A 68-year-old woman presents with insidious onset bilateral hearing loss over 2 years, worse for low frequencies. She denies tinnitus or vertigo. On examination, otoscopy is normal. Weber test shows no lateralization. Rinne test reveals air conduction better than bone conduction bilaterally. Audiometry shows a characteristic U-shaped curve with bone and air conduction thresholds tracking together. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Presbycusis (Age-Related Sensorineural Hearing Loss) ### Key Diagnostic Features **High-Yield:** The combination of: - Bilateral, symmetrical, progressive hearing loss - Normal otoscopy - Air conduction better than bone conduction (both reduced equally) - U-shaped or reverse-slope audiometric curve - Low-frequency predominance in this case This constellation is diagnostic of presbycusis, the most common cause of hearing loss in the elderly. ### Audiometric Pattern: U-Shaped Curve The **U-shaped audiogram** (also called reverse-slope or low-frequency SNHL) is characteristic of presbycusis: - Low frequencies are disproportionately affected - Mid-frequencies may be relatively preserved - High frequencies may show secondary involvement - Air and bone conduction thresholds track together (both reduced equally) — hallmark of sensorineural pathology **Mnemonic: SNHL Pattern Recognition** - **S**ymmetrical bilateral loss - **N**ormal otoscopy - **H**igh-frequency dip (noise-induced) OR low-frequency dip (presbycusis) - **L**oss of air-bone gap (AC ≈ BC, both reduced) ### Pathophysiology of Presbycusis Age-related cochlear degeneration involves: 1. Loss of inner and outer hair cells (basal turn initially) 2. Atrophy of the stria vascularis 3. Degeneration of spiral ganglion neurons 4. Stiffening of the basilar membrane The **low-frequency predominance** in this patient suggests strial presbycusis (metabolic dysfunction) rather than sensory presbycusis (hair cell loss). ### Rinne Test Interpretation **Key Point:** In presbycusis, air conduction is better than bone conduction *because both are reduced equally* — the air-bone gap is preserved (not reversed). This distinguishes SNHL from conductive loss: | Loss Type | Rinne Finding | Air-Bone Gap | |---|---|---| | Conductive | AC < BC (AC worse) | Gap present (>10 dB) | | Sensorineural | AC > BC (both reduced) | Gap absent or minimal | | Mixed | AC much worse than BC | Large gap | **Clinical Pearl:** No lateralization on Weber test in bilateral symmetric SNHL is expected; if lateralization occurs, suspect asymmetric loss or retrocochlear pathology (acoustic neuroma). ### Why This Is Not Other Conditions - **Otosclerosis:** Causes conductive or mixed hearing loss with AC < BC on Rinne; typically shows high-frequency bone conduction loss (Carhart notch at 2 kHz) - **Sudden SNHL:** Unilateral, acute onset, often high-frequency; this patient has bilateral, chronic, low-frequency loss - **Cerumen impaction:** Unilateral, visible on otoscopy, conductive pattern (AC < BC) [cite:Park 26e Ch 32; Hazarika 5e Ch 14]