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373 EFFECT OF DEXAMETHASONE AND RIMEXOLONE ON MORPHOLOGY OF THE ROUND WINDOW MEMBRANE IN LIPOPOLYSACCHARIDE-INDUCED OTITIS MEDIA.

Background The round window membrane is the only soft tissue barrier separating the middle ear from the inner ear and appears to be the main portal for passage of toxic substances into labyrinth. Many human and animal studies have demonstrated that the architecture of the round window membrane alters in diseased conditions such as otitis media. The morphological changes in the round window membrane influence its permeability as a defense mechanism. Purpose To determine the effect of topical treatment of dexamethasone and rimexolone on the thickness of round window membrane (RWM) in LPS-induced experimental otitis media with effusion in chinchillas. Methods Experimental otitis media with effusion was induced in 20 chinchillas by inoculating with lipopolysaccharide (LPS) into the bullae at 0 hour. Three control and four treatment groups were studied: saline (control, n = 2), dexamethasone vehicle (control, n = 3), rimexolone vehicle (control, n = 3), 1% dexamethasone (treatment, n = 3), 0.1% dexamethasone (treatment, n = 3), 1% rimexolone (treatment, n = 3), 0.1% rimexolone (treatment, n = 3). Seven test substances (saline, dexamethasone vehicle, rimexolone vehicle, 1% dexamethasone, 0.1% dexamethasone, 1% rimexolone, 0.1% rimexolone) were inoculated at -2, 24, and 48 hours. After 96 hours the temporal bones were extracted, fixed, and sectioned for histological analysis. Light microscopy with calibrated ocular units was used to measure the thickness of the RWM. Left and right RWM thicknesses were measured at the midpoint in each histological section. Results Both the control (29.57 ± 6.45, 26.75 ± 4.46, 28.76 ± 6.13 μm) and treatment groups (18.07 ± 3.54, 21.27 ± 4.64, 19.96 ± 4.08, 20.12 ± 4.20 μm) showed a mean membrane thickness greater than normal (13.7 ± 2.9 μm). All treatment groups demonstrated a statistically significant reduction in thickness when compared to the saline control. A significant reduction in thickness was also noted in all treatment groups when compared to their respective vehicle groups. Conclusion Topical treatment of dexamethasone and rimexolone reduced inflammation and thickness of the RWM in LPS-induced experimental otitis media with effusion.