Quantitative EEG and EEG-Derived Markers of Severity, Prognosis, and Recovery After Ischemic Stroke: A Systematic Review.

Introduction: Electroencephalography (EEG) and quantitative electroencephalography (QEEG) may provide noninvasive functional biomarkers that complement clinical and imaging predictors when evaluating stroke outcomes. This systematic review evaluated QEEG, selected routine EEG, processed EEG, and advanced neurophysiological biomarkers of severity, lesion burden, longitudinal prognosis, cognitive/language outcome, rehabilitation response, and recovery after ischemic stroke. Methods: PubMed, Embase, Scopus, and Web of Science were searched on 30 March 2026 using ischemic stroke or cerebral infarction terms, QEEG or EEG-derived biomarker terms, and prognosis, outcome, severity, infarct-volume, mortality, rehabilitation, motor-recovery, and language-recovery terms. Selected structured routine EEG, visual EEG grading, processed EEG/Bispectral Index (BIS), and EEG-derived neurovascular-coupling studies were included when they provided predefined severity, prognostic, monitoring, cognitive/language, rehabilitation, or recovery-related evidence. The search identified 2,564 records; 851 duplicates were removed, leaving 1,713 unique records for screening. Evidence was classified as cross-sectional severity or lesion-burden association, longitudinal functional prognosis, mortality or clinical deterioration, rehabilitation or motor recovery, cognitive/language outcome, selected routine or processed EEG evidence, or advanced QEEG/connectivity/nonlinear/neurovascular-coupling evidence. Risk of bias was assessed using Quality in Prognostic Studies (QUIPS)-oriented criteria, and certainty was summarized using domain-level Grading of Recommendations Assessment, Development and Evaluation (GRADE)-informed judgments. Results: Thirty-three study records were included, representing 1,696 stroke or suspected-stroke participants, 1,598 EEG/QEEG/BIS/neurovascular coupling (NVC)-analyzable participants, and 317 controls or comparators. The most consistent prognostic pattern was that greater EEG/QEEG abnormality, particularly increased slow-wave activity and higher delta/alpha ratio (DAR) or delta-theta/alpha-beta ratio (DTABR), was associated with greater neurological severity, larger infarct or lesion burden, and poorer functional outcomes. Measures of interhemispheric imbalance, including a higher brain symmetry index (BSI), pairwise-derived brain symmetry index (pdBSI), and greater hemispheric asymmetry, were also generally associated with unfavorable outcomes, including greater disability, clinical deterioration, mortality, or less favorable recovery. Reduced alpha or beta activity was similarly associated with poorer neurological or functional outcomes in several studies. Post-endovascular treatment (EVT)/mechanical thrombectomy (MT) studies suggested potential monitoring value for detecting or predicting cortical dysfunction, early neurological deterioration, cerebral edema, nonconvulsive seizures/status epilepticus, infarct growth, and unfavorable 90-day outcome. Rehabilitation and advanced QEEG studies suggested that motor/language recovery may relate to interhemispheric balance, phase synchrony, weighted node degree, nonlinear complexity, and neurovascular coupling. However, the evidence was heterogeneous, mostly exploratory, and generally low to very-low certainty; no universal prognostic threshold or pooled prognostic estimate was supported. Conclusions: EEG/QEEG abnormalities may provide candidate severity association, monitoring, prognostic, and recovery biomarkers after ischemic stroke. This review distinguishes cross-sectional severity or lesion burden associations from longitudinal prognostic, monitoring, and recovery outcomes. However, current evidence remains heterogeneous and mostly low to very low certainty and does not support a universal prognostic threshold or global pooled prognostic estimate.