Hearing Impairment (Deafness)

– Acquired or congenital diminished auditory capacity that may be classified as sensorineural, conductive, or central. Loss with no organic basis has been labeled psychogenic or functional. Hearing loss ranges from partial to complete.

Causes and Incidence

Causes of sensorineural impairment include trauma, noise, infection, aging, exposure to certain toxins, and drugs. Conductive loss results from disorders of the middle and external ear, such as otitis media, otosclerosis, or perforation of the eardrum. Central hearing loss is induced when the brain’s auditory pathways are damaged by such underlying disorders as cerebrovascular accident or a brain tumor. Congenital losses may result from fetal or neonatal anoxia; delivery trauma; fetal exposure to toxins, rubella, or syphilis; Rh incompatibilities; and bilirubin toxicity. Psychogenic loss has no traceable organic basis and is thus thought to be psychologic in origin.

Disease Process

In sensorineural impairment, damage to the cochlea or cranial nerve VIII results in interference with bone conduction of sound waves from the inner ear. Conductive loss occurs when injury to the middle or external ear results in interference with air conduction of sound waves to the inner ear. Some individuals have both conductive and sensorineural impairment. Central impairments interfere with auditory brainstem pathways. There is no organic pathologic condition in functional hearing loss.

Symptoms

The overriding manifestation is a reduced ability to distinguish sound. It is frequently progressive and may range from a mild loss to total deafness.

Potential Complications

Permanent, nontreatable deafness is the central complication.

Diagnostic Tests

Weber tuning fork
Lateralization of sound to deaf ear in conductive loss and to better ear in sensorineural loss

Rinne tuning fork
Bone conduction heard longer than or as long as air conduction in conductive loss; air conduction heard longer in sensorineural loss

Schwabach test
Examiner hears longer than examinee in sensorineural loss and vice versa for conductive loss

Audiometry
To distinguish types and identify degree of impairment

Treatments

Surgery
Stapedectomy for loss caused by otosclerosis; cochlear implants in some cases to treat profound deafness.

Drugs
None.

General
Hearing aids for conductive loss; instruction in sign language, speech, and lip reading for the profoundly deaf; use of specialized assistive devices (e.g., amplified or typed-message telephones, low-frequency or flashing doorbells, closed-caption TV decoders, flashing alarm clocks, alarm bed vibrators, flashing smoke detectors); counseling and support groups for adaptation.