Long-term hearing loss in gerbils with bacterial meningitis treated with superoxide dismutase

The treatment of superoxide dismutase (SOD) in gerbils with bacterial meningitis will not only prevent cochlear fibrosis and neo-ossification but also reduce hearing loss.

SOD an O2-scavenger, has been shown to prevent cochlear fibrosis and neo-ossification in gerbils infected with bacterial meningitis when injected intrathecally. The objective of this study is to investigate the effects of SOD on long-term hearing loss in gerbils infected with bacterial meningitis and to assess the relationship between hearing results and the amount of fibrosis. The effectiveness of middle ear infusion of SOD will also be examined.

Meningitis was induced in 3 groups of 10 gerbils with injection of Streptococcus pneumoniae into the cisterna magna. Group 1 received intrathecal SOD, group 2 received a middle ear infusion of SOD, and group 3, the control group, received no SOD. Histologic data and auditory brainstem responses were obtained from each gerbil.

In the intrathecal SOD group, the average deterioration in pure tone thresholds between the preoperative baseline and 15 weeks after induction of meningitis at 4, 8, 16, and 32 kHz was significantly less than that of the middle ear SOD and the control group (p = 0.001). There was no significant difference between the middle ear SOD and the control group. There was no fibrosis in the intrathecal SOD group, 15% of the gerbils developed an average of 11% fibrosis in the middle ear SOD group, and 20% of the gerbils developed an average of 15% in the control group.

Intrathecal infusion of SOD not only prevented cochlear fibrosis and neo-ossification after bacterial meningitis but also decreased subsequent hearing loss.