Electroclinical seizures in Lennox-Gastaut syndrome.

We analyzed electroclinical seizures observed by long video split-screen recording in 21 patients with Lennox-Gastaut syndrome (LGS). All patients had atypical absence seizures, 18 (81%) had tonic seizures, and 4 (21%) had myoclonic-atonic seizures. Tonic seizures were axial with flexion or extension of the head or trunk, or global with generalized tonic spasm mimicking infantile spasm, or involved the eyeballs only (either brief, with upward deviation of eyeballs or long, with oscillatory nystagmus). EEG showed either a bilateral 10-13-Hz rhythm or generalized synchronous spike wave at 3 Hz. Myoclonic-atonic seizures involving limbs, trunk, or neck were either brief or massive; the discharges were 2-3.5-Hz spike wave. Atypical absence seizures evolved gradually, terminated abruptly, and manifested alone or with subtle motor activity or oral automatism. EEG discharges were variable and of different types: (a) Diffuse irregular spike wave at 2-2.5 Hz with or without fragmentation (consciousness was regained during fragmentation or when spike wave discharges were < 2 Hz), (b) irregular diffuse fast activity at 10-13 Hz, or (c) a combination of fast spike wave or sharp waves of increasing amplitude followed by synchronous spike wave discharges at 3 Hz.