ESSENTIALS OF DIAGNOSIS
Three main types of hearing loss: conductive, sensory, and neural.
Most commonly due to cerumen impaction, transient eustachian tube dysfunction associated with upper respiratory tract infection, or age-related hearing loss.
Classification & Epidemiology
Table 8–1 categorizes hearing loss as normal, mild, moderate, severe, and profound and outlines the vocal equivalent as well as the decibel range.
Table 8–1.Hearing loss classification. |Favorite Table|Download (.pdf) Table 8–1. Hearing loss classification.
|Classification ||Vocal Equivalent ||Decibel (dB) Range |
|Normal ||Soft whisper ||0–20 dB |
|Mild ||Soft spoken voice ||20–40 dB |
|Moderate ||Normal spoken voice ||40–60 dB |
|Severe ||Loud spoken voice ||60–80 dB |
|Profound ||Shout ||> 80 dB |
A. Conductive Hearing Loss
Conductive hearing loss results from dysfunction of the external or middle ear. There are four mechanisms, each resulting 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 effect (eg, otosclerosis), and (4) discontinuity (eg, ossicular disruption). Conductive losses in adults are most commonly due to cerumen impaction or transient eustachian tube dysfunction associated with 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 in some cases both.
Sensory and neural causes of hearing loss are difficult to differentiate due to testing methodology, thus often referred to as “sensorineural.” Sensory hearing loss results from deterioration of the cochlea, usually due to loss of hair cells from the organ of Corti. Sensorineural losses in adults are common. The most common form is a gradually progressive, predominantly high-frequency loss with advancing age (presbyacusis). Additional common 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.
et al. Current concepts in age-related hearing loss: epidemiology and mechanistic pathways. Hear Res. 2013 Sep;303:30–8.
Neural hearing loss occurs with lesions involving the eighth nerve, auditory nuclei, ascending tracts, or auditory cortex. It is the least common clinically recognized cause of hearing loss. Causes include acoustic neuroma, multiple sclerosis, and auditory neuropathy.
et al. Auditory neuropathy/dyssynchrony revisited. B-ENT. 2014;10(2):105–12.
et al. Age-related changes in the central auditory system. Cell Tissue Res. 2015 Jul;361(1):337–58. ...