Hearing loss- hard of hearing, anacusis, or hearing impairment

Hearing loss, also known as hard of hearing, anacusis, or hearing impairment, is a partial or total inability to hear.It may occur in one or both ears. In children hearing problems can affect the ability to learn language and in adults it can cause work related difficulties. In some people, particularly older people, hearing loss can result in loneliness. Deafness is typically used to refer to those with only little or no hearing.

Hearing loss may be caused by a number of factors, including: genetics, ageing, exposure to noise, some infections, birth complications, trauma to the ear, and certain medications or toxins. A common infection that results in hearing loss is chronic ear infections. Certain infections during pregnancy such as rubella may also cause problems. Hearing loss is diagnosed when hearing testing finds that a person is unable to hear 25 decibels in at least one ear. Testing for poor hearing is recommended for all newborns. Hearing loss can be categorised as mild, moderate, severe, or profound.

Half of hearing loss is preventable. This includes by immunisation, proper care around pregnancy, avoiding loud noise, and avoiding certain medications. The World Health Organization recommends that young people limit the use of personal audio players to an hour a day in an effort to limit exposure to noise.Early identification and support are particularly important in children. For many hearing aids, sign language, cochlear implants and subtitles are useful. Lip reading is another useful skill some develop. Access to hearing aids, however, is limited in many areas of the world.

Globally hearing loss affects about 10% of the population to some degree. It causes disability in 5% (360 to 538 million) and moderate to severe disability in 124 million people. Of those with moderate to severe disability 108 million live in low and middle income countries. Of those with hearing loss it began in 65 million during childhood. Those who speak sign language and are members of Deaf culture see themselves as having a difference rather than an illness. Most members of Deaf culture oppose attempts to cure deafness and some within this community view cochlear implants with concern as they have the potential to eliminate their culture.The term hearing impairment is often viewed negatively as it emphasises what people cannot doHearing loss exists when there is diminished sensitivity to the sounds normally heard. The terms hearing impairment or hard of hearing are usually reserved for people who have relative insensitivity to sound in the speech frequencies. The severity of a hearing loss is categorized according to the increase in volume above the usual level necessary before the listener can detect it.

Deafness is defined as a degree of loss such that a person is unable to understand speech even in the presence of amplification.[8] In profound deafness, even the loudest sounds produced by an audiometer (an instrument used to measure hearing by producing pure tone sounds through a range of frequencies) may not be detected. In total deafness, no sounds at all, regardless of amplification or method of production, are heard.

Speech perception

Another aspect of hearing involves the perceived clarity of a sound rather than its amplitude. In humans, that aspect is usually measured by tests of speech perception. These tests measure one's ability to understand speech, not to merely detect sound. There are very rare types of hearing loss which affect speech understanding alone..Hearing loss has multiple causes, including ageing, genetics and injury.

Age

There is a progressive loss of ability to hear high frequencies with ageing known as presbycusis. For men, this can start as early as 25 and women at 30, but may even affect teenagers and children. Although genetically variable it is a normal concomitant of ageing and is distinct from hearing losses caused by noise exposure, toxins or disease agents. The National Institute for Occupational Safety and Health (NIOSH) recognizes that the majority of hearing loss is not due to age, but due to noise exposure. While everyone loses hearing with age, the amount and type of hearing lost is variable. By correcting for age in assessing hearing, one tends to overestimate the hearing loss due to noise for some and underestimate it for others.

Noise

Main article: Noise-induced hearing loss

Noise is the cause of approximately half of all cases of hearing loss, causing some degree of problems in 5% of the population globally.The World Health Organization estimates that half of those between 12 and 35 are at risk from using personal audio devices that are too loud.

Populations living near airports or freeways are exposed to levels of noise typically in the 65 to 75 dB(A) range. If lifestyles include significant outdoor or open window conditions, these exposures over time can degrade hearing. The U.S. EPA have set noise standards. 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 and other disruptive effects from noise, such as sleep disturbance, stress-related problems, learning detriment, etc. (EPA, 1974).

