- Clinical science
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.
|Conductive hearing loss||Sensorineural hearing loss|
|Age of Onset|| || |
|Pathophysiology|| || |
|Clinical features|| |
|(unilateral hearing loss)|| || |
|(unilateral hearing loss)|| |
|Speech audiometry|| || |
|Audiogram|| || |
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Mixed hearing loss is a combination of conductive and sensorineural hearing loss!
Initial diagnostic tests
- and : screening to determine the extent of hearing loss
- and : : 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 and )
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 (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 (cochlear or retrocochlear damage), the auditory threshold for air and bone conduction are proportionally increased.
- 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.
- 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.
- 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.
- with or without serous effusion
- Definition: buildup of tightly packed cerumen (earwax) in the outer ear .
- Risk factors
- Conductive hearing loss
- Ear discomfort
- Diagnostics: otoscopy
- 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)
Always consider the possibility of cerumen impaction in patients presenting with hearing loss!
- Noise-induced hearing loss
- Internal ear infections
- 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
- 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
- No definitive treatment is available.
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.
- 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
- 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
- No definitive treatment is available
- Prophylaxis is essential (hearing protection)
The differential diagnoses listed here are not exhaustive.
- 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.
- 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.
- 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.
- 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.