A patient on long-term amikacin therapy reports difficulty hearing high-pitched sounds such as birds and telephone rings, while conversational speech remains intact. Audiometry confirms bilateral high-frequency sensorineural loss. Which statement best explains this pattern?

• A Damage begins at the auditory nerve soma in the spiral ganglion, sparing hair cells entirely
• B The stria vascularis is destroyed selectively, sparing speech-frequency hair cells initially
• C Aminoglycosides accumulate in perilymph only at low frequencies, damaging apical cochlear cells first
• D Outer hair cells of the basal cochlear turn coding high frequencies are damaged first, and mitochondrial 12S rRNA mutations markedly increase susceptibility ✓

Explanation

Aminoglycosides accumulate in cochlear and vestibular endolymph and destroy outer hair cells beginning in the basal turn of the cochlea, which codes high frequencies, so hearing loss starts above the speech range and is detected late. Susceptibility is strongly increased by maternally inherited mutations in mitochondrial 12S rRNA, the same ribosomal target the drugs bind in bacteria. The lesion is in hair cells, not primarily the spiral ganglion or stria vascularis, and the basal turn corresponds to high frequencies, eliminating option C.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.