Incidence of first seizures, epilepsy, and seizure mimics in a geographically defined area

To determine the incidence of first seizures, epilepsy, and seizure mimics in a geographically defined area using the updated 2014 International League Against Epilepsy (ILAE) definition, which allows an epilepsy diagnosis after a single seizure when the risk of further seizures over the next 10 years is ≈60% or greater. This replaced the 1993 definition by which epilepsy was diagnosed when a person had ≥2 seizures separated by 24 hours.

Using multiple overlapping methods of case ascertainment followed by individual case classification by an epileptologist, we identified all first seizures, new diagnosis of epilepsy, and seizure mimics occurring in a defined geographic area (population 542,868) from January 1, 2017, to December 31, 2017. Incidence was age standardized to the Standard European Population. We compared incidence rates using the 2014 and 1993 ILAE definitions.

When the 2014 ILAE definition of epilepsy was applied, the incidence of new diagnosis of epilepsy was 62 per 100,000 (age standardized 74) compared to 41 per 100,000 (age standardized 48) when the 1993 definition was applied, and the difference was more pronounced at older ages. The incidence of all first seizures and of seizure mimics was 102 per 100,000 (age standardized 123) and 94 per 100,000 (age standardized 111), respectively. The most frequently encountered seizure mimic was syncope.

Application of the 2014 ILAE definition of epilepsy resulted in a higher incidence of new diagnosis of epilepsy compared to the 1993 definition. The incidence of seizure mimics almost equals that of all first seizures. Seizures, epilepsy, and seizure mimics represent a significant burden to health care systems.