Noise-induced hearing loss (NIHL) is typically centered at 3000, 4000, or 6000 Hz. As noise damage progresses, damage spreads to affect lower and higher frequencies. On an audiogram, the resulting configuration has a distinctive notch, sometimes referred to as a "noise notch." As aging and other effects contribute to higher frequency loss (6–8 kHz on an audiogram), this notch may be obscured and entirely disappear.

Louder sounds cause damage in a shorter period of time. Estimation of a "safe" duration of exposure is possible using an exchange rate of 3 dB. As 3 dB represents a doubling of intensity of sound, duration of exposure must be cut in half to maintain the same energy dose. For example, the "safe" daily exposure amount at 85 dB A, known as an exposure action value, is 8 hours, while the "safe" exposure at 91 dB(A) is only 2 hours (National Institute for Occupational Safety and Health, 1998). Note that for some people, sound may be damaging at even lower levels than 85 dB A. Exposures to other ototoxins (such as pesticides, some medications including chemotherapy agents, solvents, etc.) can lead to greater susceptibility to noise damage, as well as causing their own damage. This is called a synergistic interaction.

Some American health and safety agencies (such as the Occupational Safety and Health Administration, and the Mine Safety and Health Administration), use an exchange rate of 5 dB.While this exchange rate is simpler to use, it drastically underestimates the damage caused by very loud noise. For example, at 115 dB, a 3 dB exchange rate would limit exposure to about half a minute; the 5 dB exchange rate allows 15 minutes.

Many people are unaware of the presence of environmental sound at damaging levels, or of the level at which sound becomes harmful. Common sources of damaging noise levels include car stereos, children's toys, motor vehicles, crowds, lawn and maintenance equipment, power tools, gun use, musical instruments, and even hair dryers. Noise damage is cumulative; all sources of damage must be considered to assess risk. If one is exposed to loud sound (including music) at high levels or for extended durations (85 dB A or greater), then hearing loss will occur. Sound levels increase with proximity; as the source is brought closer to the ear, the sound level increases.

In the USA, 12.5% of children aged 6–19 years have permanent hearing damage from excessive noise exposure.

Hearing loss has been described as primarily a condition of modern society. In preindustrial times, humans had far less exposure to loud sounds and deafness appears to have been a rare condition. This began to change with the event of machinery and electrical devices in the 18th-20th centuries. Studies have noted that baby boomers most often suffer hearing loss from recreational activities while their parents' generation were more affected by occupational (i.e. workplace) noise.[citation needed] Military service in World War II, the Korean War, and the Vietnam War, has likely also caused hearing loss in large numbers of men from those generations, though proving hearing loss was a direct result of military service is problematic without entry and exit audiograms.

Genetic

Hearing loss can be inherited. Around 75–80% of all these cases are inherited by recessive genes, 20–25% are inherited by dominant genes, 1–2% are inherited by X-linked patterns, and fewer than 1% are inherited by mitochondrial inheritance.

When looking at the genetics of deafness, there are 2 different forms, syndromic and nonsyndromic. Syndromic deafness occurs when there are other medical problems aside from deafness in an individual. This accounts for around 30% of deaf individuals who are deaf from a genetic standpoint. Nonsyndromic deafness occurs when there are no other problems associated with an individual other than deafness. From a genetic standpoint, this accounts for the other 70% of cases, and represents the majority of hereditary hearing loss. Syndromic cases occur with diseases such as Usher syndrome, Stickler syndrome, Waardenburg syndrome, Alport's syndrome, and neurofibromatosis type 2. These are diseases that have deafness as one of the symptoms or as a common feature associated with it. The genetics that correspond with these various diseases are very complicated and are difficult to explain scientifically because the cause is unknown. In nonsyndromic cases where deafness is the only ‘symptom’ seen in the individual it is easier to pinpoint the genes responsible.

Recent gene mapping has identified dozens of nonsyndromic dominant (DFNA#) and recessive (DFNB#) forms of deafness.

The first gene mapped for non-syndromic deafness, DFNA1, involves a splice site mutation in the formin related homolog diaphanous 1 (DIAPH1). A single base change in a large Costa Rican family was identified as causative in a rare form of low frequency onset progressive hearing loss with autosomal dominant inheritance exhibiting variable age of onset and complete penetrance by age 30.

