Sudden senorineural hearing loss (SSNHL) has wide age distribution, but occurs most commonly in people aged 50-60 years, usually affects one ear only, and can be associated with tinnitus and vertigo. Patients with suspected SSNHL should be given an urgent and careful examination to rule out life-threatening causes such as those affecting circulation or malignant cancers.
Once such causes have been excluded, short-course corticosteroids are recommended—although no treatment is proven. The issues are discussed in a Seminar in this week's edition of The Lancet, written by Dr Benjamin E Schreiber, Royal Free Hampstead NHS Trust, London, UK, and Professor Linda M Luxon, The National Hospital of Neurology and Neurosurgery, London, UK.
SSNHL incidence varies from 5 to 30 cases per 100,000 per year, although one German study estimated 160 per 100,000 per year. SSNHL can be associated with rapidly progressive hearing loss, developing over weeks and months after an initial acute SSNHL event. Patients can delay seeking help, and can present to a range of specialties when seeking treatment. The authors say: "In primary care and non-specialist departments, patients can be inappropriately reassured, without investigation, in the mistaken view that the loss is attributable to middle-ear dysfunction secondary to upper respiratory tract infection."
Detailed investigation will show a specific cause in about 10% of patients. The severity of hearing loss is divided roughly equally into mild, moderate, and severe/profound. The configuration of the hearing loss varies and can affect high, low, or all frequencies. Tinnitus occurs in about 80% of patients, and vertigo, indicating an associated peripheral vestibular dysfunction, in about 30%. Up to 80% of patients report a feeling of ear fullness.
Various infections, and vascular and immune causes, have been proposed as causes of SSNHL. Mumps can be a cause, accounting for 7% of adult cases. Rubella, varicella zoster virus, cytomegalovirus, and Epstein-Barr virus have all been implicated, though evidence is incomplete. Proposed vascular causes include a variety of conditions affecting the cochlea (the 'hearing' part of the inner ear). Abnormal blood cholesterol levels and low blood pressure have also been suggested. Some evidence suggests SSNHL is linked to stroke, with SSNHL preceding stroke in 8% of 364 patients in one prospective series study. Abrupt, severe, and irreversible SSNHL has also been described in patients with migraine.
SSNHL may be the presenting symptom of Ménière's disease—a clinical diagnosis, which classically presents with sudden unilateral hearing loss, tinnitus, and vertigo. Acoustic neuroma is the most common cancer linked to SSNHL.
SSNHL commonly occurs with head injury and rarely after whiplash, and diving decompression sickness. Blast injuries, diving, flights in unpressurised aircraft, and even raised intracranial pressure during sneezing have also been suggested as caused of SSNHL loss and commonly vertigo. Patients with SSNHL should have an urgent assessment with a minimum of pure tone audiometry (with air and bone conduction thresholds) to avoid the pitfall of misdiagnosis of a middle-ear pathological change. When a sudden hearing loss is confirmed as sensorineural, an urgent referral to an audiovestibular physician or otolaryngologist should be made. A detailed neurological examination can then take place.
The authors say: "The prognosis in cases of isolated sudden sensorineural hearing loss is generally good, and improvement within a matter of days is common. Patients in whom there is no change within 2 weeks are unlikely to show much recovery."
Oral corticosteroids are widely used, although the supporting evidence is weak. Steroids have many effects in the inner ear, including suppression of an immune response, and changes in circulation, but whether such effects are beneficial is unclear. In the absence of definitive evidence, patients with moderate or severe sudden sensorineural hearing loss can be treated with a short course of oral prednisolone (eg, 1 mg/kg per day, or a maximum of 60 mg daily for adults, for 10 days followed by gradual tapering of dose) since clinical trials suggest some improvement with steroids. However, toxic effects have been reported with this treatment, and this regimen is probably not justified in patients with relative contraindications to corticosteroids. Other possible treatments include dexamethasone, methotrexate, low-dose aspirin anticoagulants, and oral magnesium, though conclusive evidence does not exist for any of these treatments.
The authors say that patients with persistent symptoms should be referred to the appropriate specialists for continuing management of their auditory symptoms. This management can include counselling, information about lifestyle changes, and techniques (such as amplification) for overcoming the communication handicap that hearing loss imposes. Patients should be considered for audiological rehabilitation, and those with persistent tinnitus might benefit from tinnitus retraining therapy.
They conclude: "Most patients with sudden sensorineural hearing loss cannot be given a cause for their diagnosis. Patients with sudden hearing loss presenting to general practice should be assessed with a minimum of pure tone audiometry (with air and bone conduction thresholds), and those with sensorineural hearing loss should be urgently referred to a specialist. A careful assessment is necessary to exclude life threatening or treatable causes such as vascular events and malignant disease. About half of patients show complete recovery, usually in about 2 weeks. We recommend that patients with sudden sensorineural hearing loss with no clear underlying cause after investigation are treated with a short course of oral prednisolone started within 2 weeks after onset. Much needs to be learnt about pathogenesis, and more clinical trials are necessary to establish evidence-based treatment."
Source: The Lancet