HEARING IMPAIRMENT
Hearing impairment is defined as an impairment in hearing, whether permanent or fluctuating, that adversely affects a person’s ability to hear and understand sounds. It can range from mild to profound.
But let's first see what Hearing means
Hearing starts when sound waves traveling through the air reach the outer ear, also called the pinna. The sound waves then travel through the ear canal to the middle ear.
In the middle ear, the eardrum (a thin tissue layer) vibrates. Three small bones called ossicles amplify these vibrations and carry them to the inner ear.
The inner ear contains the cochlea, a snail-shaped chamber filled with fluid and lined with tiny hair cells. When the vibrations move through the fluid, the outer hair cells amplify them. This amplification allows us to hear soft sounds.
The inner hair cells then translate the vibrations into electrical nerve impulses. These impulses travel along the auditory nerve to the brain, where they are interpreted as sound.
The cochlea is structured so that different areas detect different pitches, like the keys on a piano. From the cochlea, the sound information is transmitted to the cerebrum, where hearing interpretation takes place.
Hearing Impairment:
Hearing impairment occurs when there’s a problem with or damage to one or more parts of the ear.
- Hearing impairment is defined as an impairment in hearing, whether permanent or fluctuating, that adversely affects a person’s ability to hear and understand sounds. It can range from mild to profound.
Deafness:
- Deafness refers to a severe or profound hearing impairment where a person has very little or no functional hearing. Individuals who are deaf may have difficulty processing linguistic information through hearing alone and often rely on other forms of communication, such as sign language or assistive devices.
- Deafness is defined as a degree of loss such that a person is unable to understand speech even in the presence of amplification.
- Amplification refers to the use of hearing aids or other assistive devices to enhance sound. The statement suggests that even with the use of amplification, individuals with deafness still struggle to understand speech.
Hard of Hearing:
- This term is used to describe individuals who have a mild to moderate hearing loss. They may have enough residual hearing to benefit from hearing aids or other assistive devices to enhance their hearing abilities.
Hearing Loss:
- This is a general term used to describe any degree of impairment in hearing, ranging from mild to profound. It encompasses both temporary and permanent hearing impairments.
Deafened:
- This term is used to describe individuals who become deaf later in life, as adults. They may face different challenges compared to those who were born deaf or became deaf at a young age.
- Anacusis: Have no hearing at all.
Types of hearing loss
Conductive Hearing Loss: Conductive hearing loss occurs when there is a problem with the outer or middle ear that prevents sound from reaching the inner ear. It can be caused by conditions such as ear infections, blockages in the ear canal, perforated eardrum, or abnormalities in the middle ear bones.
- Any process that interferes with the conductive mechanism of the ear canal, tympanic membrane, or ossicles may cause a conductive hearing loss. The most common pediatric cause of conductive loss is otitis media with effusion and is usually of mild to moderate severity. Several congenital syndromes may also be associated with middle ear abnormalities, such as Apert, Crouzon, and Treacher Collins syndromes.
Sensorineural Hearing Loss: Sensorineural hearing loss occurs when there is damage to the inner ear or the auditory nerve pathways that transmit sound signals to the brain. It is the most common type of hearing loss and is often permanent.
- Sensorineural hearing loss is caused by a lesion of the cochlea, auditory nerve or central auditory pathway. SNHL can be acquired or congenital, both being equally common. The most common postnatal cause of acquired Sensorineural hearing loss is meningitis, while the most common prenatal cause is intrauterine infection (e.g. TORCHES). Other causes of acquired hearing loss include prematurity, hyperbilirubinemia, perinatal hypoxia, acquired immunodeficiency syndrome, head trauma and ototoxic medications (aminoglycosides, loop diuretics).
Mixed Hearing Loss:
Mixed hearing loss is a combination of sensorineural and conductive hearing loss. It involves both a problem in the outer or middle ear and damage to the inner ear or auditory nerve. This type of hearing loss can occur when someone with pre-existing sensorineural hearing loss develops a conductive hearing loss on top of it.
Causes of Hearing Impairment:
- Ear Infections: Ear infections, such as otitis media, can cause hearing impairment. These infections can result in inflammation and fluid buildup in the middle ear, which can interfere with the transmission of sound to the inner ear.
- Blockages in the Ear: Blockages in the ear, such as foreign bodies, impacted wax, or fluid due to cold or allergies, can also lead to hearing impairment. These blockages can prevent sound waves from reaching the inner ear properly.
