Hearing loss

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.

	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's 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 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]

• Whispered voice test: screening to determine extent of hearing loss
• Rinne test and Weber test: to classify hearing loss as conductive or sensorineural
• Pneumoscopy: (evaluates the mobility of the tympanic membrane): for conductive hearing loss
• Audiometry: for all patients without any obvious cause to hearing loss
• 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

References:^[1][2]

Conductive hearing loss

• Otosclerosis
• Otitis media with or without serous effusion
• Ear barotrauma

External auditory canal atresia

Definition: congenitally absent or stenotic external auditory canal

• Clinical features
  • Conductive hearing loss (may be bilateral or unilateral depending on whether both sides are affected or just one)
  • Increased risk of acute otitis media
• Treatment
  • Initially, bone conduction hearing aid
  • Surgical correction within the first year
  • Antibiotics for suspected acute otitis media

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 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

• Ménière disease
• Acoustic neuroma
• Internal ear infections

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:
  • 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 and 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 loud sound; (i.e., impulse) results in damage to the stereocilia of hair cells
  • 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
  • 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.