Chronic epileptic encephalopathy in adult patients with bilaterally synchronous frequent and/or prolonged subclinical epileptiform discharges.

We followed four patients with infrequent convulsive seizures for four to 10years, with periodic EEGs and neuropsychological tests. All four had bursts of frontally predominant, bilaterally synchronous 1.5–3‐Hz spike or polyspike and slow-wave discharges (SWDs) that initially comprised 15% to 88% but were reduced to 5% or less of total EEG time with appropriate antiepileptic drugs. Case 1 showed a 30-point improvement in his verbal WAIS‐R score and Case 4 a 21-point improvement in his performance WAIS‐R score, over nine- and five-year periods, respectively, with normalization of frontal executive function. Cases 2 and 3 showed no improvement in frontal executive dysfunction despite being free of SWDs for nine and five years, respectively. These patients had variable degrees of epileptic encephalopathy and subclinical SWDs. They illustrate the importance of minimizing the occurrence of SWDs with appropriate antiepileptic drugs and long-term monitoring with neuropsychological tests because chronic cognitive deficits are potentially reversible.