Hearing Loss

Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Diagnostic evaluation relies on history, physical examination (including otoscopic and tuning fork examinations), and audiology testing. Management is directed toward the underlying cause of the hearing loss to choose the appropriate course of treatment.

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Overview

Definition

Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds.

Anatomy

  • External ear: auricle and external auditory canal
  • Middle ear:
    • Tympanic membrane
    • Ossicles: malleus, incus, and stapes
  • Inner ear:
    • Cochlea
    • Semicircular canals
    • Vestibulocochlear nerve (CN VIII) 
  • CNS:
    • Brainstem auditory pathways
    • Auditory cortex
Anatomy of the external, middle, and inner ear

Diagram of the anatomy of the external, middle, and inner ear

Image by Lecturio.

Epidemiology

  • Incidence of hearing loss: 2 per 1,000 in young children
  • Prevalence in adults:
    • 21–34 years of age: 3%
    • 35–44 years of age: 6%
    • 44–54 years of age: 11%
    • 55–64 years of age: 25%
    • 65–84 years of age: 43%

Classification of hearing loss

  • Conductive hearing loss (CHL): inability of the ear to conduct sound through the structures of the ear (ossicular chain and tympanic membrane)
  • Sensorineural hearing loss (SNHL): impact on the cochlea, the CN VIII, or the central auditory pathway
  • Mixed: both conductive and sensorineural components 
  • Central auditory dysfunction: damage at the level of the CN VIII, the auditory brain stem, or the cerebral cortex

Etiology

Conductive hearing loss (CHL):

  • Otitis media (acute or chronic)
  • Otitis externa (acute or chronic)
  • Eustachian tube dysfunction/fluid retention in the middle ear
  • Cholesteatoma
  • Otosclerosis
  • Cerumen impaction
  • Neoplasm:
    • Tumor of the external auditory canal
    • Paraganglioma
    • Adenoma of the middle ear
  • Tympanosclerosis
  • Trauma:
    • Ossicular fracture
    • Tympanic membrane perforation
  • Congenital malformations:
    • External auditory canal atresia
    • Ossicular malformations

Sensorineural hearing loss (SNHL):

  • Presbycusis
  • Prolonged exposure to loud noise
  • Prenatal toxoplasmosis, other agents, rubella, cytomegalovirus, and herpes simplex (TORCH) infections:
    • Toxoplasmosis
    • Rubella
    • Cytomegalovirus (can cause asymptomatic hearing loss)
    • Herpes simplex
  • Postnatal infections:
    • Meningitis due to Neisseria meningitidis, Haemophilus influenza, or Streptococcus pneumoniae
    • Meningitis from many organisms can cause hearing loss.
  • Additional infectious causes of hearing loss:
    • Mumps
    • Syphilis
  • Genetic causes:
    • > 400 genetic syndromes (e.g., Alport syndrome)
    • Many autosomal dominant, autosomal recessive, and X-linked nonsyndromic genetic causes exist.
  • Neoplasms:
    • Acoustic neuroma
    • Meningioma
    • Tumor of the endolymphatic sac
  • Trauma: 
    • Blunt or penetrating trauma to the ear
    • Blast injury or temporal bone fracture
    • Barotrauma from diving or flying
  • Ototoxic medications:
    • Aminoglycoside antibiotics
    • Loop diuretics
    • Aspirin
    • Platinum-based chemotherapy agents
  • Radiation therapy
  • Meniere disease

Physiology of hearing

  1. Sound is received in the external auditory canal and funneled to the middle ear.
  2. The tympanic membrane vibrates → conducts sound vibrations through the ossicles → oval window → inner ear
  3. Sound travels through the inner ear perilymph (in the upper and lower chambers of the cochlea) → sensed by the hair cells on the basilar membrane in the organ of Corti (middle chamber of the cochlea), which is filled with endolymph
  4. Signals are carried through the cochlear division of CN VIII → processed in the CN VIII nucleus and auditory cortex → perception of sound (audition)

Cultural relevance

  • Members of the Deaf community in the United States are deaf, which implies profound hearing loss.
  • Members use American Sign Language. 
  • Members are not considered to have a hearing impairment or hearing loss.
  • Deafness is not a disease to be treated or cured.

History of Present Illness

Information to gather from the individual or caregiver regarding hearing loss:

  • Onset and duration of hearing loss:
    • Prelingual or postlingual (before or after a child learns to speak)
    • Sudden or chronic 
    • Fluctuating or progressive 
  • Laterality: unilateral or bilateral
  • Severity:
    • Milder forms may be unnoticed by the individual.
    • More severe forms may require assistive devices for amplification.
  • Alarm symptoms:
    • Sudden or rapid onset 
    • Rapidly progressive (possibly from ototoxic medications)
    • Tinnitus associated with acute hearing loss
    • Vertigo may indicate CN VIII pathology:
      • Meniere disease
      • Labyrinthitis
      • Neoplasm
      • Brainstem ischemia/infarct
      • Perilymph fistula
  • Recent history: 
    • Upper respiratory infection 
    • Use of aminoglycoside antibiotics
    • Recent ear surgery:
      • Pressure equalization tubes
      • Tympanoplasty
      • Mastoidectomy

Physical Examination

An otoscope is used to examine the outer and middle ear and a tuning fork is used to determine the type of hearing loss.

