A 70-year-old man treated with intravenous gentamicin for gram-negative sepsis develops imbalance worse in darkness, oscillopsia on head movement, and a broad-based gait. Audiometry is normal. Caloric testing shows absent responses bilaterally. The underlying mechanism of his condition is:

• A Endolymphatic hydrops distending the membranous labyrinth
• B Demyelination of the eighth cranial nerve
• C Selective destruction of type I hair cells of all five vestibular end organs ✓
• D Otoconia deposition in the horizontal canals

Explanation

Gentamicin is preferentially vestibulotoxic: it enters endolymph and destroys hair cells of the vestibular end organs, sparing the cochlea relatively because the stria vascularis excludes it, hence normal hearing. The result is bilateral vestibulopathy with oscillopsia and ataxia compensated by vision and proprioception. Hydrops explains Meniere's disease, demyelination suggests inflammatory neuropathy, and canalithiasis causes positional vertigo, killing B, A and D.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.