Summary

Hearing loss can be defined based on the general type of hearing loss (conductive or sensorineural) and the location of the dysfunction. Conductive hearing loss typically occurs due to dysfunction of the outer or middle ear, which prevents transmission of sound waves from reaching the inner ear. Sensorineural hearing loss, on the other hand, occurs due to dysfunction of the inner ear or auditory nerve, which prevents neuronal transmission to the brain. Sometimes hearing loss can have both conductive and sensorineural components, which is referred to as mixed hearing loss. Patients with a complaint of hearing loss should be screened with techniques such as the whispered voice or finger rub tests. Subsequently, tuning fork tests should be performed to differentiate between conductive and sensorineural hearing loss. This may be followed by otoscopy, audiometry, laboratory tests, or imaging, depending on the underlying suspected cause. Treatment depends on the underlying etiology and can include hearing aids or cochlear implants for irreversible conductive or sensorineural hearing loss, respectively.

Overview

	Conductive hearing loss	Sensorineural hearing loss
Age of Onset	More commonly presents in childhood or young adulthood	More commonly presents in middle or late age
Etiology	Otosclerosis Otitis media with or without serous effusion Ear barotrauma Cerumen impaction External auditory canal atresia	Ménière disease Acoustic neuroma Noise-induced hearing loss Internal ear infections Presbycusis
Pathophysiology	External or middle ear pathology that disrupts conduction of sound into the inner ear	Inner ear, cochlear, or auditory nerve pathology that impairs neuronal transmission to the brain
Clinical features	Hearing improves in noisy environments Volume of voice remains normal because inner ear and auditory nerve are intact Sound normally is not distorted Features of external auditory canal pathology (e.g., cerumen impaction)	Hearing worsens in noisy environments Volume of voice may be loud because nerve transmissions are impaired Tend to lose higher frequencies preferentially, such that sounds may be distorted Absent features of external auditory canal pathology
Weber test (unilateral hearing loss)	Lateralization to impaired ear (cannot hear ambient room noise well, so detection of vibration is greater)	Lateralization to unimpaired ear (sound is not transmitted by damaged inner ear or auditory nerve)
Rinne test (unilateral hearing loss)	Bone conduction > air conduction (vibrations bypass blockage to reach the cochlea)	Air conduction > bone conduction (the inner ear or auditory nerve cannot transmit sound information well regardless of how vibrations reach the cochlea)
Speech audiometry	No discrimination loss.	Discrimination loss is common.
Audiogram	Difference between air and bone conduction	Hearing loss for higher frequency sounds.
Impedance audiometry	Elevated acoustic reflex threshold	Normal acoustic reflex threshold

Mixed hearing loss is a combination of conductive and sensorineural hearing loss!

Hearing loss in the first years of life can cause a delay in speech, language, and social development!

References:^[1]^[2]

Diagnostics

Initial diagnostic tests

Whispered voice test and finger rub test: screening to determine the extent of hearing loss
Rinne test and Weber test: : to classify hearing loss as conductive or sensorineural
Otoscopy: : allows for visual assessment of the external ear and tympanic membrane
Pneumatic otoscopy: (evaluates the mobility of the tympanic membrane): for conductive hearing loss

Further diagnostic tests

Laboratory tests (e.g., blood glucose, CBC with differential, TSH, and/or syphilis testing depending on the suspected etiology): for patients with unexplained sensorineural hearing loss
MRI or CT scan: (of the posterior fossa): indicated in patients with unilateral, gradual sensorineural hearing loss to exclude acoustic neuroma
Audiometry: : for patients without any obvious cause of hearing loss (for further information see subjective audiometry and objective audiometry)

References:^[1]^[2]

Subjective audiometry

Audiogram (Pure Tone Testing)

Procedure: The patient is played various frequencies through a headphone (air conduction) and a bone oscillator (bone conduction) placed on the mastoid bones. Various frequencies are played and the patient gives a signal (e.g., raising a finger or pressing a button) as soon as a sound is heard. The auditory threshold is determined using the decibel level at which the patient's signals are 50% correct.
Interpretation: The connection of the individual auditory threshold points results in the generation of an auditory threshold curve for air and bone conduction, which allows the degree of hearing loss for individual frequencies to be determined.
- In conductive hearing loss (damage to the middle or external ear), the auditory threshold is increased in air conduction; however, the auditory threshold is normal in bone conduction
- In sensorineural hearing loss (cochlear or retrocochlear damage), the auditory threshold for air and bone conduction are proportionally increased.

Speech audiometry

Procedure: The patient is played increasingly loud words, which should be repeated by the patient. The speech reception threshold is calculated from the level at which a patient can correctly repeat 50% of words.
Interpretation: Increasing loudness eventually leads to a speech comprehension of 100% in patients with conductive hearing loss, but not in patients with sensorineural hearing loss. Loss of word comprehension is referred to as discrimination loss.

