Classification & Epidemiology

Table 8-1. Hearing Loss Classification categorizes hearing loss as normal, mild, moderate, severe, or profound and outlines the vocal equivalent as well as the decibel range.

Evaluation of Hearing (Audiology)

In a quiet room, the hearing level may be estimated by having the patient repeat aloud words presented in a soft whisper, a normal spoken voice, or a shout. Normal spoken voice is about 60 decibels. A 512-Hz tuning fork is useful in differentiating conductive from sensorineural hearing loss. In the Weber test, the tuning fork is placed directly on the forehead or front teeth. In conductive losses, the sound is heard as louder in the ear with poorer hearing; however, in sensorineural losses, the sound radiates to the ear that hears better than the other ear. In the Rinne test, the tuning fork is placed alternately on the mastoid bone (bone conduction) and in front of the ear canal (air conduction). In conductive losses greater than 25 dB, bone conduction sounds louder than air conduction.

Formal audiometric studies are performed in a soundproofed room. Pure-tone thresholds in decibels (dB) are obtained over the range of 250-8000 Hz. Conductive losses create a “gap” between the air and bone thresholds, whereas in sensorineural losses, both air and bone thresholds are equally diminished. Speech discrimination measures the clarity of hearing, reported as percentage correct (90-100% is normal). Auditory brainstem-evoked response screening method is most commonly used in newborn screening and may determine the approximate location of the lesion (eg, cochlea or brain). MRI scanning is the most sensitive and specific test to determine the possible location of a defect resulting in sensorineural hearing loss.

Every patient who reports hearing loss should be referred for audiologic evaluation unless the cause is easily remediable (eg, cerumen impaction, otitis media). Immediate audiometric referral is indicated for patients with idiopathic sudden sensorineural hearing loss because it requires treatment (corticosteroids) within a limited several-week time period. Routine audiologic screening is recommended for adults who report hearing loss. There are evolving data that suggest an association between hearing loss, cognitive decline, and depression, pointing to a potential reversible cause with hearing rehabilitation.

Hearing Amplification

Patients with hearing loss not correctable by medical therapy may benefit from hearing amplification. Contemporary hearing aids are comparatively free of distortion and have been miniaturized to the point where they often may be contained entirely within the ear canal or lie inconspicuously behind the ear. To optimize the benefit, a hearing aid must be carefully selected to conform to the nature of the hearing loss. Digitally programmable hearing aids are widely available and allow optimization of speech intelligibility and improved performance in difficult listening circumstances. Aside from hearing aids, many assistive devices are available to improve comprehension in individual and group settings, to help with hearing television and radio programs, and for telephone communication. In 2022, the US FDA changed exam and prescription mandates for hearing aids, which may both increase access and decrease cost of hearing rehabilitation devices.

For patients with conductive loss or unilateral profound sensorineural loss, bone-conducting hearing aids directly stimulate the ipsilateral cochlea (for conductive losses) or contralateral ear (profound unilateral sensorineural loss). In most adults with severe to profound sensory hearing loss, the cochlear implant—an electronic device that is surgically implanted into the cochlea to stimulate the auditory nerve—offers socially beneficial auditory rehabilitation. New trends in cochlear implantation include its use for only partially deaf patients, preserving residual hearing and allowing both acoustic and electrical hearing in the same ear, and for patients with single-sided deafness. An increasing number of insurance companies are paying for these expanded indications.