C h a p t e r 3 8
Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function
981
tinnitus. Intermittent periods of mild, high-pitched tinnitus
lasting for several minutes are common in normal-hearing
persons. Impacted cerumen is a benign cause of tinnitus,
which resolves after the earwax is removed. Medications
such as aspirin and stimulants such as nicotine and caffeine
can cause transient tinnitus. Conditions associated with
more persistent tinnitus include noise-induced hearing
loss, presbycusis (sensorineural hearing loss that occurs
with aging), hypertension, atherosclerosis, head injury,
and cochlear or labyrinthine infection or inflammation.
The physiologic mechanism underlying subjective tinnitus
is largely unknown. It seems likely that there are several
mechanisms, including abnormal firing of auditory
receptors, dysfunction of cochlear neurotransmitter
function or ionic balance, and alterations in central
processing of the signal.
Treatment measures for tinnitus are designed to
reduce the symptoms, rather than effect a cure.
58,59
They include elimination of drugs or other substances,
such as caffeine, some cheeses, red wine, and foods
containing monosodium glutamate, that are suspected
of causing tinnitus. Tinnitus retraining therapy, which
includes directive counseling and extended use of low-
noise generators to facilitate auditory adaptation to the
tinnitus, has met with considerable success.
Central Auditory Pathway Disorders
The auditory pathways in the brain involve communi-
cation between the two sides of the brain at many lev-
els. As a result, strokes, tumors, abscesses, and other
focal abnormalities seldom produce more than a mild
reduction in auditory acuity on the side opposite the
lesion. For intelligibility of auditory language, lateral
dominance becomes important. On the dominant side,
usually the left side, the more medial and dorsal portion
of the auditory association cortex is of crucial impor-
tance. This area is called the
Wernicke area,
and dam-
age to it is associated with auditory receptive aphasia.
Persons with damage to this area of the brain can speak
intelligibly and read normally but are unable to under-
stand the meaning of major aspects of audible speech.
Irritative foci that affect the auditory radiation
or the primary auditory cortex can produce roaring
or clicking sounds, which appear to come from the
auditory environment of the opposite side (i.e., auditory
hallucinations). Focal seizures that originate in or near
the auditory cortex often are immediately preceded by
the perception of ringing or other sounds preceded by a
prodrome (i.e., aura). Damage to the auditory association
cortex, especially if bilateral, results in deficiencies of
sound recognition and memory. If the damage is in
the dominant hemisphere, speech recognition can be
affected (i.e., sensory or receptive aphasia).
Hearing Loss
Nearly 36 million Americans have some degree of
hearing loss.
61
It affects persons of all age groups. Two
to 3 out of every 1000 children in the United States are
born deaf or hard of hearing.
61
Approximately 30%
of adults between the ages of 65 and 74 years and
approximately 47% of those age 75 and older have
hearing loss.
61
The level of hearing is measured in decibels (dB), where
0 dB is the threshold for perception of sound at a given
frequency in persons with normal hearing. A 10-fold
increase in sound pressure level from 0 dB is measured as 20
dB. Hearing loss is classified as mild (26 to 40 dB), moderate
(41 to 55 dB), severe (71 to 90 dB), or profound (91 dB or
greater).
61–63
“Hard of hearing” is defined as hearing loss
between 20 and 25 dB in adults and greater than 15 dB
in children. Profound deafness is defined as hearing loss
greater than 90 dB in adults
62
or 70 dB in children.
64
There are many causes of hearing loss or deafness.
Most fit into the categories of conductive, sensorineural,
or mixed deficiencies that involve a combination of
conductive and sensorineural function deficiencies of
the same ear.
63
Chart 38-1 summarizes common causes
of hearing loss. Hearing loss may be genetic or acquired,
sudden or progressive, unilateral or bilateral, partial or
complete, reversible or irreversible.
CHART 38-1
Common Causes of Conductive
and Sensorineural Hearing Loss
Conductive Hearing Loss
■■
External ear conditions
■■
Impacted earwax or foreign body
■■
Otitis externa
■■
Middle ear conditions
■■
Trauma
■■
Otitis media (acute and with effusion)
■■
Otosclerosis
■■
Tumors
Sensorineural Hearing Loss
■■
Trauma
■■
Head injury
■■
Noise
■■
Central nervous system infections (e.g., meningitis)
■■
Degenerative conditions
■■
Presbycusis
■■
Vascular
■■
Atherosclerosis
■■
Sudden deafness
■■
Ototoxic drugs (e.g., aminoglycosides, salicylates,
loop diuretics)
■■
Tumors
■■
Vestibular schwannoma (acoustic neuroma)
■■
Meningioma
■■
Metastatic tumors
■■
Idiopathic
■■
Ménière disease
Mixed Conductive and Sensorineural
Hearing Loss
■■
Middle ear conditions
■■
Barotrauma
■■
Cholesteatoma
■■
Otosclerosis
■■
Temporal bone fractures
