🦻 Hearing Loss & Otosclerosis — Clinical Reference

PART I: TYPES OF HEARING LOSS

1. Conductive Hearing Loss (CHL)

• Cerumen impaction, foreign bodies, or swelling of the external canal
• Tympanic membrane perforation
• Acute otitis media (AOM) / serous otitis media (SOM) — middle ear effusion
• Ossicular chain disruption (e.g., necrosis of the long process of incus from trauma or infection)
• Cholesteatoma — erosion of ossicles by stratified squamous epithelium in the middle ear
• Otosclerosis — stapes fixation
• Superior semicircular canal dehiscence ("third window" pathology)

2. Sensorineural Hearing Loss (SNHL)

• Can range from mild to profound in degree
• The great majority of cases are cochlear (not retrocochlear); therefore the term "sensorineural" is preferred over "nerve loss"
• With longstanding cochlear hearing loss, neuroplastic changes occur in the auditory nervous system

• Noise-induced hearing loss (NIHL)
• Presbycusis (age-related)
• Ototoxic drugs (aminoglycosides, cisplatin, loop diuretics)
• Viral labyrinthitis / bacterial meningitis
• Autoimmune inner ear disease
• Ménière's disease
• Genetic causes (connexin 26 mutations)
• Cochlear otosclerosis

• Vestibular schwannoma (acoustic neuroma)
• Other cerebellopontine angle (CPA) tumors

3. Mixed Hearing Loss

• Advanced otosclerosis (stapes fixation + cochlear involvement)
• Chronic suppurative otitis media with inner ear complications
• Trauma with both ossicular disruption and cochlear damage
• Paget's disease affecting the temporal bone

PART II: INVESTIGATIONS

1. Tuning Fork Tests

Weber Test

• Method: A 512 Hz tuning fork is placed on the center of the forehead, bridge of the nose, or anterior incisors
• Result: The sound lateralizes to the ear with the greater conductive hearing loss (in bilateral disease, to the worse ear)
• Sensitivity: Lateralizes with as little as 5 dB of conductive hearing loss
• Interpretation:
  • Lateralizes to affected ear → Conductive hearing loss in that ear
  • Lateralizes to opposite ear → SNHL in the ipsilateral ear

Rinne Test

• Method: Base of a 512 Hz or 1024 Hz fork placed over the mastoid antrum (bone conduction = BC), then tines placed 2–3 cm from the ear canal opening, parallel to the canal (air conduction = AC)
• Normal (Rinne positive): AC > BC (patient hears the fork longer/louder by air)
• Abnormal (Rinne negative): BC > AC → indicates conductive hearing loss ≥ 20–25 dB
• Clinical rule: If patient reverses both the 512 Hz and 1024 Hz forks, conductive loss is ≥ 30 dB
• Surgical implication: Surgery should not be performed if the 512 Hz fork does not reverse (i.e., Rinne still positive), as the conductive component may be insufficient for surgical correction

2. Pure Tone Audiometry

• Air conduction (AC): Headphones deliver tones; tests the entire auditory pathway
• Bone conduction (BC): Vibrator on mastoid bypasses outer/middle ear; tests cochlea and neural pathway
• Speech audiometry: Assesses speech discrimination scores (SDS); asymmetric scores suggest unilateral pathology (e.g., acoustic neuroma)

3. Impedance Audiometry (Immittance Audiometry)

Tympanometry

• Tympanogram is Type A or Type As (normal or slightly reduced compliance)
• Middle ear pressure is normal (Eustachian tube is unaffected)

Acoustic Reflex Testing

• Tests stapedial reflex (contraction of stapedius muscle at ~70–90 dB above threshold)
• In early otosclerosis: Diphasic (on-off) reflex — a negative on-off deflection
• In established otosclerosis: Absent acoustic reflex — due to stapes fixation
• An intact stapedial reflex should prompt re-evaluation of stapedial fixation as the diagnosis

PART III: OTOSCLEROSIS

Etiology

• Autosomal dominant hereditary disease with variable penetrance (25–40%)
• Approximately 60% have a positive family history; 40–50% of cases are sporadic
• Multifactorial — complex interaction of genetic and environmental factors
• COLIA1 gene implicated in some studies
• Measles virus: Viral particles have been identified in otosclerotic foci, suggesting a viral–genetic interaction
• Hormonal factors: The condition is accelerated by pregnancy; many women first notice hearing loss during or shortly after their first pregnancy
• Sex distribution: Twice as common in women (2:1 female-to-male)
• Race: Most prevalent in Caucasians of European descent (clinical prevalence 0.3–0.4%; histologic prevalence 10–12%). Rare in individuals of African descent, Asians, and Native Americans
• Age of onset: Third decade of life; bilateral in 75% of cases

