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DISEASES OF THE EAR

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HEARING LOSS

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ESSENTIALS OF DIAGNOSIS

  • Two main types of hearing loss: conductive and sensorineural.

  • Most commonly due to cerumen impaction, transient eustachian tube dysfunction from upper respiratory tract infection, or age-related hearing loss.

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Classification & Epidemiology
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Table 8–1 categorizes hearing loss as normal, mild, moderate, severe, and profound and outlines the vocal equivalent as well as the decibel range.

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Table 8–1.Hearing loss classification.
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A. Conductive Hearing Loss
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Conductive hearing loss results from external or middle ear dysfunction. Four mechanisms each result in impairment of the passage of sound vibrations to the inner ear: (1) obstruction (eg, cerumen impaction), (2) mass loading (eg, middle ear effusion), (3) stiffness (eg, otosclerosis), and (4) discontinuity (eg, ossicular disruption). Conductive losses in adults are most commonly due to cerumen impaction or transient eustachian tube dysfunction from upper respiratory tract infection. Persistent conductive losses usually result from chronic ear infection, trauma, or otosclerosis. Conductive hearing loss is often correctable with medical or surgical therapy, or both.

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B. Sensorineural Hearing Loss
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Sensory and neural causes of hearing loss are difficult to differentiate due to testing methodology, thus often referred to as “sensorineural.” Sensorineural hearing losses in adults are common.

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Sensory hearing loss results from deterioration of the cochlea, usually due to loss of hair cells from the organ of Corti. The most common form is a gradually progressive, predominantly high-frequency loss with advancing age (presbyacusis); other causes include excessive noise exposure, head trauma, and systemic diseases. An individual's genetic make-up influences all of these causes of hearing loss. Sensory hearing loss is usually not correctable with medical or surgical therapy but often may be prevented or stabilized. An exception is a sudden sensory hearing loss, which may respond to corticosteroids if delivered within several weeks of onset.

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Neural hearing loss lesions involve the eighth cranial nerve, auditory nuclei, ascending tracts, or auditory cortex. Neural hearing loss is much less commonly recognized. Causes include acoustic neuroma, multiple sclerosis, and auditory neuropathy.

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