Sudden Sensorineural Hearing Loss

Definition

Sudden sensorineural hearing loss (SSHL) is defined as a sensorineural hearing loss of 30 dB or greater across at least three contiguous audiometric frequencies, developing within 72 hours or less. This formal definition requires a pure tone audiogram to confirm, which is why urgent audiological assessment is essential.

The condition normally presents as a patient who notices, typically upon waking or within a few hours, that they have lost the ability to hear from one ear. There is usually no pain, no history of discharge, and no obvious precipitating cause. The hearing loss may be complete or partial. Associated symptoms — tinnitus, aural fullness, or vertigo — may be present and should be documented as they provide clues to aetiology and affect prognosis.

The incidence of SSHL is approximately 5–20 cases per 100,000 population per year, with a peak incidence in the fifth decade of life. It is slightly more common in men. Most cases are unilateral; bilateral SSHL is uncommon and should prompt a search for systemic causes.

Aetiology

In the majority of cases (approximately 85–90%), no definitive cause is found despite investigation — these are classified as idiopathic SSHL. This likely represents a final common pathway for several different pathological processes. The main candidate mechanisms are:

• Vascular — ischaemia or occlusion of the labyrinthine artery (an end artery with no collateral supply). Risk factors include cardiovascular disease, hypertension, diabetes, and smoking. This mechanism would explain the poor recovery rate in some patients.
• Viral — viral cochleitis caused by HSV, mumps, measles, CMV, or other viruses. Histopathological studies have demonstrated cochlear pathology consistent with viral damage in some patients with SSHL.
• Autoimmune — autoimmune inner ear disease (AIED) can cause rapidly progressive bilateral SNHL, and may also cause acute unilateral episodes. More likely if there is a history of systemic autoimmune disease or if both ears are affected.
• Intracochlear membrane rupture — rupture of Reissner's membrane or the basilar membrane, possibly triggered by physical strain. More likely in younger patients with a clear precipitating event (heavy lifting, straining, barotrauma).
• Acoustic neuroma (vestibular schwannoma) — presents as SSHL in approximately 1–2% of SSHL cases. This is the critical diagnosis to exclude because it is surgically treatable and, if missed, continues to grow. MRI is therefore mandatory in all cases.
• Multiple sclerosis — demyelination affecting the cochlear nerve can cause SSHL, particularly in younger patients.
• Ototoxic drugs — aminoglycosides, cisplatin, furosemide — always take a detailed drug history.
• Perilymph fistula — rupture of the round or oval window membrane, often following physical straining or barotrauma.

Assessment and Investigation

History

Key points to establish:

• Exact onset and time course — was it sudden (seconds to minutes) or did it develop over hours?
• The ear involved and whether there has been any previous hearing loss in that ear
• Associated symptoms: tinnitus (ringing), aural fullness, vertigo (true spinning), nausea/vomiting
• Any preceding viral illness, barotrauma, head trauma, or noise exposure
• Drug history — particularly aminoglycosides, cisplatin, loop diuretics
• Cardiovascular risk factors (hypertension, diabetes, hyperlipidaemia, smoking history)
• Family history of hearing loss
• Any history of autoimmune disease
• Any neurological symptoms — diplopia, facial numbness, dysphagia, limb weakness — which would suggest a central cause

Examination

Otoscopy is typically normal in SSHL — there is no visible abnormality of the canal or TM. If the canal or TM appears abnormal, consider an alternative diagnosis (conductive cause, cholesteatoma, haemotympanum).

Tuning fork tests should be performed at the bedside:

• Weber's test — a vibrating tuning fork (512 Hz) is placed on the vertex or centre of the forehead. In sensorineural hearing loss, the sound lateralises to the good (unaffected) ear. This is because the inner ear of the affected side is damaged and cannot process the sound as effectively — the better inner ear dominates. (Note: this is the opposite of conductive hearing loss, where the sound lateralises towards the affected ear.)
• Rinne's test — compares air conduction (AC) with bone conduction (BC). In sensorineural hearing loss, AC is greater than BC on the affected side (a positive Rinne) — but both are reduced. In conductive hearing loss, BC exceeds AC on the affected side (a negative Rinne). Sensorineural hearing loss gives a positive Rinne but with reduced overall hearing.