Otoscopic exam

  • Outer and middle ear:
    • Inspection of the ear canal (e.g., erythema, drainage, inflammation, cerumen impaction, and foreign body)
    • Examination of the tympanic membrane (e.g., perforation, bulging, retraction, and erythema)
  • Pneumatic otoscopy (a puff of air into the ear canal): 
    • An insufflator is used to determine the mobility of the tympanic membrane.
    • Fluid in the middle ear inhibits movement of the tympanic membrane.
Normal tympanic membrane

View of a normal tympanic membrane on an otoscopic exam:
Note the bony malleus attached to the tympanic membrane.

Image: “Normal tympanic membrane” by Michael Hawke, MD. License: CC BY 4.0

Tuning fork examination

  • 512 Hz tuning fork
  • Rinne test for CHL:
    • Procedure: The tuning fork is struck and placed behind the ear over the mastoid bone; once no longer heard, the fork is moved 2.5 cm from the external ear.
    • Normal: air conduction > bone conduction (vibration is still heard near the external ear) 
    • CHL: bone conduction > air conduction (vibration is no longer heard once the tuning fork is moved in front of the ear canal)
  • Weber test: 
    • The tuning fork is struck and placed on the top of the head.
    • Normal: Sound is heard equally in both ears.
    • CHL: Sound is louder in the affected ear.
    • SNHL: Sound is quieter in the affected ear.
Rinne and Weber tests

Weber and Rinne test

Image by Lecturio.

Diagnosis and Management

Diagnosis of hearing loss is based on physiologic and audiometric testing. Lab testing and imaging may also be needed to rule out another pathology.

Physiologic testing

  • Auditory brainstem response (ABR) testing: 
    • A “click” sound is used to evoke physiologic responses in the CN VIII and the auditory brainstem.
    • Recorded with surface electrodes
    • Does not assess low frequency < 1500 Hz
  • Auditory steady-state response testing: 
    • An auditory-evoked potential test (like ABR)
    • Tests several frequencies and gives specific information (unlike ABR)
  • Evoked otoacoustic emissions: assesses activity of the cochlear hair cells
  • Tympanometry: assesses mobility of the tympanic membrane and the middle ear ossicles

Audiometry

  • Behavioral testing for young children:
    • Indicated for children with delayed speech development
    • Behavioral observation audiometry: birth to 6 months of age
    • Visual reinforcement audiometry: 6 months to 2.5 years of age
  • Pure tone audiometry: 
    • Earphones are used to identify the threshold heard for a defined set of frequencies.
    • Used in adults and children mature enough to cooperate
    • Indicated in any individual with unilateral or bilateral hearing loss 
    • Normal: within 15 dB of normal threshold
    • High-frequency sounds are lost 1st with aging.
  • Hearing loss: Normal audible range is 0–180 dB (> 85 dB is damaging):
    • Severity:
      • Mild: 26–40 dB
      • Moderate: 41–55 dB
      • Moderately severe: 56–70 dB
      • Severe: 71–90 dB
      • Profound: 90 dB
    • Frequencies: Normal hearing is 20–20,000 Hz:
      • Low-frequency hearing loss: sounds < 500 Hz
      • Middle-frequency hearing loss: sounds 501–2,000 Hz
      • High-frequency hearing loss: sounds > 2,000 Hz 
    • Percentage of hearing impairment: 
      • Determined by the pure tone average in dB at 500 Hz, 1,000 Hz, 2,000 Hz, and 3,000 Hz frequencies
      • 30% impairment = 70% residual hearing at 45 dB
      • 60% impairment = 40% residual hearing at 65 dB
      • 80% impairment = 20% residual hearing at 78 dB
      • 100% impairment = no residual hearing at 91 dB
  • Functional impairment: 
    • May be misleading if based on pure tone average alone:
      • 30% impairment = 70% residual hearing at 45 dB
      • Conversational speech is approximately 50–60 dB → significant impact on the ability to function
    • A different rating scale is used for young children → mild impairments can cause significant difficulty with language development
Audiogram

Audiogram chart

Image: “Audiogram” by Audiology6. License: Public Domain

Additional testing

  • Lab tests:
    • Blood glucose: Diabetic vasculopathy can cause cochlear ischemia.
    • CBC: check for anemia and WBC count
    • Thyroid function tests
    • Serologic test for syphilis 
    • Tests for autoimmune disease (if suspected): 
      • Erythrocyte sedimentation rate (ESR)
      • ANA
      • Rheumatoid factor (RF)
  • Imaging:
    • MRI: recommended in cases of asymmetric or unilateral SNHL
    • CT scan of the temporal bone: 
      • Identifies abnormal bone findings
      • Localizes effusions and abnormal soft tissue

