Multifocal independent Spike syndrome: relationship to hypsarrhythmia and the slow spike-wave (Lennox-Gastaut) syndrome
During a 3 year period EEGs were performed in 64 children with multifocal independent spikes (MIS), 17 with slow spike-wave complexes (SSWC), 22 with MIS and SSWC and 15 with hypsarrhythmia. Only EEG records containing adequate wakefulness and sleep were analyzed in 40 children with two or more serial EEGs at least 5 months apart. Transitions from one pattern to another occurred in 25/40 patients, consistent in all cases with the following sequence: Hypsarrythmia-->MIS-->MIS and generalized discharges-->SSWC. Patients with and without transitions did not differ in their age at presentation or duration of follow-up. Eleven of 12 patients whose initial EEG showed hypsarrhythmia or multifocal independent spikes underwent transitions, compared to 0/8 patients with SSWC (p < 0.001), indicating that SSWC is a stable pattern in children. Over a 6 month period, we also prospectively analyzed EEGs of 20 patients with multifocal spikes, hypsarrhythmia, and slow spike-wave complexes. Sleep activated additional spike foci, increased the frequency of generalized spike discharges and produced synchronization of bitemporal and bifrontal spike-wave discharges at 1.5-2.5 Hz the same as SSWC.