If a tuning fork is not available, an informal test can be performed: ask the patient whether their own voice sounds more prominent in the affected ear (suggestive of a conductive hearing loss, as the occlusion effect enhances bone conduction) or exclusively in the good ear (suggestive of sensorineural hearing loss). Alternatively, gently scratch the patient's upper front teeth with a fingernail — this generates bone-conducted sound that can serve as a crude Weber's test.

Investigations

The following investigations should be arranged urgently:

• Pure tone audiogram (PTA) — the single most important investigation. It confirms the diagnosis (sensorineural pattern), quantifies the degree of hearing loss, and establishes a baseline for monitoring treatment response. Arrange this as a matter of urgency — ideally within 24–48 hours of presentation. The PTA establishes which frequencies are affected and how severely.
• MRI of the internal auditory meati (MRI IAMs) — mandatory in all cases of SSHL to exclude an acoustic neuroma (vestibular schwannoma). Approximately 1–2% of patients presenting with SSHL are found to have an acoustic neuroma on MRI. Small neuromas are entirely curable; missed neuromas continue to grow and may ultimately threaten adjacent structures (including the facial nerve). MRI with gadolinium enhancement is the gold standard — the neuroma enhances strongly. CT is not adequate to exclude an acoustic neuroma.
• Bloods:
  • Full blood count (FBC) — polycythaemia raises blood viscosity and can compromise inner ear perfusion
  • ESR and CRP — non-specific but elevated in autoimmune and vasculitic causes
  • Lipid profile — hyperlipidaemia is a risk factor for vascular SSHL
  • Fasting glucose and HbA1c — diabetes is a risk factor
  • Clotting screen
  • Autoimmune screen (ANA, ANCA, anti-dsDNA) — particularly if bilateral or if systemic autoimmune disease is suspected
  • Viral titres (if clinically indicated — mumps, syphilis serology) in the appropriate clinical context
  • Thyroid function (TFTs) — thyroid disease can cause hearing loss
• Tympanometry — to confirm normal middle ear function and exclude a conductive component

Treatment

Oral Corticosteroids — Standard First-Line Treatment

High-dose oral corticosteroids are the standard first-line treatment for SSHL. They are believed to work through anti-inflammatory and immunomodulatory mechanisms, reducing endolymphatic hydrops, improving cochlear blood flow, and dampening any autoimmune process. The treatment is most effective when started early — ideally within 2 weeks of symptom onset, and certainly within 4 weeks.

The standard regimen is:

• Prednisolone 1 mg/kg/day (maximum 60 mg/day) orally for 7–14 days, with a taper over the final few days. Some centres use a fixed dose of 60 mg for 7 days. Prescribe with gastric protection (omeprazole or lansoprazole).

The evidence base has evolved considerably. The landmark study by Rauch et al. (JAMA, 2011) — a randomised non-inferiority trial — compared oral prednisolone with intratympanic methylprednisolone for SSHL and found that oral steroids were not inferior to intratympanic steroids as primary treatment. This confirmed oral steroids as the appropriate first-line treatment. A Cochrane systematic review (Wei et al.) also supports the use of corticosteroids, demonstrating statistically significant improvements in hearing recovery compared with placebo, though the evidence base remains limited by trial quality.

Note: the evidence base has changed significantly since this page was originally written in 2007. Earlier Cochrane reviews found insufficient evidence for steroids, but subsequent higher-quality trials and more recent reviews do support their use. Current guidelines (NICE NG98, ENT UK) recommend high-dose oral corticosteroids as standard of care for SSHL.

Intratympanic Steroids

Intratympanic (IT) steroid injections involve injecting a steroid solution (typically methylprednisolone or dexamethasone) directly into the middle ear through the tympanic membrane, allowing diffusion across the round window membrane into the cochlea. This achieves much higher perilymph drug concentrations than oral steroids without systemic side-effects.

