Abstracts

Diffuse electrodecremental events (DEDE) are sometimes seen at seizure onset, and may be followed by focal rhythmic discharge. The clinical relevance of this initial ictal electrophysiologic pattern, particularly in terms of subsequent localization of the ictal onset region, is not well defined. We examined the association of initial ictal DEDE with surgical outcome in extratemporal epilepsy.
All extratemporal epilepsy surgery patients who underwent chronic intracranial recording between 1990 and 1999 with minimum follow-up of 1 year were reviewed. Patients who had any seizures with DEDE at ictal onset were identified. Ictal DEDE was defined as diffuse background flattening coinciding with habitual ictal clinical behavior. Data was analyzed for DEDE frequency, electrophysiologic evolution, pathological substrate, and surgical outcome.
51 intracranial recordings of 44 patients with 398 seizures were identified. DEDE were seen in 18 of 51 recordings (35.3%) as the first ictal changes in some (6/18) or most (12/18) of the seizures. No particular lobe or pathological substrates were more commonly seen in patients with DEDE. Patients with DEDE had similar long term surgery outcome to the whole group studied. Diffuse EDE lasted between 2-10 seconds, after which focal evolution emerged in 12 and diffuse pattern persisted in 6 (Table 1). Patients with diffuse evolution had consistently poor resection outcome (p=0.03).
In patients with extratemporal epilepsy, DEDE at seizure onset were a common pattern. Persistence of diffuse changes with no focal progression predicted poor surgical outcome. On the other hand, evolution to focal changes was as useful as initial focal change for localization of the ictal onset area, as judged by surgical outcome.[table1]