Electroencephalographic changes before the onset of symptomatic West syndrome.

To clarify the characteristics of the mode of appearance and morphology of epileptiform discharges before the onset of West syndrome (WS). The subjects were 25 infants whose electroencephalograms (EEGs) were recorded before the onset of WS and whose first EEG was recorded before 6 months of corrected age (CA). We extensively analyzed the chronological and topographical changes of the epileptiform discharges before the onset of WS. The location of the initial epileptiform discharges was in the posterior areas in 14 (Group O), the multiple areas in 7 (Group M), and areas other than occipital in 4 (Group non-O). Twelve of the 14 patients in Group O were premature infants, and all but one had PVL. Most patients in Group M were full-term infants or near full-term infants who had hypoxic damage. The ages at the appearance of the initial epileptiform discharges in Group O were significantly later than those in Group M: 3.0-5.9 months of CA in Group O vs. -0.1 to 2.0 months of CA in Group M. These facts suggest that the difference of brain damage is related to both the topographical characteristics and the age at the appearance of initial epileptiform discharges, and around 3 months of CA is a critical period for the appearance of occipital hyperexcitability. Hypsarrhythmia and tonic spasms appeared almost simultaneously from 4 to 6 months of CA in most patients. To predict the occurrence of WS in high-risk infants, EEG follow-ups from early infancy are very useful.