EEG Reactivity and Etiology as Prognostic Modifiers in Alpha and Theta Coma: A Systematic Review and Meta-analysis

Alpha/theta coma is an uncommon electroencephalographic (EEG) pattern observed in deeply comatose patients and has traditionally been regarded as a malignant finding, particularly after hypoxic-ischemic injury following cardiac arrest. Classically, it is associated with a nonreactive alpha/theta rhythm and high mortality. However, occasional neurological recovery suggests greater prognostic heterogeneity than historically believed, while it remains uncertain whether historical diagnostic definitions of alpha/theta coma are comparable with contemporary concepts of disorders of consciousness. We conducted a systematic review and meta-analysis to clarify outcome heterogeneity, identify prognostic modifiers associated with recovery, and re-appraise the historical literature.

A systematic search of PubMed, EMBASE, and Cochrane databases was conducted through December 2025. Original human studies reporting outcomes in comatose patients with alpha coma, theta coma, or alpha-theta coma were included. Functional outcomes were categorized into four ordinal categories. Random- or common-effects models were applied according to heterogeneity. Prespecified prognostic analyses focused on EEG reactivity.

Six studies (n = 152) were included. Overall, 83.7% (95% CI 76.8-88.8%, I² = 21.6%) experienced severe disability or death, and mortality was 74.0% (95% CI 43.2-91.4, I² = 41.3%). EEG reactivity was present in 45.4% (95% CI 24.0-68.6%, I² = 52.2%). Nonreactive EEG was significantly associated with mortality (OR 5.67, 95% CI 1.22-26.31, I² = 0%) and reduced odds of good outcome (OR 0.12, 95% CI 0.03-0.48). Reactive EEG was associated with increased odds of favorable outcome (OR 8.68, 95%, CI 2.08-36.24). Hypoxic-ischemic injury predominated, whereas toxic or metabolic etiologies were more frequent among patients with better outcomes.

Alpha/theta coma is not uniformly fatal. EEG reactivity identifies a lower-risk subgroup without guaranteeing recovery, while etiology further shapes prognosis. These findings should be interpreted in the context of historical diagnostic uncertainty, and contemporary studies are needed to better define alpha/theta coma using current concepts of disorders of consciousness.