P0742 - Improving the Diagnosis of Neonatal Encephalopathy: Validation of a Novel Encephalopathy Scale for Hypoxic-Ischemic Encephalopathy (HIE) using Electroencephalogram (EEG)

Background: Encephalopathy severity in neonates evaluated for therapeutic hypothermia (TH) has traditionally been determined by neurologic exam, sometimes alongside amplitude-integrated electroencephalogram (aEEG). The original 1976 report describing the progressive stages of encephalopathy (PMID 987769) led to modified versions of the Sarnat exam, which were utilized in randomized trials evaluating TH, with or without aEEG. However, there has been minimal validation of exam scores as measures of encephalopathy, distinct from outcome, and the relationship between neurologic exam, aEEG, and conventional EEG (cEEG) is not fully understood. Determining the best method to identify encephalopathy severity is critical to select neonates for TH. We developed a novel, simplified encephalopathy scale at Boston Children’s Hospital (BCH) to detect and grade encephalopathy in asphyxiated neonates and validated this scale by gold standard neurophysiology measures.

Objective: To validate the BCH neonatal encephalopathy scale by determining its relationship to aEEG and cEEG, and to identify which modality is most sensitive to detect encephalopathy.

Methods: We analyzed data from 176 neonates evaluated for encephalopathy from 2008-2018 who were ≥34 weeks’ gestation and had no known genetic diagnoses or major congenital anomalies. Neurologic exams were scored using the BCH encephalopathy scale (Figure 1). The aEEG and cEEG background patterns were determined using previously published systems (PMID 25035312, PMID 23545767). We used Spearman rank order correlations to evaluate the relationship between encephalopathy score, aEEG, and cEEG. Pairwise correlations were compared using the confidence interval method (PMID 18179351).

Results: There was a strong correlation between initial encephalopathy score and aEEG background pattern (Spearman r=0.67, p<0.0001) and between aEEG and cEEG background patterns (Spearman r=0.60, p<0.0001), and a moderate correlation between initial encephalopathy score and cEEG background pattern (Spearman r=0.45, p<0.0001) (Figure 2). Neonates with intermediate severity of encephalopathy by aEEG/cEEG (a discontinuous or burst suppression aEEG or mildly/moderately abnormal cEEG) had a greater variation in encephalopathy scores compared to those with a continuous, low voltage, or inactive aEEG or a normal or severely abnormal cEEG (p<0.001). Of the neonates with an encephalopathy score of 0-3, who would not typically be considered for TH, 31% had an abnormal aEEG and 49% had an abnormal cEEG.

Conclusions: We found a strong, statistically significant correlation between our novel encephalopathy scale and aEEG/cEEG measures of encephalopathy, supporting its validity and utility in evaluating encephalopathy and hence eligibility for TH. The correlation between initial encephalopathy score and aEEG was strongest, likely because these evaluations are completed at more similar time points than cEEG. Importantly, neonates with low encephalopathy scores, who wouldn’t typically be considered for TH, frequently had an abnormal aEEG/cEEG, suggesting added sensitivity of these modalities to detect more subtle encephalopathy and the importance of including neurophysiology studies in decision-making regarding TH.