Sensorineural hearing loss 1187487 224312184 2008-07-08T08:14:10Z Littlealien182 3345501 Repaired link to [[Wikipedia:WikiProject Disambiguation|disambiguation]] page using [[Project:AutoWikiBrowser|AWB]] {{Infobox_Disease | Name = Sensorineural hearing loss | Image = Cochlea-crosssection.png | Caption = Cross section of the cochlea. | DiseasesDB = 2874 | ICD10 = {{ICD10|H|90|3|h|90}}-{{ICD10|H|90|5|h|90}} | ICD9 = {{ICD9|389.1}} | ICDO = | OMIM = | MedlinePlus = | eMedicineSubj = | eMedicineTopic = | MeshID = D006319 | }} '''Sensorineural hearing loss''' is a type of [[hearing loss]] in which the root cause lies in the [[vestibulocochlear nerve]] ([[Cranial nerve]] VIII), the inner [[ear]], or central processing centers of the [[brain]]. The [[Weber test]], in which a tuning fork is touched to the head, localizes to the normal [[ear]] in people with this condition. The [[Rinne test]], which tests air conduction ''vs.'' bone conduction is positive (normal), though both bone and air conduction are reduced equally. Sensorineural hearing loss can be mild, moderate, or severe, including total deafness. The great majority of human sensorineural hearing loss is caused by abnormalities in the [[hair cells]] of the [[organ of Corti]] in the cochlea. There are also very unusual sensorineural hearing impairments that involve the VIIIth [[cranial nerve]] (the [[Vestibulocochlear nerve]]) or the auditory portions of the brain. In the rarest of these sorts of hearing loss, only the auditory centers of the brain are affected. In this situation, [[central hearing loss]], sounds may be heard at normal thresholds, but the quality of the sound perceived is so poor that speech can not be understood. Most sensory hearing loss is due to poor hair cell function. The hair cells may be abnormal at birth, or damaged during the lifetime of an individual. There are both external causes of damage, like noise trauma and infection, and intrinsic abnormalities, like deafness genes. Sensory hearing loss (also called sensorineural hearing loss) may also result from abnormalities of the VIII cranial nerve. Sensory hearing loss that results from abnormalities of the central auditory system in the brain is called Central Hearing Impairment. Since the auditory pathways cross back and forth on both sides of the brain, deafness from a central cause is unusual. ==Differential diagnosis== Sensorineural hearing loss may be [[congenital]] or acquired. ===Congenital=== * Lack of development ([[aplasia]]) of the [[cochlea]] * [[chromosome|Chromosomal]] syndromes (rare) * Congenital [[cholesteatoma]] - [[squamous epithelium]] is normally present on either side of the tympanic membrane. Externally, within the [[external auditory meatus]] or [[ear canal]] and internally within the [[middle ear]]. Within the middle ear the simple epithelium gradually transitions into ciliated pseudostratified epithelium lining the [[Eustachian tube]] now known as the [[pharyngotympanic tube]] becoming continuous with the [[respiratory epithelium]] in the pharynx. The squamous epithelium hyperplasia within the middle ear behaves like an invasive [[tumour]] and destroys middle ear structures if not removed * Delayed familial progressive ===Acquired=== * [[inflammation|Inflammatory]] ** [[Suppurative labyrinthitis]] ** [[Meningitis]] ** [[Mumps]] ** [[Measles]] ** [[Virus|Viral]] ** [[Syphilis]] * [[Ototoxicity|Ototoxic]] drugs ** [[Aminoglycosides]] (most common cause; ''e.g.'', [[tobramycin]]) ** [[Loop diuretics]] (''e.g.'', [[Furosemide]]) ** [[Antimetabolites]] (''e.g.'', [[Methotrexate]]) ** [[Salicylate]]s (''e.g.'', [[Aspirin]]) * [[Physical trauma]] - either due to a [[fracture]] of the [[temporal bone]] affecting the [[cochlea]] and [[middle ear]], or a [[shearing]] injury affecting [[cranial nerve]] VIII. * Noise-induced - prolonged exposure to loud noises (>90 [[Decibel|dB]]) causes hearing loss which begins at 4000Hz (high frequency). The normal hearing range is from 20 Hz to 20,000 Hz. * [[Presbyacusis]] - age-related hearing loss that occurs in the high frequency range (4000Hz to 8000Hz). * Sudden hearing loss ** [[Idiopathic]] (ISSHL: idiopathic sudden sensoneurinal hearing loss), [http://www.who.int/classifications/apps/icd/icd10online/ H91.2] ** Vascular [[ischemia]] of the [[inner ear]] or CN 8 ** Perilymph [[fistula]], usually due to a rupture of the [[round window|round]] or [[oval window|oval]] windows and the leakage of [[perilymph]]. The patient will most likely also experience [[Vertigo (medical)|vertigo]] or [[Equilibrioception|imbalance]]. A history of an event that increased [[intracranial pressure]] or caused trauma is usually present). * [[Autoimmune]] - a prompt injection of [[steroid]]s into ear is necessary. * Cerebellopontine angle tumour (junction of the [[pons]] and [[cerebellum]]) (the cerebellopontine angle is the exit site of both CN7 and CN8. Patients with these tumours often have signs and symptoms corresponding to compression of both nerves) ** ''[[Acoustic neuroma]] (Vestibular schwannoma)'' - this is a [[schwannoma]] (benign neoplasm of [[Schwann cell]]s) ** [[Meningioma]] - benign tumour of the [[pia mater|pia]] and [[arachnoid mater]]s * [[Meniere's disease]] - causes sensorineural hearing loss in the low frequency range (125 Hz to 1000 Hz). Meniere's disesase is characterized by sudden attacks of vertigo lasting minutes to hours preceded by [[tinnitus]], aural fullness, and fluctuating hearing loss. ====Long term exposure to environmental noise==== Populations of people living near airports or freeways 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. The [[United States Environmental Protection Agency|U.S. EPA]] and various states have set noise standards to protect people from these adverse health risks. The EPA has identified the level of 70 db(A) for 24 hour exposure as the level necessary to protect the public from hearing loss (EPA, 1974). * Noise-Induced Hearing Loss (NIHL) typically is centered at 4000 Hz. * The louder the noise is, the shorter the safe amount of exposure is. Normally, the safe amount of exposure is reduced by a factor 2 for every additional 3 dB. For example, the safe daily exposure amount at 85 dB is 8 hours, while the safe exposure at 91 dB(A) is only 2 hours (National Institute for Occupational Safety and Health, 1998). Sometimes, a factor 2 per 5 dB is used. * Personal electronic audio devices, such as [[Apple iPod|iPods]] (iPods often reaching 115 decibels or higher), can produce powerful enough sound to cause significant Noise-Induced Hearing Loss, given that lesser intensities of even 70 dB can also cause hearing loss.<ref name="def1">{{cite web|url=http://www.hearingconservation.org/docs/virtualPressRoom/portnuff.htm|title=Sound Output Levels of the iPod and Other MP3 Players: Is There Potential Risk to Hearing?|accessdate=2007-11-20}}</ref> ====Genetic==== Hearing loss can be inherited. Both [[dominant gene|dominant]] and [[recessive gene]]s exist which can cause mild to profound impairment. If a family has a dominant gene for deafness it will persist across generations because it will manifest itself in the offspring even if it is inherited from only one parent. If a family had genetic hearing impairment caused by a recessive gene it will not always be apparent as it will have to be passed onto offspring from both parents Dominant and recessive hearing impairment can be syndromic or nonsyndromic. Recent gene mapping has identified dozens of nonsyndromic dominant (DFNA#) and recessive (DFNB#) forms of deafness. *The most common type of congenital hearing impairment in developed countries is [[DFNB1]], also known as [[Connexin 26 deafness]] or [[GJB2-related deafness]]. *The most common dominant syndromic forms of hearing impairment include [[Stickler syndrome]] and [[Waardenburg syndrome]]. *The most common recessive syndromic forms of hearing impairment are [[Pendred syndrome]], [[Large vestibular aqueduct syndrome]] and [[Usher syndrome]]. ====Disease or illness==== *[[Measles]] may result in [[Vestibulocochlear nerve|auditory nerve]] damage *[[Meningitis]] may damage the auditory nerve or the [[cochlea]] *[[Autoimmune disease]] has only recently been recognized as a potential cause for [[cochlea]]r damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. [[Wegener's granulomatosis]] is one of the autoimmune conditions that may precipitate hearing loss. *[[Mumps]] (Epidemic parotitis) may result in profound [[sensorineural hearing loss]] (90 [[Decibel|dB]] or more), unilateral (one ear) or bilateral (both ears). *[[Presbyacusis]] is deafness due to loss of perception to [[high tones]], mainly in the [[elderly]]. It is considered by some to be a degenerative process, although there has never been a proven link to aging. (See impact of environmental noise exposure above.) *[[Adenoids]] that do not disappear by [[adolescence]] may continue to grow and may obstruct the [[Eustachian tube]], causing conductive hearing impairment and nasal infections that can spread to the [[middle ear]]. *[[AIDS]] and [[AIDS-related complex|ARC]] patients frequently experience auditory system anomalies.