Management

  • Medical management: 
    • Give antibiotics if an infection is present.
    • Evacuation of obstruction: cerumen or other foreign body
    • Treatment of underlying conditions:
      • Autoimmune disease
      • Cerebrovascular disease
      • Meningitis
      • Multiple sclerosis
      • Syphilis
  • Otolaryngology specialty referral:
    • Cochlear implant (surgical procedure):
      • Indicated for SNHL
      • > 6 months of age
    • Otologic emergency:
      • Sudden SNHL
      • Trauma
    • Surgical management depends on the etiology:
      • Repair of a perforated tympanic membrane
      • Stapedectomy for otosclerosis 
      • Ossicular chain reconstruction 
      • Tumor (e.g., acoustic neuroma)

Clinical Relevance

Common conditions causing hearing loss: 

  • Otitis media: infection in the middle ear characterized by mucosal inflammation and retention of fluid. The most common pathogens are S. pneumoniae, H. influenzae, and Moraxella catarrhalis. Otitis media can present with fever, otalgia, and hearing loss. Diagnosis is made by history and physical exam. Management is with oral antibiotics. Procedures may be needed for recurring infections. 
  • Otitis externa (swimmers ear): infection of the external auditory canal. Otitis external is most often caused by acute bacterial infection and is frequently associated with hot, humid weather and water exposure. Individuals commonly present with ear pain, pruritus, discharge, and hearing loss. Diagnosis is made by history and physical exam. Management is with topical antibiotics, pain relief, and protection of the ear.
  • Meningitis: inflammation of the meninges (the protective membranes of the brain and spinal cord). The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis can cause SNHL due to the spread of infection to the cochlea. Diagnosis of meningitis is made clinically with full neurologic examination and CSF analysis. Management includes immediate broad-spectrum antibiotics and supportive care. 
  • Multiple sclerosis: a chronic inflammatory autoimmune disease leading to demyelination of the CNS. The clinical presentation varies widely depending on the site of the lesions. Hearing may be compromised with significant involvement of the CN VIII. The diagnosis is made by clinical and CSF exams and MRI imaging. Management involves corticosteroids for acute exacerbations and disease-modifying agents to slow the progression of the disease.
  • Syphilis: a bacterial infection caused by Treponema pallidum, a spirochete, typically spread through sexual contact. Varying clinical presentations may range from a painless genital ulcer (primary syphilis), to a rash (secondary syphilis), to severe neurological deterioration (tertiary syphilis). Individuals can experience hearing loss and vertigo due to ear involvement in secondary syphilis. Diagnosis is through lab testing. Treatment is with penicillin and the duration depends on the stage of the disease. 
  • Meniere disease: a disorder of the inner ear characterized by hearing loss, fluctuating aural symptoms (e.g., tinnitus), and spontaneous episodes of vertigo. Diagnosis is made with a thorough history, physical exam, and full otologic exam. An audiogram is a key component of the evaluation. Management includes diet and lifestyle modification, vasodilators, diuretics, antihistamines, benzodiazepines, antiemetics, glucocorticoids, surgical intervention, and/or hearing aids.

References

  1. Shapiro, S.B., Noij, K.S., Naples, J.G., & Samy, R.N. (2021). Hearing Loss and Tinnitus. Medical Clinics of North America, 105(5), 799–811. https://doi.org/http://dx.doi.org/10.1016/j.mcna.2021.05.003 
  2. Molina, F.J. (2012). Chapter 18. Hearing Loss. In M. C. Henderson, L. M. Tierney, & G. W. Smetana (Eds.), The Patient History: An Evidence-Based Approach to Differential Diagnosis, 2nd ed. The McGraw-Hill Companies. http://accessmedicine.mhmedical.com/content.aspx?aid=56852049 
  3. Berkowitz, A.L. (2016). The auditory and vestibular pathways and approach to hearing loss and dizziness/vertigo: Cranial nerve 8. In Clinical Neurology and Neuroanatomy: A Localization-Based Approach. McGraw-Hill Education. http://accessmedicine.mhmedical.com/content.aspx?aid=1160204039 
  4. Krogmann, R.J., & Al Khalili, Y. (2021). Cochlear Implants. StatPearls. Retrieved September 23, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK544280/
  5. Weber, P.C. (2020). Etiology of hearing loss. UpToDate. Retrieved September 23, 2021, from https://www.uptodate.com/contents/etiology-of-hearing-loss-in-adults
  6. Weber, P.C. (2021). Evaluation of hearing loss in adults. UpToDate. Retrieved September 23, 2021, from https://www.uptodate.com/contents/evaluation-of-hearing-loss-in-adults
  7. Smith, R.J.H. & Gooi, A. (2021). Hearing loss in children: Etiology. UpToDate. Retrieved September 23, 2021, from https://www.uptodate.com/contents/hearing-loss-in-children-etiology

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