A 32-year-old woman presents with progressive bilateral hearing loss over the past 18 months. She reports tinnitus and occasional vertigo. On examination, Weber test shows bone conduction better than air conduction bilaterally (bone conduction threshold 20 dB, air conduction threshold 40 dB). Otoscopy reveals a normal tympanic membrane. Audiometry confirms conductive hearing loss with an air-bone gap of 20 dB. CT temporal bone shows bilateral stapes fixation with normal ossicular chain. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Otosclerosis ### Key Clinical Features **Key Point:** Otosclerosis is a primary bone dysplasia of the otic capsule causing progressive fixation of the stapes footplate, leading to conductive hearing loss. ### Diagnostic Criteria Met in This Case | Feature | Finding | Significance | |---------|---------|---------------| | Age of onset | 32 years (young adult) | Typical age 20–40 years; rare before age 15 | | Gender | Female | 2:1 female predominance | | Progression | Bilateral, gradual | Bilateral involvement in ~70% of cases | | Hearing pattern | Conductive (air-bone gap 20 dB) | Stapes fixation reduces ossicular mobility | | Weber test | Bone conduction > air conduction | Confirms conductive loss | | Otoscopy | Normal TM | Rules out middle ear infection | | CT findings | Bilateral stapes fixation, normal ossicles | Pathognomonic for otosclerosis | | Associated symptoms | Tinnitus, vertigo | Common in otosclerosis | ### Pathophysiology 1. **Abnormal bone remodeling** in the otic capsule (endochondral bone) 2. **Stapes footplate fixation** at the oval window 3. **Reduced ossicular chain mobility** → conductive hearing loss 4. Progression may lead to **mixed or sensorineural hearing loss** (cochlear involvement) ### High-Yield Mnemonic: **OTOSCLEROSIS** - **O**tic capsule dysplasia - **T**ypical age 20–40 years - **O**ssicular fixation (stapes) - **S**ensorineural + conductive loss possible - **C**arhart notch (bone conduction peak at 2 kHz on audiometry) - **L**ateral canal (anterior oval window involvement) - **E**ndochondral bone remodeling - **R**adiolucent foci on HRCT (lytic phase) - **O**ssicles normal on imaging - **S**urgical cure: stapedectomy/stapedotomy - **I**nheritance: autosomal dominant (60% of cases) - **S**ymmetrical bilateral involvement common ### Carhart Sign **Clinical Pearl:** A characteristic **bone conduction peak at 2 kHz** (Carhart notch) on audiometry is highly suggestive of otosclerosis, though not pathognomonic. This represents the resonance frequency of the ossicular chain when stapes is fixed. ### Imaging Findings ```mermaid flowchart TD A[Otosclerosis on HRCT]:::outcome --> B{Phase of disease}:::decision B -->|Lytic phase| C[Radiolucent foci around oval window]:::action B -->|Mixed phase| D[Both radiolucent and sclerotic areas]:::action B -->|Sclerotic phase| E[Sclerotic bone, stapes fixation]:::action C --> F[Stapes footplate fixation]:::outcome D --> F E --> F F --> G[Conductive hearing loss]:::outcome ``` ### Natural History **High-Yield:** Progressive hearing loss occurs in ~2/3 of patients; ~1/3 remain stable. Pregnancy may accelerate progression (hormonal factors). ### Management - **Hearing aids** for mild-to-moderate loss - **Stapedectomy or stapedotomy** (gold standard surgical treatment) - Success rate: >90% restoration of air-bone gap - Risks: sensorineural hearing loss, facial nerve injury, perilymphatic fistula - **Sodium fluoride** (experimental; evidence weak) — may slow progression in some cases [cite:Dhingra ENT 8e Ch 11]