Hydrocephalus and epilepsy: an actuarial analysis.

OBJECTIVE: To determine the prevalence of epilepsy among patients with hydrocephalus and to identify risk factors.
METHODS: Retrospective chart review at a single institution was conducted. The definition of epilepsy used was long-term administration of antiepileptic drugs (AEDs) for suppression of seizures. Actuarial methodology was used, with initiation of AED therapy as the endpoint of the analysis.
RESULTS: Insertion or revision of cerebrospinal fluid (CSF) shunts was performed on 464 patients at the study institution from 1976 through 1989. At the time of initial CSF shunt insertion, 12% of patients had already been treated with AEDs. After the 2nd year, the hazard rate for initiation of AED treatment was a constant 2% per year, and by 10 years after initial shunt insertion the estimated prevalence of AED treatment had risen to 33%. The cause of the hydrocephalus was a strong determinant of the prevalence of AED treatment, but most of the statistical effect of the cause was already manifest at the time of initial CSF shunt insertion. Age of patient at diagnosis of hydrocephalus, burr hole site, number of CSF shunt operations during follow-up, and history of shunt infection were factors that had no detectable association with AED treatment.
CONCLUSION: Epilepsy is common among patients with hydrocephalus, and the risk of the development of epilepsy continues indefinitely for those patients. The complications of CSF shunt surgery seem to play a relatively minor role in the development of epilepsy in this patient population.