A 52-year-old man presents to the ENT clinic with progressive hearing loss over the past 6 months. He reports difficulty hearing high-pitched sounds and tinnitus in both ears. Otoscopy reveals normal tympanic membranes bilaterally. Weber test shows lateralization to the right ear, and Rinne test demonstrates bone conduction better than air conduction bilaterally. Pure tone audiometry shows a high-frequency dip at 4 kHz. What is the most likely type of hearing loss?

Explanation

## Clinical Diagnosis: Sensorineural Hearing Loss (SNHL) — Noise-Induced Pattern ### Key Audiometric & Clinical Findings **High-Yield:** The combination of normal otoscopy, absent air-bone gap on Rinne test (with both AC and BC reduced), Weber lateralization to the *better-hearing* ear, and a 4 kHz notch on pure tone audiometry is pathognomonic for sensorineural hearing loss with a noise-induced pattern. ### Understanding the Rinne Test in SNHL **Key Point:** In SNHL, both air conduction (AC) and bone conduction (BC) are reduced proportionally — there is **no air-bone gap**. The Rinne test shows BC ≥ AC (or AC ≈ BC), which can be misread as a "negative Rinne." However, this differs fundamentally from conductive loss: in conductive loss, BC is *preserved* while AC is impaired, creating a true air-bone gap. In SNHL, both pathways are equally diminished because the cochlear transduction itself is impaired, not the sound transmission mechanism. ### Weber Test Interpretation In SNHL, the Weber test lateralizes to the **better-hearing (less affected) ear** — sound appears louder on the side with more intact cochlear function. In this vignette, lateralization to the right ear implies the *left* ear has greater sensorineural impairment. This is the opposite of conductive loss, where Weber lateralizes to the *worse* (more affected) ear. ### Pattern Recognition: 4 kHz Notch The characteristic **high-frequency dip at 4 kHz** is the classic audiometric signature of noise-induced hearing loss (NIHL). This notch occurs because: - The basal cochlear region encoding 4 kHz is maximally vulnerable to acoustic trauma - Outer hair cells (OHCs) in this region are preferentially damaged by intense sound - The notch typically widens to adjacent frequencies (3–6 kHz) with continued exposure **Differential of 4 kHz notch:** - **Occupational noise exposure** (most common): sustained loud machinery, construction - **Recreational exposure**: firearms, concerts, headphone use - **Ototoxicity** (aminoglycosides, cisplatin): typically causes high-frequency loss but may not show a discrete 4 kHz notch ### Differential Features | Feature | Conductive Loss | Sensorineural Loss | |---------|---|---| | Otoscopy | Abnormal (TM perforation, fluid, ossicular fixation) | Normal | | Rinne Test | BC > AC (true air-bone gap) | AC ≈ BC (no air-bone gap; both reduced) | | Weber Test | Lateralizes to *worse* (conductive) ear | Lateralizes to *better-hearing* ear | | Audiometry | Flat loss across frequencies | Frequency-specific (4 kHz notch in NIHL) | | Tinnitus | Rare | Common | ### Why Other Options Are Incorrect - **Option A (Mixed loss):** Mixed loss shows both an air-bone gap AND reduced BC. Here, BC is reduced without a gap — pure SNHL pattern. - **Option B (Ossicular disruption):** Would show abnormal Rinne with preserved BC and a significant air-bone gap; otoscopy may be abnormal. - **Option C (Cerumen impaction):** Would cause conductive loss with abnormal otoscopy; cerumen would be visible on otoscopy. **Clinical Pearl:** Normal tympanic membranes on otoscopy effectively rule out most causes of conductive hearing loss (TM perforation, otitis media with effusion, cerumen impaction). High-frequency predominance and tinnitus strongly favor cochlear pathology. [cite: Scott-Brown's Otorhinolaryngology 8e Ch 233; Cummings Otolaryngology 7e Ch 152; Harrison's Principles of Internal Medicine 21e Ch 36]