Diagnostic utility of eight-channel EEG for detecting generalized or hemispheric seizures and rhythmic periodic patterns

Abstract

Objectives: To compare the diagnostic utility of electroencephalography (EEG) using reduced, 8-channel montage (rm-EEG) to full, 18-channel montage (fm-EEG) for detection of generalized or hemispheric seizures and rhythmic periodic patterns (RPPs) by neurologists with extensive EEG training, neurology residents with minimal EEG exposure, and medical students without EEG experience.

Methods: We presented EEG samples in both fm-EEG (bipolar montage) and rm-EEG (lateral leads of bipolar montage) to 20 neurologists, 20 residents, and 42 medical students. Unanimous agreement of three senior epileptologists defined samples as seizures (n = 7), RPPs (n = 10), and normal or slowing (n = 20). Differences in median accuracy, sensitivity, and specificity were assessed using Wilcoxon signed-rank tests.

Results: Full and reduced EEG demonstrated similar accuracy when read by neurologists (fm-EEG: 95%, rm-EEG: 95%, p = 0.29), residents (fm-EEG: 80%, rm-EEG: 80%, p = 0.05), and students (fm-EEG: 60%, rm-EEG: 51%, p = 0.68). Moreover, neurologists' sensitivity for detecting seizure activity was comparable between fm-EEG (100%) and rm-EEG (98%) (p = 0.17). Furthermore, the specificity of rm-EEG for seizures and RPP (neurologists: 100%, residents: 90%, students: 86%) was significantly greater than that of fm-EEG (neurologists: 93%, p = 0.03; residents: 80%, p = 0.01; students: 69%, p < 0.001).

Conclusions: The reduction of the number of EEG channels from 18 to 8 does not compromise neurologists' sensitivity for detecting seizures that are often a core reason for performing urgent EEG. It may also increase their specificity for detecting rhythmic and periodic patterns, and thereby providing important diagnostic information to guide patient's management.

Significance: Our study is the first to document the utility of a reduced channel EEG above the hairline compared to full montage EEG in aiding medical staff with varying degrees of EEG training to detect generalized or hemispheric seizures.

Keywords: Electroencephalography; Reduced channel montage; Rhythmic and periodic patterns; Seizure detection; Sensitivity; Specificity.

Fig. 1

Training samples of full and reduced montage EEG. Calibration bar: time scale represents 1 s (s), voltage scale represents 50 microvolts (μV). Abbreviations: RPP, rhythmic and periodic pattern.

Fig. 2

STARD flow diagram. Abbreviations: FN, false negative; FP, false positive; RPP, rhythmic and periodic pattern; TN, true negative; TP, true positive.

Fig. 3

Diagnostic utility of full and reduced montage EEG for detection generalized or hemispheric seizures and rhythmic periodic patterns. Data (accuracy, sensitivity, and specificity) are given as median values, p values calculated using Wilcoxon signed-rank tests. Abbreviations: Gen, generalized; RPP, rhythmic or periodic patterns (not including seizure); Sz, seizure.

Fig. 4

Rhythmic or periodic EEG samples misclassified on reduced montage by the majority of neurologists. (Panel A) Periodic activity missed by 95% on rm-EEG (fm-EEG: 65%). (Panel B) Frontal intermittent rhythmic delta activity (FIRDA) classified by reference standard as rhythmic, periodic activity but labeled as normal/slow by 75% on rm-EEG (fm-EEG: 45%). (Panel C) Rhythmic and periodic activity identified by 95% on fm-EEG but classified as normal/slow by 50% on rm-EEG. Calibration bar: time scale represents 1 s (s), voltage scale represents 50 microvolts (μV).

Fig. 5

Samples with seizure activity misclassified by reference standard epileptologists. (Panel A) Right temporal seizure obscured by abundant myogenic artifact (due to associated automatisms) detected by 75% and 35% of neurologists using fm-EEG and rm-EEG, respectively. (Panel B) Right frontotemporal seizure detected by 95% of neurologists on rm-EEG (fm-EEG: 80%), but classified as non-seizure/seizure-like by reference standard. (Panel C) Patient had continuous multifocal nonconvulsive seizures, seen during this epoch in left frontal and medial channels, that was missed by all three senior epileptologists who formed the reference standard and the majority of neurologists (fm-EEG: 80%, rm-EEG: 95%). Calibration bar: time scale represents 1 s (s), voltage scale represents 50 microvolts (μV).