Hearing Loss – Causes, Symptoms, Diagnosis, Treatment

Hearing loss is an extremely common medical condition, progressing in incidence and severity with age. The affected population is also vast, varying between neonates to elderly patients, and is nearly omnipresent in the 70+ age group.[rx] The diagnosis and management require a multi-disciplinary team that includes the general practitioner, otolaryngologist, speech therapist, audiologist, and social worker. To correctly address hearing loss, understanding the nature of hearing loss, and the equipment that is needed to improve auditory reception is crucial. In terms of children’s hearing loss, pediatricians need to be integrated into their care to ensure the normal hearing and language development of the child.[rx][rx]

Hearing loss is a partial or total inability to hear.^[rx] Hearing loss may be present at birth or acquired at any time afterward.^[rx][rx] Hearing loss may occur in one or both ears.^[rx] In children, hearing problems can affect the ability to learn spoken language, and in adults, it can create difficulties with social interaction and at work.^[rx] Hearing loss can be temporary or permanent. Hearing loss related to age usually affects both ears and is due to cochlear hair cell loss.^[rx] In some people, particularly older people, hearing loss can result in loneliness.^[rx] Deaf people usually have little to no hearing.^[rx]

Types of Hearing Loss

• Sudden sensorineural hearing loss (SSHL) – presumed to be of viral origin, is an otologic emergency that is medically treated with corticosteroids.
• Sensorineural hearing loss – can occur from head trauma or abrupt changes in air pressure (e.g., airplane descent), which can cause inner ear fluid compartment rupture or leakage, which can be toxic to the inner ear. There has been a variable success with emergency surgery when this happens.
• Bilateral progressive hearing loss – over several months, also diagnosed as autoimmune inner ear disease, is managed medically with long-term corticosteroids and sometimes with drug therapy. Autoimmune inner ear disease is when the body’s immune system misdirects its defenses against the inner ear structures to cause damage in this part of the body.
• Fluctuating sensorineural hearing loss – may be from an unknown cause or associated with Ménière’s disease. Symptoms of Meniere’s disease are hearing loss, tinnitus (ringing in the ears), and vertigo. Ménière’s disease may be treated medically with a low-sodium diet, diuretics, and corticosteroids. If the vertigo is not medically controlled, then various surgical procedures are used to eliminate vertigo.
• Sensorineural hearing loss from disease – in the central nervous system may respond to medical management for the specific disease affecting the nervous system. For example, hearing loss secondary to multiple sclerosis may be reversed with treatment for multiple sclerosis.
• Irreversible sensorineural hearing loss – the most common form of hearing loss, maybe managed with hearing aids. When hearing aids are not enough, this type of hearing loss can be surgically treated with cochlear implants.

There are four levels of deafness or hearing impairment. These are

• Mild deafness or mild hearing impairment – The person can only detect sounds between 25 and 29 decibels (dB). They may find it hard to understand the words other people are saying, especially if there is a lot of background noise.
• Moderate deafness or moderate hearing impairment – The person can only detect sounds between 40 and 69 dB. Following a conversation using hearing alone is very difficult without using a hearing aid.
• Severe deafness – The person only hears sounds above 70 to 89 dB. A severely deaf person must either lip-read or use sign language in order to communicate, even if they have a hearing aid.
• Profound deafness – Anybody who cannot hear a sound below 90dB has profound deafness. Some people with profound deafness cannot hear anything at all, at any decibel level. Communication is carried out using sign language, lip-reading, or reading and writing.

Causes of Hearing Loss

The normal hearing function involves sound waves arriving at the auricle, passing through the external auditory canal (EAC), causing a vibration of the tympanic membrane [rx]. Vibration then gets transmitted via the ossicles (malleus, incus, stapes) to the cochlea. Subsequently, hair cells inside the cochlea stimulate the eighth cranial nerve that transfers the stimuli to the brain. Processing of crude sounds occurs in the higher cortices of the brain and this includes the comprehension of language.

