A 72-year-old woman presents with gradual bilateral hearing loss over the past 20 years. She reports difficulty understanding conversations, especially in noisy environments, and says "I can hear but cannot understand." Otoscopy is normal. Pure tone audiometry shows bilateral high-frequency sensorineural hearing loss with air-bone gap <5 dB. Speech discrimination score is 45%, which is disproportionately lower than expected from the pure tone thresholds. What is the most likely diagnosis?

Explanation

## Diagnosis: Age-Related Hearing Loss (Presbycusis) **Key Point:** Presbycusis is characterized by **bilateral high-frequency sensorineural hearing loss** with **disproportionately poor speech discrimination** — a hallmark finding that distinguishes it from other causes of hearing loss. ### Audiogram Pattern and Speech Discrimination Mismatch | Feature | Presbycusis | NIHL | Acoustic Neuroma | Congenital SNHL | |---------|-------------|------|------------------|------------------| | **Frequency pattern** | High frequencies (>2 kHz) | 4 kHz notch | Variable, often high freq | Variable | | **Symmetry** | Bilateral symmetrical | Bilateral symmetrical | Usually unilateral | Bilateral or unilateral | | **Speech discrimination** | **Disproportionately poor** | Relatively preserved | Poor (retrocochlear sign) | Variable | | **Age of onset** | >60 years (gradual) | Any age (occupational) | Any age | Birth or early childhood | | **Air-bone gap** | <5 dB (sensorineural) | <5 dB (sensorineural) | <5 dB (sensorineural) | <5 dB (sensorineural) | | **Occupational risk** | No | Yes | No | No | | **Otoscopy** | Normal | Normal | Normal | Normal | **High-Yield:** The **"I can hear but cannot understand"** complaint is the clinical hallmark of presbycusis. This dissociation between pure tone thresholds and speech discrimination is due to cochlear degeneration affecting inner hair cell function and neural processing, not just mechanical hearing loss. **Clinical Pearl:** In presbycusis, the speech discrimination score is **disproportionately worse** than predicted from pure tone thresholds. For example, a patient with a 40 dB hearing loss might have only 45% speech discrimination (expected ~70%), indicating central auditory processing dysfunction. **Mnemonic: "PREP for Presbycusis"** — - **P**rogressive (gradual over decades) - **R**elative preservation of low frequencies - **E**xaggerated loss of high frequencies - **P**oor speech discrimination (disproportionate) ### Pathophysiology of Presbycusis Presbycusis involves multiple age-related changes: 1. **Cochlear (sensory) presbycusis** — loss of outer hair cells in basal turn 2. **Neural presbycusis** — degeneration of cochlear neurons and spiral ganglion cells 3. **Metabolic presbycusis** — atrophy of stria vascularis reducing endolymphatic potential 4. **Conductive presbycusis** — stiffening of basilar membrane The neural component explains why speech discrimination is disproportionately poor — auditory nerve degeneration impairs the ability to process rapid temporal changes in sound, critical for speech understanding. ### Why This Patient? - **Age 72 years** → classic age for presbycusis (>60 years) - **20-year gradual onset** → presbycusis is insidious and progressive - **Bilateral high-frequency loss** → typical pattern for age-related hearing loss - **"I can hear but cannot understand"** → pathognomonic complaint indicating disproportionate speech discrimination loss - **45% speech discrimination** (far worse than expected from pure tone thresholds) → hallmark of presbycusis - **Normal otoscopy, <5 dB air-bone gap** → sensorineural, not conductive - **No occupational history mentioned** → rules out NIHL [cite:Hazarika ENT Ch 5; Dhingra ENT 8e Ch 3]