Vertigo (cont.)
Medication damage to inner ear (ototoxicity)
Ototoxicity refers to the damage caused to the inner ear (labyrinth) from the
use of various medications. These medications can damage the inner ear's
balance (vestibular) system or hearing (auditory) system or both. It turns out
that patients are often bedridden and very ill when given these medications.
Therefore, it is often only after they have recovered from their illness that
they begin to realize the devastating effects of this damage to the inner ear.
The aminoglycosides are common antibiotics that are known to damage the inner
ear. Streptomycin and gentamicin more selectively damage the vestibular system,
whereas kanamycin, tobramycin, and amikacin (Amikin) more selectively damage the
auditory system. For example, gentamicin toxicity can cause symptoms of
imbalance and even oscillopsia. Oscillopsia results from a loss of balance
function in both inner ears. As a result, these patients are unable to focus on
an object when they move their head or are walking.
Salicylates (e.g., aspirin) can cause hearing loss, ringing in the ears
(tinnitus), dizziness, loss of balance, and sometimes vertigo. Unlike other
medications that damage the inner ear, however, salicylates cause symptoms of
ototoxicity that go away (are reversible) within 24 hours after stopping the
drug.
Cisplatinum is a common chemotherapeutic drug used in the treatment of
cancer. Unfortunately, it has both auditory and vestibular ototoxicity. The
frequency of damage to the inner ear has been reported to be as high as 50% of
patients. Its damaging effects can be diminished, however, by a slow
administration of the drug and dividing up the dose of the drug over a prolonged
time.
Once ototoxicity occurs, the damage is usually irreversible. Physical therapy
(vestibular rehabilitation exercises) is often helpful. But, many elderly people
lack the ability to fully compensate for the vestibular loss. The key to
management of ototoxicity is both patient and physician awareness and prevention
of the potential side effects of these drugs. If a patient notices a loss of
hearing or a sense of imbalance, these symptoms should be reported to the
physician immediately. And, if practical, the drug should be discontinued.
Acoustic neuromas and other cerebellopontine angle (CPA) tumors
An acoustic neuroma is a benign tumor of the insulating cells (Schwann cells)
of the eighth cranial (vestibulocochlear) nerve. The tumor develops on the
vestibular portion of the eighth cranial nerve as it exits the brainstem at the
cerebellopontine angle (CPA). So, the main initial symptoms of an acoustic
neuroma are usually related to impaired balance.
An acoustic neuroma is also known as a vestibular schwannoma or a CPA tumor.
(Actually, any tumor arising in this location of the brainstem is also known as
a CPA tumor.) The vestibular nerve then travels through the internal auditory
canal of the temporal bone to the inner ear. In addition to two vestibular
branches, the internal auditory canal also houses the single cochlear (hearing)
nerve (the other part of the eighth cranial nerve) and the seventh cranial
(facial) nerve.
Acoustic neuromas are found sporadically in the population, or specifically
in association with a condition called neurofibromatosis Type 2.
Neurofibromatosis is a rare inherited disorder associated with bilateral
acoustic neuroma tumors and other neural tumors. In either case, both types of
acoustic neuromas are associated with a particular genetic (inherited)
abnormality (a defect in the NF-2 gene located on chromosome 22). Acoustic
neuromas represent 6% of all brain tumors, but 80% of all CPA tumors. Acoustic
neuromas occur with an annual incidence of 1 per 100,000 people.
Acoustic neuromas usually grow out from the internal auditory canal spilling
into the cerebellopontine angle. As the tumor grows, it compresses and damages
the cochlear (hearing) division of the eighth cranial nerve and its blood
supply. This nerve damage then results in impaired hearing. For the most part,
acoustic neuromas are slow growing. Thus, 90% of these tumors grow at a rate no
faster than one mm per year.
Next: Benign paroxysmal positional vertigo (cupulolithiasis) »
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