Key Facts

Sensorineural hearing loss results from dysfunction of the cochlea, cochlear hair cells, or the vestibulocochlear nerve (CN VIII). It is the most common type of hearing loss overall and significantly impacts quality of life, communication, and cognitive function.

Epidemiology

• Accounts for >90% of all hearing loss
• Presbycusis affects >50% of those >70 years
• Noise-induced hearing loss: estimated 17% of adults have measurable noise damage
• Congenital SNHL: 1-2 per 1,000 live births
• Vestibular schwannoma: incidence 1-2 per 100,000 per year

Aetiology

• Congenital: genetic (Connexin 26/GJB2 most common, Pendred syndrome, Usher syndrome, Waardenburg syndrome), TORCH infections (CMV most common infectious cause), prematurity, hypoxia, kernicterus
• Acquired: presbycusis, noise-induced, ototoxic drugs (aminoglycosides, cisplatin, loop diuretics, high-dose aspirin), Ménière disease, labyrinthitis, vestibular schwannoma, autoimmune inner ear disease, head trauma, otosyphilis
• Sudden SNHL: idiopathic (most common), viral (CMV, mumps, measles), vascular (cochlear infarction), autoimmune, perilymph fistula

Pathophysiology

• Cochlear (sensory): damage to outer hair cells (OHCs) initially, then inner hair cells (IHCs)
  • OHC damage reduces cochlear amplification and frequency selectivity
  • IHC damage reduces afferent signal to auditory nerve
• Neural (retrocochlear): CN VIII compression (schwannoma), demyelination (MS), auditory neuropathy
• Presbycusis involves multiple mechanisms: sensory (hair cell loss), strial (atrophy of stria vascularis), neural (spiral ganglion degeneration)
• Hair cell loss is irreversible in mammals — no spontaneous regeneration

Symptoms

• Difficulty hearing, especially speech in background noise
• Bilateral, symmetric, gradual loss (presbycusis, noise-induced)
• Unilateral or asymmetric loss (vestibular schwannoma, sudden SNHL)
• Tinnitus (very common association)
• Recruitment: abnormally rapid growth of loudness (cochlear cause)
• Difficulty with high-pitched sounds (consonants, alarms, birdsong)

Associated Features by Cause

• Ménière disease: episodic vertigo, fluctuating low-frequency SNHL, tinnitus, aural fullness
• Vestibular schwannoma: unilateral tinnitus, imbalance, facial numbness (CN V involvement)
• Noise-induced: occupational or recreational noise exposure history, 4kHz audiometric notch
• Ototoxicity: temporal relationship with drug exposure

Red Flags

• Sudden SNHL (<72 hours) — ENT emergency
• Unilateral/asymmetric SNHL — exclude vestibular schwannoma
• Associated facial nerve palsy
• Progressive unilateral SNHL
• SNHL in a child (developmental implications)

Bedside

• Otoscopy: typically normal in SNHL
• Tuning fork tests (512Hz):
  • Rinne: positive (AC > BC) — consistent with normal or SNHL
  • Weber: lateralises to unaffected ear
• Whispered voice test

Bloods

• Guided by clinical suspicion:
  • FBC, ESR, CRP (inflammatory/autoimmune)
  • TFTs (hypothyroidism)
  • Glucose/HbA1c (diabetes)
  • Syphilis serology (RPR/VDRL, TPHA)
  • Autoimmune screen (ANA, anti-dsDNA) if autoimmune inner ear disease suspected
  • Genetic testing (Connexin 26/GJB2) for congenital SNHL

Imaging

• MRI IAM with gadolinium: gold standard for excluding vestibular schwannoma in unilateral/asymmetric SNHL
• CT temporal bones: for pre-cochlear implant assessment, congenital anomalies

Special Tests

• Pure tone audiometry: air and bone conduction; no significant air-bone gap (<10dB) in pure SNHL
• Speech audiometry: disproportionately poor speech discrimination suggests retrocochlear pathology
• Otoacoustic emissions (OAE): test OHC function; present = cochlea working
• Auditory brainstem response (ABR): threshold estimation, retrocochlear assessment
• Electrocochleography (ECoG): for Ménière disease (elevated SP/AP ratio)

Non-pharmacological

• Hearing aids: first-line for mild-moderate SNHL (NICE NG98)
• Communication strategies: lip reading, sign language, assistive devices
• Noise protection: hearing protection for occupational/recreational exposure
• Environmental modification: reduce background noise, loop systems, visual alerts

Pharmacological

• Sudden SNHL: oral prednisolone 1mg/kg (max 60mg) OD for 7-14 days (start ASAP, ideally within 72 hours)
  • Intratympanic dexamethasone (0.5-1ml of 4mg/ml): salvage therapy if oral steroids fail, or first-line if oral steroids contraindicated
• Autoimmune inner ear disease: systemic corticosteroids, steroid-sparing agents (methotrexate, azathioprine)
• Ménière disease: betahistine 16mg TDS, intratympanic gentamicin for refractory cases
• Ototoxic drug management: therapeutic drug monitoring (aminoglycosides), dose adjustment, alternative agents

Surgical

• Cochlear implants (NICE TA566):
  • Bilateral severe-profound SNHL (≥80dB at 2 and 4kHz)
  • Inadequate benefit from optimally fitted hearing aids
  • Bilateral simultaneous or sequential implantation
• Bone-anchored hearing aid (BAHA/Osia): for single-sided deafness (routes sound to contralateral cochlea)
• Vestibular schwannoma: surgical excision (translabyrinthine, retrosigmoid, middle fossa) or stereotactic radiosurgery (Gamma Knife)

Referral Criteria

• Emergency: sudden SNHL (<72 hours)
• Urgent (2-week wait): unilateral/asymmetric SNHL, suspected vestibular schwannoma
• Routine: bilateral symmetric SNHL for audiological assessment and hearing aid fitting
• Paediatric: any child with suspected hearing loss — urgent audiology referral

• Presbycusis: progressive but hearing aids significantly improve quality of life
• Sudden SNHL: 30-65% achieve some spontaneous recovery; better prognosis with early steroid treatment, younger age, mild-moderate loss, and no vertigo
• Noise-induced: preventable; once established, permanent; tinnitus often accompanies
• Cochlear implants: speech perception improves in >80% adults; children implanted before age 2 have best language outcomes
• Vestibular schwannoma: hearing preservation possible with radiosurgery or observation for small tumours
• Untreated SNHL: associated with 2-5× increased risk of cognitive decline and dementia (Lancet Commission 2020)
• Congenital SNHL: early identification and intervention (hearing aids/CI before age 3) essential for speech and language development

Causes of Congenital SNHL

Common Ototoxic Drugs

Audiometric Patterns