common conditions can increase risk of hearing loss in elderly people high blood pressure, diabetes or use of medications harmful ear. while loses hearing age, amount , type of hearing loss variable.

noise

noise exposure cause of approximately half of cases of hearing loss, causing degree of problems in 5% of population globally. national institute occupational safety , health (niosh) recognizes majority of hearing loss not due age, due noise exposure. correcting age in assessing hearing, 1 tends overestimate hearing loss due noise , underestimate others.

hearing loss due noise may temporary, called temporary threshold shift , reduced sensitivity sound on wide frequency range resulting exposure brief loud noise gunshot, firecracker, jet engine, jackhammer, etc. or exposure loud sound on few hours such during pop concert or nightclub session. recovery of hearing within 24 hours, may take week. both constant exposure loud sounds (85 db(a) or above) , one-time exposure extremely loud sounds (120 db(a) or above) may cause permanent hearing loss.

noise-induced hearing loss (nihl) typically manifests elevated hearing thresholds (i.e. less sensitivity or muting) between 3000 , 6000 hz, centered @ 4000 hz. noise damage progresses, damage spreads affect lower , higher frequencies. on audiogram, resulting configuration has distinctive notch, called noise notch. aging , other effects contribute higher frequency loss (6–8 khz on audiogram), notch may obscured , entirely disappear.

various governmental, industry , standards organizations set noise standards.

the u.s. environmental protection agency has identified level of 70 db(a) (40% louder twice loud normal conversation; typical level of tv, radio, stereo; city street noise) 24‑hour exposure level necessary protect public hearing loss , other disruptive effects noise, such sleep disturbance, stress-related problems, learning detriment, etc. noise levels typically in 65 75 db (a) range living near airports of freeways , may result in hearing damage if sufficient time spent outdoors.

louder sounds cause damage in shorter period of time. estimation of safe duration of exposure possible using exchange rate of 3 db. 3 db represents doubling of intensity of sound, duration of exposure must cut in half maintain same energy dose. workplace noise regulation, safe daily exposure amount @ 85 db a, known exposure action value, 8 hours, while safe exposure @ 91 db(a) 2 hours. different standards use exposure action values between 80dba , 90dba. note people, sound may damaging @ lower levels 85 db a. exposures other ototoxins (such pesticides, medications including chemotherapy agents, solvents, etc.) can lead greater susceptibility noise damage, causing own damage. called synergistic interaction. since noise damage cumulative on long periods of time, persons exposed non-workplace noise, recreational activities or environmental noise, may have compounding damage sources.

some national , international organizations , agencies use exchange rate of 4 db or 5 db. while these exchange rates may indicate wider zone of comfort or safety, can underestimate damage caused loud noise. example, @ 100 db (nightclub music level), 3 db exchange rate limit exposure 15 minutes; 5 db exchange rate allows hour.

many people unaware of presence of environmental sound @ damaging levels, or of level @ sound becomes harmful. common sources of damaging noise levels include car stereos, children s toys, motor vehicles, crowds, lawn , maintenance equipment, power tools, gun use, musical instruments, , hair dryers. noise damage cumulative; sources of damage must considered assess risk. if 1 exposed loud sound (including music) @ high levels or extended durations (85 db or greater), hearing loss occur. sound intensity (sound energy, or propensity cause damage ears) increases dramatically proximity according inverse square law: halving distance sound quadruples sound intensity.

in usa, 12.5% of children aged 6–19 years have permanent hearing damage excessive noise exposure. world health organization estimates half of between 12 , 35 @ risk using personal audio devices loud.

hearing loss due noise has been described condition of modern society. in preindustrial times, humans had far less exposure loud sounds. studies of primitive peoples indicate of has been attributed age-related hearing loss may long term cumulative damage sources, noise. people living in preindustrial societies have considerably less hearing loss similar populations living in modern society. among primitive people have migrated modern society, hearing loss proportional number of years spent in modern society. military service in world war ii, korean war, , vietnam war, has caused hearing loss in large numbers of men generations, though proving hearing loss direct result of military service problematic without entry , exit audiograms.

hearing loss in adolescents may caused loud noise toys, music headphones, , concerts or events.

genetic

hearing loss can inherited. around 75–80% of these cases inherited recessive genes, 20–25% inherited dominant genes, 1–2% inherited x-linked patterns, , fewer 1% inherited mitochondrial inheritance.

when looking @ genetics of deafness, there 2 different forms, syndromic , nonsyndromic. syndromic deafness occurs when there other signs or medical problems aside deafness in individual. accounts around 30% of deaf individuals deaf genetic standpoint. nonsyndromic deafness occurs when there no other signs or medical problems associated individual other deafness. genetic standpoint, accounts other 70% of cases, , represents majority of hereditary hearing loss. syndromic cases occur diseases such usher syndrome, stickler syndrome, waardenburg syndrome, alport s syndrome, , neurofibromatosis type 2. these diseases have deafness 1 of symptoms or common feature associated it. many of genetic mutations giving rise syndromic deafness have been identified. in nonsyndromic cases, deafness finding, more difficult identify genetic mutation although have been discovered.

