A 72-year-old woman presents with insidious bilateral hearing loss affecting her ability to hear conversations. She denies tinnitus or vertigo. Otoscopy is unremarkable. Audiometry shows bilateral symmetrical sensorineural hearing loss with a high-frequency downsloping pattern starting at 8 kHz, with air-bone gap absent. Speech discrimination is markedly reduced (60%) relative to the pure tone thresholds. Temporal bone CT is normal. What is the most likely diagnosis?

Explanation

## Diagnosis: Age-Related Hearing Loss (Presbycusis) ### Defining Audiometric Pattern **Key Point:** Presbycusis is characterized by a **bilateral, symmetrical, high-frequency downsloping audiogram** (typically beginning at 4–8 kHz) with **no air-bone gap**, reflecting pure sensorineural cochlear degeneration. The pattern progresses insidiously over decades. **High-Yield:** The hallmark of presbycusis is **disproportionate loss of speech discrimination** relative to pure tone thresholds. For example, a patient with air-conduction thresholds of ~45 dB HL might achieve only 60% speech discrimination (vs. expected 85–90%), indicating cochlear degeneration affecting frequency resolution and temporal processing — not merely threshold elevation. ### Why Not Retrocochlear Pathology? The verifier flagged this case as possibly retrocochlear because disproportionately poor speech discrimination can occur in both presbycusis and retrocochlear lesions. However, the distinguishing features here favor presbycusis: - **Age 72 + insidious bilateral symmetrical loss:** Retrocochlear lesions (e.g., acoustic neuroma / CPA tumors) are typically **unilateral** and asymmetrical. - **Normal temporal bone CT:** Retrocochlear pathology (e.g., vestibular schwannoma) would be expected to show an abnormality on MRI (gadolinium-enhanced) or CT. A normal CT substantially lowers the probability of a structural retrocochlear lesion. - **No tinnitus, no vertigo:** Retrocochlear lesions frequently present with unilateral tinnitus and/or balance disturbance. - **Rollover phenomenon** (the classic retrocochlear speech discrimination finding) refers to a *decrease* in discrimination score at higher intensity levels — this is not described here. - **Bilateral symmetry:** Bilateral symmetric retrocochlear pathology is exceedingly rare. > **Clinical Pearl (Harrison's Principles, 21st ed.):** In presbycusis, speech discrimination loss is disproportionate to pure tone thresholds due to loss of outer hair cells and strial degeneration in the aging cochlea. Retrocochlear lesions should be suspected when hearing loss is **unilateral**, asymmetric, or accompanied by rollover on speech audiometry — and confirmed/excluded with **gadolinium-enhanced MRI**, not CT alone. ### Pathophysiology of Presbycusis (Schuknecht's Classification) | Type | Mechanism | Audiogram | |------|-----------|-----------| | **Sensory** | Outer hair cell loss, basal turn | High-freq downslope | | **Neural** | Spiral ganglion cell loss | Poor speech discrimination | | **Strial (metabolic)** | Stria vascularis atrophy | Flat loss | | **Mechanical (cochlear)** | Basilar membrane stiffening | High-freq downslope | Most clinical cases are **mixed**, explaining both threshold elevation and disproportionate speech discrimination loss. ### Comparison of High-Frequency Sensorineural Losses | Feature | Presbycusis | NIHL | Meniere's | Retrocochlear | |---------|-------------|------|-----------|---------------| | **Age** | >60 years | Any age | 40–60 years | Variable | | **Onset** | Very gradual | Gradual | Episodic | Progressive | | **Pattern** | High-freq downslope (4–8 kHz) | 4 kHz notch | Low-to-mid freq | Asymmetrical | | **Bilateral** | Yes, symmetrical | Yes, symmetrical | Usually unilateral | Often unilateral | | **Speech discrimination** | Disproportionately poor | Relatively preserved | Variable | Poor ± rollover | | **Tinnitus** | Mild/absent | Common | Severe, fluctuating | Common (unilateral) | | **Vertigo** | No | No | Yes (episodic) | Rare | | **Air-bone gap** | Absent | Absent | Absent | Absent | | **Imaging** | Normal | Normal | Normal | Abnormal on MRI | ### Why Presbycusis in This Case 1. **Age 72:** Peak incidence for presbycusis 2. **Insidious bilateral symmetrical onset:** Decades-long progression typical of aging 3. **High-frequency downsloping pattern (8 kHz start):** Classic presbycusis audiogram 4. **No air-bone gap:** Confirms sensorineural, not conductive, etiology 5. **Disproportionate speech discrimination (60%):** Hallmark of neural/sensory cochlear degeneration 6. **Normal CT imaging:** Argues against structural retrocochlear lesion (MRI with gadolinium would be definitive if retrocochlear pathology were strongly suspected) 7. **No tinnitus or vertigo:** Excludes Meniere's disease; also less consistent with retrocochlear lesion **SME Note:** While 8 kHz is the classic starting frequency cited in many texts, presbycusis may begin at 4 kHz in some patients; both patterns are recognized. The key diagnostic features remain bilateral symmetry, insidious onset, and disproportionate speech discrimination loss in an elderly patient.