Auditory brainstem responses before and after shunting in patients with suspected normal pressure hydrocephalus.

Auditory brainstem responses (ABRs) were studied in 15 adults with suspected normal pressure hydrocephalus (NPH) before and after shunting. The patients were divided into Groups A (shunt-ineffective) and B (shunt-effective). The pre- and postoperative ABRs of each patient were compared with those of 20 normal volunteers, and the relationships between ABRs and certain clinical findings were investigated. Preoperatively, nine patients (60%) showed prolonged central conduction time (CCT) (interpeak latency of wave I-V or neural-axonal conduction time) relative to the mean control value plus 2 SD. There was no significant difference between Groups A and B in the percentage of patients with abnormal CCT, and no specific ABR abnormalities that were predictive of the efficacy of shunting. However, a significantly higher percentage of Group B patients (p less than 0.05) showed a postoperative reduction in the CCT of more than 1 SD of the mean control value. In Group A, the CCT was positively correlated with preoperative clinical disability. These results suggest that brainstem dysfunction may be reversed by shunting, but is not correlated with clinical disability in patients in whom shunting is effective, that is, in those with NPH. It appears that measurement of ABRs is a useful technique for the clinical monitoring of shunted patients.