A 68-year-old man who received intravenous amikacin for 3 weeks now complains of a sensation that the environment oscillates when he walks (oscillopsia) and marked unsteadiness, worst in darkness. Bedside head impulse testing is abnormal bilaterally. The most likely diagnosis is:

• A Bilateral vestibulopathy from ototoxicity ✓
• B Cerebellar vermis infarction
• C Bilateral posterior canal BPPV
• D Peripheral polyneuropathy

Explanation

Aminoglycosides are preferentially vestibulotoxic, damaging type I hair cells of the cristae and maculae, and produce bilateral vestibular failure. The hallmark triad is oscillopsia with head movement, gait unsteadiness worsened by poor lighting or uneven surfaces, and bilaterally positive head impulse tests. Cerebellar lesions cause dysmetria and ataxia but the head impulse test remains normal, which is the key discriminator. BPPV causes positional vertigo, not oscillopsia, and polyneuropathy impairs proprioception with preserved vestibulo-ocular reflexes.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.