Ictal-Interictal Continuum

Which EEG patterns warrant treatment in the critically ill?


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The IIC graph modified by Struck, et al.



Modification uses current ACNS terminology, with the addition of PET metabolism from hypometabolic (blue) to hypermetabolic (red).  X-axis = spectrum of cerebral dysfunction and Y-axis = neuronal damage

*SB suppression burst, RDA rhythmic delta activity, LPD lateralized periodic discharges, SW spike wave, GPD generalized periodic discharges, SIRPIDs stimulus-induced rhythmic, periodic, or ictal discharges, NCS non-convulsive seizures, GCSE generalized convulsive status epilepticus, NCSE nonconvulsive electrographic status epilepticus, EPC epilepsia partialis continua



  • strong correlation between PDs on the IIC and subsequent NCSZs or non-convulsive status epilepticus (NCSE)
  • link between PDs on the IIC and functional outcome remains less certain
  • link between interictal periodic patterns and secondary brain injury (as inferred by increased vasogenic or cytotoxic edema [8, 9] or increase in lactate-pyruvate ratio [10]), seen as similar sequelae to those resulting from NCSZs


Chong, Derek J., and Lawrence J. Hirsch. “Which EEG Patterns Warrant Treatment In The Critically Ill? Reviewing The Evidence For Treatment Of Periodic Epileptiform Discharges And Related Patterns”. Journal of Clinical Neurophysiology 22.2 (2005): 79-91.


Struck, Aaron F. et al. “Metabolic Correlates Of The Ictal-Interictal Continuum: FDG-PET During Continuous EEG”. Neurocritical Care 24.3 (2016): 324-331.

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