Depth EEG studies in the Lennox-Gastaut syndrome

Depth EEG recordings were carried out in 16 patients with clinical and EEG evidence of the Lennox-Gastaut syndrome (LGS), in attempts to identify a surgically-resectable focus. Structures explored included the mesial temporal (amygdaloid) areas, the orbito-frontal cortex, the superior parasagittal cortex, and in three cases deep cerebellar nuclei. All patients showed disordered and slow background activity in depth leads. Slow spike-waves were prominent in orbito-frontal and parasagittal frontal areas, but were generally reflected as well in surface frontal leads. Runs of rapid spikes were recorded in 7 patients, again mainly in deep frontal leads. Independent interictal spikes were observed in 9 patients, chiefly from one or both amygdaloid areas. Ictal events were recorded in 9 patients. Frontal lobes were most often involved at the start, and a few cases showed origin of apparently generalized surface activity beginning unilaterally in deep frontal lobe. None of the identified interictal nor ictal foci were sufficiently dominant to justify local surgical resection. Frontal bilateral synchrony, when present, was adequately visualized by noninvasive surface EEG recording. Depth electroencephalography in our hands therefore has a very limited role in evaluation of patients with LGS.