IT steroids are used in two situations in SSHL:

• Salvage (rescue) therapy — for patients who have failed to respond adequately to oral steroids (defined as less than 10 dB improvement in hearing at 2 weeks). IT steroids at this stage may still achieve further recovery.
• Primary treatment — in patients for whom systemic corticosteroids are contraindicated (uncontrolled diabetes, active peptic ulcer disease, poorly controlled hypertension, psychiatric history of steroid psychosis). The Rauch et al. trial demonstrated that IT steroids as primary treatment were non-inferior to oral steroids in terms of hearing recovery.

IT steroid injections are performed in the clinic under otomicroscopic guidance; a small volume (0.4–0.5 mL) is injected through the inferior TM. A series of 3–4 injections over 1–2 weeks is typical. The patient should lie with the ear up for 20–30 minutes after each injection to facilitate diffusion through the round window. The TM heals spontaneously without intervention.

Treatments with Limited or No Evidence

Several other treatments have been or are being used for SSHL. The evidence for most of these is currently insufficient to support routine use:

• Antiviral agents — level 1 evidence from multiple trials shows no benefit of aciclovir or valaciclovir in SSHL, whether given alone or with steroids. Antivirals are not recommended as routine treatment for SSHL.
• Carbogen inhalation — a mixture of 95% oxygen and 5% carbon dioxide, inhaled for 5 minutes every waking hour for 24–48 hours. Carbon dioxide causes cerebral vasodilation, which theoretically improves inner ear blood flow. However, the trial by Cinnamon et al. (2001) showed no benefit, and carbogen is no longer recommended.
• Hyperbaric oxygen therapy (HBOT) — a Cochrane systematic review demonstrated a statistically significant improvement in hearing for patients treated with HBOT compared with controls. However, the improvement was modest and the clinical significance was uncertain, and practical access to HBOT is very limited. Some specialist centres offer HBOT as an adjunct in severe or refractory SSHL.
• Plasma expanders, vasodilators, and prostaglandin E1 — have all been shown in trials to have no significant benefit.

Practical Management Pathway

1. Arrange urgent PTA (within 24–48 hours)
2. Start oral prednisolone 1 mg/kg/day (max 60 mg) if no contraindications, ideally within 2 weeks of onset
3. Request bloods (FBC, ESR, CRP, lipids, glucose, clotting, autoimmune screen)
4. Arrange MRI IAMs with gadolinium (can be done as non-urgent within 4–6 weeks if the patient is being treated)
5. ENT outpatient follow-up at 2 weeks with repeat PTA to assess treatment response
6. If insufficient hearing recovery at 2 weeks, arrange salvage intratympanic steroid injections
7. If MRI shows acoustic neuroma, refer to skull base/neuro-otology MDT

Prognosis

The prognosis for SSHL is variable and difficult to predict for an individual patient. The overall rate of spontaneous recovery (without treatment) is approximately 32–65%. Treatment with oral corticosteroids improves the recovery rate. Key prognostic factors:

Favourable prognostic factors (associated with better recovery):

• Younger age
• Early presentation and treatment (within 2 weeks of onset)
• Low-frequency hearing loss pattern (affects the lower frequencies — the cochlea "heals from the apex")
• Absence of vertigo
• Mild-to-moderate degree of hearing loss rather than profound loss

Poor prognostic factors:

• Profound hearing loss at presentation (especially above 90 dB HL)
• Associated vertigo (suggesting more extensive inner ear damage)
• Delay in seeking treatment (more than 2 weeks from onset)
• Extremes of age (very young and very old)
• High-frequency hearing loss pattern
• Pre-existing contralateral hearing loss

Patients who do not recover useful hearing should be referred for hearing aid assessment and counselling. Those with profound unilateral SSHL may be candidates for a CROS (Contralateral Routing of Signal) hearing aid, a bone-anchored hearing aid (BAHA), or in selected cases a cochlear implant.