Otoprotective Effects of Dexamethasone in the Management of Pneumococcal Meningitis: an Animal Study

Abstract

OBJECTIVE: To determine whether treating pneumococcal meningitis with a combined antibiotic and steroid regime will prevent cochlear damage, a common pneumococcal meningitis side effect. STUDY DESIGN: Prospective animal study. METHODS: Gerbils were randomly assigned to three experimental groups. Animals in group 1 received intrathecal saline injections. Animals in groups 2 and 3 received intrathecal injections of Streptococcus pneumoniae to induce meningitis. Group 2 was treated for 7 days with intraperitoneal penicillin injections (48,000 units). Animals from group 3 received intraperitoneal dexamethasone (0.5 mg/kg) injections for 4 days in addition to 7 days of intraperitoneal penicillin. Three months after the meningitis was induced, the animals' cochlear functions were determined using auditory brainstem responses (ABRs). After measuring cochlear function, the animals were sacrificed for cochlear histopathology. Spiral ganglion cell densities at Rosenthal's canal were determined. RESULTS: ABR thresholds were significantly elevated in animals from group 2 when compared with the animals in groups 1 and 3 (P < .05). ABR thresholds for animals from group 3 and group 1 were similar (P > .05). Damage of cochlear structures was detected in animals from group 2. The degree of the damage varied: one animal in group 2 had no identifiable hair cells and pillar cells and showed damage of the tectorial membrane. Spiral ganglion density in the basal turn was significantly less in animals from group 2 when compared with controls (P < .05). Although spiral ganglion cell density was less in the dexamethasone-treated group (group 3) when compared with group 1 (control group), but greater than observed in animals treated with antibiotics only (group 2), the differences were statistically not significant (P > .5). Nuclear diameters of the spiral ganglion cells decreased on average from 7.24 +/- 0.48 microm (group 1) to 6.28 +/- 0.76 microm (group 3, animals that received dexamethasone) to 5.57 +/- 0.82 microm (group 2, animals that received antibiotics only). Differences were significant (P < .05). Differences in stria vascularis thickness were not significant among the animals. CONCLUSION: Dexamethasone has a protective effect on the cochlea when given together with antibiotics in the treatment of pneumococcal meningitis.