Sudden Sensorineural Hearing Loss (SSNHL)

Definition

• Cummings Otolaryngology Head and Neck Surgery

Epidemiology

Etiology

Infectious

• Viral (most commonly implicated): mumps, measles, herpes zoster oticus, HSV, VZV, CMV, HIV, EBV, influenza, parainfluenza, Lassa fever, Zika, West Nile virus
  • 28% of patients report a viral URTI within 1 month before onset
  • Mumps virus has been directly isolated from perilymph of SSNHL patients
• Bacterial: syphilis (important and treatable), Lyme disease, mycoplasma, meningitis (Streptococcal, cryptococcal)

Neoplastic

• Vestibular schwannoma (acoustic neuroma): ~1% of SSNHL presentations - this is the key "must not miss" diagnosis
• Meningioma, epidermoid, hemangioma, temporal bone metastases, lymphoma, leukemia

Traumatic

• Temporal bone fracture, acoustic trauma, inner ear concussion, perilymphatic fistula, barotrauma

Ototoxic

• Aminoglycosides, loop diuretics, cisplatin, quinine, aspirin (high dose)

Immunologic/Autoimmune

• Autoimmune inner ear disease (AIED), Cogan syndrome, polyarteritis nodosa, SLE, Wegener granulomatosis

Vascular

• Labyrinthine artery occlusion, hypercoagulable states, polycythemia, leukemia, macroglobulinemia

Other / Idiopathic

• The majority of cases remain idiopathic after thorough evaluation
• Principal pathogenetic theories for idiopathic cases:
  1. Viral cochleitis/neuritis
  2. Vascular occlusion of the labyrinthine artery
  3. Intracochlear membrane breaks
  4. Autoimmune damage

Clinical Presentation

• Most common: unilateral hearing loss noticed on awakening (patient woke up deaf in one ear)
• Progressive loss over hours to days
• Aural fullness - very common, sometimes the only complaint
• Tinnitus - variable; may precede hearing loss
• Vertigo/dysequilibrium - present in ~40% of patients; a poor prognostic sign

Diagnosis

Pure-Tone Audiogram

Investigations

Prognosis

1. Severity of loss - more severe = worse prognosis; profound losses have exceptionally poor prognosis
2. Audiogram shape - upsloping and mid-frequency losses recover better; downsloping and flat losses do worse
3. Presence of vertigo - poor prognostic indicator, especially with downsloping loss
4. Age - older age associated with worse outcomes

Management

First-Line: Systemic (Oral) Corticosteroids

• Cummings Otolaryngology

Intratympanic (IT) Steroids

1. Primary treatment: randomized controlled data shows no significant difference vs. oral steroids - reinforces oral route as first-line
2. Salvage therapy: for patients who fail oral steroids - multiple retrospective and prospective studies show audiometric improvement. Key principle: IT salvage should be used as soon as it is clear oral steroids are not working, preferably within the first 2 weeks of the original insult. The longer the delay, the worse the salvage outcome.

• Dexamethasone: 1-25 mg/mL; or methylprednisolone 62.5 mg/mL
• Volume: 0.3-0.5 mL to fill the middle ear space
• Route: direct IT injection or through tympanostomy tube

Other Treatments (Limited/Investigational)

• Hyperbaric oxygen therapy (HBO): used as adjunct in some centers; a 2026 systematic review (PMID 40747804) examined the evidence - benefit remains debated, especially when added to steroids
• Vasodilators / rheological agents (carbogen, histamine, dextran, pentoxifylline): used in some European centers; evidence quality is low
• Antiviral therapy: acyclovir - no robust evidence supporting routine use for idiopathic cases
• Anticoagulants: no proven benefit in idiopathic SSNHL

Treat Identified Causes

• Syphilis → IV penicillin
• Lyme disease → doxycycline or IV ceftriaxone
• Autoimmune inner ear disease → prolonged immunosuppression

Rehabilitation

• Patients with residual loss: hearing aids, or cochlear implant evaluation for profound losses
• Contralateral CROS/BiCROS hearing aids for single-sided deafness

Summary Flowchart

Sudden hearing loss (≥30 dB, 3 frequencies, ≤72 hrs)
        ↓
Confirm SNHL on audiogram (rule out CHL with tuning forks / tympanometry)
        ↓
Treat as otologic emergency — start oral prednisone ASAP
        ↓
Urgent MRI IAC + gadolinium (exclude acoustic neuroma)
        ↓
Targeted bloodwork (FTA-ABS, CBC, ESR, ANA, glucose, lipids)
        ↓
No improvement after 2 weeks?
        ↓
Intratympanic steroid salvage (within 2 weeks of onset)
        ↓
Audiology follow-up; consider HBO, hearing rehabilitation

Recent Evidence (2024-2026)

• SSNHL is an otologic emergency - treat promptly with oral steroids (prednisone 1 mg/kg/day)
• MRI IAC with gadolinium is mandatory to exclude retrocochlear pathology (acoustic neuroma)
• Intratympanic steroids are valuable salvage if oral steroids fail - use within 2 weeks
• Spontaneous recovery occurs in 30-65% without treatment, so all recovery rates must be interpreted against this background rate