The association between central nervous system (CNS) infections and epilepsy: epidemiological approaches and microbiological and epileptological perspectives.

The causal association between central nervous system (CNS) infections and epilepsy is predictable but poorly documented due to constraints in epidemiological, epileptological, and microbiologic methods. The large number of CNS infections with varied geographic distributions means that epidemiological studies in many different regions are required in order to establish their association with epilepsy. Whenever infectious diseases occur in the community, the majority of the infected cases are either asymptomatic or develop only mild symptoms. Those with neurological involvement and hence at risk of developing epilepsy constitute the tip of the iceberg. Furthermore, there is no one-to-one relationship between surrogate markers of infection used in epidemiological studies (e.g., seropositivity or brain imaging abnormalities) and neurological involvement (and hence epilepsy). As a result, there are individuals in the community who have no neurological symptoms but may either be seropositive or demonstrate imaging abnormalities compatible with the neurological infectious disorder and conversely, those who have seizures (or epilepsy) but may be seronegative. Relevant to the epidemiological study of seizures and epilepsy in relation to CNS infections is the classification of seizures as provoked and unprovoked. Accordingly, seizures that occur during the active stage of infection are considered provoked and those that occur later are unprovoked. Finally, with the burden of infections being concentrated in the less-developed countries, epidemiological studies are required to be carried out in these locations, which present logistic, financial and technical barriers for them to be accomplished.