Pathology

• Osteoclasts resorb normal lamellar otic capsule bone → pseudovascular spaces form
• Lesions extend into the otic capsule in finger-like projections
• Lesion cells have an affinity for hematoxylin → bone appears darker histologically
• Osteoclasts are multinucleated and appear at the advancing edge
• Earliest lesions appear adjacent to the fissula ante fenestram (anterior oval window)

1. Lesions spread across the stapedial annular ligament → stapedial fixation → Conductive hearing loss
2. If the lesion progresses to flow across the ligament onto the footplate → obliteration of annular ligament → "biscuit" footplate (solid footplate)
3. If the lesion extends medially to involve the endosteum of the cochlea → collagen deposition in the spiral ligament → hyalinization → SNHL (cochlear otosclerosis)
4. Spread in both directions → mixed hearing loss

Differential Diagnosis

Medical Management of Otosclerosis

1. Hearing rehabilitation — Hearing Aids
   • Amplification is effective especially in early/mild-to-moderate disease
   • Useful for patients who are poor surgical candidates, decline surgery, or have bilateral disease requiring interim management
   • The better-hearing ear is typically fitted first
2. Fluoride Therapy (Sodium Fluoride)
   • Proposed mechanism: Fluoride ion replaces hydroxyl ions in hydroxyapatite crystals → converts active otospongiosis to more stable fluoroapatite → reduces bone resorption and stabilizes disease
   • Used mainly for cochlear otosclerosis to arrest progression of SNHL
   • Dose: Typically sodium fluoride 20–40 mg/day with calcium and vitamin D supplementation
   • Evidence for efficacy is of uncertain value (Harrison's Internal Medicine 22E)
   • Not curative; does not reverse established fixation
3. Bisphosphonates (e.g., etidronate, risedronate)
   • Inhibit osteoclastic activity; investigated as alternative to fluoride therapy
   • May slow disease progression in active otospongiosis
   • Used when fluoride is contraindicated or poorly tolerated
4. Management of Vestibular Symptoms
   • If vestibular symptoms (dysequilibrium) coexist with otosclerosis, vestibular suppressants may be used
   • If otosclerotic focus is around the vestibular labyrinth with elevated blood glucose/lipids, fluoride therapy is indicated

Surgical Management of Otosclerosis

Pre-Surgical Considerations

• Thorough counseling regarding risks and alternatives
• The poorer-hearing ear is selected for surgery first
• Never operate on the only hearing ear
• 512 Hz Rinne must reverse (BC > AC) before surgery is considered; if the 512 Hz fork does not reverse, there may be increased risk of mobilizing the stapes

Options for Surgical Treatment

Stapedotomy (Preferred Technique)

1. Procedure performed under local anesthesia + IV sedation (MAC) or general anesthesia
2. Four-quadrant canal block with 1% lidocaine + 1:100,000 epinephrine
3. Tympanomeatal flap incisions, elevation; enter middle ear beneath annulus; free chorda tympani
4. Remove bone from posterosuperior canal wall for visualization
5. Separate incudostapedial joint; section stapedius tendon
6. Remove stapes superstructure
7. Create fenestra in footplate using micropick, microdrill, or laser
   • Laser types used: KTP-532 (green), Argon (green), CO₂ (infrared)
   • Advantage of laser: greater accuracy, less mechanical trauma
8. Measure distance from incus to footplate; select prosthesis length
9. Prosthesis placement: Piston (wire/clip) inserted into fenestra, crimped to long process of incus

Stapedectomy vs. Stapedotomy

• Stapedotomy now favored by most surgeons — limited fenestration = lower risk of inner ear trauma, lower risk of post-op high-frequency SNHL
• Slightly better early/late post-op thresholds at 4 kHz with stapedotomy
• Long-term hearing outcomes are equivalent in experienced hands

Prosthesis Types

• Wire piston, Teflon piston, titanium clips
• All modern prostheses are MRI-compatible
• Measurement taken from incus to footplate

Post-Operative Care

• Head elevated 30° post-operatively
• Discharge ~1–2 hours post-procedure if no vertigo
• Dry-ear precautions for 3 weeks
• Swimming/diving permitted 3 weeks post-surgery
• Tuning fork examination at 3-week follow-up
• First audiogram at 3-month follow-up

Complications

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