The most common type of congenital hearing loss in developed countries is DFNB1, also known as connexin 26 deafness or GJB2-related deafness.

The most common dominant syndromic forms of hearing loss include Stickler syndrome and Waardenburg syndrome.

The most common recessive syndromic forms of hearing loss are Pendred syndrome, large vestibular aqueduct syndrome and Usher syndrome.

The congenital defect microtia can cause full or partial deafness depending upon the severity of the deformity and whether or not certain parts of the inner or middle ear are affected.

Mutations in PTPRQ are a cause of autosomal-recessive nonsyndromic hearing loss.

Conditions

Measles may cause auditory nerve damage.

Meningitis may damage the auditory nerve or the cochlea.

Autoimmune disease has only recently been recognized as a potential cause for cochlear damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Granulomatosis with polyangiitis is one of the autoimmune conditions that may precipitate hearing loss.

Mumps (Epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilateral (one ear) or bilateral (both ears).

Presbycusis is a progressive hearing loss accompanying age, typically affecting sensitivity to higher frequencies (above about 2 kHz).

Adenoids that do not disappear by adolescence may continue to grow and may obstruct the Eustachian tube, causing conductive hearing loss and nasal infections that can spread to the middle ear.

People with HIV/AIDS may develop hearing problems due to medications they take for the disease, the HIV virus, or due to an increased rate of infection.[25]

Chlamydia may cause hearing loss in newborns to whom the disease has been passed at birth.

Fetal alcohol spectrum disorders are reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake.

Premature birth causes sensorineural hearing loss approximately 5% of the time.

Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of infected children will eventually become deaf.

Otosclerosis is a hardening of the stapes (or stirrup) in the middle ear and causes conductive hearing loss.

Medulloblastoma and other types of brain tumors can cause hearing loss, whether by the placement of the tumor around the vestibulocochlear nerve, surgical resection, or platinum-based chemotherapy drugs such as cisplatin.

Superior canal dehiscence, a gap in the bone cover above the inner ear, can lead to low-frequency conductive hearing loss, autophony and vertigo.

People with Down syndrome are more likely to have hearing loss.

Neurological disorders

Neurological disorders such as multiple sclerosis and strokes can have an effect on hearing as well. Multiple sclerosis, or MS, is an autoimmune disease where the immune system attacks the myelin sheath, a covering that protects the nerves. Once the myelin sheaths are destroyed they cannot be repaired. Without the myelin to protect the nerves, nerves become damaged, creating disorientation for the patient. This is a painful process and may end in the debilitation of the affected person until they are paralyzed and have one or more senses gone. One of those may be hearing. If the auditory nerve becomes damaged then the affected person will become completely deaf in one or both ears. There is no cure for MS. Depending on what nerves are damaged from a stroke, one of the side effects can be deafness. Charcot–Marie–Tooth disease variant 1E (CMT1E) is noted for demyelinating in addition to deafness.

Medications

Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the aminoglycosides (main member gentamicin) and platinum based chemotherapeutics such as cisplatin.

Some medications may reversibly affect hearing. This includes some diuretics, aspirin and other NSAIDs, and macrolide antibiotics. The link between nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and hearing loss tends to be greater in women, especially those who take ibuprofen six or more times a week.[30] Others may cause permanent hearing loss. On October 18, 2007, the U.S. Food and Drug Administration (FDA) announced that a warning about possible sudden hearing loss would be added to drug labels of PDE5 inhibitors, which are used for erectile dysfunction.

Chemicals

In addition to medications, hearing loss can also result from specific drugs; metals, such as lead; solvents, such as toluene (found in crude oil, gasoline and automobile exhaust,for example); and asphyxiants. Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss.

