Chapter 561

According to the World Health Organization, status epilepticus (SE) is defined as seizures that are sufficiently frequent or prolonged to produce an “enduring epileptic condition.”1 Implicit in this definition is the concept that the event’s duration renders it physiologically distinct from other seizure types and, therefore, it requires specialized workup and management.

Although there is no well-determined absolute duration beyond which a prolonged seizure is definitively distinct from shorter ones, in practice SE is defined as continuous seizures, or a cluster of seizures without return to consciousness, lasting 30 minutes or more. With this definition, the incidence of SE in children approximates 18 to 38 per 100,000 persons/year.2 More than 40% of SE cases occur in children younger than 2 years of age.3

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 longer than 5 minutes are often treated acutely. Accordingly, there is a trend toward reducing the duration required for diagnosis of SE, with some reports defining minimal SE duration as 5, 10, or 20 minutes; incidence of SE by these definitions has not been extensively studied.4

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).5 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 more. The rationale for earlier treatment of SE is also supported by data from animal seizure models that show loss and dysfunction of GABAA receptors and reduced sensitivity to benzodiazepines after prolonged seizures in rats.6-9

### Classification

Numerous seizure types, if prolonged, can comprise SE. With some overlap, these can be divided into convulsive and nonconvulsive subgroups. Prolonged primary or secondary generalized tonic-clonic seizures, including febrile seizures, are the most common form of convulsive SE in children.

Nonconvulsive SE (NCSE) is a relatively heterogenous group of disorders.11 The clinical picture is often that of depressed consciousness ranging from confusion to coma. Particularly in the intensive care unit (ICU), NCSE is now becoming more widely recognized, in part due to increased use of electroencephalogram (EEG) monitoring. In a recent report, EEG ordered to evaluate unresponsiveness in the pediatric ICU showed a pattern consistent with NCSE in 33% of 178 cases.12 Prolonged absence seizures (absence status) are also a form of NCSE characterized by altered consciousness, at times lasting hours until the diagnosis is made by EEG. Another form of NCSE, one in which consciousness is typically preserved, ...

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