Occupational Medicine
Rhoda Wynn
Andrew C. Goldman
Occupational and environmental medicine is a specialty that focuses on the prevention, diagnosis, and management of diseases related to the workplace and environment. Given the proximity of the head and neck to potentially injurious agents, disorders of the ear, nose, and throat are implicated in numerous occupational diseases. Because most occupational diseases cannot be differentiated from nonoccupational diseases, a detailed exposure history may provide the key information for determining causation. Inquiry as to the presence and use of protective equipment is routine. In some cases, reported work exposure should be confirmed with supporting data. Potentially useful sources include employer exposure records, health and regulatory agencies, unions and community groups, and the patient’s medical records. The interests of patients, employers, and governing bodies often are at stake when patients have work-related disorders; therefore, accurate accounting of the exposure may be pivotal.
NOISE
Exposure to noise represents the single most common exposure in the workplace. It has been estimated that 20 million persons in the United States (14% of the working population) are exposed to noise intensities sufficient to cause hearing loss. Furthermore, many people routinely and willingly expose themselves to excessive noise in recreational and social activities, engendering cumulative forces on developing a hearing loss.
Noise is defined as any sound, agreeable or disagreeable. Continuous sound with intensity greater than 90 dB can cause injury to the cochlear hair cells. The effects of noise have been studied extensively. Clinically relevant patterns of response to sound have led to government-ordained standards of allowable noise exposure.
A patient with hearing loss needs a directed examination and specific audiologic testing. At the initial and subsequent examinations it is important to document the ear examination findings, including response to multiple-frequency tuning fork testing, and the otoscopic findings. Audiologic testing quantifies the hearing loss with pure-tone audiometry, speech thresholds, and discrimination. Tympanic membrane impedance is tested, which helps in understanding abnormalities of the tympanic membrane and middle ear. Baseline audiometric findings must be compared with routine follow-up results to identify any changes. Transient threshold shifts (TTS) may be common after direct exposure to loud noise (impulse or continuous). A permanent threshold shift (PTS) may indicate irreversible loss in hearing related to prolonged exposure.
NOISE-INDUCED HEARING LOSS
Noise-induced hearing loss is accumulated damage from repeated prolonged exposure to damaging noise. U.S. Occupational Safety and Health Administration (OSHA) regulations define any exposure greater than 90 dB during an 8-hour workday as dangerous. To inspect work sites, OSHA uses equipment that measures noise exposure in terms of amplitude (loudness) and frequency (pitch). These records should be available to every employee, as should OSHA recommendations for safety precautions, which may include use of earplugs, earmuffs, or ear canal caps. Long-term noise exposure tends to cause sensorineural hearing loss to one or both ears depending on which ear is directly exposed to the greatest noise level. Prevention is preferable to treatment.
Quantification of hearing loss for compensation requires standard behavioral audiometry, consisting of air-conduction, boneconduction, and speech recognition thresholds. A period of 48 hours free of noise prior to compensation is usually adequate to ensure that there is no TTS. However, compensation assessment in cases of a major blast accident or head injury should not take place until a minimum of 3 months after the accident.
BLAST TRAUMA
A sudden blast can cause an immediate change in hearing thresholds. Hearing loss can be conductive or sensorineural but is typically a mixed pattern (conductive and sensorineural). Injury may occur to the tympanic membrane, ossicles, oval and round windows, and labyrinthine membranes. Symptoms include pain, bloody otorrhea, vertigo, and tinnitus. Recovery is variable and depends on the severity of the injury. Nonurgent repair of conductive mechanisms (perforated tympanic membrane and ossicular dislocation) can be considered if healing is inadequate.
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