Elsevier

Clinical Neurophysiology

Volume 118, Issue 8, August 2007, Pages 1660-1670
Clinical Neurophysiology

Invited review
Nonconvulsive seizures: Developing a rational approach to the diagnosis and management in the critically ill population

https://doi.org/10.1016/j.clinph.2006.11.312Get rights and content

Abstract

Originally described in patients with chronic epilepsy, nonconvulsive seizures (NCSs) are being recognized with increasing frequency, both in ambulatory patients with cognitive change, and even more so in the critically ill. In fact, the majority of seizures that occur in the critically ill are nonconvulsive and can only be diagnosed with EEG monitoring. The semiology of NCSs and the associated EEG findings are quite variable. There are a number of periodic, rhythmic or stimulation-related EEG patterns in the critically ill of unclear significance and even less clear treatment implications. The field struggles to develop useful diagnostic criteria for NCSs, to standardize nomenclature for the numerous equivocal patterns, and to devise studies that will help determine which patterns should be treated and how aggressively. This review surveys the evidence for and against NCSs causing neuronal injury, and attempts to develop a rational approach to the diagnosis and management of these seizures, particularly in the encephalopathic 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

References (85)

  • K. Abou Khaled et al.

    Generalized Periodic Discharges: prognostic significance and relation to seizures

    Neurology

    (2006)
  • N. Adachi et al.

    Intellectual prognosis of status epilepticus in adult epilepsy patients: analysis with Wechsler Adult Intelligence Scale-revised

    Epilepsia

    (2005)
  • C. Armon et al.

    Addendum to assessment: prevention of post-lumbar puncture headaches: report of the Therapeutic and Technology Assessment Subcommittee of the American Academy of Neurology

    Neurology

    (2005)
  • M.A. Bergsneider et al.

    Cerebral hyperglycolysis following severe human traumatic brain injury: a positron emission tomography study

    J Neurosurg

    (1997)
  • J.-M. Boulanger et al.

    Triphasic waves versus nonconvulsive status epilepticus: EEG distinction

    Can J Neurol Sci

    (2006)
  • R.P. Brenner et al.

    Periodic EEG patterns: classification, clinical correlation, and pathophysiology

    J Clin Neurophysiol

    (1990)
  • R.S. Briellmann et al.

    Seizure-associated hippocampal volume loss: a longitudinal magnetic resonance study of temporal lobe epilepsy

    Ann Neurol

    (2002)
  • M. Brussiere et al.

    Prolonged deficits after focal inhibitory seizures

    Neurocrit Care

    (2005)
  • R. Bullock et al.

    Evidence for prolonged release of excitatory amino acids in severe human head trauma: relationship to clinical events

    Ann NY Acad Sci

    (1995)
  • D.J. Chong et al.

    Which EEG patterns warrant treatment in the critically ill? Reviewing the evidence for treatment of periodic epileptiform discharges and related patterns

    J Clin Neurophysiol

    (2005)
  • J. Claassen et al.

    Treatment of refractory status epilepticus with pentobarbital, propofol, or midazolam: a systematic review

    Epilepsia

    (2002)
  • J. Claassen et al.

    Detection of electrographic seizures with continuous EEG monitoring in critically ill patients

    Neurology

    (2004)
  • A.J. Cole

    Status epilepticus and periictal imaging

    Epilepsia

    (2004)
  • O.C. Cockerell et al.

    Complex partial status epilepticus: a recurrent problem

    J Neurol Neurosurg Psychiatry

    (1994)
  • J. Correale et al.

    Status epilepticus increases CSF levels of neuron specific enolase and alters the blood–brain barrier

    Neurology

    (1998)
  • R.J. DeLorenzo et al.

    A prospective, population-based epidemiologic study of status epilepticus in Richmond, Virginia

    Neurology

    (1996)
  • R.J. DeLorenzo et al.

    Persistent nonconvulsive status epilepticus after the control of convulsive status epilepticus

    Epilepsia

    (1998)
  • C.M. DeGiorgio et al.

    Serum neuron-specific enolase in the major subtypes of status epilepticus

    Neurology

    (1999)
  • C.M. DeGiorgio et al.

    Hippocampal pyramidal cell loss in human status epilepticus

    Epilepsia

    (1992)
  • L.J. Dennis et al.

    Nonconvulsive status epilepticus after subarachnoid hemorrhage

    Neurosurgery

    (2002)
  • C.B. Dodrill et al.

    Intellectual impairment as an outcome of status epilepticus

    Neurology

    (1990)
  • M.E. Drake et al.

    Triphasic discharges in metrizamide encephalopathy

    J Neurol Neurosurg Psychiatry

    (1984)
  • F.W. Drislane

    Evidence against permanent neurologic damage from nonconvulsive status epilepticus

    J Clin Neurophysiol

    (1999)
  • F.W. Drislane

    Who’s afraid of status epilepticus?

    Epilepsia

    (2006)
  • J.M. Ellis et al.

    Acute prolonged confusion in later life as an ictal state

    Epilepsia

    (1978)
  • J. Engel et al.

    Prolonged partial complex status epilepticus: EEG and behavioral observations

    Neurology

    (1978)
  • N.B. Fountain et al.

    Effects of benzodiazepines on triphasic waves: implications for nonconvulsive status epilepticus

    J Clin Neurophysiol

    (2001)
  • D.G. Fujikawa

    Prolonged seizures and cellular injury: understanding the connection

    Epilepsy Behav

    (2005)
  • A. Guberman et al.

    Nonconvulsive generalized status epilepticus clinical features, neuropsychological testing, and long-term follow-up

    Neurology

    (1986)
  • M.A. Granner et al.

    Nonconvulsive status epilepticus: EEG analysis in a large series

    Epilepsia

    (1994)
  • J.T. Hormes et al.

    Periodic sharp waves in baclofen-induced encephalopathy

    Arch Neurol

    (1988)
  • L.J. Hirsch et al.

    The ACNS Subcommittee on Research Terminology for Continuous EEG Monitoring: proposed standardized terminology for rhythmic and periodic EEG patterns encountered in critically ill patients

    J Clin Neurophysiol

    (2005)
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    Current address: Department of Neurology and Neurosurgery, McGill University Health Center, Montreal, Canada

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