Selective Cognitive Impairment During Focal and Generalized Epileptiform Eeg Activity

Abstract

It is well established that generalized epileptiform EEG discharges unaccompanied by overt clinical change may nevertheless be associated with transitory cognitive impairment (TCI) detectable by appropriate psychological testing. However, the tests employed in most research studies of this phenomenon are of little use for routine clinical application. They are suitable for administration only over short periods of time and are therefore applicable only to patients with a high discharge rate, a serious limitation, as the discharges are generally depressed by the tests themselves. We have developed two short-term memory tasks, one using verbal, the other nonverbal material presented in the form of television games which patients are generally prepared to perform for up to an hour or longer. Forty-six patients with subclinical EEG discharges have been studied. They were screened by video monitoring before and during testing to exclude any with overt clinical changes during the discharges. Despite this rigorous selection, in 50 per cent TCI was demonstrable with a confidence level (within the individual patient) of 10 per cent. Discharges during stimulus presentation were most disruptive of performance and those confined to the period when the patient was responding were without demonstrable effect. A significant association was found between the laterality of focal or asymmetrical generalized discharges and impairment of one or other task, left-sided discharges being associated with errors in the verbal task and right-sided with impairment of the nonverbal test. Two case histories are cited illustrating patients who were clearly handicapped by TCI and whose functioning improved when the subclinical discharges were suppressed by medication. To determine how many patients suffer such disabilities or can be helped by appropriate medication, further prospective studies are required.

Generalized epileptic discharges show thalamocortical activation and suspension of the default state of the brain

“…This explanation may provide a more accurate understanding of the mental state of patients during spike-and-wave discharges than the usual ''loss of consciousness,'' which Gloor (20) thought unspecific and not a very useful description of the manifestation of epileptic seizures. Patients with spike-and-wave do not experience a clinical absence with every burst, but responsiveness is often impaired during such bursts (21), and the level of cognitive impairment increases when discharges become longer (see ref.…”

Impaired Executive Function by Interictal Epileptiform Discharges in Patients with Idiopathic Generalized Epilepsy

“…Epileptiform discharges not accompanied by obvious clinical events are generally regarded as subclinical or interictal. Investigations have confirmed the occurrence of cognitive deficits during Interictal Epileptiform Discharges (IEDs) [4,7]. Epileptiform discharges can result in Transitory Cognitive Impairment (TCI), with the type of deficit dependent on where in the cortex the Epileptiform discharges arises [8].…”

The electrophysiological “delayed effect” of focal interictal epileptiform discharges. A low resolution electromagnetic tomography (LORETA) study

“…Some symptoms like transient abolition of muscle tone (Rubboli et al, 1995), increased reaction time (Shewmon and Erwin, 1988a), and transient impairment of cognitive functions (Aarts et al, 1984;Binnie and Marston, 1992;Aldenkamp et al, 2005) are strictly time-locked to the IEDs. However, other investigators described fluctuating neurological symptoms, disturbed speech and cognitive impairment that were related to the presence of frequent IEDs but not strictly time-locked to them.…”