Invited reviewNonconvulsive seizures: Developing a rational approach to the diagnosis and management in the critically ill population
Introduction
Early descriptions of convulsive seizures are found in Babylonian tablets from 2000 BC that emphasize the supernatural nature of these events. Centuries later, Hippocrates wrote on the “sacred disease” and argued that epileptic convulsions were manifestations of a diseased brain and recommended physical treatments. Detailed accounts of less overt epilepsies began in the 18th and 19th century with the French description of “petit mal” seizures and Hughlings Jackson’s “uncinate fits” (Kaplan, 2002). The advent of EEG in the 20th century allowed physicians to discover unequivocal seizures in previously unsuspected circumstances, yet the field still struggles to define the extent of EEG patterns that should be considered ictal and to determine when these events should be treated. This review examines nonconvulsive seizures in the critically ill population, particularly emphasizing controversies as to which EEG patterns should be considered ictal, and exploring the evidence whether such seizures are intrinsically harmful. Whenever possible the American Academy of Neurology classification of evidence scheme is used (Appendix, for example, see Armon and Evans, 2005).
Section snippets
Nonconvulsive seizures in encephalopathic patients
The clinical spectrum in nonconvulsive seizures (NCSs) is protean (Table 1). In the community, NCSs present most frequently in patients who are confused but remain ambulatory, while in the hospital NCSs are most frequently diagnosed in the intensive care unit (ICU). We focus on the obtunded or comatose patients for this article, and in these cases the clinical diagnosis is often challenging as manifestations are often absent or may consist of only subtle myoclonic limb, facial or ocular
Nonconvulsive seizures: evidence for neuronal injury
Much of the evidence for the deleterious effects of NCSs is derived from animal models or from human studies in epileptic patients. The concepts of excitoxicity and selective CNS vulnerability that have emerged from this literature are likely applicable to the emerging field involving the critically ill population. The still limited range of studies involving the critically ill is explored later.
The detrimental effects of prolonged seizures have long been emphasized in the neurological
Treatment of nonconvulsive seizures and status epilepticus
While it would appear that NCSs are damaging to the brain, it is far less obvious that single NCSs or NCSE needs to be treated as aggressively as convulsive varieties for reasons outlined above. Claassen et al. (2002) performed a systematic review comparing various continuous IV infusion AEDs and pentobarbital in patients treated for refractory convulsive and nonconvulsive status epilepticus, and found a poor outcome overall (50% mortality) regardless of the agent utilized or the titration goal
Future directions
Clearly our understanding of how best to manage patients with subclinical rhythmic or periodic EEG patterns is in its infancy. An important initial step to this end has begun with the proposal of standardized terminology for these patterns last year (Hirsch et al., 2005). Undoubtedly further refinement of this nomenclature will occur in the future, and perhaps even some agreement on the definition of a NCS. Deciding which EEG patterns are harmful, and how aggressively cessation of this activity
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Current address: Department of Neurology and Neurosurgery, McGill University Health Center, Montreal, Canada