Single-sided deafness refers to significant or total sensorineural hearing loss unilaterally. There are about 200 new cases of single-sided deafness per million inhabitants in the world and approximately 4000 new cases in Australia annually. Initial assessment should include full history and examination. Examination should assess the tympanic membrane and include tuning fork testing for sensorineural hearing loss. Referral to an ENT surgeon with an audiogram is required. The more acute the deafness, the more urgent the referral, as the quality of life impact is greater. The most common causes of single-sided deafness are trauma (head injury, surgery), infections (viral or bacterial), tumours in or around the ear, and sudden hearing loss.
Around 10% of new cases of single-sided deafness per year will be sudden. Sudden hearing loss occurs rapidly, over a 72-hour period. The usual audiometric criterion is a decrease in hearing of 30dB or more, affecting at least three consecutive frequencies. The cause of sensorineural hearing loss is unknown or uncertain in more than 90% of cases. Despite thorough evaluation, treatment decisions are generally made without knowledge of aetiology. The two most common theories of causation are circulatory disturbance and viral infection. A clinical practice guideline on sensorineural hearing loss was released by the American Academy of Otolaryngology Head and Neck Surgery. Some of the key points addressed were:
- The importance of clinical and audiometric testing, which should be early and ongoing.
- The need to avoid delay in evaluation and treatment.
- The need to avoid unnecessary and non-targeted laboratory blood tests.
- CT of the head/brain should not be ordered in the initial evaluation as MRI is preferred. This is because up to 10% of those with sudden hearing loss will have a cerebellopontine angle tumour.
- Systemic corticosteroids should be administered orally (1mg/kg/day prednisone for 14 days) if no contraindications or risk factors exist, ideally within the first two weeks and no later than six weeks.
- Intratympanic “salvage” corticosteroid therapy should be commenced for patients who do not recover hearing with systemic steroids. This is generally administered via repeated steroid injection through an intact tympanic membrane or insertion of a grommet for instilling steroids.
- Hyperbaric oxygen therapy may be offered within three months.
- Antivirials, thrombolytics, vasodilators, vasoactive substances or antioxidants should not routinely be prescribed.
The Biblical proverb “two are better than one” has a place in otology too. Studies show the benefit of binaural hearing in those with normal hearing, as well as those needing bilateral amplification. Unilateral amplification in the presence of bilateral loss diminishes auditory function.