Hearing loss

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.

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!

Presbycusis

• Definition: : age-related, sensorineural hearing loss
• Pathophysiology: progressive and irreversible 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
  • Usually first noticed in the sixth decade of life
  • 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)
  • Difficulty hearing in noisy, crowded environments.
  • Can cause depression and/or isolation
• Treatment
  • No definitive treatment is available.
  • Hearing aids or cochlear implants

Sudden sensorineural hearing loss (SSNHL)

• Definition: sudden, usually unilateral loss of hearing over a period of 3 days
• Epidemiology
  • Incidence: 2–30:100,000 ^[2]
  • Peak incidence: 40–50 years old ^[2]
  • ♂ = ♀ ^[3]
• Etiology: Many disorders that cause sensorineural hearing loss may present as SSNHL (see “Overview” above). ^[2]
  • Idiopathic (e.g., Meniere disease)
  • Congenital or hereditary
  • Aging (i.e., presbycusis)
  • Traumatic (e.g., noise-induced hearing loss)
  • Neurologic (e.g., acoustic neuroma)
  • Ototoxic drugs (e.g., aminoglycosides)
  • Infectious (e.g., viral cochleitis, post pneumococcal meningitis)
  • Autoimmune (e.g., vasculitis)
• Clinical features
  • Acute, usually unilateral hearing loss, often upon awakening
  • Blocked ear sensation
  • Tinnitus, vertigo
• Diagnostics
  • Audiometry
    AND
  • Head MRI or brainstem auditory evoked potential (AEP): detect retrocochlear disorders (e.g., acoustic neuroma)
• Treatment ^[4]
  • Initiate within 2 weeks of symptom onset
  • Glucocorticoids (systemically or intratympanically) and/or hyperbaric oxygen therapy
• Prognosis: spontaneous recovery in 35–40% of patients within the first 2 weeks of symptom onset ^[5]

Assess response to initial treatment with follow-up audiometry, 2 weeks and 6 months post-treatment. ^[4]

Initial diagnostic tests ^[1]

• 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 (esp. for conductive hearing loss)

Further diagnostic tests ^[1]

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

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

Otoacoustic emissions (OAE)

• Description: sound emissions originating from the cochlea that arise spontaneously or in response to acoustic stimulation and can be measured in the auditory canal to assess cochlear function
• Types of OAE
  • Spontaneous OAE (SOAE): physiological, acoustic emissions that originate from the outer hair cells of the ear and reach the auditory canal via the auditory ossicles and tympanic membrane
  • Evoked OAE (EOAE): acoustic emissions that arise in response to acoustic stimuli
• Measurement of OAE
  • Indication: newborn hearing screening (EOAE)
  • Procedure: noninvasive OAE measurement using a microphone within the external auditory canal
  • Interpretation
    • Detectable OAE: normal outer hair cell function (cochlear function intact)
    • Absent OAE: cochlear hearing loss > 30 dB

Conductive hearing loss

• Otosclerosis
• Otitis media with or without serous effusion
• Cholesteatoma
• Ear barotrauma
• Cerumen impaction
• External auditory canal atresia

Sensorineural hearing loss

• Aging, i.e., presbycusis
• Idiopathic (e.g., Meniere disease)
• Infectious (e.g., viral cochleitis, meningitis, otosyphillis)
• Traumatic: (e.g., noise-induced hearing loss, head injury, inner ear barotrauma)
• Neurologic (e.g., acoustic neuroma, stroke, multiple sclerosis)
• Autoimmune (e.g., vasculitis)
• Ototoxic drugs (e.g., aminoglycosides, loop diuretics)

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.

Hearing aids ^[1]

• 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 ^[1]

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