Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss (SSNHL) is a sensorineural hearing loss of at least 30 decibels over at least three contiguous frequencies occurring within 72 hours. Incidence is about 5 to 27 per 100,000 per year (probably higher because of underreporting), with a peak at 50 to 60 years. It is usually unilateral (bilateral in 1 to 2 percent).

It is an otologic emergency, since early treatment improves recovery. Spontaneous partial or complete recovery occurs in about 32 to 65 percent of untreated patients, mostly within 2 weeks.

The cause is identified in only about 10 to 15 percent of patients (idiopathic in 85 to 90 percent).

Proposed mechanisms:

• viral infection (herpes viruses, mumps, measles, cytomegalovirus)
• vascular compromise of the cochlear circulation (microvascular occlusion, thrombosis, vasospasm)
• intracochlear membrane rupture (round window or oval window fistula)
• autoimmune inner ear disease

Identified causes:

• vestibular schwannoma (in about 1 to 3 percent, may present with SSNHL)
• Ménière disease
• multiple sclerosis
• stroke (anterior inferior cerebellar artery territory)
• trauma (head injury, barotrauma)
• ototoxic drugs
• infection (syphilis, Lyme disease, HIV, meningitis)
• autoimmune disease, neoplasm, sickle cell disease, and hyperviscosity or coagulopathy

Favourable prognostic factors: milder loss, low frequency loss, younger age, early treatment (within 7 to 14 days), absence of vertigo, and the rate of recovery in the first week.

Unfavourable prognostic factors: severe or profound loss, down sloping audiogram, vertigo, age over 60, and delay in treatment.

• Sudden unilateral hearing loss noticed on waking or abruptly during the day, with a sense of aural fullness, muffled sound, distortion and diplopacusis.
• Tinnitus in 80 to 90 percent, and vertigo in about 30 to 40 percent.
• Normal otoscopic examination; Weber test lateralises to the better ear, and Rinne test is normal (positive) or reduced equally.
• Associated symptoms of the underlying cause: facial weakness (Ramsay Hunt syndrome), rash, neurological deficits, headache, or a history of trauma, drugs, or infection.
• Anxiety and impairment of daily life.

• Urgent audiometry (within 24 hours of presentation): pure tone audiometry and speech discrimination, with the definition of at least 30 dB loss over three adjacent frequencies; acoustic reflexes and tympanometry exclude conductive loss and middle ear disease.
• Contrast enhanced MRI of the brain and internal auditory canals to exclude retrocochlear pathology, especially vestibular schwannoma (visible in about 2 to 10 percent of cases), stroke, and demyelination; performed within weeks.
• Laboratory tests are not routine; selective tests: glucose, full blood count, erythrocyte sedimentation rate, syphilis serology, Lyme serology, autoimmune screen, lipid profile, coagulation studies, and thyroid function when a systemic cause is suspected. Auditory brainstem response if MRI is not possible.
• Vestibular tests if vertigo is present.
• Diagnosis of exclusion; conductive loss from cerumen, otitis media with effusion, or perforation must be excluded first.

Treatment aims to improve hearing recovery; start within 2 weeks of onset (best within 72 hours) and without waiting for MRI.

• Systemic corticosteroids (first line): prednisolone 1 mg/kg daily as a single morning dose (maximum 60 mg, some use 60 to 80 mg) for 7 to 14 days, followed by a taper over 1 to 2 weeks. A typical regimen is 60 mg daily for 7 days, 40 mg for 3 days, 20 mg for 3 days, 10 mg for 3 days, and stopped.
• Alternatives: dexamethasone 10 to 16 mg daily for 5 to 7 days then taper, or methylprednisolone 1 g daily for 3 days in some centres.
• Short term adverse effects (hyperglycaemia, insomnia, mood change, hypertension, gastric irritation) require monitoring and gastric protection. Use cautiously in diabetes, peptic ulcer disease and uncontrolled hypertension.
• Intratympanic steroids: dexamethasone 10 mg/mL (0.4 to 0.8 mL) or methylprednisolone 40 mg/mL injected through the tympanic membrane (anterior inferior quadrant, under topical anaesthesia with phenol or lidocaine). The patient lies 20 to 30 minutes with the head tilted 45 degrees. Repeat 3 to 4 times over 1 to 2 weeks (days 1, 3, 5 and 7 or weekly).
• Use as salvage therapy for failure of systemic therapy after 2 to 6 weeks, since benefit is greatest within 2 to 6 weeks of onset. Use as primary therapy for patients with diabetes or contraindication to systemic steroids. Use in combination with systemic steroids for severe profound loss.
• Complications: pain, transient vertigo, persistent perforation (about 1 to 2 percent), and infection.
• Hyperbaric oxygen therapy (2.0 to 2.5 atmospheres absolute, for 90 minutes daily for 10 to 20 sessions, often in addition to steroids) is an option for patients with severe loss, especially within 2 weeks of onset, with a modest additional benefit.
• Antivirals (valaciclovir 1 g three times a day for 7 to 10 days) have no proven benefit in idiopathic cases, but may be used in suspected herpes zoster or Ramsay Hunt syndrome. Vasodilators, anticoagulants, volume expanders, carbogen and vitamins have no proven efficacy.
• Treat identified causes:
  • stop ototoxic drugs
  • syphilis: benzathine penicillin 2.4 million units weekly for 3 weeks, or intravenous penicillin G for neurosyphilis
  • autoimmune disease: prednisolone with a steroid sparing agent such as methotrexate 7.5 to 25 mg weekly or azathioprine 2 mg/kg daily
  • vestibular schwannoma: observation, radiosurgery or surgery
  • perilymph fistula: bed rest, avoid straining, surgical exploration and patching with fascia if there is no improvement
• Rehabilitation: hearing aid (conventional or contralateral routing of signals) or bone anchored aid for unilateral deafness, cochlear implant for single sided deafness in selected patients, tinnitus management (sound therapy, cognitive behavioural therapy), and counselling.
• Follow up audiometry at 2 weeks, 6 weeks, and 3 months, with MRI repeated at 6 months if initially negative, since schwannoma may appear later in a small percentage.
• Recurrent episodes, bilateral involvement, or progressive fluctuation prompt a workup for autoimmune disease.
• Prognosis: complete recovery in about 30 to 40 percent, partial recovery in a similar proportion, with the rest having persistent hearing loss.