HEARING LOSS
 
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HEARING LOSS

 

DEFINITION:

Loss of hearing ranging from mild (<60 dB), to severe (60-80 dB), to profound (>85 dB).

EPIDEMIOLOGY:

  • prevalence: 1/1000 children (severe to profound hearing loss)
  • incidence: 1/1000 babies born deaf
    • 1/50 infants from an NICU have significant hearing loss
    • 1/10 children develop hearing problems at some time
  • age of onset:
    • any
  • risk factors:
    • see differential diagnosis

DIFFERENTIAL DIAGNOSIS:

1. Trauma

  • Head
  • Acoustic (Loud Noise)

2. Toxic

1. Aminoglycosides

  • gentamicin
  • kanamycin
  • neomycin
  • vancomycin

2. Others

  • ASA
  • chloroquin
  • cisplatin
  • ethacrynic acid
  • furosemide
  • quinine

3. Infectious

1. Congenital Infections

  • toxoplasmosis
  • other (syphilis)
  • rubella
  • CMV
  • HSV

2. Recurrent Otitis Media

  • +/- middle ear effusions

3. Bacterial Meningitis

  • Strep. pneumonia
  • H. flu

4. Others

  • mumps
  • mastoiditis

4. Genetic

1. Sporadic

2. Autosomal Recessive

  • Lange-Jervell-Nielsen Syndrome
  • Pendred Syndrome
  • Usher Syndrome

3. Autosomal Dominant

  • Alport Syndrome
  • Treacher Collins Syndrome
  • Waardenburg Syndrome

4. X-Linked Recessive

  • Alport Syndrome
  • Hunter Syndrome

5. Mitochondrial Disorders

  • Kearns-Sayre Syndrome

6. Malformations

  • 1. Craniofacial Anomalies
    • cleft lip +/- palate
    • Crouzon Syndrome
    • Goldenhar Syndrome
    • Mondini Malformation
    • Pierre Robbin Syndrome
    • Treacher Collins Syndrome
    • Trisomy 21

    • 5. Miscellaneous

    • Prematurity
    • Hyperbilirubinemia

    PATHOPHYSIOLOGY:

    • pathology may take place at many levels:

    1. Conductive Hearing Loss

    • defect in the external or middle ear
    • deficiency in the transduction of energy in the form of sound waves in air to hydraulic waves in the inner ear - results in low frequency hearing loss
    • middle ear effusions
      • can produce a hearing loss up to 30 dB (whisper)
    • malformation of the external and middle ears
      • can produce a hearing loss up to 60 dB (talking)
    • thus a severe conductive hearing loss will not produce total deafness but can interfere with language development

    2. Sensorineuronal Hearing Loss ("Nerve Deafness")

    • defect in the inner ear
    • inadequate transduction of hydraulic waves to neural activity
    • site of pathology is usually the organ of Corti
    • seen in disorders associated with bilateral acoustic neurinomas (i.e., Neurofibromatosis - Type 2)
    • genetic disorders may cause conductive and/or sensori-neuronal hearing loss

    3. Cortical Hearing Loss

    • inadequate transmission of the neural impulses from the inner ear to the temporal lobes
    • associated with diseases of the White Matter
    • results in several different types of hearing loss:

    1. Cortical Deafness

    • affects perception of all sounds

    2. Cortical Agnosia

    • affects perception of environmental sounds

    3. Verbal Auditory Agnosia

    • affects perception of language and results in severe receptive dysphagia

    CLINICAL FEATURES:

    1. Unresponsive to Sounds

    • in 70% of cases, it is the grandmother who first notices a hearing disorder
    • different levels of sound intensity to determine threshold
      • 30 dB - whisper
      • 60 dB - talking
      • 90 dB - shout
    • may lack the startle reflex in response to a loud sound

    2. Speech and Language Delays

    • congentially deaf patients may coo normally and may babble (but babbling is not varied)
    • patient may be congenitally deaf or loose hearing during infancy and childhood so look for delays and plateaus in speech and language development

    3. Vestibular Impairment

    1. Acute

    • ataxia
    • forcefully maintained head tilt
    • nausea/vomiting

    2. Chronic

    • gross motor developmental delay
      • delays in holding head up, sitting, and walking
      • hypotonia
    • others
      • stumble in dark
      • difficulty on one foot
      • unable to walk on balance beam

    4. Specific Entities

    1. Lange-Jervell-Nielson Syndrome

    • a rare syndrome characterized by a deaf child with heart block (recurrent fainting spells +/- sudden death)

    2. Usher Syndrome

    • a rare syndrome characterized by a deaf child with retinitis pigmentosa (blindness in young to middle adulthood)

    3. Recurrent Otitis Media

    • commonest cause of hearing loss in childhood
    • high risk groups for otitis media with effusion:
      • cleft palate, craniofacial malformations, premature or ventilated for >7 days, Trisomy 21, unilateral atresia (effusion in the normal ear)

