The clinical and prognostic relevance of the postictal slow focus in the electrocorticogram.

Electrocorticograms of 192 complex partial seizures which were recorded via chronically implanted subdural electrodes during presurgical evaluation of 64 patients with medically intractable epilepsy were visually analysed. The objective was to assess the diagnostic and prognostic relevance of postictal slow foci (PISF) in the electrocorticogram which were defined as focal isoelectric activity or as a focal burst-suppression pattern. The following results were obtained: (1) PISF were seen in a total of 114 of 192 seizures (59.4%), (2) 48 of 64 patients (75%) demonstrated at least 1 PISF in 3 seizures, (3) PISF were more frequent in seizures of temporal lobe origin (66%) than in those of extratemporal origin (33.3%), (4) no PISF developed if the electrographic seizure duration was < 32 sec, (5) PISF were (predominantly) localized in the lobe of seizure origin in 85% of the seizures, (6) there was a strong correlation between frequent occurrence of temporal PISF and favourable seizure outcome following temporal lobe surgery. In conclusion, PISF contribute valuable data as to the localization of the epileptogenic zone during presurgical evaluation of epilepsy and indicate favourable seizure outcome following temporal lobe surgery.