Hearing Impairment and Deafness Overview

Hearing Impairment and Deafness

• Hearing loss occurs when hearing is elevated to 20dB or above
• Severity of hearing loss is categorized as follows:
  • -10 to 20 dB: Normal hearing
  • 20 to 40 dB: Mild hearing loss
  • 40 to 60 dB: Moderately severe hearing loss
  • 60 to 80 dB: Severe hearing loss
  • 80 to 100 dB: Profound hearing loss

Types of Hearing Loss

• Conductive hearing loss
• Sensorineural hearing loss
• Mixed hearing loss

Conductive Hearing Loss

• Caused by interference with sound reaching the cochlea
• Interference points include the external ear, tympanic membrane, middle ear, and ossicles

Causes of Conductive Hearing Loss

• Congenital issues (maldevelopment of the external and middle ear)
  • Atresia of the external auditory canal
  • Anotia/microtia
  • Complete atresia of the middle ear cavity
  • Congenital absence or fusion of ossicles
  • Stenosis of the external auditory canal
  • Treacher-Collins syndrome
    • Congenital meatal atresia
    • Mandibulofacial anomalies (e.g., hypoplastic mandible)
• Acquired issues
  • Cerumen impaction (most common cause)
  • Middle ear effusion
  • External and middle ear infections
  • Trauma to the ear (e.g., slap to the external ear, explosion near the ear, head injury)
  • Tumours (e.g., meatal osteomas and exostosis, ceruminoma, glomus jugulare and tympanicum)
  • Degenerative disorders (e.g., otosclerosis, tympanosclerosis, osteitis deformans (Paget's disease), osteogenesis imperfecta)

Sensorineural Hearing Loss

• Results from lesions of the cochlea, 8th nerve, or central auditory pathways
• Perceptive hearing loss (cochlear)
• Neural hearing loss
• Difficult to distinguish, so sensorineural hearing loss is used as a broad term

Causes of Sensorineural Hearing Loss

• Congenital (Genetic & Non-Genetic)
  • Genetic:
    • 50% are genetic.
    • Intermarriage increases chance.
    • Pendred's disease (non-endemic goiter and sensorineural deafness at birth)
    • Michels aplasia (total or near total aplasia of the inner ear)
    • Waardenburg's syndrome (iris heterochromia and congenital deafness)
    • Hypertelorism and premature graying of the hair
  • Non-Genetic
    • Rubella syndrome
      • Congenital deafness
      • Congenital cataracts
      • Congenital heart disease
      • Mental retardation
    • Kernicterus (Rh incompatibility is a common cause)
    • Endemic cretinism
• Acquired
  • Delayed genetic SNHL (genetically predetermined phenotypic expression later in life)
    • Familial progressive SNHL
    • Alports disease (progressive renal insufficiency, progressive SNHL, cataract formation)
  • Infections
    • Mumps
    • Measles
    • Ramsay Hunt syndrome (herpes zoster oticus)
    • Bacterial meningitis
    • Congenital syphilis
  • Trauma (head injury or fractures of the petrous bone)
  • Tumours (e.g., cerebello pontine angle tumours, acoustic neuroma, meningioma etc)
  • Ototoxicity (e.g., aminoglycosides, rapid-action diuretics, quinine, cytotoxic drugs)
  • Noise-induced hearing loss
  • Aging (presbyacusis)

Evaluation of Hearing Loss

• Otoscopy: Examination of the ear drum (normal, wax blockage, perforated)
• Rinne Test: Compares bone conduction and air conduction (used to determine if hearing loss is conductive or sensorineural)
• Weber's Test: Determines if sound lateralizes to one ear (used to determine if hearing loss is conductive or sensorineural)
• Tympanometry: Measures the movement of the eardrum in response to air pressure changes (to check for middle ear effusion)
• Pure Tone Audiometry: Measures hearing sensitivity at various frequencies (used to create an audiogram)

Audiogram Interpretation

• Normal audiogram: shows hearing sensitivity within normal range
• Conductive hearing loss audiogram: shows impaired bone conduction in the audiogram
• Sensorineural hearing loss audiogram: shows impaired air conduction in the audiogram
• Mixed hearing loss audiogram: shows impaired both air and bone conduction in the audiogram

Management of Hearing Loss

• Conductive hearing loss: Usually correctable
  • Removal of cerumen impaction
  • Treatment of otitis media and externa
  • Excision of meatal swellings
  • Myringotomy and grommet insertion
  • Tympanoplasty
• Sensorineural hearing loss: Generally not treatable
  • Rehabilitation is key

Rehabilitation of a Patient with a Hearing Handicap

• Rehabilitation helps cope with demands of social environment
• Types include
  • Lip reading
  • Sign language
  • Hearing aid machines
  • Cochlear implant

Types of Hearing Aids

• Conventional hearing aids
• Implantable hearing aids

Prevention of Hearing Loss

• Avoiding noise
• Wearing earplugs
• Vaccinations
• Syphilis screening during pregnancy.

Rehabilitation of a Child with a Hearing Handicap

• Parent guidance
• Education in special classes with normal children together
• Organization (doctor, speech therapist, social worker, psychologist, and teacher work closely)