Key Facts

Conductive hearing loss occurs when sound waves cannot be efficiently transmitted from the external environment through the ear canal, tympanic membrane, and ossicular chain to the oval window. Unlike sensorineural hearing loss, many causes of CHL are treatable medically or surgically.

Epidemiology

• CHL accounts for approximately 10-15% of all hearing loss in adults
• OME affects virtually all children at some point; persistent bilateral OME affects 5-10% of school-age children
• Otosclerosis affects 0.3-0.4% of the population; clinical disease in 0.1%
• Chronic suppurative otitis media: prevalence 1-2% in developed countries

Aetiology

• External ear: cerumen impaction, otitis externa, foreign body, exostoses (surfer's ear), canal stenosis/atresia
• Tympanic membrane: perforation (trauma, infection), tympanosclerosis, retraction
• Middle ear: OME (most common in children), otosclerosis (most common in young adults), cholesteatoma, ossicular discontinuity/fixation, chronic suppurative otitis media, haemotympanum

Pathophysiology

• Sound waves require mechanical transmission through air in the EAC, vibration of the TM, and ossicular chain leverage to amplify sound at the oval window
• The ossicular chain provides approximately 25-30dB of amplification through the impedance-matching mechanism
• Any obstruction or disruption in this pathway causes an air-bone gap on audiometry
• Maximum CHL is approximately 60dB (the limit of bone conduction hearing)
• In otosclerosis, abnormal bone remodelling around the stapes footplate causes fixation and progressive CHL

Symptoms

• Reduced hearing, often noticed as needing to increase volume
• May hear better in background noise (paracusis of Willis — classic for otosclerosis)
• Ear fullness or pressure sensation
• History of ear discharge, infection, or surgery
• Autophony (hearing own voice louder)

Examination Findings

• Otoscopy: may reveal cerumen, effusion, perforation, retraction pocket, cholesteatoma, tympanosclerosis
• Tuning fork tests (512Hz):
  • Rinne: negative on affected side (BC > AC)
  • Weber: lateralises to affected ear
• Normal external canal appearance in otosclerosis (Schwartze sign — pink blush on promontory — rare)

Red Flags

• Unilateral CHL with foul discharge (cholesteatoma)
• Facial nerve palsy with CHL
• Blood behind tympanic membrane (haemotympanum — trauma, barotrauma, skull fracture)
• Progressive CHL in young adult (otosclerosis — family history)
• Conductive hearing loss in a child not improving (persistent OME, cholesteatoma)

Bedside

• Otoscopy (pneumatic otoscopy if OME suspected)
• Tuning fork tests (512Hz): Rinne and Weber
• Whispered voice test

Bloods

• Not routinely required

Imaging

• CT temporal bones: for cholesteatoma, otosclerosis (rarely needed), congenital anomalies, trauma
• MRI: if cholesteatoma suspected (DWI for post-operative surveillance)

Special Tests

• Pure tone audiometry: air-bone gap >10dB confirms conductive component
  • Carhart notch at 2kHz: characteristic of otosclerosis (artefact of stapes fixation)
• Tympanometry:
  • Type A: normal
  • Type B: effusion or perforation
  • Type C: negative middle ear pressure (Eustachian tube dysfunction)
  • Type As: reduced compliance (otosclerosis, tympanosclerosis)
  • Type Ad: increased compliance (ossicular discontinuity)
• Speech audiometry: typically good speech discrimination in CHL (unlike retrocochlear SNHL)
• Stapedial reflexes: absent in otosclerosis

Non-pharmacological

• Cerumen removal: microsuction (gold standard), irrigation, manual removal
• Hearing aids: option for all causes of CHL, particularly if surgery declined or unsuitable
• Watchful waiting: for OME (3 months observation, spontaneous resolution likely)

Pharmacological

• OME: no effective medical treatment (antibiotics, decongestants, antihistamines NOT recommended — NICE NG233)
• Active ear infection: topical or systemic antibiotics as appropriate
• Otosclerosis: sodium fluoride (historical; rarely used now)

Surgical

• Grommets (ventilation tubes): for bilateral OME >3 months with hearing loss ≥25dB (NICE NG233)
• Stapedectomy/stapedotomy: definitive treatment for otosclerosis; >90% success in closing air-bone gap
• Tympanoplasty: repair of TM perforation (success rate 85-95%)
• Ossiculoplasty: reconstruction of disrupted ossicular chain
• Mastoidectomy: for cholesteatoma
• Canalplasty: for exostoses or canal stenosis
• Bone-anchored hearing aid (BAHA): for CHL where conventional hearing aids or surgery not suitable

Referral Criteria

• ENT referral: persistent CHL, suspected cholesteatoma, progressive CHL in young adult (otosclerosis), bilateral OME >3 months in children
• Audiology: all patients for formal assessment
• Emergency: facial nerve palsy, suspected intracranial complication

• Cerumen: immediate restoration of hearing after removal
• OME: >90% resolve spontaneously within 12 months; grommets effective in >90%
• Otosclerosis: stapedectomy success rate >90% for closure of air-bone gap; 1% risk of dead ear
• Tympanoplasty: success rate 85-95% for perforation closure
• Cholesteatoma: requires surgery; recurrence 10-30%
• Maximum CHL: approximately 60dB (remaining hearing via bone conduction)
• Overall, CHL has a better prognosis than SNHL as many causes are surgically correctable

Comparison of Common CHL Causes

Otosclerosis Key Facts