Pediatric Epileptic Syndromes

to a spasm is one or more generalized, high-voltage slow or sharp-slow waves followed by abrupt voltage attenuation of background activity lasting from 1 to several seconds, the so-called electrodecremental event (Figure 12-6) (17). Type of spasm does not always correlate well with a particular EEG ictal pattern, and neither do all spasms have EEG correlates. EEG and clinical improvement usually parallel one another, but they may be dissociated.

Electroencephalography is crucial for accurate classification of different forms of epilepsy. The following are brief descriptions of EEG findings in the more common epileptic syndromes encountered in childhood.

Infantile Spasms (West Syndrome)

The EEG is always abnormal, grossly so if obtained when seizures are well established. Gibbs and Gibbs (14) identified the most characteristic pattern, hypsarhythmia, which consists of high-voltage, irregular slow waves occurring asynchronously and randomly over all head regions, intermixed with spikes and polyspikes from multiple independent loci (Figure 12-5). fiVariations of the pattern (modified hypsarhythmia) occur in up to 10% to 15% of children with infantile spasms (15). These other abnormalities, however, are more likely to occur in older infants or if the EEG is performed later in the course of the disorder. Like infantile spasms, hypsarhythmia is age-specific. It is usually most pronounced in slow-wave sleep and may disappear completely in REM. Ictal recordings show various patterns (16), but the most common accompaniment

Childhood Absence Epilepsy

EEGs are rarely normal in untreated children with childhood absence epilepsy (formerly referred to as petit mal epilepsy), and hyperventilation is particularly effective in provoking the characteristic EEG abnormality. In fact, repeated normal EEGs in a child with lapse attacks argue strongly against a diagnosis of childhood absence epilepsy. Each absence seizure is accompanied by generalized, symmetric, stereotyped 3- to 4-Hz spike-wave activity (Figure 12-7A). Background activity is otherwise normal or near normal. Sleep produces striking effects on appearance of the epileptiform activity (Figure 12-7B). Classic features are lost, and instead epileptiform bursts are fragmented, are of shorter duration, and contain more single spikes and multiple spikes.

Spike-wave paroxysms begin abruptly, producing immediate alteration in the child's responsiveness (18). Conversely, when the 3-Hz spike-wave discharge ends, the child's behavior becomes normal at once (18). Detailed analysis of motor and cognitive effects reveals differences in their time course and evolution

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