A 38-year-old woman presents with progressive bilateral hearing loss over 6 months. Otoscopy is normal. Weber test shows lateralization to the left ear, and Rinne test shows bone conduction better than air conduction bilaterally. Which investigation is most appropriate to confirm the type of hearing loss and guide further management?

Explanation

## Investigation of Choice: Pure Tone Audiometry ### Clinical Context The patient presents with: - Progressive bilateral hearing loss - Normal otoscopy (rules out obvious conductive pathology) - Weber lateralizing to left ear (suggests asymmetric hearing loss) - Rinne showing bone conduction > air conduction bilaterally (suggests sensorineural pattern) ### Why Pure Tone Audiometry? **Key Point:** Pure tone audiometry is the gold standard and most appropriate initial investigation for characterizing and quantifying hearing loss. It provides: 1. **Frequency-specific thresholds** for both air and bone conduction across the speech range (250–8000 Hz) 2. **Air-bone gap measurement** — the hallmark discriminator between conductive and sensorineural loss 3. **Severity grading** (mild, moderate, severe, profound) 4. **Asymmetry documentation** — essential for unilateral or asymmetric sensorineural hearing loss (ASHL), which may indicate retrocochlear pathology **High-Yield:** In this case, bilateral air-bone gaps would suggest conductive loss; absent air-bone gaps (both air and bone thresholds equally elevated) would confirm sensorineural loss. Asymmetry warrants MRI to exclude acoustic neuroma. ### Comparison with Other Investigations | Investigation | Role | Why Not First-Line Here | |---|---|---| | **Pure Tone Audiometry** | Gold standard; defines type & severity | **CORRECT** — diagnostic & quantitative | | **Tympanometry** | Assesses middle ear compliance & pressure | Useful for conductive loss; normal here (otoscopy normal) | | **Otoacoustic Emissions (OAE)** | Cochlear outer hair cell function | Screening tool; not diagnostic for type or severity | | **Auditory Brainstem Response (ABR)** | Retrocochlear pathway assessment | Reserved for asymmetric SNHL or suspected 8th nerve lesion | **Clinical Pearl:** The Weber lateralization to the left ear in a patient with bilateral sensorineural loss suggests *asymmetric* SNHL — the left ear has *better* bone conduction than the right. This asymmetry is a red flag for retrocochlear pathology (e.g., acoustic neuroma) and would warrant ABR and MRI *after* pure tone audiometry confirms the pattern. ### Algorithm for Hearing Loss Investigation ```mermaid flowchart TD A[Hearing loss complaint]:::outcome --> B[Otoscopy + Weber + Rinne]:::action B --> C{Normal TM?}:::decision C -->|Yes| D[Pure Tone Audiometry]:::action C -->|No| E[Tympanometry + Audiometry]:::action D --> F{Air-bone gap?}:::decision F -->|Yes| G[Conductive loss]:::outcome F -->|No| H[Sensorineural loss]:::outcome H --> I{Asymmetric?}:::decision I -->|Yes| J[ABR + MRI brain]:::action I -->|No| K[Manage per etiology]:::action ``` **Mnemonic:** **PATA** — **P**ure tone audiometry is **A**lways **T**he first **A**udiometric test.