An unknown quantity--the worldwide prevalence of epilepsy.

The reported incidence (rate of new cases in a population) of epilepsy is consistently lower in high-income than in lower-income economies, whereas opinions vary regarding comparative prevalence rates (proportion of the population with epilepsy). For any condition that does not influence mortality, lifetime prevalence should approximate to the cumulative incidence. We suspected that epilepsy prevalence might be uniform throughout the world, whereas incidence is higher in resource-poor countries. To test whether our suspicion was reasonable, we conducted a Medline search to estimate the prevalence of active and lifetime epilepsy in different economic areas throughout the world. We found that the range of estimated prevalence of epilepsy may be broadly similar throughout the world, but comparison is limited by lack of door-to-door studies in high-income economies and by variations in the definitions of active epilepsy. We contend that any inconsistencies between incidence and prevalence are due largely to the excess premature death rate in people with epilepsy in lower-income economies. Much of the variability in epidemiologic indices arises from differences in study methodology, definitions, and risk factors. The epidemiology of epilepsy, and particularly its mortality, needs thorough investigation using uniform definitions that do not include antiepileptic drug use; causes of death should be identified and actions, including treatment and education, should be taken to avoid preventable deaths. Wiley Periodicals, Inc.