Ototoxic hearing loss is sensorineural damage caused by drugs or chemicals toxic to the inner ear. Because much ototoxic exposure is planned — chemotherapy, treatment of serious infection — it is one of the few sensorineural losses that can be watched for and sometimes caught early.

The audiometric signature

Ototoxicity classically produces a bilateral, symmetrical, high-frequency sensorineural loss that begins at the highest frequencies and progresses downward over the course of treatment. Early on, the standard audiogram up to 8 kHz may still look normal even though damage has begun above that range.

Normal hearing

Ototoxic hearing loss

O Right ear, air
X Left ear, air
< Right ear, bone
> Left ear, bone

Signature: Bilateral, symmetrical, steeply sloping high-frequency sensorineural loss progressing downward over time.

Figure 1. Ototoxic hearing loss versus normal hearing. A bilateral, symmetrical, steeply sloping high-frequency sensorineural loss; the highest frequencies are affected first and most severely.

The common culprits

The drugs most often implicated fall into a few groups: aminoglycoside antibiotics; platinum-based chemotherapy agents; loop diuretics; and high-dose salicylates. The first two cause a permanent, cumulative sensorineural loss; the last two more often cause a loss that is at least partly reversible when the drug is stopped.

Trainee The progression matters for monitoring. Because the earliest damage is at frequencies above the conventional 8 kHz limit, extended high-frequency audiometry — testing beyond 8 kHz — can detect ototoxic change before it reaches the speech frequencies. A monitoring programme during ototoxic treatment relies on a good baseline audiogram before the drug starts and serial testing during it, so that a shift can be caught while the patient still has useful hearing to protect.

Clinician Ototoxic monitoring is a clear example of audiometry used to change management in real time: an early high-frequency shift may prompt a change of agent or dose where the clinical situation allows. It also illustrates why the audiogram is read against a baseline — a single audiogram showing a high-frequency loss in a patient on cisplatin says little without the pre-treatment chart to compare it with. Some ototoxic agents are also vestibulotoxic, so balance symptoms may accompany or even precede the hearing change.

Special tests

Ototoxicity is a cochlear loss, the damage again falling on the outer hair cells first. Recruitment is therefore typically present and the SISI tends to be positive, while tone decay is not a feature. As elsewhere, the special tests confirm the cochlear site; the diagnosis comes from the exposure history and the characteristic progressive, symmetrical, high-frequency pattern.