Electroencephalographic evolution of hypsarrhythmia: toward an early treatment option

Purpose: A retrospective study for a classification of prehypsarrhythmic elecroencephalographies (EEGs) was carried out to enable an early treatment option for West syndrome. Methods: Out of 39 infants with symptomatic West syndrome, 18 infants (age 3–14 months) with 61 serial non‐REM sleep EEG records of the prehypsarrhythmic phase were identified. The prehypsarrhythmic phase encompassed 2 to 13 months (mean 4.5 months) after an initial insult. A classification system of three EEG types corresponding to the clinical states prior to West syndrome occurrence was developed. In addition, follow‐up of all patients presenting with type 2 EEGs (n = 22) was evaluated. Results: Three clinical states and corresponding EEG types were classified. Clinical state 1 (weeks to months, silent phase) presented with (multi‐)focal epileptic discharges <50% of the non‐REM EEG recording time (type 1 EEG). Clinical state 2 (several weeks, beginning mental deterioration) was accompanied by type 2 EEG with bihemispheric epileptic discharges >50% of the non‐REM EEG recording time within abnormal background activity (imminent hypsarrhythmia). Clinical state 3 (mental deterioration) was characterized by hypsarryhthmia. Interrater reliability of seven blinded raters was good (median weighted κ 0.67). Out of 22 patients presenting with type 2 EEGs, two were lost for follow‐up, and 16 developed West syndrome, whereas four were treated early with anti‐epileptic drugs and remained stable. Conclusions: Infants with West syndrome could be reliably identified several weeks before the occurrence of hypsarrhythmia by a typical EEG pattern (type 2), thereby opening the way for early intervention studies.