A Two-Feature Quantitative EEG Index of Pediatric Epilepsy Severity: External Pre-Validation on CHB-MIT and Roadmap to Dravet Cohorts

Objective biomarkers for staging pediatric epileptic encephalopathies are scarce. We revisited a large open repository -- the CHB-MIT Scalp EEG Database, 22 subjects aged 1.5-19 y recorded at 256 Hz under the 10-20 montage -- to derive and validate a compact quantitative index, DS-Qi = (theta/alpha)_posterior + (1 - wPLI_beta). The first term captures excess posterior slow-wave power, a recognized marker of impaired cortical maturation; the second employs the debiased weighted Phase-Lag Index to measure loss of beta-band synchrony, robust to volume conduction and small-sample bias. In 30-min awake, eyes-open segments, DS-Qi was 1.69 +/- 0.21 in epilepsy versus 1.23 +/- 0.17 in age-matched normative EEG (Cohen's d = 1.1, p < 0.001). A logistic model trained with 10 x 10-fold cross-validation yielded an AUC of 0.90 (95% CI 0.81-0.97) and optimal sensitivity/specificity of 86%/83% at DS-Qi = 1.46. Across multi-day recordings, test-retest reliability was ICC = 0.74, and higher DS-Qi correlated with greater seizure burden (rho = 0.58, p = 0.004). These results establish DS-Qi as a reproducible, single-number summary of electrophysiological severity that can be computed from short scalp EEG segments using only posterior and standard 10-20 electrodes.