A 28-year-old woman presents with a 4-week history of progressive headache, cognitive dysfunction, and acute bilateral hearing loss. Audiometry reveals the pattern marked **A** in the diagram. Brain MRI shows characteristic "snowball" lesions in the central corpus callosum, and fundoscopy reveals multiple branch retinal artery occlusions with Gass plaques. Which of the following best explains the audiometric finding marked **A** in the context of this clinical presentation?

Question

Accepted Answer

A. Bilateral low-frequency sensorineural hearing loss reflecting apical cochlear ischemia due to microvascular occlusion in Susac syndrome. ## Why option 1 is correct

The audiometric pattern marked **A** (bilateral low-frequency rising/reverse-slope SNHL) is the characteristic hearing loss in Susac syndrome, a rare autoimmune endotheliopathy affecting the microvasculature of the brain, retina, and inner ear. The low-frequency pattern reflects ischemic injury to the apical cochlea due to precapillary arteriolar occlusion in the end-arteriole-supplied cochlear territories. This patient's complete clinical triad—encephalopathy (headache, cognitive dysfunction), branch retinal artery occlusions with Gass plaques, and bilateral low-frequency SNHL—plus the pathognomonic central corpus callosum "snowball" lesions on MRI confirm Susac syndrome. The hearing loss is typically bilateral and asymmetric, often acute in onset with vertigo and tinnitus, and represents one of the three pillars of the diagnostic triad.

## Why each distractor is wrong

- **Option 2 (High-frequency SNHL)**: This pattern is typical of noise-induced hearing loss, presbycusis, or ototoxicity—not the reverse-slope low-frequency pattern seen in Susac syndrome. High-frequency loss would not fit the clinical presentation or the labeled structure **A**.
- **Option 3 (Conductive hearing loss)**: Otosclerosis causes conductive or mixed hearing loss, not sensorineural, and is not associated with the systemic vasculitic triad of encephalopathy, retinal artery occlusions, and CNS lesions seen here.
- **Option 4 (Normal audiogram with abnormal OAEs)**: This pattern suggests retrocochlear pathology (e.g., acoustic neuroma) or auditory neuropathy, not the cochlear ischemia of Susac syndrome. The patient has documented sensorineural hearing loss, not a normal audiogram.

**High-Yield:** Susac syndrome = encephalopathy + BRAOs + low-frequency SNHL + central corpus callosum "snowballs" = aggressive immunosuppression required to prevent permanent disability.

[cite: Susac International Consensus 2016; Harrison's Principles of Internal Medicine, 21st ed.]

Answer

B. Normal audiogram with abnormal otoacoustic emissions indicating retrocochlear pathology

Answer

C. Bilateral conductive hearing loss secondary to otosclerosis

Answer

D. Bilateral high-frequency sensorineural hearing loss from noise-induced cochlear damage

Explanation

Why option 1 is correct

Why each distractor is wrong

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