Status epilepticus is the most common neurological emergency in childhood and continues to be associated with significant mortality and morbidity. Although the main determinant of adverse outcome following status epilepticus is etiology, there continues to be concern that status epilepticus itself contributes to the outcome. Therefore, an understanding of the types of status epilepticus, the mechanisms, and frequencies of adverse outcomes and appropriate treatments is essential for defining strategies that aim to reduce morbidity associated with status epilepticus.
Status epilepticus is traditionally divided into convulsive and nonconvulsive forms. The aim of the current chapter is to provide an overview of nonconvulsive status epilepticus (NCSE) in terms of definition, clinical features, outcomes, treatments, and its relationship with epileptic encephalopathy. However, many of these aspects are not universally agreed and therefore there will also be discussion of the controversies surrounding NCSE.
In April 2004, a group of physicians with an interest in NCSE, representing a spectrum of opinion, met in Oxford1 to discuss and debate the definition, diagnosis, and treatment of NCSE. There was no consensus on a specific definition and therefore the following broad definition was made; NCSE is a range of conditions in which electrographic seizure activity is prolonged and results in nonconvulsive clinical symptoms.
The International League Against Epilepsy suggest that status epilepticus should be defined as a seizure that shows no clinical signs of arresting after a duration encompassing the great majority of seizures of that type in most patients or recurrent seizures without interictal resumption of baseline central nervous system function. However, these definitions are not particularly useful in clinical practice as there is too much breadth; that is, what is prolonged?, and the definitions about clinical features are vague.
A time definition that is frequently used for NCSE is 30 minutes, which is the same as that commonly used to define convulsive status epilepticus. This construct appears to work for convulsive status epilepticus; after 30 minutes the seizure becomes self-sustaining, is more likely to cause brain injury and is associated with systemic decompensation, that is, hypotension, hypoglycemia, etc. However, the construct is less applicable to NCSE as 30 minutes may not describe a point following which there are potential pathophysiological changes that separate NCSE from short seizures with similar clinical manifestations.
The proposed definition from the Oxford meeting uses the term nonconvulsive clinical symptoms, which potentially means that any clinical feature (e.g., dizziness and headache) could be considered as a feature of NCSE if there were consistent electroencephalogram (EEG) features. The agreed component of the definition is that the features need to be associated with EEG abnormalities, but if any neurological symptom can be a manifestation of NCSE then many patients with neurological symptoms will require an EEG to rule out NCSE. It is likely that this is neither practical nor necessary.