A 32-year-old woman presents with progressive bilateral conductive hearing loss over 2 years. Otoscopy reveals a normal tympanic membrane. Weber test shows lateralization to the right ear, and Rinne test demonstrates bone conduction better than air conduction bilaterally. Which investigation is most appropriate to confirm the diagnosis of otosclerosis?

Explanation

## Investigation of Choice to Confirm Otosclerosis **Key Point:** Tympanometry with acoustic reflex testing is the most appropriate investigation to confirm the clinical diagnosis of otosclerosis, demonstrating a characteristic Type As (stiffness-type) tympanogram with absent ipsilateral and contralateral acoustic reflexes. ### Why Tympanometry + Acoustic Reflex Testing is the Answer 1. **Type As tympanogram** — reduced compliance (shallow peak) due to stapes footplate fixation; this is the hallmark finding in otosclerosis 2. **Absent acoustic (stapedial) reflexes** — stapes fixation prevents the stapedius muscle from producing the normal reflex contraction; absence is highly characteristic and virtually diagnostic in the right clinical context 3. **Non-invasive, widely available, and reproducible** — the first-line confirmatory test in clinical practice 4. **Directly tests middle ear mechanics** — otosclerosis is fundamentally a disease of stapes fixation, and tympanometry + acoustic reflexes assess exactly this pathophysiology ### Role of Other Investigations | Investigation | Finding in Otosclerosis | Diagnostic Value | |---|---|---| | **Tympanometry + acoustic reflex** | Type As tympanogram; absent stapedial reflexes | **Confirmatory — investigation of choice** | | **Pure tone audiometry** | Carhart notch (BC dip at 2 kHz); conductive/mixed loss | Functional assessment, supports diagnosis but not confirmatory | | **HRCT temporal bone** | Lucency around stapes footplate ("halo" / "fisheye" lesion); otic capsule demineralization | Used for surgical planning (pre-stapedectomy), NOT the primary confirmatory test; early disease may be CT-negative | | **Electrocochleography** | May show cochlear involvement in advanced cases | Research tool, not routine diagnostic | **High-Yield:** The classic tympanometric profile in otosclerosis is **Type As** (reduced compliance, normal peak pressure) with **absent ipsilateral and contralateral acoustic reflexes** — this combination in a patient with conductive hearing loss and normal otoscopy is virtually diagnostic (Scott-Brown's Otorhinolaryngology, 8th ed.; Dhingra's Diseases of Ear, Nose & Throat, 7th ed.). **Clinical Pearl:** HRCT temporal bone is reserved for **pre-operative assessment** (confirming fenestral vs. cochlear otosclerosis, assessing footplate thickness, ruling out superior semicircular canal dehiscence) — it is NOT the first-line confirmatory investigation. Early otosclerosis may not even show CT changes, whereas acoustic reflex testing will already be abnormal. **Why not HRCT (Option A)?** Although HRCT can visualise the "halo sign" around the stapes footplate, it is insensitive in early disease and is primarily used for surgical planning, not initial confirmation. Tympanometry + acoustic reflex testing is the standard first-line confirmatory investigation. **Mnemonic: "STAR" in Otosclerosis** - **S**tapes fixation - **T**ympanometry → Type As - **A**coustic reflex → Absent - **R**inne → BC > AC (negative Rinne)