Ototoxicity

What is Ototoxicity?

Ototoxicity is, quite simply, ear poisoning (oto = ear, toxicity = poisoning), which results from exposure to drugs or chemicals that damage the inner ear or the vestibulo-cochlear nerve (the nerve sending balance and hearing information from the inner ear to the brain). Because the inner ear is involved in both hearing and balance, ototoxicity can result in disturbances of either or both of these senses. The occurrence and degree of inner ear poisoning depends upon the drug involved as well as other factors such as heredity. Ototoxicity can be temporary or permanent (Vestibular Disorders Association, 2015).

What substances can cause ototoxicity?

Aspirin and quinine are well known to cause temporary ototoxicity resulting in tinnitus. They may also reduce hearing, particularly when given at high doses. Quinine products can also temporarily reduce balance ability (Boettcher and Salvi, 1991).
Loop diuretics are known to occasionally cause temporary ototoxicity. These drugs cause ringing in the ears or decreased hearing that reverses when the drug is stopped (Rybak, 1993).
Aminoglycoside antibiotics are well known for their potential to cause permanent ototoxicity if they enter the inner ear (Selimoglu, 2007).
Anti-neoplastics (anti-cancer drugs) work by killing cancer cells. Unfortunately some can also damage or kill cells elsewhere in the body, including the ears.

What damage occurs?

Two areas can be damaged or destroyed through ototoxicity: the hair cells within the inner ear, and the vestibulo-cochlear nerve that links the inner ear to the brain. When damage occurs, any degree and combination of hearing loss and balance disruption are possible depending upon the part(s) affected.

Hair cells are located in both the cochlea and the vestibular areas of the inner ear. They are composed of a cell body with a hair-like attachment. When these “hairs” are normally bent with sound vibrations or movement, they send electrical signals to the brain about hearing or balance function. In ototoxicity, these hairs can be damaged to the point that they no longer stand up, thus reducing the auditory and/or balance signals sent to the brain.

Ototoxicity symptoms include:

Mild tinnitus to total hearing loss

Mild imbalance to total incapacitation

Headache
Feeling of fullness in ear
Oscillopsia
Inability to tolerate head movement
A wide-based gait
Difficulty walking in the dark
Unsteadiness or the sensation of unsteadiness
Lightheadedness
Significant fatigue

(Roland and Rutka, 2004)

What is the treatment?

At present there are no treatments that can reverse the damage. Currently available treatments focus on reducing the effects of the damage and rehabilitating function. Specifically, individuals with hearing loss may be helped with hearing aids; those with profound bilateral (two-sided) hearing loss have been shown to benefit from cochlear implants.

When a loss of balance function has occurred, physiotherapy can help the brain become accustomed to the altered balance signals coming from the inner ear. Therapists can also assist an individual in developing other ways to maintain balance such as emphasizing the use of vision and proprioception, and structuring a program of general physical conditioning and exercises designed to strengthen and tone muscles.