Deafness Notes

Deafness

  • Definition: Partial or total loss of hearing in one or both ears.

Types of Hearing Loss

  • According to the site of pathology:
    • Conductive HL: External or middle ear.
    • Sensorineural HL: Inner ear, auditory nerve, or higher centers.
    • Mixed.
    • Psychogenic HL.

Causes of Deafness

  • Congenital (Genetic):

    • Syndromal (e.g., Down syndrome, Treacher Collins syndrome, achondroplasia).
    • Non-syndromal (autosomal recessive (80%), dominant (20%), or X-linked (2%)).

  • Pendred Syndrome:

    • Autosomal recessive.
    • SNHL associated with iodine metabolism defect leading to euthyroid goiter.
    • Mutation in SLC26A4.

  • Non-Genetic:

    • Intrauterine infection (rubella, measles, toxoplasmosis, or syphilis).
    • Ototoxic drugs during pregnancy (Aspirin, Aminoglycosides).
    • Perinatal causes: anoxia, hyperbilirubinemia, or birth trauma.

  • Acquired (Postnatal):

    • Conductive:
      • External ear: ear wax, FB, otitis externa, atresia, tumors.
      • Tympanic membrane: perforation due to trauma or infection.
      • Middle ear: ossicular disruption or fixation, otitis media, hemotympanum, otosclerosis, tumors.
    • Sensorineural:
      • Sensory: damage to the sensory cells of the inner ear due to trauma, noise-induced hearing loss (>) 85 dB, blast injury, endolymphatic hydrops, presbycusis, autoimmune disease, ototoxic drugs.
      • Neural: damage to cochlear nerve fibers or auditory centers due to trauma, infection (meningitis), tumors, vascular issues, multiple sclerosis.

Approach to Diagnosis

  • History:
    • Age of presentation.
    • Progression.
    • Events during pregnancy.
    • Birth trauma.
    • Neonatal infection.
    • Other ear symptoms.
    • Loud noise exposure and occupational history.
    • Drug history (aminoglycosides, loop diuretics).
    • Family history.
  • Examination:
    • Ear, nose, and throat: thorough exam.
    • General examination: stigmata of congenital anomaly.
    • Examination of other systems: including CNS, Cranial nerves, CVS.

Investigations

  • Auditory tests: Qualitative (sensory vs. conductive) & quantitative (level of deafness).
    • Pure tone audiometry (PTA): Subjective, tests both air and bone conduction using pure tones of different frequencies (Hz) and intensities (dB).
      • Normal persons can hear pure tones at 20-25 dB or less.
    • Speech audiometry: Subjective, phonetically balanced words presented at different intensities.
      • Normally 100% of words repeated at 40 dB and 50% at 25 dB (speech discrimination score).
    • Tympanometry: Objective, graphical representation of middle ear pressure and compliance.
      • Type A: Normal.
      • Type B: Flat curve (otitis media with effusion or TM perforation).
      • Type C: Negative ME pressure (Eustachian tube dysfunction).
      • Type Ad: Hypercompliant (ossicular disconnection).
    • Oto-acoustic emission: Screening test of hearing in newborns. Detects sound signals generated by hair cells of the inner ear.
      • Results: Pass or Refer.
    • Electric response audiometry: Diagnostic. Measures action potentials along the auditory nerve. Useful in young children and mentally handicapped patients; can be done under general anesthesia.
  • Other Tests:
    • Blood tests: full blood count, ESR, bleeding profile.
    • Biochemistry: sugar, urea, creatinine, electrolytes, thyroid hormones.
    • Serological: for syphilis, TORCH.
    • Autoimmune profile: rheumatoid factor, antinuclear factor.
    • Urine analysis.
    • Radiological: skull, mastoids, and sinuses (plain, CTS, and MRI).

Treatment

  • Treat the underlying cause.
  • General measures:
    • Vasodilators: betahistine, Ca channel blockers, low molecular weight dextran.
    • Steroids: for vascular and autoimmune causes.
  • Hearing aids: for conductive or sensorineural deafness.
  • Cochlear implantation: Converts mechanical sound energy into electrical signals, stimulating auditory nerve fibers. For bilateral severe or profound hearing loss.

Sudden Sensorineural Hearing Loss (SSNHL)

  • Rapid onset of ≥30≥30 dB HL over >3 consecutive frequencies developing over ≤3≤3 days.

  • Majority of cases are idiopathic but may include:

    • labyrinthine viral infection,
    • vascular insult,
    • intracochlear membrane rupture,
    • autoimmune inner ear disease.

  • Shorter history = better prognosis.

  • Bad prognosis:

    • age >60 years,
    • presence of vertigo,
    • more severe HL with a down-sloping audiogram.

  • Spontaneous recovery in 32-65% of cases.

  • Specific Management

    • Steroids
    • Hyperbaric Oxygen Therapy (HBOT)

Noise-Induced Hearing Loss (NIHL)

  • Sound levels <80 dB(A) will not cause damage.
  • Sounds ≥130≥130 dB(A) will definitely cause damage.
  • Temporary threshold shift (TTS) occurs initially.

Hearing Aids

  • Electronic, sound amplifying device.
    • Microphone: acoustic energy into electricity.
    • Amplifier: increases the electrical signal.
    • Receiver or ear phone (loud speaker): transduces the electrical signal back into acoustic energy.
  • Types:
    • Ear level HA: behind the ear HA or completely in the canal.
    • Bone conduction HA.

Cochlear Implantation

  • Converts mechanical sound energy into electrical signals that directly stimulate auditory nerve fibers.