Introduction

Auditory disabilities are the result of hearing loss. The seriousness of a patient's disability depends on when hearing loss sets in, how severe and permanent it is, and whether it affects one or both ears.
Hearing loss may originate in the outer, middle, or inner ear or in the central auditory pathway.
Depending on where the dysfunction occurs, hearing loss may be classified as either conductive or sensorineural, or mixed (a combination of the two).

1  -  Hearing loss


Conductive hearing loss results from dysfunction in the :

  • outer ear (pinna and external auditory canal);
  • middle ear (tympanic membrane, ossicles, mastoid, Eustachian tube).

Such problems may be due to malformations, and thus congenital in origin. More often they are acquired following an inflammation or infection (chronic otitis). Hearing loss can also be caused by degenerative conditions leading to otosclerotic stapes fixation, such as in otospongiosis in adults. Auditory impairments of this kind occur when the middle ear fails to perform its impedance-matching function properly. Loss of hearing is thus at most 60 dB (50-60 dB in major malformation syndromes).

Sensorineural hearing loss is most often caused by damage to the inner ear, the acoustic nerve, or very rarely the central auditory pathways.

Inner ear involvement is predominant in congenital bilateral hearing loss, often of genetic or idiopathic origin. The severity of such hearing loss varies on a case-by-case basis from 20 to over 120 dB. Bilateral profound congenital sensorineural hearing loss is a major sensory disability and can lead to severe communication disorders.

1 . 1  -  Categories of hearing loss severity


Determined as follows (based on the better ear) :

  • mild hearing loss: 20-39 dB lost;
  • moderate hearing loss: 40-69 dB lost;
  • severe hearing loss: 70-89 dB lost;
  • profound hearing loss: more than 90 dB lost.

The 40-dB level is the first major disability level, because speech can only be heard if the speaker raises his or her voice. At 90 dB, speech can no longer be heard.

1 . 2  -  Functional assessment of hearing loss


Functional assessment is based, in children and adults, on behavioral audiometry.

1 . 2 . 1  -  In children


Behavioral audiometry techniques can generally be used starting at the age of 3 months (once psychomotor development is far enough along for a baby to hold its head up). Tests are performed using headphones and skull vibrators to determine response thresholds elicited by air and bone conduction across all frequencies. Conditioning techniques and audio equipment are selected in accordance with the child's age. This data is crucial for establishing indications and recommending hearing prosthetic aids, which need to be performed as effective as possible beginning as early as 6 months of age, currently the optimal time for diagnosing congenital hearing loss.

Other techniques, such as oto-acoustic emissions or automated testing of short-latency auditory evoked potentials, can be used in maternity wards to screen for neonatal hearing loss. Brainstem auditory evoked potentials are also useful for obtaining initial data on high-frequency hearing thresholds. Impedance measurement is used to facilitate diagnosis of middle-ear disorders.

Screening for hearing loss is recommended not only in newborns but also systematically at the ages of 9 months, 2 years, and 4 years. Such screening involves risk factor analysis, parent interviews, vocal stimulation tests, and hearing tests with sound-emitting toys.

If any hearing loss is suspected, age-appropriate behavioral audiometry (as described above) should be carried out by a specialized team.

1 . 2 . 2  -  In adults


Audiometric assessments should always include pure-tone and speech audiometry, as well as impedance measurements. Auditory brainstem evoked potential testing should be reserved for the topographic diagnosis of sensorineural hearing loss.

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