A 28-year-old woman presents to the ENT clinic with progressive bilateral hearing loss over the past 18 months. She 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 is normal. Audiometry reveals a low-frequency sensorineural hearing loss with a characteristic 2 kHz dip. She denies otalgia, otorrhea, or recent head trauma. What is the most likely diagnosis?

Explanation

## Diagnosis: Otosclerosis ### Clinical Presentation **Key Point:** Otosclerosis is a primary disorder of bone metabolism affecting the otic capsule, causing progressive conductive or mixed hearing loss, typically in young adults (20–40 years), with female predominance (2:1). ### Diagnostic Features in This Case | Feature | Finding | Significance | |---------|---------|---------------| | **Age & sex** | 28-year-old woman | Peak incidence; female predominance | | **Onset** | Insidious, progressive over 18 months | Typical gradual progression | | **Tinnitus** | Present | Common early symptom | | **Vertigo** | Occasional | Occurs when stapes footplate fixation affects vestibular input | | **Weber test** | Lateralizes to right (bone conduction better) | Indicates conductive or mixed loss on right | | **Rinne test** | Bone > air bilaterally | Hallmark of conductive/mixed hearing loss | | **Otoscopy** | Normal | Rules out external/middle ear pathology | | **Audiometry pattern** | Low-frequency SNHL with 2 kHz dip | **Carhart notch** — pathognomonic for otosclerosis | ### Pathophysiology **High-Yield:** Otosclerosis involves abnormal bone remodeling in the otic capsule, most commonly at the **stapes footplate–oval window junction**. This leads to: 1. **Stapes fixation** → conductive hearing loss (initial) 2. **Cochlear involvement** → sensorineural component (cochlear otosclerosis) 3. **Mixed hearing loss** in advanced disease ### Carhart Notch **Mnemonic:** **CARHART** = **C**ochleal **A**bnormality **R**elated **T**o **H**earing **A**nd **R**emodeling **T**issue - A characteristic **bone conduction dip at 2 kHz** (or 500 Hz–2 kHz range) - Seen on audiometry in ~90% of otosclerosis cases - Reflects cochlear involvement despite stapes fixation - Improves after successful stapes surgery ### Imaging & Diagnosis **Clinical Pearl:** High-resolution CT temporal bones shows: - **Lucency around the oval window** ("halo sign") - **Demineralization of otic capsule** - **Stapes footplate fixation** Confirmatory test: **Tympanometry** shows **Type A curve** (normal middle ear pressure and compliance) — rules out fluid or TM perforation. ### Management Overview ```mermaid flowchart TD A[Otosclerosis diagnosed]:::outcome --> B{Hearing loss severity & patient preference?}:::decision B -->|Mild, observation acceptable| C[Watchful waiting + hearing aid trial]:::action B -->|Moderate-severe, surgical candidate| D[Stapedectomy/Stapes replacement]:::action C --> E[Annual audiometry monitoring]:::action D --> F[Excellent success rate ~90%]:::outcome D --> G[Risks: SNHL, vertigo, facial nerve injury]:::urgent ``` **Key Point:** Sodium fluoride therapy has limited evidence and is not standard of care in most guidelines.