- Damage to Tympanic Membrane and Ossicles: Damage to the tympanic membrane (eardrum) or the tiny bones in the middle ear called ossicles can cause hearing impairment. A tear in the eardrum or damage to the ossicles can disrupt the transmission of sound vibrations to the inner ear.
- Genetic Disorders: Some genetic disorders can interfere with the development of the inner ear and auditory nerve, leading to hearing impairment. These disorders can affect the structure or function of the auditory system, resulting in varying degrees of hearing loss.
- Complications during Pregnancy: Certain complications during pregnancy, such as TORCHES infections (Toxoplasmosis, Other infections, Rubella, Cytomegalovirus, Herpes simplex, Syphilis), or exposure to chemotherapy drugs, can cause hearing impairment in the developing fetus.
- Perinatal problems: 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 can be associated with sensorineural hearing loss because of an increased risk of hypoxia, hyperbilirubinemia, ototoxic medication and infection as well as noise exposure in the neonatal units. The risk of hearing loss is greatest for those weighing less than 1500 g at birth.
- Sudden Loud Noise: Exposure to sudden loud noises over time can damage the tiny hair cells in the cochlea, which are responsible for transmitting sound signals to the auditory nerve. Prolonged exposure to loud noise, such as in noisy work environments or attending loud concerts without hearing protection, can lead to permanent hearing loss.
- Head Injury: Traumatic head injuries can also cause hearing impairment. Damage to the auditory nerve or the structures of the ear due to a head injury can result in partial or complete hearing loss.
- Disorders; such as
- Strokes: Depending on which blood vessels are affected, a stroke can cause deafness.
- Multiple Sclerosis (MS): MS is an autoimmune disease where the immune system attacks the myelin sheath, protecting nerves. Damage to the auditory nerve can lead to complete deafness in one or both ears.
- Perilymph fistula: A microtear in the round or oval window (membranes separating the middle and inner ear) of the cochlea allows perilymph to leak into the middle ear. This usually occurs due to trauma, including barotrauma, and can cause vertigo and hearing loss.
11. Infections:
- Viral: Viral ear infections (labyrinthitis) can cause sensorineural hearing loss.
- Measles, Mumps, Rubella: These childhood illnesses can cause deafness in newborns.
- Herpes Viruses: Cytomegalovirus (CMV) can cause deafness in newborns and progressive sensorineural hearing loss in children.
- Meningitis:: It can also lead to hearing loss.
12. Inherited:
- Down Syndrome: Individuals with Down syndrome are more likely to experience hearing loss, often due to middle ear effusions in childhood. They can also develop high-frequency sensorineural hearing loss later in life.
- Otosclerosis: This condition causes fixation of the stapes in the middle ear, leading to conductive hearing loss.
- Vestibular Schwannoma (Acoustic Neuroma): This tumor can cause hearing loss by compressing the vestibulocochlear nerve.
13. Congenital Problems: Superior Semicircular Canal Dehiscence: A gap in the bone covering the inner ear can lead to low-frequency conductive hearing loss, autophony, and vertigo.
14. Medications: Ototoxic Medications: Some medications can temporarily or permanently affect hearing. Examples include loop diuretics (furosemide, bumetanide), NSAIDs, and aminoglycosides.
15. Chemicals: Environmental Toxins: Metals (lead) and solvents (toluene) can cause irreversible high-frequency hearing loss by damaging the cochlea and auditory system.
16. Physical Trauma: Head Injury: Damage to the ear or brain centers responsible for processing auditory information can lead to temporary or permanent hearing loss or tinnitus.
17. Sensorineural Hearing Impairment:
- Genetic Disorders: Some inherited disorders affect the development of the inner ear and/or auditory nerve.
- Ear or Head Injuries: Skull fractures can cause hearing loss.
- Complications During Pregnancy or Birth: Infections or illnesses during pregnancy can affect inner ear development, leading to hearing impairment in newborns. Premature babies are also at higher risk.
- Infections or Illnesses: Repeated ear infections, mumps, measles, chickenpox, and brain tumors can damage inner ear structures.
- Medications: Certain antibiotics and chemotherapy drugs can cause hearing loss.
- Loud Noise: Sudden loud noises or prolonged exposure to high noise levels can damage hair cells in the cochlea, leading to permanent hearing loss.
Signs, Symptoms, and Associated Conditions of Hearing Loss
Primary Symptoms:
- Difficulty understanding speech: Trouble following conversations, especially in noisy environments. Difficulty understanding children and women (higher frequencies). Needing people to repeat themselves frequently.