Hearing loss can be conductive, sensorineural, or mixed.[rx] Conductive hearing loss takes place with disruption of the transmission of the sound waves to the cochlea. The most common causes include abnormal formation of the auricle or helix, cerumen impaction, ear canal foreign bodies, otitis externa, dysfunction or fixation of the ossicular chain, and middle ear effusion. Cholesteatoma, a benign though locally-destructive trapping of squamous debris arising from the tympanic membrane, as well as other benign or malignant tumors, can result in conductive hearing loss.

Sensorineural hearing loss (SNHL) usually results from problematic transmission of the stimuli at or after the cochlea.[rx] This loss could be related to hair cell dysfunction or a disorder of the eighth nerve itself. The main difference between the two kinds of hearing loss, apart from the pathophysiological features, is that patients with conductive hearing loss perceive the sounds diminished, while SNHL patients may perceive the sounds diminished and distorted.

Hearing loss that involves problematic transmission before and after the cochlea is called mixed hearing loss.

There are multiple reasons for hearing impairment. In the pediatric population, genetic causes are the most common, accounting for more than 50% of hearing loss. Genetic causes involve various syndromes that have hearing loss as one of their features; however, there is an entire entity of non-syndromic genetic hearing loss, wherein patients suffer hearing loss while the rest of their function is normal.[rx] Mutations, autosomal differences, as well as unknown genetic diversity, relates to this type of hearing loss.[rx] Prenatal causes can also relate to hearing loss in infants. These include exposure to various bacterial or viral infections as well as different teratogens. Perinatal causes are less common, predominantly related to prematurity, low APGAR score, neonatal jaundice, and sepsis.[rx] Postnatal causes such as meningococcal infections and mumps can also cause hearing loss as a late complication, as well as head injuries or chronic or recurrent otitis media.[rx]

Age-related hearing loss involves a gradual reduction of hearing capacity of the individual and poor speech discrimination scores, most noticeable initially in noisy environments, which is likely related to age-related degeneration of the cochlea in various sites, particularly the hair cells.[rx] Otosclerosis and cholesteatomas are leading causes of conductive hearing loss.[rx] Another entity that can occur in the adult population is sudden sensorineural hearing loss.[rx] This condition is very specific, with a sudden or rapid onset of hearing loss in one ear. This is often preceded by a viral upper respiratory infection, and virally-mediated inflammatory markers are the presumed cause.[rx]

Hearing loss can be broadly characterized as congenital or acquired in the pediatric population.

Congenital causes may lead to hearing loss being present or acquired soon after birth. Hearing loss can be caused by hereditary and non-hereditary genetic factors or by certain complications during pregnancy and childbirth, including:

• maternal rubella, syphilis, or certain other infections during pregnancy;
• low birth weight;
• birth asphyxia (a lack of oxygen at the time of birth);
• inappropriate use of particular drugs during pregnancy, such as aminoglycosides, cytotoxic drugs, antimalarial drugs, and diuretics;
• severe jaundice in the neonatal period, which can damage the hearing nerve in a newborn infant.

Acquired causes

Acquired causes may lead to hearing loss at any age, such as:

• infectious diseases including meningitis, measles and mumps;
• chronic ear infections;
• collection of fluid in the ear (otitis media);
• use of certain medicines, such as those used in the treatment of neonatal infections, malaria, drug-resistant tuberculosis, and cancers;
• injury to the head or ear;
• excessive noise, including occupational noise such as that from machinery and explosions;
• recreational exposure to loud sounds such as that from use of personal audio devices at high volumes and for prolonged periods of time and regular attendance at concerts, nightclubs, bars and sporting events;
• ageing, in particular due to degeneration of sensory cells; and
• wax or foreign bodies blocking the ear canal.

Among children, chronic otitis media is a common cause of hearing loss.

