• Clinical science

Hearing loss

Abstract

Hearing loss can be defined based on the location of dysfunction as either conductive or sensorineural hearing loss. Conductive hearing loss is due to dysfunction of the outer or middle ear, which prevents transmission of sound waves from reaching the inner ear. In comparison, sensorineural hearing loss is 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 who present with hearing loss should be screened with tests such as the whispered voice test. After confirming the diagnosis, Rinne and Weber testing should be performed to differentiate between conductive or sensorineural hearing loss. This may be followed by audiometry, pneumoscopy, 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 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 good ear (sound is not transmitted by damage 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)

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

References:[1][2]

Differential diagnoses

Conductive hearing loss

External auditory canal atresia

Definition: congenitally absent or stenotic external auditory canal

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
  • 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 a forceps, a curette, or with 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
    • Slowely 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)

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.
    • Children:
      • Causes of hearing loss that can be treated surgically include tumors, cholesteatomas, and stenosis/atresia of the external auditory canal
      • Pressure equalization tubes in the tympanic membrane can improve hearing in children with hearing loss from recurrent otitis media, middle ear effusions, or dysfunction or the eustachian tube.
    • Adults: Most adults experience age-related hearing loss which is not treatable; other etiologies should nonetheless be investigated.
  • 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][8]