RESUMO
OBJECTIVE/HYPOTHESIS: Local treatment of the cochlea after electrode insertion trauma with dexamethasone base conserves hearing against trauma-induced loss. STUDY DESIGN: Laboratory animal study. METHODS: A guinea pig model of electron insertion trauma (EIT)-induced hearing loss (HL) used 44 guinea pigs sub-divided into four groups: 1) unoperated, controls (Controls, n = 44); 2) EIT, untreated (EIT, n = 15); 3) EIT plus artificial perilymph (EIT + AP, n = 15); and 4) EIT plus dexamethasone base (EIT + DXMb, n = 14). Cochleae that received EIT were randomly selected with contralateral, unoperated cochleae as internal controls. Auditory brainstem responses (ABRs) in response to 0.5 to 16 kHz pure tones were obtained before surgery, immediately after surgery (0 day), and on post-EIT days 3, 7, 14, and 30. Hair cell counts were obtained from stained organ of Corti specimens from all four groups (n = 3/group). Data were analyzed using analysis of variance and a Tukey-Kramer honestly significant difference post hoc test with significance alpha set at <0.05 (hearing) and <0.001 (hair cells). RESULTS: There were significant differences (<0.05) between the ABR thresholds of unoperated (control) and contralateral operated (experimental) ears of EIT and of EIT + AP groups for all tested frequencies. There was no statistical difference (>0.05) in ABR thresholds in the EIT + DXMb versus control groups for 0.5 to 4 kHz tones. DXMb treatment protected hair cells from EIT-induced damage and loss while AP treatment did not. CONCLUSION: The absence of significant differences in hearing thresholds between the EIT + DXMb group and control ears in response to 0.5 to 4 kHz tones demonstrates that DXMb is as effective as the aqueous form of dexamethasone in conserving hearing against EIT-induced loss.