A 28-year-old man with a 3-year history of progressive conductive hearing loss is suspected to have otosclerosis. His audiogram shows a characteristic dip at 2 kHz with better bone conduction than air conduction. Which investigation would be most specific to confirm stapes fixation and rule out other causes of conductive hearing loss?

Explanation

## Confirming Stapes Fixation: Impedance Audiometry **Key Point:** Impedance audiometry (tympanometry) with acoustic reflex measurement is the most specific functional test to confirm stapes fixation in otosclerosis by demonstrating absent or severely reduced stapedial reflexes. ### Impedance Audiometry in Otosclerosis **High-Yield:** Impedance audiometry findings in otosclerosis: - **Type A tympanogram** — Normal middle ear compliance (rules out TM perforation, ossicular discontinuity) - **Absent or severely reduced stapedial reflexes** — Indicates stapes fixation (pathognomonic for otosclerosis when combined with conductive hearing loss) - **Bilateral findings** — Often present in otosclerosis ### Differential Diagnosis Using Impedance Audiometry | Condition | Tympanogram | Stapedial Reflex | Air-Bone Gap | |-----------|-------------|------------------|---------------| | **Otosclerosis** | Type A | Absent/reduced | Present | | **Ossicular discontinuity** | Type A | Absent | Present | | **TM perforation** | Type B | Absent | Variable | | **Middle ear effusion** | Type B | Absent | Present | | **Normal ear** | Type A | Present | Absent | **Clinical Pearl:** The combination of **Type A tympanogram + absent stapedial reflexes + conductive hearing loss** is highly suggestive of stapes fixation from otosclerosis. However, HRCT is still required to visualize the bony pathology and confirm the diagnosis. ### Why Impedance Audiometry is Specific 1. **Stapes fixation** → Stapedius muscle cannot move the fixed stapes → Acoustic reflex absent 2. **Normal middle ear pressure** → Type A tympanogram (rules out middle ear pathology) 3. **Non-invasive and rapid** — Can be performed in the clinic **Warning:** Absent stapedial reflexes are NOT pathognomonic for otosclerosis alone. They can also occur in: - Ossicular discontinuity (but usually Type A tympanogram) - Severe conductive hearing loss (any cause) - Facial nerve paralysis (stapedius innervation) **Mnemonic:** **STAR** = **S**tapes fixation → **T**ype A tympanogram, **A**bsent **R**eflex [cite:Park 26e Ch 72]