Ototoxicity- Causes, Symptoms, Diagnosis, and Management

Introduction:

Different medications and chemicals are taken by the person, either self, prescribed, or over-the-counter drugs to treat various clinical conditions. Many drugs and chemicals can lead to poisoning of the ear and cause hearing dysfunction. Drug-induced hearing loss has been reported frequently nowadays. The problem of drug-induced hearing loss either gets cured by discontinuing the medications, or it may even cause permanent damage to the ears, which is irreversible.

The vestibulocochlear nerve helps to maintain the sensory transmission between the inner ear and the brain. Ototoxic drugs tend to damage the vestibulocochlear nerve resulting in loss of hearing and functional balance.

What Are the Drugs or Chemicals Causing Toxicity to Ears?

Further, many scientific studies are required to prove if the drug is ototoxic or not. Although many substances are reported to have a toxic effect on ears, such as:

• Aminoglycosides drugs like Amikacin and Gentamicin.

• Chemotherapeutic agents (cancer drugs) like Cisplatin and Carboplatin.

• Antimalarial drugs like Chloroquine.

• Diuretics like Furosemide and Torsemide..

• Macrolides like Erythromycin and Clarithromycin.

• Non steroidal anti-inflammatory drugs (NSAIDs) like Aspirin.

• Environmental chemicals like mercury, carbon monoxide, lead, styrene, xylene, hexane, and manganese.

Do We Need to Stop These Medications if Prescribed by the Doctor?

The answer is no. It is not advisable to stop using medications prescribed by the physician for the concerned disease treatment. The ototoxicity caused by these drugs may be temporary or permanent. However, if it is taken under a physician's guidance, the drug should not be stopped abruptly without the physician's consent. Any abnormal changes noted after taking the medications should be reported to the physician immediately, and a regular check-up with the doctor is recommended to prevent drug-induced adverse events affecting the ear.

How Do Drugs Cause Damage to the Ear?

Some of the drugs or chemicals are found to damage the cell membrane lining the hair cells of the inner ear and the vestibulocochlear nerve (eighth cranial nerve), resulting in a sensory disturbance between the inner ear and the brain and thus causing loss of hearing and balance mechanism.

What Are the Signs and Symptoms of Ototoxicity?

• Tinnitus (ringing sensation in the ear) - Initial sign of ototoxicity.

• Feeling of ear fullness.

• Reduced ability to hear or complete hearing loss.

• Imbalance while walking.

• Dizziness.

• Nausea and vomiting.

• Spinning sensation in the head (vertigo).

• Nystagmus (involuntary eye movement)

How to Diagnose Ototoxicity?

Ototoxicity can be diagnosed mostly based on signs and symptoms reported by the patients. However, there has been no particular test till now to exactly diagnose the drug-induced toxicity, but a few tests that can be run to check for hearing efficiency and balance functions are:

• Vestibular Autorotation Test (VAT): It is a computerized test for assessing the coordination of movements of the head and eyes (vestibulo-ocular reflex movements).

• Auditory Brainstem Response (ABR): This test is used to detect any defect in the hearing pathway by evaluating the impulse transmission of the nervous system in response to the sound produced in the ear with the help of an earphone and electrodes which are placed behind the ears and on the scalp.

• An Otoacoustic Emission (OAE) Test: This test is used to evaluate the “echo” produced by the cochlear cells present in the hairs of the inner ear in response to the sound produced by the tiny speaker or probe in the ear.

• Computerized Posturography Test (CPT): It is done to determine the person's ability to balance themselves on a stable or unstable platform. It is used to detect functional balance.

• Audiometry (Hearing Test): This test is done to evaluate hearing efficiency by monitoring the sound produced in the ear by the earphones at different frequencies.

What Is the Cure for Ototoxicity?

Currently, there is no permanent cure for treating the functional damage caused by ototoxicity. However, few treatment modalities emphasize minimizing the drug-induced ototoxicity:

• Practice Balance Exercises: In case loss of balance has occurred, try to practice some balance exercises like walking, climbing steps, and head-turning exercises with the help of a therapist or trainer in vestibular rehabilitation centers.

• Cochlear Implants: In cases of hearing loss due to ototoxicity, a small device is placed in the ears which senses the sound and helps in hearing.

• Hearing Aids: It is a small device that helps to hear the sound loud and clear.

How Can We Prevent Ototoxicity?

• Replacement With Alternate Drugs: Any signs and symptoms noted to the prescribed drugs should be reported to the physician urgently so that they can replace the medications with an alternate drug regimen.

• Ototoxic Monitoring Protocols: It can be implemented by genetic screening of individuals who are more prone to ototoxic drugs. In such patients, these drugs can be avoided, and alternate drugs can be given.

• Avoid Combination Drug Therapy: Avoid using multiple ototoxic drugs at a time.

• Avoid Chemical Triggers: Stay away from airborne chemical exposure for a longer duration in closed spaces. Keep adequate ventilation.

What Research Is Ongoing to Prevent Ototoxicity?

• Many kinds of research are ongoing for the development of otoprotective agents. Clinical trials for studying the efficacy of these otoprotective agents are needed further.

• Several studies on cochlear gene therapy and stem cell therapy are under trial to monitor their effects on the prevention of ototoxicity.

• Although there are various treatments for managing the damage caused by ototoxicity, furthermore research and clinical trials are needed in the area to understand how to prevent ototoxicity induced by the drugs.

Conclusion:

There are numerous medical conditions in which the use of different medications is done by the doctor for the needful treatment. Many of these drugs and chemicals have been suspected of having a strong potency to affect the inner ear and vestibular nerve, which may be either reversible or irreversible. So the person under these drugs should report any abnormal changes noticed to the doctor urgently. However, no permanent treatment has been developed so far for curing ototoxicity. Frequent follow-up with the doctor is a key to the prevention of drug-induced ototoxicity.