- Reduced volume perception: Sounds or speech seem dull, muffled, or attenuated. Need to increase volume on TV, radio, music, and other audio sources
- Difficulty using the telephone: Inability to hear clearly on the phone, needing to use speakerphone or headphones
- Loss of directionality of sound: Difficulty locating the source of sound, feeling disoriented in noisy environments
- Difficulty discriminating speech against background noise (cocktail party effect): Trouble understanding conversations in crowded places or with background noise
Sensory Symptoms:
- Pain or pressure in the ears
- A blocked feeling
Secondary Symptoms:
- Tinnitus: Ringing, buzzing, hissing, or other sounds in the ear when no external sound is present
- Vertigo and disequilibrium: Sensation of dizziness, spinning, or imbalance
- Tympanophonia: Abnormal hearing of one’s own voice and respiratory sounds, usually due to a patulous Eustachian tube or dehiscent superior semicircular canals
- Disturbances of facial movement: Indicating a possible tumor or stroke, affecting cranial nerves
Other Associated Conditions:
- Headaches: May be associated with hearing loss, especially in cases of pressure or pain in the ear.
- Emotional distress: Hearing loss can lead to social isolation, frustration, and depression.
- Cognitive decline: Studies suggest a correlation between hearing loss and cognitive decline, including memory problems and dementia.
According to age
Infant
- Wakes only to touch, not environmental noises
- Does not startle to loud noises
- Does not turn to sound by 4 months of age
- Does not babble at 6 months of age
- Does not progress with speech development
Young child
- Does not speak by 2 years of age
- Communicates needs through gestures
- Does not speak distinctly, as appropriate for his or her age
- Displays developmental (cognitive) delays
- Prefers solitary play
- Displays immature emotional behavior
- Does not respond to ringing of the telephone or doorbell
- Focuses on facial expressions when communicating
Older child
- Often asks for statements to be repeated
- Is inattentive or daydreams
- Performs poorly at school
- Displays monotone or other abnormal speech
- Gives inappropriate answers to questions except when able to view face of speaker
Classification/Grading of Hearing Loss
Hearing loss is categorized by type or severity. Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral). Hearing loss can be temporary or permanent, sudden or progressive.
Normal Hearing: Hearing thresholds are within the normal range, typically up to 25 decibels (dB)
- Mild Hearing Loss(Slight): Hearing thresholds range from 26 to 40 dB. Individuals with mild hearing loss may have difficulty hearing soft or distant speech.
- Moderate Hearing Loss: Hearing thresholds range from 41 to 60dB. Individuals with moderate hearing loss may have difficulty understanding speech, especially in noisy environments.
- Severe Hearing Loss: Hearing thresholds range from 61 to 80 dB. Individuals with severe hearing loss may rely heavily on amplification, such as hearing aids, to communicate.
- Profound Hearing Loss: Hearing thresholds are 81 dB or greater. Individuals with profound hearing loss have very limited or no hearing and may benefit from cochlear implants or other assistive devices.
Diagnosis and Investigations of Hearing Impairment
1. History
- Case history: Hearing loss can be difficult to diagnose in infants and babies because they haven’t yet developed communication skills. However, the parents are assessed about prenatal history, delivery history whether, got birth injuries etc
- Medical History: Healthcare providers will ask about your medical history, including the onset of symptoms, whether the hearing loss is in one or both ears, exposure to loud noise, medications taken, and any family history of hearing loss.
2. Examination:
- Otoscopy: An otolaryngologist (ear, nose, and throat doctor) may perform a physical examination using an otoscope, a handheld device with a light and magnifying lens, to examine the ear canal and eardrum. This examination can identify structural damage, earwax buildup, or other substances that may affect hearing.
- Tympanometry: This test measures the movement of the eardrum in response to changes in air pressure, providing information about the middle ear function.
- Differential testing: Tests such as the Weber, Rinne, Bing, and Schwabach tests use a low-frequency tuning fork to assess auditory function and determine the type of hearing loss (unilateral/bilateral, conductive, or other).
- Tuning Fork Test: A tuning fork test helps determine the cause of hearing loss. A vibrating tuning fork is placed against different parts of the face, head, and ears to identify where the sound is loudest. This test can help differentiate between conductive and sensorineural hearing loss.
- Audiometry: Audiometry is a measurement of a person’s hearing sensitivity and range. It helps determine the degree and configuration of hearing loss.
- Pure Tone Audiometry: This test is commonly used for individuals older than 5 years. It involves listening to pure tones at different frequencies and volumes through headphones or earplugs. The person indicates when they hear the sound, and the results are plotted on an audiogram.
