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Original Investigation
February 2017

Association of Periodic and Rhythmic Electroencephalographic Patterns With Seizures in Critically Ill Patients

Author Affiliations
  • 1Emory University School of Medicine, Atlanta, Georgia
  • 2Georgia Institute of Technology, Atlanta
  • 3Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
  • 4Yale University School of Medicine, New Haven, Connecticut
  • 5Université Libre de Bruxelles, Brussels, Belgium
  • 6Thomas Jefferson University, Philadelphia, Pennsylvania
  • 7Mission Health, Asheville, North Carolina
JAMA Neurol. 2017;74(2):181-188. doi:10.1001/jamaneurol.2016.4990
Key Points

Question  What are the specific characteristics of periodic and rhythmic electroencephalographic patterns that confer risk for seizures?

Findings  This multicenter cohort study of 4772 consecutive critically ill adult patients undergoing continuous electroencephalographic monitoring found that lateralized periodic discharges, lateralized rhythmic delta activity, and generalized periodic discharges were associated with seizures, but generalized rhythmic delta activity was not. High frequency and Plus modifier were associated with an additional risk in all patterns except generalized rhythmic delta activity; and increased pattern prevalence was associated with risk for seizures in lateralized periodic discharges and generalized periodic discharges.

Meaning  A detailed electroencephalographic interpretation using standardized nomenclature can assist seizure risk stratification.


Importance  Periodic and rhythmic electroencephalographic patterns have been associated with risk of seizures in critically ill patients. However, specific features that confer higher seizure risk remain unclear.

Objective  To analyze the association of distinct characteristics of periodic and rhythmic patterns with seizures.

Design, Setting, and Participants  We reviewed electroencephalographic recordings from 4772 critically ill adults in 3 academic medical centers from February 2013 to September 2015 and performed a multivariate analysis to determine features associated with seizures.

Interventions  Continuous electroencephalography.

Main Outcomes and Measures  Association of periodic and rhythmic patterns and specific characteristics, such as pattern frequency (hertz), Plus modifier, prevalence, and stimulation-induced patterns, and the risk for seizures.

Results  Of the 4772 patients included in our study, 2868 were men and 1904 were women. Lateralized periodic discharges (LPDs) had the highest association with seizures regardless of frequency and the association was greater when the Plus modifier was present (58%; odds ratio [OR], 2.00, P < .001). Generalized periodic discharges (GPDs) and lateralized rhythmic delta activity (LRDA) were associated with seizures in a frequency-dependent manner (1.5-2 Hz: GPDs, 24%,OR, 2.31, P = .02; LRDA, 24%, OR, 1.79, P = .05; ≥ 2 Hz: GPDs, 32%, OR, 3.30, P < .001; LRDA, 40%, OR, 3.98, P < .001) as was the association with Plus (GPDs, 28%, OR, 3.57, P < .001; LRDA, 40%, P < .001). There was no difference in seizure incidence in patients with generalized rhythmic delta activity compared with no periodic or rhythmic pattern (13%, OR, 1.18, P = .26). Higher prevalence of LPDs and GPDs also conferred increased seizure risk (37% frequent vs 45% abundant/continuous, OR, 1.64, P = .03 for difference; 8% rare/occasional vs 15% frequent, OR, 2.71, P = .03, vs 23% abundant/continuous, OR, 1.95, P = .04). Patterns associated with stimulation did not show an additional risk for seizures from the underlying pattern risk (P > .10).

Conclusions and Relevance  In this study, LPDs, LRDA, and GPDs were associated with seizures while generalized rhythmic delta activity was not. Lateralized periodic discharges were associated with seizures at all frequencies with and without Plus modifier, but LRDA and GPDs were associated with seizures when the frequency was 1.5 Hz or faster or when associated with a Plus modifier. Increased pattern prevalence was associated with increased risk for seizures in LPDs and GPDs. Stimulus-induced patterns were not associated with such risk. These findings highlight the importance of detailed electroencephalographic interpretation using standardized nomenclature for seizure risk stratification and clinical decision making.