A 52-year-old male presents to the ENT clinic with progressive bilateral hearing loss over 6 months. He denies ear discharge, tinnitus, or vertigo. Otoscopy reveals normal tympanic membranes bilaterally. Weber test shows lateralization to the right ear, and Rinne test demonstrates bone conduction better than air conduction bilaterally. Pure tone audiometry shows a bilateral air-bone gap of 30 dB across all frequencies. What is the most likely diagnosis?

Explanation

## Diagnosis: Bilateral Conductive Hearing Loss ### Clinical Reasoning **Key Point:** The presence of an air-bone gap (ABG) of 30 dB is the hallmark of conductive hearing loss. In this patient, bone conduction thresholds are significantly better than air conduction thresholds bilaterally, confirming conductive pathology. ### Audiometric Interpretation | Finding | Conductive HL | Sensorineural HL | Mixed HL | |---------|---------------|------------------|----------| | Air-bone gap | Present (≥20 dB) | Absent | Present | | Bone conduction | Normal/near-normal | Elevated | Elevated | | Air conduction | Elevated | Elevated | Elevated | | Weber lateralization | To affected ear | Away from affected ear | Variable | **High-Yield:** A positive air-bone gap of 30 dB is diagnostic of conductive hearing loss. The normal tympanic membranes on otoscopy rule out otitis media; ossicular chain pathology (otosclerosis, ossicular discontinuity) or eustachian tube dysfunction are the likely causes. ### Weber and Rinne Test Interpretation **Clinical Pearl:** In conductive hearing loss: - **Weber test** lateralizes to the affected (worse-hearing) ear because bone conduction bypasses the conductive defect, making the affected side relatively louder. - **Rinne test** shows bone conduction > air conduction (BC > AC) because the conductive defect impairs air conduction preferentially. **Mnemonic: CONDUCTIVE LOSS = BC > AC, Weber to affected side** ### Differential Considerations 1. **Otosclerosis** — most common cause of progressive conductive HL in adults; bilateral involvement in ~70% of cases; normal TM on otoscopy. 2. **Ossicular discontinuity** — trauma, erosion from cholesteatoma, or congenital. 3. **Eustachian tube dysfunction** — less likely to cause 30 dB ABG bilaterally without TM retraction. [cite:Dhingra 8e Ch 5] --- ### Why Sensorineural Hearing Loss is Wrong Sensorineural loss would show **no air-bone gap**; both air and bone conduction would be equally elevated. Rinne would show AC > BC (air > bone). ### Why Mixed Hearing Loss is Wrong Mixed loss would show both an air-bone gap AND elevated bone conduction thresholds. Here, bone conduction is normal/near-normal, ruling out a significant sensorineural component. ### Why Sudden Sensorineural Hearing Loss is Wrong SSNHL presents with rapid onset (hours to days), not gradual progression over 6 months. It would lack an air-bone gap and show AC = BC elevation.