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 10 years, 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.

Chronically Impaired Frontal Lobe Function from Subclinical Epileptiform Discharges.

Subclinical epileptiform discharges (SEDs) are a common occurrence on electroencephalograms (EEGs). Their potential for acutely disrupting cognitive functions has been well documented, but detailed studies of cognitive performance by patients with chronic exposure to disruptive SEDs have been lacking and scant data have been available to guide treatment decisions or to assist in predicting recovery. We identified a patient with frequent frontotemporally (FT) predominant SEDs and monitored cognitive performance over time with periodic neuropsychological testing and EEGs. Over a 16-year period, Full Scale IQ rose 23 points and Verbal IQ rose 30 as SEDs were suppressed. Severity of impairment, reflected by the marked increase in cognitive performance over time, was not predicted by his appearance and performance on routine tests of cognitive functions in the clinic. Quantitating total SED duration per EEG provided an objective marker to track severity over time. The cumulative effects of chronic exposure to disruptive SEDs may create a sustained "cognitive burden" or encephalopathic state that persists even in the absence of ongoing discharges.