Occurrence of epileptiform activity in the routine EEG of epileptic patients.

In a retrospective study, the occurrence of epileptiform activity (EA) in routine EEG records of epileptic patients was investigated. Data were obtained from 1078 EEGs of 373 patients (199 men and 174 women; aged 17-87 (mean 34.2 +/-14.7)). The percentage of 38% of patients with EA in a single EEG could be increased to 77% by repeated records. After the 5th record however, the gain in new information decreased remarkably. No differences between seizure types could be detected. There was a relationship between EA and nonspecific EEG abnormalities. High EA rates were found for short time intervals since last seizure, young patients, long durations of the seizure disorder and for high seizure frequencies.