Inner Ear Conditions (Sudden Onset Sensorineural Hearing Loss)

What is Sudden Onset Sensorineural Hearing Loss?

Sudden onset sensorineural hearing loss (SSNHL) is defined as loss of hearing of more than 30 dB over three contiguous frequencies within three days. The pathogenesis is thought to be viral in origin. The incidence is reported to be about 20 per 100000 population, more common with increasing age. The natural history of the condition is for 65 to 70% of patients to recover a significant degree of their hearing. SSNHL is thought to be the result of a viral infection (of cochlea or VII nerve), vascular problems (ischaemia or occlusion) or inner ear membrane rupture. This condition should be considered an emergency and the patient should be referred immediately.

Symptoms and Signs

Typically, patients present with a unilateral hearing loss over 24 to 48 hours. Commonly, there is no preceding or predisposing factor. A proportion will give a history of an upper respiratory tract infection. The degree of hearing loss can range from mild to profound. About 70 to 75% will complain of associated tinnitus and 50% will have concomitant vertigo.
The ear examination is likely to be normal. Tuning fork test will reveal sensorineural hearing loss in the affected ear. The Weber test will show lateralisation to the normal ear. The Rinne test can reveal bone conduction (due to cross-over hearing from the other ear) that is better than air conduction.

Investigations

An audiogram should be performed to confirm the diagnosis and determine the severity and shape of the deafness. Many authors have suggested that the following blood tests be performed in idiopathic SSNHL:
FTA-Abs, ANA, Rheumatoid factor, Autoimmune screen, ESR, Coagulation profile, Full Blood Count (FBC), TSH, Fasting Glucose, Cholesterol and Triglycerides.
However, it is uncommon for any of these tests to reveal the cause of hearing loss.
An MRI to exclude acoustic neuroma can be performed if no recovery of hearing thresholds is seen after six months.

Management

This condition should be treated as a semi-emergency. An audiogram should be performed within the first 48 hours. Many medications have been used but there are no adequate randomised controlled trials to substantiate any treatment except possibly for the use of steroids (Prednisolone 1mg/kg/day for 10 days). Preferably, steroid therapy should be instituted as soon as possible from the onset of hearing loss (patients with mild hearing loss are likely to recover without medication, those with severe hearing loss are unlikely to recover despite treatment). Significant poor prognostic factors include age (less than 15 years, more than 65 years, poorer prognosis) and the presence of vertigo. Good prognostic factors include early commencement of treatment and low-frequency hearing loss.
Surgery is indicated only when a perilymph fistula is suspected.