recent gene mapping has identified several nonsyndromic dominant (dfna#) , recessive (dfnb#) forms of deafness. first gene mapped non-syndromic deafness, dfna1, involves splice site mutation in formin related homolog diaphanous 1 (diaph1). single base change in large costa rican family identified causative in rare form of low frequency onset progressive hearing loss autosomal dominant inheritance exhibiting variable age of onset , complete penetrance age 30. common type of congenital hearing loss in developed countries dfnb1, known connexin 26 deafness or gjb2-related deafness.
the common dominant syndromic forms of hearing loss include stickler syndrome , waardenburg syndrome.
the common recessive syndromic forms of hearing loss pendred syndrome , usher syndrome.
the congenital defect microtia, deformed or unformed outer ear, can associated partial or complete conductive deafness, depending upon severity of deformity , whether middle ear affected. can associated abnormalities of inner ear giving rise additional sensorineural component hearing loss (mixed deafness).
mutations in ptprq cause of autosomal-recessive nonsyndromic hearing loss.

perinatal problems

fetal alcohol spectrum disorders reported cause hearing loss in 64% of infants born alcoholic mothers, ototoxic effect on developing fetus plus malnutrition during pregnancy excess alcohol intake.
premature birth can associated sensorineural hearing loss because of increased risk of hypoxia, hyperbilirubinaemia, ototoxic medication , infection noise exposure in neonatal units. risk of hearing loss greatest weighing less 1500 g @ birth.

disorders

strokes - depending on blood vessels affected stroke, 1 of symptoms can deafness.
multiple sclerosis can have effect on hearing well. multiple sclerosis, or ms, autoimmune disease immune system attacks myelin sheath, covering protects nerves. if auditory nerve becomes damaged, affected person become deaf in 1 or both ears. there no cure ms.
perilymph fistula - microtear in either round or oval window (membranes separating middle , inner ear) of cochlea causing perilymph leak middle ear. occurs consequence of trauma, including barotrauma, , can give rise vertigo hearing loss.
viral - viral infections of ear can cause sensorineural hearing loss consequence of labyrinthitis. patient may unwell @ time.

measles may cause auditory nerve damage gives rise chronic middle ear problem giving rise mixed hearing loss.
mumps (epidemic parotitis) may result in profound sensorineural hearing loss (90 db or more), unilateral (one ear) or bilateral (both ears).
congenital rubella (also called german measles) syndrome, can cause deafness in newborns
several varieties of herpes viruses cause other diseases can infect ear, , can result in hearing loss: congenital infection cytomegalovirus responsible deafness in newborn children , progressive sensorineural hearing loss in childhood; herpes simplex type 1, oral herpes associated cold sores; epstein barr virus causes mononucleosis; varicella zoster oticus causes facial paralysis (ramsay hunt syndrome)
people hiv/aids may develop hearing problems due medications take disease, hiv virus, or due increased rate of other infections.
west nile virus, can cause variety of neurological disorders, can cause hearing loss attacking auditory nerve


meningitis may damage auditory nerve or cochlea.
syphilis commonly transmitted pregnant women fetuses, , third of infected children become deaf.
inherited

people down syndrome more have hearing loss. due middle ear effusions in childhood towards end of second decade may develop high frequency sensorineural hearing loss can progressively worse time.
charcot–marie–tooth disease variant 1e (cmt1e) noted demyelinating in addition deafness.
autoimmune disease recognized cause cochlear damage. although rare, possible autoimmune processes target cochlea first presentation. granulomatosis polyangiitis 1 of autoimmune conditions may precipitate hearing loss. cogan s syndrome commonly presents hearing loss.


otosclerosis condition can cause fixation of stapes (or stirrup) in middle ear preventing movement , causing conductive hearing loss.
vestibular schwannoma, erroneously known acoustic neuromas, , other types of brain tumors can cause hearing loss infringement of tumor on vestibulocochlear nerve
congenital problems

superior semicircular canal dehiscence, gap in bone cover above inner ear, can lead low-frequency conductive hearing loss, autophony , vertigo.


recurring ear infections or concommitant secondary infections (such bacterial infection subsequent viral infection) can result in hearing loss

medications

some medications may reversibly affect hearing. these medications considered ototoxic. includes loop diuretics such furosemide , bumetanide, non-steroidal anti-inflammatory drugs (nsaids) both over-the-counter (aspirin, ibuprofen, naproxen) prescription (celecoxib, diclofenac, etc.), paracetamol, quinine, , macrolide antibiotics. link between nsaids , hearing loss tends greater in women, take ibuprofen 6 or more times week. others may cause permanent hearing loss. important group aminoglycosides (main member gentamicin) , platinum based chemotherapeutics such cisplatin , carboplatin.

on october 18, 2007, u.s. food , drug administration (fda) announced warning possible sudden hearing loss added drug labels of pde5 inhibitors, used erectile dysfunction.

chemicals

in addition medications, hearing loss can result specific chemicals: metals, such lead; solvents, such toluene (found in crude oil, gasoline , automobile exhaust, example); , asphyxiants. combined noise, these ototoxic chemicals have additive effect on person’s hearing loss.

hearing loss due chemicals starts in high frequency range , irreversible. damages cochlea lesions , degrades central portions of auditory system. ototoxic chemical exposures, particularly styrene, risk of hearing loss can higher being exposed noise alone.

solvents

toluene, styrene, xylene, n-hexane, ethyl benzene, white spirits/stoddard, carbon disulfide, jet fuel, perchloroethylene, trichloroethylene, p-xylene


asphyxiants

carbon monoxide, hydrogen cyanide


heavy metals

lead, mercury, cadmium, arsenic, tin-hydrocarbon compounds (trimethyltin)


pesticides , herbicides - evidence weak regarding association between herbicides , hearing loss; hearing loss in such circumstances may due concommitant exposure insecticides.

paraquat, organophosphates



physical trauma

there can damage either ear or brain centers process aural information conveyed ears. people sustain head injury vulnerable hearing loss or tinnitus, either temporary or permanent.