According to the World Health Organization (WHO), status epilepticus (SE) is defined as seizures that are sufficiently frequent or prolonged to produce an “enduring epileptic condition.” Implicit in this definition is the concept that the event’s duration renders it physiologically distinct from other seizure types and requires specialized workup and management. Notably, this definition accommodates multiple seizure types, including convulsive seizures with prominent motor features and prolonged nonconvulsive seizures.
Although there is no well-determined absolute duration beyond which the biology of a prolonged seizure is certainly distinct from a shorter one, in practice, for the past quarter-century, SE has been defined as continuous seizures or a cluster of seizures without return to consciousness lasting 30 minutes or longer. Accordingly, most of the epidemiologic work in the SE field has been based on this 30-minute-long definition. The incidence of convulsive SE in children, by this traditional definition, approximates 10 to 30 cases per 100,000 persons per year, with more than 40% of cases in children younger than age 2 years.
A reasonable and more inclusive definition of SE takes into account observations that individual seizures rarely last longer than 5 minutes and that, in clinical practice, seizures lasting longer than 5 minutes are often treated acutely. The Neurocritical Care Society 2012 guideline for the management of SE in children thus defines SE as “5 minutes or more of (i) continuous clinical and/or electrographic seizure activity or (ii) recurrent seizure activity without recovery (returning to baseline) between seizures.” The incidence of SE according to this shorter-duration definition is not established.
The recent trend toward reducing seizure duration in the definition of SE is supported by clinical and experimental data. For instance, Shinnar and colleagues found a bimodal distribution of new-onset seizure durations in children clustered around 2 means: 3.6 minutes (76% of cases) and 31 minutes (24% of cases). This corroborates the observation that seizures lasting longer than 5 minutes are likely to continue for at least several minutes longer and fits well with the widely accepted practice to administer anticonvulsants acutely for seizures lasting 5 minutes or longer. The rationale for earlier treatment of SE is also supported by data from animal seizure models, which show loss and dysfunction of γ-aminobutyric acid A (GABAA) receptors and reduced sensitivity to benzodiazepines after prolonged seizures.
A recent International League Against Epilepsy (ILAE) Task Force on Classification of Status Epilepticus has proposed a definition that accommodates a range of seizure types and current knowledge about SE pathophysiology. The definition published in 2015 is as follows: “[SE] is a condition resulting either from the failure of the mechanisms responsible for seizure termination or from the initiation of mechanisms which lead to abnormally prolonged seizures (after time point t1). It is a condition that can have long-term consequences (after time point t2), including neuronal death, neuronal injury, ...