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Original Investigation |

Similarity of Lateralized Rhythmic Delta Activity to Periodic Lateralized Epileptiform Discharges in Critically Ill Patients

Nicolas Gaspard, MD, PhD1,2; Louis Manganas, MD, PhD1,2; Nishi Rampal, MD1,2; Ognen A. C. Petroff, MD1,2; Lawrence J. Hirsch, MD1,2
[+] Author Affiliations
1Comprehensive Epilepsy Center, Department of Neurology, Yale University School of Medicine, New Haven, Connecticut
2Department of Clinical Neurophysiology, Yale–New Haven Hospital, New Haven, Connecticut
JAMA Neurol. 2013;70(10):1288-1295. doi:10.1001/jamaneurol.2013.3475.
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Importance  The increasing use of continuous electroencephalography (EEG) monitoring in the intensive care unit has led to recognition of new EEG patterns that are of unclear or unknown significance.

Objective  To describe an EEG pattern, lateralized rhythmic delta activity (LRDA), encountered in critically ill subjects and determine its clinical significance in this setting.

Design, Setting, and Participants  Retrospective review at an academic medical center of EEG recordings, medical records, and imaging studies of critically ill patients with LRDA and comparison with subjects with lateralized periodic discharges (also known as periodic lateralized epileptiform discharges), subjects with focal nonrhythmic slowing, and controls.

Intervention  Electroencephalography or continuous electroencephalography.

Main Outcomes and Measures  Cross-sectional prevalence of lateralized rhythmic delta activity; EEG characteristics; etiology, clinical, and radiological correlates; and risk of early seizures.

Results  We identified LRDA in 4.7% of acutely ill subjects undergoing EEG or continuous EEG monitoring. It was often associated with other focal EEG abnormalities, including lateralized periodic discharges in 44% of cases. The most common conditions associated with LRDA were intracranial hemorrhage and subarachnoid hemorrhage. Lateralized rhythmic delta activity was an independent predictor of acute seizures, with 63% of subjects having seizures during their acute illness, a proportion similar to subjects with lateralized periodic discharges (57%) and significantly higher than associated with focal nonrhythmic slowing (20%) or in control subjects (16%). Most patients (80%-90%) in the LRDA and lateralized periodic discharges groups who had seizures while undergoing continuous EEG monitoring had only nonconvulsive seizures, whereas this was the case for only 17% of patients in the other groups. Lateralized rhythmic delta activity and lateralized periodic discharges were both associated with lesions involving the cortex or juxtacortical white matter.

Conclusions and Relevance  Lateralized rhythmic delta activity in critically ill patients has a similar clinical significance as lateralized periodic discharges. It reflects the presence of a focal lesion and is associated with a high risk of acute seizures, especially nonconvulsive.

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Figures

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Figure 1.
Acute Left Parietal Intracranial Hemorrhage, Lateralized Rhythmic Delta Activity, and Focal Seizures in a 75-Year-Old Man

A, Ten-second electroencephalography (EEG) page showing a run of lateralized rhythmic delta activity characterized by 2.5/s to 3/s, 50-µV, unilateral sinusoidal activity maximal over the posterior right hemisphere. There was no clinical correlate. B, Twenty-second EEG epoch showing a focal seizure arising from the right posterior region and spreading throughout the right hemisphere. The seizure onset is characterized by a 2.5-second run of quasirhythmic delta (underlined) followed by faster activity that then evolves in amplitude, morphology, and location (box). A 1-Hz high-pass filter and 30-Hz low-pass filter were applied to the EEGs. The notch filter was off.

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Figure 2.
Encephalomyelitis, Bilateral Independent Rhythmic Delta Activity, and Bilateral Independent Seizures in a 22-Year-Old Man

A, Ten-second electroencephalography (EEG) page showing a run of lateralized rhythmic delta activity characterized by rhythmic 2/s, 70-µV, unilateral activity maximal over the right frontotemporal region. There was no clinical correlate. Note the presence of embedded sharp waves (a) and the sharply contoured morphology of some of the delta waves (underlined). B, Twenty-second EEG epoch showing a focal seizure arising from the same region as the lateralized rhythmic delta activity and spreading to the left hemisphere. The seizure onset is characterized by quasiperiodic sharp waves (denoted by a) followed by rhythmic sharp theta activity (underlined) that then evolves. A 1-Hz high-pass filter and 70-Hz low-pass filter were applied to the EEGs. The notch filter was off.

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Figure 3.
Risk of Acute Seizures in Subjects With Lateralized Rhythmic Delta Activity (LRDA) and Comparison Groups of Lateralized Periodic Discharges (LPDs), Focal Nonrhythmic Slowing, and Controls

The risk of acute seizures, and in particular electrographic seizures, in critically ill subjects with LRDA is similar to subjects with LPDs and greater than the risk in subjects with focal nonrhythmic slowing or in control subjects. A, The incidence of seizures (both total and while undergoing continuous electroencephalography [CEEG] recording) is similar in subjects with LRDA or LPDs but is higher than in control subjects and higher than in subjects with focal nonrhythmic slowing (a1 and a2; P < .006 for all comparisons; Fisher exact test). There is some overlap between groups (see text). Dark blue bars indicate total (clinical before CEEG and seizures seen while undergoing CEEG, whether clinical or not) and light blue bars indicate seizures while undergoing CEEG. EEG indicates electroencephalography. B, The incidence of seizures occurring during CEEG monitoring is similar when LRDA or LPDs are seen in the first hour of CEEG but is significantly higher than in control subjects in the first hour (a1 and a2; P < .006; Fisher exact test) and tends to be higher than in subjects when only focal nonrhythmic slowing is seen (b1 and b2; P < .05). C, The proportion of individuals with only electrographic seizures during CEEG (as opposed to only clinical or both clinical and electrographic seizures) is similar in subjects with LRDA and LPDs but is higher in subjects with LPDs than in control subjects (a2; P < .006 for both comparisons; Fisher exact test). Similarly, the proportion of patients with only electrographic seizures during CEEG tends to be higher in subjects with LRDA than in subjects with focal nonrhythmic slowing or in control subjects (b1; P < .05 for both comparisons; Fisher exact test). The number of subjects in each group is indicated. Error bars indicate ±1 SE.

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