Brief potentially ictal rhythmic discharges and paroxysmal fast activity as scalp electroencephalographic biomarkers of seizure activity and seizure onset zone. (12th February 2021)

• Record Type: Journal Article
• Authors: Yoo, Ji Yeoun; Jetté, Nathalie; Kwon, Churl‐Su; Young, James; Marcuse, Lara V.; Fields, Madeline C.; Gaspard, Nicolas; Hirsch, Lawrence J.
• Is Part Of: Epilepsia. Volume 62:issue 3(2021)
• Page Start: 742
• Page End: 751
• Publication Date: 2021-02-12
• Subjects: critical care -- drug‐resistant epilepsy -- electroencephalography -- intensive care unit EEG monitoring -- nonconvulsive seizures; Epilepsy -- Periodicals; 616.853
• DOI: 10.1111/epi.16822
• Languages: English
• ISSNs: 0013-9580

Abstract

Abstract: Objective: The electroencephalographic (EEG) terms "brief potentially ictal rhythmic discharges" (BIRDs) and "paroxysmal fast activity" (PFA) are considered distinct entities; however, their definitions overlap, and they may have similar clinical significance. We investigated their clinical significance and their association with seizures and the seizure onset zone (SOZ). Methods: We retrospectively identified an adult cohort (July 2015 to March 2018) whose long‐term (>12 h) EEGs in any setting reported BIRDs (>4 Hz, lasting .5–10 s) and/or PFA. Different frequency cutoffs for PFA (>13 Hz or ≥8 Hz) were tested to compare their clinical significance. Patient demographics, clinical history, and EEG features were recorded. Results: We identified 94 patients with BIRDs/PFA out of 3520 patients (3%); 36 were critically ill (12 with epilepsy), and 58 were noncritically ill (all with epilepsy). The frequency of BIRDs/PFA was largely dependent on EEG background: it tended to be slower (theta) in the absence of a posterior dominant rhythm or in the presence of continuous focal slowing in the same region ( p = .01). Sixty‐two of 94 patients (66%; 32/36 [89%] critically ill, 30/58 [52%] noncritically ill) had electrographic seizures during the recording. The scalp EEG SOZ colocalized with BIRDs/PFA in all cases. BIRDs with faster frequency (also qualifying as PFA by definition) had similar seizure risk to that of slower BIRDs (62%–71%), regardless of frequency cutoff used to define PFA. In addition, 30 of 30 (100%) patients with evolving BIRDs/PFA (which lasted a median of 6 s, range = 2–9.5 s) had electrographic seizures (>10 s), compared to 32 of 64 (50%) with nonevolving BIRDs (median = 1 s, range = .5–3.5 s; p < .01). Significance: A high proportion of patients with BIRDs/PFA had seizures on EEG, regardless of their frequency (i.e., whether they also qualified as PFA), and their location colocalized with scalp SOZ in all cases. BIRDs appear to be a scalp EEG biomarker of uncontrolled seizure activity and a reliable localizing sign of the SOZ.