A 58-year-old man presents with progressive bilateral hearing loss over 2 years. He denies tinnitus, vertigo, or ear discharge. Otoscopy is normal. Pure tone audiometry shows bone conduction thresholds of 15 dB HL and air conduction thresholds of 45 dB HL at 500 Hz, 50 dB HL at 1 kHz, and 55 dB HL at 2 kHz. Speech discrimination is 88%. What does this audiogram pattern indicate?

Explanation

## Audiogram Interpretation ### Key Findings The audiogram shows: - **Air conduction (AC) thresholds:** 45–55 dB HL (elevated) - **Bone conduction (BC) thresholds:** 15 dB HL (normal) - **Air-bone gap (ABG):** 30–40 dB HL - **Speech discrimination:** 88% (preserved) ### Definition of Conductive Hearing Loss **Key Point:** Conductive hearing loss is defined by an air-bone gap of ≥15 dB HL at two or more frequencies. The presence of normal bone conduction with elevated air conduction indicates the problem lies in the external or middle ear, not the cochlea. ### Why This Is Conductive Hearing Loss 1. **Normal BC thresholds** → cochlear function is intact 2. **Elevated AC thresholds** → sound transmission is impaired 3. **Preserved speech discrimination** → inner ear processing is normal (typical of conductive loss; sensorineural loss often shows poor discrimination) 4. **Normal otoscopy** → suggests middle ear pathology (otosclerosis, ossicular discontinuity, serous otitis media, or stapes fixation) ### Common Causes of Conductive Hearing Loss with Normal Otoscopy | Condition | Key Feature | Age Group | | --- | --- | --- | | Otosclerosis | Carhart's notch at 2 kHz; progressive | 20–40 years | | Ossicular discontinuity | Post-traumatic or congenital | Any age | | Serous otitis media | Fluid level on otoscopy or imaging | Children > adults | | Stapes fixation | Reduced stapes mobility on impedance | Middle-aged | **Clinical Pearl:** The absence of tinnitus and vertigo, combined with normal otoscopy and preserved speech discrimination, makes otosclerosis the most likely diagnosis in this age group. Otosclerosis typically presents with a **Carhart's notch** (bone conduction dip at 2 kHz), though not always evident on initial audiometry. ### High-Yield Mnemonic: ABG Classification **ABG = Air-Bone Gap** - **ABG ≥15 dB:** Conductive hearing loss - **ABG <15 dB:** Sensorineural hearing loss - **ABG ≥15 dB + elevated BC:** Mixed hearing loss [cite:Glasscock-Shambaugh Surgery of the Ear Ch 2]