A reliable interictal EEG grading scale for children with infantile spasms - The 2021 BASED score

Abstract

Objective: To develop an improved interictal electroencephalogram (EEG) grading scale for children with infantile spasms founded on elements with adequate inter-rater reliability (IRR) to justify its further study for clinical and research purposes.

Methods: Three blinded reviewers assessed five-minute sleep epochs in 93 EEGs from 62 children (31 consecutive controls, 31 consecutive infantile spasms [pretreatment and posttreatment studies]) using a longitudinal bipolar montage. We determined the IRR of background amplitude, epileptiform discharges, >3 spike foci (including <50 % or >50 %), grouped multifocal spikes, paroxysmal voltage attenuations, and symmetry of sleep spindles. Data were used to finalize the 2021 BASED (Burden of AmplitudeS and Epileptiform Discharges) score.

Results: All elements included in the 2021 BASED score had moderate to near perfect IRR. Among controls, >200 μv background waves occurred commonly in the bilateral posterior temporal (T3-T5, T4-T6) and midline (Fz-Cz, Cz-Pz) regions. Excluding midline and occipital channels (which have normal high amplitude background waves), we designated abnormal high amplitude background waves as >200 μv for most channels, but >300 μv for T3-T5 and T4-T6. The IRR was moderate to near perfect for <50 % >3 spike foci, >50 % >3 spike foci, paroxysmal voltage attenuations, grouped multifocal spikes (GMFS), and symmetric sleep spindles. Paroxysmal voltage attenuations, GMFS, and >50 % >3 spike foci all significantly distinguished pretreatment from posttreatment studies whereas symmetric sleep spindles did not (as planned, the latter was not included in the 2021 BASED score). When the 2021 BASED score was applied to the 22 children with infantile spasms achieving clinical remission with treatment, 19 met criteria for electroclinical remission and three did not.

Significance: The 2021 BASED score includes elements with high levels of IRR and correlates well with the presence or absence of infantile spasms.

Keywords: Epileptic encephalopathy; Hypsarhythmia; Hypsarrhythmia; Infantile spasms; West syndrome.