Objective audiometry

Impedance audiometry

Description: a test that measures changes in the acoustic impedance of the middle ear in response to changes in air pressure. Impedance audiometry may also include stapedius reflex measurement and tympanometry.
Procedure: This test uses pneumoscopy to gradually increase pressure in the ear.

Tympanometry

Description: In tympanometry, the reflected sound from the tympanic membrane is measured by applying various pressures to the external auditory canal. This information can be used to estimate mobility of the tympanic membrane and the pressure in the middle ear, which, e.g., may provide evidence of Eustachian tube dysfunction or secretory otitis media.
Procedure: Entry to the auditory canal is sealed by a probe and is airtight, which can manipulate the pressure in the external auditory canal and emit various sound frequencies. The sound reflected from the tympanic membrane provides information on the compliance of the tympanic membrane and is measured as a function of the generated positive and negative pressure (between +300 Pa and -300 Pa). Results are recorded on a tympanogram.
Interpretation
- Normal middle ear function: maximum compliance of ∼0 Pa
- Eustachian tube dysfunction: displacement of normal compliance in the region of negative pressure
- Secretory otitis media: flat tympanometry curve without an identifiable maximum

Differential diagnoses

Conductive hearing loss

Otosclerosis
Otitis media with or without serous effusion
Cholesteatoma
Ear barotrauma
Cerumen impaction

Cerumen impaction

Definition: buildup of tightly packed cerumen (earwax) in the outer ear .
Risk factors
- Anatomic deformity and/or increased number of hairs in external auditory canal
- Barriers to wax extrusion (e.g., use of earplugs, hearing aids)
Clinical findings
- Conductive hearing loss
- Ear discomfort
Diagnostics: otoscopy
Treatment
- Irrigation (e.g., warm saline containing a bacteriostatic substance; cerumenolytics can be added as well)
- Cerumenolytics (e.g., docusate sodium)
- Mechanical removal (e.g., with forceps, curette, or suction)

References:^[3]

Always consider the possibility of cerumen impaction in patients presenting with hearing loss!

References:^[4]^[5]^[6]

Sensorineural hearing loss

Presbycusis

Definition: age-related, sensorineural hearing loss
Pathophysiology: progressive damage of the hair cells of the organ of Corti (especially near the basal turn of the cochlea) that impairs high-frequency hearing
Epidemiology:
- Most common cause of sensorineural hearing loss
- Incidence increases with age:
  - Age 50: 10-15%
  - Age 75: > 50%
  - Age 90: nearly 100%
Clinical features
- Progressive bilateral hearing loss, particularly of higher frequencies → Using a low-pitched and clear voice to speak with older patients can improve communication.
- Usually first noticed in the sixth decade of life
- Difficulty hearing in noisy, crowded environments.
- Can cause depression and/or isolation
Treatment
- No definitive treatment is available.
- Hearing aids or cochlear implants

References:^[7]

Noise-induced hearing loss (NIHL)

Definition: hearing loss that occurs due to exposure to loud sound
Risk factors: repeated exposure to sounds louder than 85 dB or even a single exposure to sounds greater than 120–155 dB.
Pathophysiology
- Sudden or repeated loud sounds result in damage to the stereocilia of hair cells of the organ of Corti
- Repeated or constant noise exposure (e.g., occupational) → accumulated microtrauma → sensorineural hearing loss
- Sudden extremely loud sound may also lead to tympanic membrane rupture → conductive hearing loss
Clinical features
- Slowly progressive hearing loss with loss of high-frequency hearing first
- Difficulty hearing in noisy, crowded environments
- As it progresses, difficulty hearing high-pitched voices (e.g., women's, children's) occurs
Treatment
- No definitive treatment is available
- Prophylaxis is essential (hearing protection)

References:^[8]

The differential diagnoses listed here are not exhaustive.

Treatment

Treatment depends on the underlying etiology of the hearing loss.
For irreversible causes, hearing devices such as hearing aids (for conductive hearing loss) or cochlear implants (for cochlear dysfunction) can be considered.

Hearing aids

Definition: devices that amplify sound to assist individuals with impaired hearing
Prerequisite: All patients should undergo a thorough ENT-examination to rule out treatable causes and an audiological examination to determine the severity of hearing loss.
Indications
- Both conductive and sensorineural hearing loss (regardless of severity)
- Mild to severe hearing loss
  - Children should be fitted with a hearing aid as soon as possible to avoid a developmental delay in speech.

Cochlear implants

Bilateral cochlear implants can improve speech discrimination in background noise.

Definition: Prosthetic devices that are surgically implanted and function by electrical stimulation of the auditory nerve (CN VIII).
Prerequisite: the auditory nerve and auditory system are intact.
Indications
- Moderate to severe sensorineural hearing loss
- Unsuccessful prior treatment attempt with hearing aids

References:^[1]^[2]^[9]