    4. Congenital Rubella Syndrome

    • most frequent TORCH infection causing hearing loss
    • hearing loss may be asymmetrical and range from mild to profound
    • retinopathy and hearing loss are the most frequent complications

    5. Congential Syphilis

    • hearing loss develops in childhood, is progressive but treatable

    6. Bacterial Meningitis

    • 5-20% incidence of severe sensorineuronal hearing loss
    • always associated with vestibular impairment
    • may be prevented by high dose steroids given at onset

    7. Mumps

    • 6% incidence of unilateral hearing loss

    8. Kernicterus

    • usually high tone hearing loss but may be severe or profound across all frequencies
    • due to damage to the nuclei of the central auditory pathway

    9. Acoustic Trauma

    • brief exposure to a loud noise may result in a temporary raising of the threshold for hearing at the frequency to which the ear was exposed
    • recurrent exposure may result in a permanent notch in the audiogram and represent a permanent hearing loss

    10. Midfacial Malformations

    • usually have eustachian tube malfunction +/- chronic middle ear effusions

    INVESTIGATIONS:

    1. Behavioural Observational Audiometry (BOA)

    • reliable in patients older than 6-8 months of age
    • a subjective test indicating whether or not the patient has received, processed, and responded to the signal
    • sounds of specific frequency are presented by one audiologist through speakers and the second audiologist observes for behavioural changes in the child
    • test limitations:
      • subjective
      • cannot test each ear separately
    • in visual reinforcement audiology, a brightly lighted toy moves when the child turns their head towards the side where the nose has occurred

    2. Tympanometry (Impedance Audiometry)

    • reliable in patients older than 6-7 months of age
    • an objective test for conductive hearing loss
      • measures the mechanical properties of the tympanic membrane and middle ear function
      • most sensitive way to discover middle ear effusions or malformations and to test for tympanostomy tube patency - does not test the childs ability to process and respond to sound and thus is not a hearing test
      • may be used to confirm the results of behavioural tests in young and handicapped children
      • sounds are presented to the ear through a probe and the amount of sound reflected back from the eardrum is measured
        • transmission in ear is optimal when the pressures on both sides of the eardrum are equal (peak conductance when the relative pressure in the external canal and middle ear is equal or zero)
        • compliance is the objective measure of sound transmission through the middle ear
        • by determining the air pressure in the external canal which gives rise to maximum compliance, the pressure and mobility of the middle ear can be determined
      • types of tympanograms:

    1. Flattened

    • indicates increased impedance (stiffness) of the tympanic membrane ™
    • TM damage (retracted, fibrosed, sclerosed), middle ear effusion, ossicular fixation, anky-losis of ossicles, eustachian tube occlusion

    2. Peaked

    • indicates decreased impedance of the TM
    • flaccid or thinned TM, dislocated ossicles

    3. Shifted Peak

    • indicates shift in middle ear pressure
    • shift to the left indicates recovery from acute otitis media or eustachian tube dysfunction

    4. Unable to Test

    • indicates TM perforation or patent tympanostomy tubes

    3. Brainstem Auditory-Evoked Response (BAER)

    • reliable in all patients from prematures to adults
    • an objective test for sensorineuronal and cortical hearing loss
      • measures the function of the cochlea and acoustic nerve and the transmission time along the brainstem auditory nuclei - does not test the childs ability to process and respond to sound and thus is not a hearing test
      • may be used to confirm the results of behavioural tests in young and handicapped children
      • may identify areas of demyelination (prolonged wave forms)

    4. Other Tests

    1. Vestibular

    • tests function of the labyrinth
    • indicated in those with developmental delay, meningitis, Usher Syndrome, acoustic nerve tumors, labyrintine fistulas

    2. Language Development

    • Early Language Milestone (ELM) test
    • Denver Developmental Screening Test

    MANAGEMENT:

    1. Hearing Test Referral Criteria

    • exposure to risk factors (see Differential Diagnosis)
    • other neonatal factors:
      • small for gestational age or birth weight < 1500 g
      • birth asphyxia (APGAR <3) or prolonged severe hypoxia
      • hypoxic ischemic encephalopathy (HIE)
      • ventilated > 7 days
      • Apnea of Prematurity
      • Respiratory Distress Syndrome
      • Bronchopulmonary Dysplasia
      • hyperbilirubinemia requiring exchange transfusion

    2. Supportive

    • multidisciplinary approach
      • Paediatrics, Audiology, ENT, Ophthalmology
      • Genetic Counselling - if history of congenital hearing loss
      • Psychology - to help family deal with long term disability

    3. Hearing Aids

    • can be fitted into children as young as 3 months of age
    • can amplify sound by 70 dB but this will increase the background noise as well
    • can be used in those with conductive hearing loss by bypassing the defective area
    • have a high intensity cutoff to prevent acoustic trauma
    • cochlea must be intact for hearing aids to work

    4. Education

    • special vs integrated
    • lip reading vs sign language

    5. Surgery

    • to correct any defects
    • cochlear implants are still experimental

     

     

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