Abstract
This study was undertaken to evaluate the inner ear damage risk of chlorhexidine applied directly to the middle ear in cases of otological disinfection. The effects of this drug applied to the round window niche were investigated not only regarding the various electrical phenomena in the cochlea but also on the morphological findings in cochlea of guinea-pigs. Using a microelectrode, the endocochlear DC potential, the intracellular negative DC potential and the cochlear microphonics were recorded from the basal turn of the cochlea. After application of the drug, the cochlear microphonics showed a marked decline, at first among all electrical phenomena in the cochlea, and then a subsequent decrease of endocochlear DC potential. The deleterious effects of the drug on these potentials were irreversible and progressive, and they reached a magnitude of 10 to 5% of the pre-drug level 30 minutes after the application. The magnitude of the negative DC potential in the organ of corti also began to decrease from about 20 to 30 minutes after the application. In the morphological examination, no remarkable change was observed in the organ of Corti under scanning electron microscope, while the decrease of microvilli and the swelling of cell bodies were evident on the surface of marginal cells of the stria vascularis.
It is well known that cochlear microphonics are generated from the hair cells, while the origin of the endocochlear DC potential probably is in the stria vascularis. From this point of view, although no histological changes were evident on the organ of Corti, it may be concluded that the earlier decline in the amplitude of cochlear microphonics indicates hair cell lesions induced by drug application, and the subsequent decrease of endocochlear DC potential suggests the delayed lesion in the stria vascularis.
Consequently, it must be considered that the topical use of chlorhexidine induces inner ear lesion.
