What are the physical and audiometric findings in otosclerosis?

Physical and Audiometric Findings in Otosclerosis

Otosclerosis is characterized by normal otoscopic examination with conductive hearing loss, a negative Rinne test, and an audiogram showing a low-frequency air-bone gap with potential high-frequency sensorineural hearing loss. 1

Physical Examination Findings

Otoscopic Examination

• Tympanic membrane appears normal in most cases 2
• Occasionally, a pinkish hue behind the tympanic membrane may be visible (Schwartz sign) due to increased vascularity of the promontory 1
• Unlike other causes of conductive hearing loss, there are no visible abnormalities of the ear canal, tympanic membrane, or middle ear space 1

Tuning Fork Tests

• Weber test: Sound lateralizes to the affected ear (indicating conductive hearing loss) 1
• Rinne test: Bone conduction is perceived as louder than air conduction (negative Rinne) in the affected ear 1

Audiometric Findings

Pure Tone Audiometry

• Conductive hearing loss (primary finding)

  • Air-bone gap typically 20-60 dB 1
  • Most pronounced in low frequencies (250-500 Hz) 1
  • "Carhart notch": A characteristic depression in bone conduction thresholds at 2000 Hz 1

• Mixed hearing loss (in advanced cases)

  • Sensorineural component develops over time 3
  • High-frequency bone conduction threshold elevation 3
  • Correlates with duration of hearing loss 3

Speech Audiometry

• Word recognition scores typically remain good despite significant hearing loss 1
• Speech recognition threshold correlates with pure tone average 1

Tympanometry

• Type A tympanogram (normal middle ear pressure and compliance) 1
• Unlike other causes of conductive hearing loss, tympanometry is typically normal 1

Distinguishing Features from Other Conditions

• Unlike otitis media, no middle ear effusion or tympanic membrane abnormalities 1
• Unlike ossicular discontinuity, the air-bone gap is usually more pronounced in lower frequencies 1
• Unlike non-otosclerotic stapes ankylosis, high-frequency sensorineural hearing loss develops over time 3

Clinical Course and Progression

• Typically begins unilaterally but becomes bilateral in 70-80% of cases 2
• Progressive conductive hearing loss that may develop a sensorineural component 4
• Tinnitus is common, reported in approximately 65% of patients 4
• Vertigo is rare, and its presence should prompt investigation for other diagnoses 2

Diagnostic Pitfalls to Avoid

• Do not rely solely on otoscopic examination as it appears normal in most cases 2
• Do not mistake the conductive component for sensorineural hearing loss without proper audiometric testing 1
• Remember that a negative Rinne test may be falsely positive in cases of profound sensorineural hearing loss 1
• High-resolution CT of the temporal bone may be needed to confirm diagnosis, especially when surgical intervention is being considered 1

The combination of normal otoscopic findings with conductive hearing loss on audiometry should always raise suspicion for otosclerosis, particularly in middle-aged adults with a family history of progressive hearing loss.