- Visual-Reinforcement Audiometry: This test is performed on younger children who may not understand instructions. It uses visual stimuli, such as toys or lights, to reinforce the response when a sound is heard.
3. Laboratory testing:
- In cases of infection or inflammation, blood or other body fluids may be submitted for laboratory analysis to identify the underlying cause of hearing loss.
4. Hearing tests:
- Speech-in-noise test: This test measures how well a person can understand speech in a noisy environment, providing an indication of their ability to hear in challenging conditions.
- Otoacoustic emissions test: This objective hearing test can be administered to toddlers and young children who may not be able to cooperate in a conventional hearing test. It can also be useful in older children and adults.
5. Scans:
MRI and CT scans: These imaging scans can be used to identify the pathology of various causes of hearing loss. They are typically reserved for selected cases where there is a need to further investigate the underlying condition.
- Otoacoustic Emissions (OAE) Test: This test measures the sounds produced by the inner ear in response to sound stimulation. It helps assess the function of the inner ear and can detect certain types of hearing loss.
- Auditory Brainstem Response (ABR) Test: This test measures the electrical activity of the auditory nerve and brainstem in response to sound. It is often used for infants and young children who cannot participate in conventional hearing tests. ABR can provide information about the integrity of the auditory pathway.
Management of Hearing Impairment
The treatment approach depends heavily on the cause, type, and extent of hearing loss.
1. Understanding the Cause:
- Age-related or noise-induced hearing loss: These are the most common causes and often progressive, making them irreversible. Treatment focuses on managing the loss with assistive devices.
- Specific conditions: A few types of hearing loss respond to surgical intervention.
2. Management Strategies:
a) Assistive Devices:
- Hearing Aids: These amplify sound to improve hearing and speech comprehension. They are customizable and adjusted by audiologists for optimal performance. Treatment of significant Sensorineural hearing loss may require the use of hearing aids from as early as 3 months of age.
- Assistive Listening Devices: These aid in specific situations like phone calls (TTY/Textphone), watching television, or attending meetings.
b) Surgical Interventions:
- Tympanostomy tubes: For mild to moderate conductive hearing loss, treatment options include tympanostomy tubes (to keep the tympanic membrane aerated).
- Tympanoplasty: (surgical reconstruction of the tympanic membrane and or ossicles), if a perforation is present.
- Superior Canal Dehiscence Correction: Surgical repair of a defect in the bone covering the inner ear can address certain types of hearing loss, autophony, and vertigo.
- Myringotomy & Ventilation Tubes: A small incision in the eardrum (myringotomy) and insertion of ventilation tubes can address ear infections and fluid build-up.
- Vestibular Schwannoma/Acoustic Neuroma Treatment: Radiotherapy or surgical removal of these tumors can help, but hearing preservation is often challenging.
- Stapedectomy/Stapedotomy: Replacing or reshaping the stapes bone in the middle ear can restore hearing in cases of conductive hearing loss caused by otosclerosis.
c) Treatment of Underlying Conditions:
- Wax or Dirt Removal: Simple ear cleaning can address some cases of hearing loss.
- Infections: Prompt treatment of ear infections is crucial to prevent further damage.
- Structural Problems: Surgery may be needed to repair damage to the eardrum or ossicles.
d) Cochlear Implants:
- For severe hearing loss, a cochlear implant can bypass the damaged parts of the inner ear and directly stimulate the auditory nerve, allowing sound perception.
- Surgery for cochlear implants in the management of childhood hearing loss. Bilateral cochlear implantation may be considered for infants as young as 12 months of age who have a profound bilateral hearing loss and may be considered even earlier if the hearing loss is due to meningitis (to bypass the damaged middle ear).
- If a child has never had auditory stimulus (secondary to profound congenital deafness), cochlear implantation before 6 years of age is important to develop the auditory cortex for sound awareness and speech development. Sign language and deaf education programs should be considered for children who are not candidates for cochlear implantation.
3. Prevention:
- Noise-induced hearing loss: Limiting exposure to loud noises, using hearing protection, and following guidelines for safe noise levels are crucial for prevention.
- Congenital hearing loss: Immunizations (rubella, H. influenza, S. pneumoniae) can reduce the risk of preventable causes.
- Regular Oto-Checkups: Routine hearing screenings can detect early signs of hearing loss and allow for timely intervention.
4. Living with Hearing Loss:
- Communication Strategies: Learning sign language, using assistive devices, and practicing clear communication techniques can help overcome challenges.
- Support Groups: Connecting with others facing similar experiences can provide emotional support and practical advice.