Epidemiology of status epilepticus in adults: Apples, pears, and oranges - A critical review

Status epilepticus (SE) is a severe neurologic condition associated with high morbidity and mortality. Population-based studies in adults have found a wide range of incidences in various regions in the world. Although the incidence of SE increases almost exponentially in the elderly, data on census-based population statistics in these studies are scarce. This study provides a critical review with an emphasis on census-based population statistics and study characteristics in adults.

We performed a systematic search of population-based studies on SE in adults in PubMed using "status epilepticus" in combination with "epidemiology", "population", and "incidence" as search terms, and also screened references. For each identified study, we assessed and extracted the respective population pyramids of study and reference population, and study characteristics.

We identified 22 population-based studies (eleven from Europe, six from North America, three from Asia, one from Africa, and one from Australasia). Incidence rates of patients with SE ranged from 1.29 to 73.7/100,000 adults (95% confidence interval (CI): 76.6-80.3) and of SE episodes up to 81.1/100,000 adults (95% CI: 75.8-87.0). The proportions of elderly and very old patients varied by a factor of 2.6 and 8.5, respectively, depending on study period and place. Further major reasons for heterogeneity were retrospective or prospective study design, definition of time to diagnose SE, variable detection of nonconvulsive SE (NCSE), different etiologies, inclusion of children, recurrent episodes, postanoxic patients, exclusion of patients with preexisting epilepsy or patients identified outside the emergency department, and choice of reference population for age- and gender adjustment. The most recent definition and classification of SE by the International League Against Epilepsy (ILAE) 2015 was used in two studies. Four studies (18.2%) reported incidences per ten-year age strata necessary for age adjustment to various reference populations.

This critical review reveals a marked heterogeneity among population-based studies on SE in adults. It provides comprehensive details on census-based population statistics in study and reference populations and various study designs and characteristics essential for direct comparisons between studies. Reporting on these essential key features should be improved in population-based studies on SE.