High-risk factors in neonates

• Damage to the inner ear – Aging and exposure to loud noise may cause wear and tear on the hairs or nerve cells in the cochlea that send sound signals to the brain. When these hairs or nerve cells are damaged or missing, electrical signals aren’t transmitted as efficiently, and hearing loss occurs. Higher pitched tones may become muffled to you. It may become difficult for you to pick out words against background noise.
• The gradual buildup of earwax – Earwax can block the ear canal and prevent conduction of sound waves. Earwax removal can help restore your hearing.
• Ear infection and abnormal bone growths or tumors – In the outer or middle ear, any of these can cause hearing loss.
• Ruptured eardrum (tympanic membrane perforation) – Loud blasts of noise, sudden changes in pressure, poking your eardrum with an object and infection can cause your eardrum to rupture and affect your hearing.
• Congenital infections
• Family history
• Craniofacial anomalies
• Hyperbilirubinemia
• Birth weight 1500 g
• Low Apgar
• Bacterial meningitis
• Need to prolonged intubation
• chickenpox
• cytomegalovirus
• mumps
• meningitis
• sickle cell disease
• syphilis
• lyme disease
• diabetes
• hypothyroidism
• arthritis
• some cancers
• teenagers exposed to second-hand smoke

Symptoms of Hearing Loss

Signs and symptoms of hearing loss may include:

• Muffling of speech and other sounds
• Difficulty understanding words, especially against background noise or in a crowd
• Trouble hearing consonants
• Frequently asking others to speak more slowly, clearly and loudly
• Needing to turn up the volume of the television or radio
• Withdrawal from conversations
• Avoidance of some social settings
• difficulty using the telephone
• loss of sound localization
• difficulty understanding speech, especially of children and women whose voices are of a higher frequency.
• difficulty understanding speech in the presence of background noise (cocktail party effect)
• sounds or speech sounding dull, muffled or attenuated
• need for increased volume on television, radio, music and other audio sources
• pain or pressure in the ears
• a blocked feeling
• hyperacusis, heightened sensitivity with accompanying auditory pain to certain intensities and frequencies of sound, sometimes defined as “auditory recruitment”
• tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is present
• vertigo and disequilibrium
• trypanophobia, also known as Euphonia, abnormal hearing of one’s own voice and respiratory sounds, usually as a result of a patulous (a constantly open) eustachian tube or dehiscent superior semicircular canals
• disturbances of facial movement (indicating a possible tumor or stroke) or in persons with Bell’s Palsy

Hearing impairment in infants

The following signs may indicate a hearing problem:

• Before the age of 4 months, the baby does not turn their head toward a noise.
• By the age of 12 months, the baby still has not uttered a single word.
• The infant does not appear to be startled by a loud noise.
• The infant responds to you when they can see you, but respond far less or do not respond at all when you are out of sight and call out their name.
• The infant only seems to be aware of certain sounds.

Hearing impairment in toddlers and children

These signs might become more evident in slightly older children:

• The child is behind others the same age in oral communication.
• The child keeps saying “What?” or “Pardon?”
• The child talks in a very loud voice, and tends to produce louder-than-normal noises.
• When the child speaks, their utterances are not clear.

Diagnosis of Hearing Loss

History and Physical

History in pediatric cases is critical for early diagnosis of hearing loss. This history involves questions regarding the prenatal history of the child, their delivery, and the first days of life as well as the post-natal history up until the moment of the symptom presentation, as well as a family history of hearing loss. A child with hearing loss may present with non-reaction to sounds, behavioral problems, speech issues, language delay, or even school failure, as well as mispronouncing words. Family history, especially if there is a member with early hearing loss, also has great value in suspecting hearing loss.[rx]

Adult history acquisition is more straightforward and involves questions regarding the onset of symptoms, the severity, the presence of vertigo, neurological symptoms, infections, and other conditions that could be related to hearing loss. Past medical history, as well as family history, along with work and noise exposure, are also important. In this way, there is a differentiation between the causes of hearing loss, and the clinician can proceed to the appropriate investigations.[rx]

Physical examination involves a full otolaryngology examination, with otoscopy bilaterally (including pneumatic otoscopy) to rule out any obvious conductive hearing loss.[rx] Foreign bodies, cerumen, infections, tympanic membrane perforations, as well as middle ear effusion, need to be ruled out in the first instance. Subsequently, identification of dysmorphic and other physical findings is essential, especially in young children and infants. These can include facial abnormalities or asymmetry, ear, neck and skin anomalies, other organ dysfunction, or even balance irregularities. As a result, a comprehensive inspection, otoscopy, and neurological examination are crucial to reach the correct diagnosis. Weber and Rinne tests are easy, fast, and globally useful to differentiate between SNHL and conductive hearing loss and may aid in interpreting the formal audiogram.

