[Potentiation of inner ear damage following electron beam irradiation with CDDP administration]

The study was designed to examine the combined ototoxic effect of CDDP (Cisplatin, Cis-diammine dichloroplatinum) and electron beam irradiation, using guinea pigs. One group received physiological saline solution of 4 ml/kg/day, and another group received CDDP of 2 mg/kg/day for five days. And following the injection of saline or CDDP, the electron beam of 14Gy/day was applied to the both groups to the right ear for five days. Animals were sacrificed after 21 days, and temporal bones of these animals were removed for the inner ear histopathology. Temporal bones were classified into four groups (control, electron beam irradiation, CDDP administration, and combined administration group), and the inner ears were observed by the surface preparation technique with a phase contrast microscope, and by scanning and transmission electron microscopy, and by temporal bone study of serial sectioned slides. The main pathologic findings of the inner ear are as follows: Electron beam irradiation group showed no hair cell damage. CDDP group induced slight damage to the outer hair cells. Combined administration group (CDDP + electron beam irradiation) showed severe outer hair cell damage. Stria vascularis was degenerated moderately in the combined administration group and slightly in some animals of electron beam irradiation group. And Reissner's membrane and Hensen's cells, were damaged in the basal turn of cochlea of the combined administration group. All other cochlear structures (spiral ganglion, spiral lamina, basilar membrane, spiral prominence, tectorial membrane, blood vessels of the cochlea) and vestibular organs were lack of significant changes in all groups by a light microscopic observation. This study was clarified that combined administration of CDDP and electron beam irradiation showed severe ototoxic potentiation. Therefore, it is important that we must pay attention to the inner ear damage caused by combined therapy of CDDP and electron beam irradiation involving inner ear for the head and neck tumor.