Hearing loss due to chemicals starts in the high frequency range and is irreversible. It damages the cochlea with lesions and degrades central portions of the auditory system. For some ototoxic chemical exposures, particularly styrene, the risk of hearing loss can be higher than being exposed to noise alone. Controlling noise and using hearing protectors are insufficient for preventing hearing loss from these chemicals. However, taking antioxidants helps prevent ototoxic hearing loss, at least to a degree. The following list provides an accurate catalogue of ototoxic chemicals:

Drugs

antimalarial, antibiotics, anti-inflammatory (non-steroidal), antineoplastic, diuretics

Solvents

toluene, styrene, xylene, n-hexane, ethyl benzene, white spirits/Stoddard, carbon disulfide, fuels, perchloroethylene, trichloroethylene, p-xylene

Asphyxiants

carbon monoxide, hydrogen cyanide

Metals

lead, mercury, organotin compounds (trimethyltin)

Pesticides and herbicides

paraquat, organophosphates

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. I. King Jordan lost his hearing after suffering a skull fracture as a result of a motorcycle accident at age 21.

Lesions to the auditory association cortex produced by physical trauma can result in deafness and other problems in auditory perception. The place where the lesion occurs on the auditory cortex plays an important role in what type of hearing deficit will occur in a person. A study conducted by Clarke et al. (2000) tested three subjects for the ability to identify a produced environmental sound, the source of the sound, and whether or not the source is moving. All three subjects had trauma to different parts of the auditory cortex, and each patient demonstrated a different set of auditory deficits, suggesting that different parts of the auditory cortex controlled different parts of the hearing process. This means, lesion one part of auditory cortex and it could result in one or two deficits. It would take larger lesions at the right parts to produce deafness.

Neurobiological factors

From a neurobiological perspective, there are simply two reasons that could cause a person to have hearing loss: either there is something wrong with the mechanical portion of the process, meaning the ear, or there is something wrong with the neural portion of the process, meaning the brain.

The process of understanding how sound travels to the brain is imperative in understanding how and why these two reasons would cause a person develops hearing loss. The process is as follows: sound waves are transmitted to the outer ear, sound waves are conducted down to ear canal, bringing the sound waves to the eardrum where they vibrate, these vibrations are now passed through the 3 tiny ear bones in the middle, which cause the fluid to move in the inner ear, the fluid moves the hair cells, the movement of the hair cells cause the vibrations to be converted into nerve impulses, the nerve impulses are taken to the brain by the auditory nerve, the auditory nerve takes the impulses to the medulla oblongata, the brainstem send the impulses to the midbrain, which finally goes to the auditory cortex of the temporal lobe to be interpreted as sound.

This process is complex and involves several steps that depend on the previous step in order for the vibrations or nerve impulses to be passed on. This is why if anything goes wrong at either the mechanical or neural portion of the process, it could result in sound not being processed by the brain, hence, leading to hearing lossThe severity of a hearing loss is ranked according to the additional intensity above a nominal threshold that a sound must be before being detected by an individual; it is (measured in decibels of hearing loss, or dB HL). Hearing loss may be ranked as mild, moderate, moderately severe, severe or profound as defined below:

Mild:

for adults: between 26 and 40 dB HL

for children: between 20 and 40 dB HL

Moderate: between 41 and 54 dB HL

Moderately severe: between 55 and 70 dB HL

Severe: between 71 and 90 dB HL

Profound: 91 dB HL or greater

Totally deaf: Have no hearing at all.

Hearing sensitivity varies according to the frequency of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on an audiogram.

For certain legal purposes such as insurance claims, hearing loss is described in terms of percentages. Given that hearing loss can vary by frequency and that audiograms are plotted with a logarithmic scale, the idea of a percentage of hearing loss is somewhat arbitrary, but where decibels of loss are converted via a recognized legal formula, it is possible to calculate a standardized "percentage of hearing loss" which is suitable for legal purposes only.

Another method for quantifying hearing loss is a speech-in-noise test. As the name implies, a speech-in-noise test gives an indication of how well one can understand speech in a noisy environment. A person with a hearing loss will often be less able to understand speech, especially in noisy conditions. This is especially true for people who have a sensorineural loss – which is by far the most common type of hearing loss. As such, speech-in-noise tests can provide valuable information about a person's hearing ability, and can be used to detect the presence of a sensorineural hearing loss. A triple-digit speech-in-noise test was developed by RNID as part of an EU funded project Hearcom. The RNID version is available over the phone, on the web.

Classification

Hearing loss are categorized by their type, their severity, and the age of onset (before or after language is acquired). Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral). There are three main types of hearing loss, conductive hearing loss and sensorineural hearing loss and a combination of the two called mixed hearing loss.

