A patient with refractory Meniere's disease is being considered for intratympanic gentamicin injection. What is the SPECIFIC mechanism by which this treatment controls vertigo, and what is its main risk?

• A Sclerosing the endolymphatic sac to reduce endolymph overproduction; risk of total SNHL
• B Preferential destruction of vestibular hair cells (type I) reducing abnormal vestibular signals; risk of unacceptable sensorineural hearing loss ✓
• C Blocking the ion channels of cochlear hair cells to reduce action potential generation; risk of tinnitus amplification
• D Inducing perilymph fistula to equalise endolymphatic pressure; risk of chronic otorrhoea

Explanation

Intratympanic gentamicin achieves vestibular ablation (chemical labyrinthectomy) by selectively destroying vestibular type I hair cells (which have less regenerative capacity than type II cells and are more sensitive to aminoglycoside toxicity). This eliminates the abnormal unilateral vestibular signals responsible for Meniere's attacks. The main risk is irreversible sensorineural hearing loss due to inadvertent cochlear hair cell damage, as the cochlear and vestibular membranes share common fluid spaces. Lower doses and titration protocols reduce but do not eliminate this risk.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.