Evaluation of individuals with known or suspected noise damage to hearing

Abstract

The diagnosis of hearing impairment due to noise damage is based on the assessment of the type and level of exposure to noise, the patient's medical history, and a clinical and audiometric evaluation. The risk for developing hearing loss increases substantially when the equivalent sound pressure levels of noise exceed 80dB(A). Very high exposures (above 100dB(A)), usually to impulse noise (e.g. fireworks), can result in acoustic trauma. In this case, sensorineural hearing loss develops immediately after exposure and is frequently accompanied by tinnitus. It can be unilateral or asymmetrical, and temporary (temporary threshold shift – TTS) or permanent (permanent threshold shift – PTS). Noise-induced hearing loss (NIHL) that develops after prolonged occupational exposures to relatively moderate levels of noise (85–100dB(A)) is a bilateral, symmetrical, or almost symmetrical, and permanent sensorineural hearing loss progressing slowly over the years of employment. The most dynamic rise in PTS can be seen during the first years of exposure to noise. Audiometric characteristics of NIHL include: hearing threshold shift at high frequencies, with a typical notch at 4–6 kHz; presence of recruitment; amplitude reduction or loss in otoacoustic emission, mostly at frequencies corresponding to hearing loss; and impairment of speech intelligibility. The tinnitus associated with NIHL may be more variable in both prevalence and severity than that associated with acoustic trauma. Nevertheless, it requires thorough investigation. In differential diagnosis, age-related hearing loss, aminoglycoside ototoxicity as well as retrocochlear pathology should be considered. To date, NIHL is an irreversible disease, thus an effective protection against noise is the only way to preserve hearing.

• acoustic trauma
• noise-induced hearing loss
• aminoglycoside ototoxicity
• permanent threshold shift
• diagnostics