Seizure prognosis in long-stay mentally subnormal epileptic patients: interrater EEG and clinical studies

Two groups of long-stay mentally subnormal epileptic patients, those with a chronically high seizure frequency and those who had become seizure-free, were studied for clinical and EEG factors relating to the prognosis of seizures. The mean period of observation was 20 and 22 years, respectively. All patients had a detailed clinical examination including psychometric testing, and for each, two EEG records were selected for blind semi-quantitative interrater analysis: an admission EEG and an EEG obtained within 6 months of the start of the study. Early onset of seizures, a high initial seizure frequency, multiple seizure types, upper motor neuron signs, and severe mental retardation characterized the seizure group. Significant admission EEG findings in this group included an absence of posterior dominant rhythmic activity, generalized delta activity, and frequent generalized paroxysmal discharges. Results of a linear discriminant analysis confirm that the admission EEG and clinical findings provide a basis for predicting outcome with a reliability on the order of 80%.