Sudden Hearing Loss (Sudden Sensorineural Hearing Loss)

Definition and epidemiology

Sudden sensorineural hearing loss (SSNHL) is defined as an inner-ear/nerve hearing loss of 30 dB or more developing within 72 hours across at least three consecutive frequencies. The great majority of cases are idiopathic; that is, no definite cause is found despite detailed investigation (Chandrasekhar et al., 2019).

The annual incidence is reported at about 5-27 per 100,000; although it can occur at any age, it is most common in middle-to-older age and is usually one-sided.

Because the loss is at the level of the cochlea (inner ear) or auditory nerve, it is sensorineural; distinguishing it from a conductive loss is critical for treatment.

Symptoms and signs

The patient usually wakes with, or notices during the day, sudden fullness, reduced hearing and tinnitus in one ear. Not being able to hear when holding the phone to that ear is a typical presentation.

Dizziness accompanies a proportion of cases and usually points to a more severe picture. Ear fullness and tinnitus are common additional symptoms.

Symptoms are sometimes perceived as “water got in my ear / wax blocked it” and dismissed; this delays treatment. Sudden, one-sided hearing decline should therefore not be neglected.

Causes and risk factors

In about 90% of cases no definite cause is found (idiopathic). Proposed mechanisms include viral infections, inner-ear circulation disorders, membrane tears and autoimmune processes.

Detectable causes include retrocochlear tumours such as acoustic neuroma (vestibular schwannoma), Ménière’s disease, trauma, certain drugs and infections; differential diagnosis is therefore important.

In one-sided cases that do not recover, MRI is recommended to exclude retrocochlear pathology (Chandrasekhar et al., 2019).

Audiological and clinical assessment

The first step is to determine whether the loss is conductive or sensorineural. Tuning-fork tests and examination help quickly exclude outer/middle-ear causes (wax, effusion).

• Pure-tone and speech audiometry: determines the type, degree and configuration of the loss; it is the basis of diagnosis.
• Tympanometry and acoustic reflexes: exclude middle-ear causes.
• Otoacoustic emissions (OAE): give information about cochlear outer hair-cell function.
• MRI: recommended to exclude retrocochlear pathologies (e.g., acoustic neuroma).
• Blood tests: routine broad screening is not recommended; selected tests are done based on history.

Guidelines emphasise that in SSNHL diagnosis should be made quickly and treatment should not be delayed.

Treatment and audiological rehabilitation

Corticosteroids are the most widely used treatment; they can be given systemically (orally) or by injection through the eardrum (intratympanic). Starting treatment early increases the chance of recovery; the decision and dosing rest with the physician (Chandrasekhar et al., 2019).

In cases not responding to first-line treatment, intratympanic steroid as salvage therapy and, in selected centres, hyperbaric oxygen therapy may be considered. The level of evidence is moderate, but it may be beneficial in the early period.

In patients who develop a permanent loss, a hearing aid is the first-line rehabilitation. CROS systems for one-sided severe loss; and cochlear implantation for bilateral very severe loss may come onto the agenda.

Impact on quality of life and advice

Even a one-sided loss makes it harder to understand speech in noise and to localise sound; tinnitus and dizziness can increase anxiety. These effects should be monitored with patient-reported scales.

The most important advice is speed: those who notice a sudden hearing decline should see a physician within hours, not days. Even if recovery is partial, a hearing aid and communication strategies markedly improve quality of life.