A 35-year-old man presents with progressive hearing loss over 6 months. Otoscopy reveals a retracted tympanic membrane with fluid level. Weber test shows lateralization to the affected ear, and Rinne test demonstrates bone conduction better than air conduction on the affected side. Which single finding best distinguishes this conductive hearing loss from sensorineural hearing loss?

Explanation

## Distinguishing Conductive from Sensorineural Hearing Loss ### Rinne Test Interpretation **Key Point:** The Rinne test is the single most reliable bedside discriminator between conductive and sensorineural hearing loss. - **Conductive loss:** Bone conduction (BC) > Air conduction (AC) — because the ossicular chain is bypassed when vibrations are applied directly to the mastoid. - **Sensorineural loss:** Air conduction (AC) > Bone conduction (BC) — both pathways are affected equally or AC is relatively preserved. ### Comparison Table | Feature | Conductive HL | Sensorineural HL | |---------|---------------|------------------| | **Rinne test** | BC > AC | AC > BC | | **Weber test** | Lateralizes to affected (poorer) ear | Lateralizes to normal (better) ear | | **Audiometry pattern** | Flat or low-frequency loss | High-frequency loss (notch at 4 kHz) | | **Stapedial reflex** | Absent or reduced | Present (unless severe) | | **Recruitment** | Absent | Present | | **Speech discrimination** | Good (if hearing restored) | Often poor | ### Why BC > AC is the Best Discriminator **High-Yield:** The Rinne test result is pathognomonic for conductive loss. When bone conduction is better than air conduction, it immediately tells you the inner ear (cochlea) is functioning normally — the problem is in the conductive pathway (external ear, tympanum, or ossicles). **Clinical Pearl:** In this case, the fluid level (serous otitis media) blocks sound transmission through the ossicular chain, but the cochlea itself is intact. Bone vibrations bypass the fluid and reach the inner ear directly, hence BC > AC. ### Mechanism 1. Normal ear: AC > BC (air is more efficient at driving the stapes) 2. Conductive block: AC is attenuated; BC reaches cochlea directly → BC > AC 3. Sensorineural damage: Both AC and BC are reduced equally → AC still > BC, but both are poor