<ref name="faqGal">{{cite web|url=http://library.gallaudet.edu/dr/faq-etiol.html|title=Frequently Asked Questions: Etiologies and Causes of Deafness|accessdate=2006-12-02}}</ref> *[[HIV]] (and subsequent opportunistic infections) may directly affect the cochlea and central auditory system.<ref name="faqGal"/> *[[Chlamydia infection|Chlamydia]] may cause hearing loss in newborns to whom the disease has been passed at birth.<ref name="faqGal"/> *[[Fetal alcohol syndrome]] is reported to cause hearing loss in up to 64% of infants born to [[alcoholism|alcoholic]] mothers, from the [[ototoxic effect]] on the developing fetus plus malnutrition during pregnancy from the excess [[ethanol|alcohol]] intake.<ref name="faqGal"/> *[[Premature birth]] results in [[sensorineural hearing loss]] approximately 5% of the time.<ref name="faqGal"/> *[[Syphilis]] is commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf.<ref name="faqGal"/> * [[Otosclerosis]] is a hardening of the stapes (or stirrup) in the middle ear and causes [[conductive hearing loss]]. ====Medications==== :''See also [[Ototoxicity]]'' 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]]). Various other medications may reversibly affect hearing. This includes some [[diuretic]]s, [[aspirin]] and [[NSAID]]s, and [[macrolide]] antibiotics. Extremely heavy [[hydrocodone|Vicodin]] abuse is known to cause hearing impairment. There has been speculation that radio talk show host [[Rush Limbaugh]]'s hearing loss was at least in part caused by his admitted addiction to narcotic pain killers, in particular Vicodin and [[Oxycodone|OxyContin]]. ====Physical trauma==== * There can be damage either to the ear itself or to the brain centers that process the aural information conveyed by the ears. * People who sustain head injury are especially vulnerable to hearing loss or [[tinnitus]], either temporary or permanent. * Exposure to very loud [[noise]] (90 [[Decibel|dB]] or more, such as jet engines at close range) can cause progressive hearing loss. 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.<ref>[http://www.4hearingloss.com/archives/2005/05/sonic_tonic.html Hearing Loss News and Articles: Sonic tonic<!-- Bot generated title -->]</ref> ''Table 1''. A table comparing sensorineural to [[conductive hearing loss]] {| cellspacing=0 cellpadding=10 | |bgcolor=#cccccc align=center|'''''Criteria''''' |bgcolor=#eeeeee align=center|'''''Sensorineural hearing loss''''' |bgcolor=#eeeeee align=center|'''''Conductive hearing loss''''' |- |bgcolor=#eeeeee|'''Anatomical Site''' |[[Inner ear]], [[cranial nerve]] VIII, or central processing centers |[[Middle ear]] (ossicular chain), [[tympanic membrane]], or [[external ear]] |- |bgcolor=#eeeeee|'''Weber Test''' |Sound localizes to normal [[ear]] |Sound localizes to affected ear (ear with conductive loss) |- |bgcolor=#eeeeee|'''Rinne Test''' |Positive Rinne; Air conduction > Bone conduction (both air and bone conduction are decreased equally, but the difference between them is unchanged). |Negative Rinne; Bone Conduction > Air Conduction (Bone/Air Gap) |} ==Treatment== At present, sensorineural hearing loss is treated with [[hearing aid]]s, which amplify sounds at pre-set frequencies to overcome a sensorineural hearing loss in that range; or [[cochlear implant]]s, which stimulate the [[cochlear nerve]] directly. Some research suggests that [[idebenone]] alone or combined with [[Vitamin E]] may delay the onset of hearing loss or perhaps reverse it. Use of these agents for this purpose is considered experimental at this time. ==References== <references /> ==External links== * [http://www.medicineau.net.au/clinical/ent/SNHL.html Sensorineural Hearing Loss], Dr Peter Grant {{Diseases of the ear and mastoid process}} [[Category:Otology]] [[de:Hörsturz]] [[ja:突発性難聴]] [[zh:感觉神经性耳聋]]