Evaluation

An accurate hearing evaluation is possible for the population of all ages, though there are specific limitations that are age- or cognition-related regarding formal audiometric evaluation that may complicate the picture. According to the American Academy of Pediatrics as well as the Joint Committee on Infant Hearing, all infants should undergo a hearing evaluation to rule out any hearing impairment at birth, or by the age of one month.[rx] Additionally, all newborns and infants with hearing loss need to get a comprehensive evaluation that focuses on medical and birth history as well as a family history for the previous three generations according to the American College of Medical Genetics and Genomics.[rx]

Hearing loss evaluation can differ according to the age of the child. BAER (brainstem audio-evoked response) test is the method for early diagnosis of hearing loss in newborns and infants. Otoacoustic emissions are also an option in newborns, and it is an easy, inexpensive technique, but they are less reliable than BAER tests. Finally, audiometry works with older children, aged 4 to 5 and older, who can respond to sound stimuli according to instructions. There are age-specific audiometric tests that can be performed. Young, pre-lingual, children can be conditioned to respond to play stimuli that can assess whether they can hear. This method of testing is not ear-specific, and can only confirm they have at least one ear that can hear at a given test level. This is important because as long as there is one ear that hears at a normal level, normal language development can be expected. Tympanograms and audiograms are of value in adults and children, but provide information only regarding the mobility of the tympanic membrane.[rx]

General screening test

A doctor may ask the patient to cover one ear and describe how well they hear words spoken at different volumes, as well as checking sensitivity to other sounds. If the doctor suspects a hearing problem, they will probably be referred to either an ear, nose, and throat (ENT) specialist or an audiologist.

Further tests will be carried out, including:

• A tuning fork test – This is also known as the Rinne test. A tuning fork is a metal instrument with two prongs that produces a sound when it is struck. Simple tuning fork tests may help the doctor detect whether there is any hearing loss, and where the problem is. A tuning fork is vibrated and placed against the mastoid bone behind the ear. The patient is asked to indicate when they no longer hear any sound. The fork, which is still vibrating, is then placed 1 to 2 centimeters (cm) from the auditory canal. The patient is asked again whether they can hear the fork.
• Audiometer test – The patient wears earphones, and sounds are directed into one ear at a time. A range of sounds is presented to the patient at various tones. The patient has to signal each time a sound is heard. Each tone is presented at various volumes, so that the audiologist can determine at which point the sound at that tone is no longer detected. The same test is carried out with words. The audiologist presents words at various tones and decibel levels to determine where the ability to hear stops.
• Bone oscillator test – This is used to find out how well vibrations pass through the ossicles. A bone oscillator is placed against the mastoid. The aim is to gauge the function of the nerve that carries these signals to the brain.
• App-based hearing tests – Mobile apps are available that you can use by yourself on your tablet to screen for moderate hearing loss.
• Tuning fork tests – Tuning forks are two-pronged, metal instruments that produce sounds when struck. Simple tests with tuning forks can help your doctor detect hearing loss. This evaluation may also reveal where in your ear the damage has occurred.
• Audiometer tests – During these more-thorough tests conducted by an audiologist, you wear earphones and hear sounds and words directed to each ear. Each tone is repeated at faint levels to find the quietest sound you can hear.

