A 52-year-old man from Delhi presents with progressive bilateral hearing loss over 6 months. He reports tinnitus and occasional vertigo. On examination, Weber test shows lateralization to the right ear, and Rinne test demonstrates bone conduction better than air conduction bilaterally. Otoscopy reveals normal tympanic membranes. Pure tone audiometry shows air-bone gap of 35 dB at 2 kHz. What is the most likely diagnosis?

Explanation

## Diagnosis: Bilateral Conductive Hearing Loss ### Clinical Reasoning **Key Point:** The presence of an air-bone gap (ABG) on pure tone audiometry is the hallmark of conductive hearing loss. An ABG of 35 dB at 2 kHz is diagnostic of conductive pathology. **High-Yield:** In conductive hearing loss: - Bone conduction (BC) thresholds remain normal (≤20 dB HL) - Air conduction (AC) thresholds are elevated - ABG = AC threshold − BC threshold - ABG ≥20 dB indicates conductive loss ### Audiometric Interpretation The Rinne test showing BC > AC bilaterally confirms conductive pathology. Weber test lateralization to the right ear suggests either: 1. Worse conductive loss on the right (bone conduction pathway favors the better ear) 2. Asymmetric disease Normal otoscopy does not exclude conductive loss—ossicular chain pathology (otosclerosis, ossicular fixation, or discontinuity) can present with normal tympanic membranes. ### Differential Diagnosis of Bilateral Conductive Loss | Condition | Features | Age of Onset | |-----------|----------|---------------| | **Otosclerosis** | Progressive, bilateral, stapes fixation, normal TM | 20–50 years | | **Chronic OME** | Fluid level, air-fluid interface, conductive loss | Any age | | **Ossicular fixation** | Trauma, infection, or idiopathic | Variable | | **Congenital ossicular anomaly** | Present since birth, progressive | Birth | **Clinical Pearl:** Otosclerosis is the most common cause of progressive bilateral conductive hearing loss in adults aged 40–60 years, particularly in women. The normal otoscopy and progressive nature over 6 months fit this diagnosis perfectly. ### Why Tinnitus and Vertigo Occur Otosclerosis can cause: - **Tinnitus:** From stapes footplate fixation and altered cochlear mechanics - **Vertigo:** From labyrinthine involvement (cochlear otosclerosis) ### Management Implications Confirmatory investigations: - **High-resolution CT temporal bones:** Shows stapes footplate thickening and demineralization - **Stapedial reflex:** Absent or reduced (stiffened ossicular chain) - **Tympanometry:** Type A (normal) in otosclerosis, Type B in OME **Tip:** Always differentiate conductive from sensorineural loss before ordering imaging. The ABG is your diagnostic anchor.