• Clinical science

Hearing loss

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
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 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

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

Further diagnostic tests

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

Tympanometry

Differential diagnoses

Conductive hearing loss

Cerumen impaction

  • Definition: buildup of tightly packed cerumen (earwax) in the outer ear .
  • Risk factors
  • Clinical findings
  • 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 organ of Corti, especially near the basal turn of the cochlea, which impairs high-frequency hearing
  • Epidemiology:
  • 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

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
  • 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 (eg, 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

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

References:[1][2][9]