Curriculum · ENT, Ophthalmology, and Dermatology
Noise-induced hearing loss
What it is
Noise-induced sensorineural hearing loss is the loss that follows exposure to loud sound, and it comes in two forms. In the temporary form, exposure to loud sound gives decreased sensitivity, or an increased threshold for sound, with or without aural fullness and tinnitus; once the noise is removed, hearing returns to normal. In the permanent form hearing does not return to its previous state.
Causes and risk
The exposure that does it is 85-90 dB over months or years, or a single sound above 135 dB. Noise exposure is one of the inner ear causes of sensorineural hearing loss, so a patient who complains of hearing loss is asked about noise at the work place.
How it presents
The hearing loss is bilateral and sensorineural, and the patient has difficulty with speech discrimination.
How it is diagnosed
Audiometry carries the diagnosis. The audiogram dips at 4000 Hz, a notch known as the boilermaker's notch and also as the aviators notch or acoustic dip, and hearing improves again at the very high frequencies. Both ears show the notch, and air and bone conduction fall together, so the loss is sensorineural. The speech reception threshold (SRT) is the other test named.