Conductive hearing loss

A conductive hearing loss is present when the sound is not reaching the inner ear, the cochlea. This can be due to external ear canal malformation, dysfunction of the eardrum or malfunction of the bones of the middle ear. The ear drum may show defects from small to total resulting in hearing loss of different degree. Scar tissue after ear infections may also make the ear drum dysfunction as well as when it is retracted and adherent to the medial part of the middle ear.

Dysfunction of the three small bones of the middle ear – malleus, incus, and stapes – may cause conductive hearing loss. The mobility of the ossicles may be impaired for different reasons and disruption of the ossicular chain due to trauma, infection or anchylosis may also cause hearing loss.

Middle ear implants or bone conduction implants can help with this kind of hearing loss.

Sensorineural hearing loss

Main article: Sensorineural hearing loss

A sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea, the nerve that transmits the impulses from the cochlea to the hearing centre in the brain or damage in the brain. The most common reason for sensorineural hearing loss is damage to the hair cells in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing. Cochlear implants can help with this kind of hearing loss.

Mixed hearing loss

Mixed hearing loss is a combination of the two types discussed above. Chronic ear infection (a fairly common diagnosis) can cause a defective ear drum or middle-ear ossicle damages, or both. Surgery is often attempted but not always successful. On top of the conductive loss, a sensory component is often added. If the ear is dry and not infected, an air conduction aid could be tried; if the ear is draining, a direct bone condition hearing aid is often the best solution. If the conductive part of the hearing loss is more than 30–35 dB, an air conduction device could have problems overcoming this gap. A bone-anchored hearing aid could, in this situation, be a good option. The active bone conduction hearing implant Bonebridge is also an option. This implant is invisible under the intact skin and therefore minimises the risk of skin irritations.

Before language

Prelingual deafness is hearing loss that is sustained before the acquisition of language, which can occur due to a congenital condition or through hearing loss in early infancy. Prelingual deafness impairs an individual's ability to acquire a spoken language. Children born into signing families rarely have delays in language development, but most prelingual hearing loss is acquired via either disease or trauma rather than genetically inherited, so families with deaf children nearly always lack previous experience with sign language. Cochlear implants allow prelingually deaf children to acquire an oral language with remarkable success if implantation is performed within the first 2–4 years.

After language

Post-lingual deafness is hearing loss that is sustained after the acquisition of language, which can occur due to disease, trauma, or as a side-effect of a medicine. Typically, hearing loss is gradual and often detected by family and friends of affected individuals long before the patients themselves will acknowledge the disability. Common treatments include hearing aids, cochlear implants, middle ear implants, bone conduction implants, implants for electric-acoustic stimulation and learning lip reading. Post-lingual deafness is far more common than pre-lingual deafness. Those who lose their hearing later in life, such as in late adolescence or adulthood, face their own challenges, living with the adaptations that allow them to live independently.

Unilateral and bilateral

People with unilateral hearing loss or single-sided deafness (SSD) have difficulty in:

hearing conversation on their impaired side

localizing sound

understanding speech in the presence of background noise.

In quiet conditions, speech discrimination is approximately the same for normal hearing and those with unilateral deafness; however, in noisy environments speech discrimination varies individually and ranges from mild to severe.

A similar effect can result from King-Kopetzky syndrome (also known as auditory disability with normal hearing and obscure auditory dysfunction), which is characterized by an inability to process out background noise in noisy environments despite normal performance on traditional hearing tests.

One reason for the hearing problems these patients often experience is due to the head shadow effect. Newborn children with no hearing on one side but one normal ear could still have problems.Speech development could be delayed and difficulties to concentrate in school are common. More children with unilateral hearing loss have to repeat classes than their peers. Taking part in social activities could be a problem. Early aiding is therefore of utmost importance. Cochlear implants as well as bone conduction implants can help with single sided deafness.

Screening

The United States Preventive Services Task Force recommends screening for all newborns.

The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:

When they enter school

At ages 6, 8, and 10,

At least once during middle school

At least once during high school

There is not enough evidence to determine the utility of screening in adults over 50 years old who do not have any symptom.