[Cognitive effects of subclinical EEG discharges]

Many patients with epilepsy display cognitive deficits and consequent psychosocial dysfunction. Of the various biological factors contributing to these problems, the most distinctive is the momentary disruption of psychological function by subclinical EEG discharges. This is demonstrable in 50% of subjects with subclinical epileptiform activity performing a suitable task under EEG control. Transitory cognitive impairment (TCI) can often be detected during even brief focal discharges, including single spikes. The effects are material specific: right-sided discharges are more likely to affect verbal functions, whereas the left-sided produce more deficits demonstrable by non-verbal tasks. Monitoring of children during neuropsychological or educational testing shows that subclinical discharges can selectively impair performance of specific subtests, giving abnormal test profiles, and lead to errors in reading. The impact of such transitory cognitive impairment on psychosocial function in daily life is uncertain. If TCI produced significant disability, anti-epileptic drugs could improve cognition by suppressing EEG discharges, provided that any benefits were not outweighed by sedation. The author has reported a randomised, double-blind, controlled trial which showed significant improvement on the Conner's rating scales when sodium valproate was added to the drug regimen. Further studies are required to determine the role of TCI in the psychosocial dysfunction in epilepsy and the indications for pharmacological treatment.