Cognitive correlates of interictal discharges.

Interictal discharges can occur silently without apparent simultaneous clinical manifestations. Nevertheless, formal testing during electroencephalographic (EEG) recording may demonstrate transitory cognitive impairment (TCI). The probability of demonstrating TCI is related to the nature of the test employed and the type of epileptiform discharge. Difficult tasks are more useful to detect TCI, and working memory and language tests may be particularly sensitive. Generalized 3-Hz spike-wave bursts lasting at least 3 s are most likely to produce demonstrable TCI, but they can also be found during briefer and even focal discharges. The latter exhibit some specificity: left-sided focal spiking more frequently produces errors in verbal tasks, whereas right-sided discharges are more often accompanied by impairment in handling nonverbal material. TCI may adversely affect the patient's psychosocial functioning in daily life, as has been shown by some studies pointing out an impairment of educational skill in epileptic children and of driving performance in motorists. Our study on benign childhood epilepsy with Rolandic spikes also detected TCI in the majority of the patients. Nevertheless, it is not possible to claim that everyone with subclinical EEG discharges has TCI that adversely affects their psychosocial functioning. It may be possible to treat TCI by antiepileptic drugs.