A 28-year-old man with a 1-year history of progressive unilateral conductive hearing loss is suspected to have otosclerosis. Otoscopy and tympanometry are normal. Which single investigation would BEST confirm stapes fixation and support the diagnosis?

Explanation

## Acoustic Reflex Testing in Otosclerosis Diagnosis **Key Point:** Acoustic reflex threshold (ART) testing is the BEST single functional investigation to detect stapes fixation in otosclerosis. Absent or elevated reflexes (>100 dB HL) are highly suggestive of stapes fixation. ### Mechanism of Acoustic Reflex in Otosclerosis 1. **Normal reflex arc:** Sound stimulus → cochlea → CN VIII → CN VII nucleus → stapedius muscle contraction → stapes footplate immobilized 2. **In otosclerosis:** Stapes footplate fixation → stapedius contraction cannot move the stapes → reflex absent or threshold elevated 3. **Sensitivity:** Absent or elevated ART is present in ~95% of otosclerosis cases ### Tympanometry vs. Acoustic Reflex in Otosclerosis | Test | Finding | Interpretation | |---|---|---| | **Tympanometry** | Type A or As (normal or slightly stiffened) | Tympanic membrane and ossicular chain intact; does NOT detect stapes fixation reliably | | **Acoustic reflex** | Absent or threshold >100 dB HL | **Indicates stapes fixation** — highly specific for otosclerosis | | **Acoustic reflex decay** | Abnormal (>50% decay in 10 sec) | Suggests retrocochlear pathology; NOT typical in otosclerosis | **High-Yield:** The combination of **normal tympanometry + absent/elevated acoustic reflex + conductive hearing loss = stapes fixation until proven otherwise.** ### Why Other Options Are Suboptimal **Bone conduction audiometry** (Option B): - Assesses bone conduction thresholds and documents Carhart notch - Functional test; does NOT confirm the anatomical diagnosis of stapes fixation - Requires HRCT for definitive diagnosis **Stroboscopic otomicroscopy** (Option C): - Allows visualization of stapes footplate movement - Requires operative setup; not a routine diagnostic tool - Not practical for initial diagnostic confirmation **Temporal bone MRI with gadolinium** (Option D): - Better for soft tissue and cochlear involvement assessment - Inferior to HRCT for detecting otic capsule lucency and stapes footplate changes - Not the investigation of choice for confirming stapes fixation **Clinical Pearl:** In a patient with normal otoscopy, normal tympanometry, but absent acoustic reflex + conductive hearing loss, otosclerosis is the diagnosis until proven otherwise. HRCT should follow to confirm and stage the disease before surgery. **Mnemonic: "ART" in Otosclerosis** - **A**coustic reflex **T**hreshold elevated or absent = stapes fixation - **R**eflexes are the **R**eal functional indicator of stapes movement - **T**ympanometry alone is **T**oo insensitive to detect fixation