Objective To determine which findings on routine clinical EEGs correlate with delirium severity across various presentations, and to determine whether EEG findings independently predict important clinical outcomes. Methods We prospectively studied a cohort of non-intubated inpatients undergoing EEG for evaluation of altered mental status. Patients were assessed for delirium within one hour of EEG using the 3-Minute Diagnostic Interview for Confusion Assessment Method (3D-CAM) and 3D-CAM severity score (3D-CAM-S). EEGs were interpreted clinically by neurophysiologists, and reports were reviewed to identify features such as theta or delta slowing and triphasic waves. Generalized linear models were used to quantify associations between EEG findings, delirium, and clinical outcomes, including length of stay, Glasgow Outcome Scale scores, and mortality. Results We evaluated 200 patients (median age 60 years, IQR 48.5-72); 121 (60.5%) met delirium criteria. The EEG finding most strongly associated with delirium presence was a composite of generalized theta or delta slowing (OR 10.3, 95% CI 5.3-20.1). The prevalence of slowing correlated not only with overall delirium severity (R2 = 0.907), but also with the severity of each feature assessed by CAM-based delirium algorithms. Slowing was common in delirium even with normal arousal. EEG slowing was associated with longer hospitalizations, worse functional outcomes, and increased mortality, even after adjusting for delirium presence or severity. Conclusions Generalized slowing on routine clinical EEG strongly correlates with delirium and may be a valuable biomarker for delirium severity. Additionally, generalized EEG slowing should trigger elevated concern for the prognosis of patients with altered mental status.

SupplementSupplementary Tables and Figures for "Clinical EEG Slowing Correlates with Delirium Severity and Predicts Poor Clinical Outcomes"DeliriumEEG_Neurology_Supplement.pdf