Routine screening of children

The American Academy of Pediatrics (AAP) recommends that children have their hearing tests at the following times:

• when they start school
• at 6, 8, and 10 years of age
• at least once when they are in middle school
• once during high school

Testing newborns

The otoacoustic emissions (OAE) test involves inserting a small probe into the outer ear; it is usually done while the baby is asleep. The probe emits sounds and checks for “echo” sounds bouncing back from the ear. If there is no echo, the baby might not necessarily have a hearing problem, but doctors will need to carry out further tests to make sure and to find out why

Treatment of Hearing Loss

Management of conductive hearing loss focuses on the treatment of the underlying disease. Conservative methods such as removal of the foreign body, micro-suction of the cerumen or discharge in the ear canal are necessary if the ear canal is blocked [rx]. With regards to otitis media, myringotomy to release the middle ear fluid will allow the sound wave to reach the cochlea, while ventilation tubes are useful if the otitis media is persistent, causing hearing loss. However, evidence shows that hearing loss can represent a post-operative complication due to tympanosclerosis, though this is very rare.[rx] Finally, if the hearing loss is due to cholesteatoma, this requires surgical removal with results in hearing restoration dependent upon the degree of destruction of the middle ear structures. Chronic or refractory, inoperable, conductive hearing loss can be treated with bone-conduction hearing aids or via a BAHA, a bone-implanted conduction aid, with excellent results.[rx]

Conservative treatment of sensorineural hearing involves the use of assistive listening devices and amplification. Hearing aids are devices designed to improve audition up to 40 to 60 dB with good results. They require individualized fittings and venting plans and can be very expensive.  The overall results are very good.[rx] Surgical treatment is provided to infants diagnosed with SNHL, as they undergo cochlear implantation under the age of 6 months.[rx] The intervention requires an ear, nose, and throat specialist, and long-term monitoring is essential to ensure normal linguistic and social development of the child. Similarly, refractory, severe SNHL in adults can be treated with cochlear implantation. This will destroy any remnant native hearing, replacing it with the device, so this must be done judiciously. Excellent outcomes have been achieved routinely with this procedure in severe SNHL.

Staging

According to the American National Standards Institute, hearing loss ranking is as follows:

• Slight hearing loss: 16 to 25 dB
• Mild hearing loss: 26 to 40 dB
• Moderate hearing loss: 41 to 55 dB
• Severe hearing loss: 71 to 90 dB
• Profound: over 90 dB

Complications

Complications of hearing loss in children involve speech delay and failure to thrive in school. Any child with a speech delay requires a formal hearing evaluation, as this is the most common cause.

Adult patients, who are frequently elderly, can easily become isolated and depressed if their hearing loss is not addressed.[rx]

WHO response

WHO assists Members States in developing programs for ear and hearing care that are integrated into the primary health-care system of the country. WHO’s work includes:

• providing technical support to the Member States in the development and implementation of national plans for hearing care;
• providing technical resources and guidance for training of health-care workers on hearing care;
• developing and disseminating recommendations to address the major preventable causes of hearing loss;
• undertaking advocacy to raise awareness about the prevalence, causes, and impact of hearing loss as well as opportunities for prevention, identification, and management;
• developing and disseminating evidence-based tools for effective advocacy;
• observing and promoting World Hearing Day as an annual advocacy event;
• building partnerships to develop strong hearing care programmes, including initiatives for affordable hearing aids, cochlear implants and services;
• collating data on deafness and hearing loss to demonstrate the scale and the impact of the problem;
• launching and promoting the WHO-ITU global standard for personal audio systems and devices;
• promoting safe listening to reduce the risk of recreational noise-induced hearing loss through the WHO Make Listening Safe initiative;
• raising awareness on safe listening to reduce the risk of recreational noise-induced hearing loss through the WHO Make Listening Safe initiative;
• promoting the social inclusion of people with disabilities, including people with hearing loss and deafness, for example, through community-based rehabilitation networks and programs.
• launching and hosting the World Hearing Forum, which is a global advocacy alliance of all stakeholders in the field of hearing.
• In 2017, the 70^th World Health Assembly adopted a resolution on the prevention of deafness and hearing loss. This resolution calls upon the Member States to integrate strategies for ear and hearing care within the framework of their primary health care systems, under the umbrella of universal health coverage. It also requests WHO to undertake a number of actions for the promotion of ear and hearing care at the global level, including many of those noted above.

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