Unbiased quantification of Scarpa's ganglion neurons in aminoglycoside ototoxicity

While most studies have demonstrated damage to the cochlear and vestibular endorgan as the primary site of aminoglycoside toxicity, the effect on the primary afferent neurons of the vestibular ganglion remains to be determined. This study used the unbiased stereology-optical fractionator method to obtain estimates of the vestibular ganglion neuronal number. Archival temporal bone specimens from seven subjects with a history of gentamicin (n=3) and streptomycin (n=4) aminoglycoside ototoxicity were used. The post-ototoxicity survival time ranged from two months to 8 years, with an average of 2.2 years. Seven archival human temporal bone specimens from age-matched subjects with no history of audiovestibular symptoms or ototoxicity served as controls. Group means were compared using unpaired, two-tailed student's t test. The average vestibular ganglion neuronal number in the aminoglycoside ototoxicity group was 20, 733 neurons (CV=0.073), which was significantly lower (p<0.005) than the average number in the age-matched control group of 24, 902 neurons (CV=0.109). These findings may be consistent with either retrograde degeneration or a direct neurotoxic effect of the aminoglycosides on the vestibular ganglion neuron.