8-01: Hearing Loss

ESSENTIALS OF DIAGNOSIS

CLASSIFICATION & EPIDEMIOLOGY

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

A. Conductive Hearing Loss

Conductive hearing loss results from a mechanical disruption of the external auditory canal or middle ear. Several mechanisms may result in impairment of the passage of sound vibrations to the inner ear, such as obstruction (eg, cerumen impaction), mass loading (eg, middle ear effusion), stiffness (eg, otosclerosis), and discontinuity (eg, ossicular disruption). Conductive losses in adults are most commonly due to cerumen impaction or transient eustachian tube dysfunction from upper respiratory tract infection. Persistent conductive losses usually result from chronic ear infection, trauma, or otosclerosis. Perforations of the tympanic membrane may also result in a conductive hearing loss. Conductive hearing loss is often correctable with medical (eg, use of a hearing aid) or surgical (eg, repair of tympanic membrane and ossicular chain) therapy, or both. CT of the temporal bone may be used as an adjunct to physical examination to determine the potential cause of conductive hearing loss.

B. Sensorineural Hearing Loss

Sensorineural hearing losses are common in adults and generally result from deficits of the inner ear or central (brain) auditory pathway. Sensory hearing loss results from deterioration of the cochlea, usually due to loss of sensory hair cells within the organ of Corti. The most common form of sensorineural hearing loss is age-related hearing loss that manifests as a gradually progressive, predominantly high-frequency hearing loss. Other causes of sensorineural hearing loss include excessive noise exposure; head trauma; ototoxic medications, such as cisplatin-based chemotherapy; and systemic diseases. Sensorineural hearing loss may be gradual or sudden.

Sudden sensorineural hearing loss, often called idiopathic sudden sensorineural hearing loss, is considered an otologic emergency and may be treatable with oral or intratympanic corticosteroids if delivered within several weeks of onset. Long-term severe to profound sensorineural hearing loss due to deficits at the level of the inner ear may be correctable with surgery, such as cochlear implantation. Sensorineural hearing loss may also be due to deficits at the level of the central auditory pathway, including lesions involve the eighth cranial nerve, auditory nuclei, ascending tracts, or auditory cortex. Examples of central causes of hearing loss include acoustic neuroma, multiple sclerosis, ...