OBJECTIVETo explore the characteristics of various seizure types in infantile spasm (IS) and to recognize the clinical and electrophysiological differences among spasm, myoclonic and tonic seizures.

METHODSTotally 681 seizures of 8 infants with IS were analyzed, including 20 episodes of non-cortical myoclonus which were finally ruled out by video-electroencephalogram-electromyogram polygraphic recordings (VEEG-EMG) and off-line analysis of jerk-locked back averaging (JLA). As a control, the data of 58 myoclonic seizures collected from an infant with Aicardi syndrome within two months before his typical clinical presentations of IS were also analyzed.

RESULTSThree types of seizures were recorded from the 8 infants, including spasm, myoclonic and tonic seizures with the incidence of 94.4%, 4.5%, and 1.1%, respectively. Spasms were mostly presented as body muscle contraction axially, which often occurred in clusters and evolved in a crescendo-decrescendo manner; 85.7% of them lasted for 0.4 - 3.0 s and 14.3% for 3 - 7 s. In addition, there were 273 seizures which were identified as subtle spasms according to their ictal EEG with high voltage slow wave (HVS) and fast wave bursts in most. There was no constantly time-locked EEG correlating to spasms even when JLA was applied for analysis. Myoclonic seizures were shock-like muscle constraction lasting for less than 400 ms with or without visible epileptic discharges in its ictal EEG. However, there was a time-locked cortical discharge discerned by JLA in epileptic myoclonus. Tonic seizures were consisted of sustained muscle contractions involving limbs and trunk, lasting for more than 3 s. Its ictal EEGs were more likely low amplitude fast waves and medium amplitude theta activities. Some spasms, named as tonic spasm, could be distinguished from tonic seizure according to the seizure duration which was always less than 2 s in tonic spasms and their different EEG patterns.

CONCLUSIONSThere were various seizure types in IS but spasm was the predominant one. With polyneuroelectrophysiological tests including EEG-EMG and JLA, it would be much helpful to precisely recognize the different common seizure types including spasm, tonic spasm, myoclonic and tonic seizure during infancy which is important for the diagnosis, classification and treatment of infantile epilepsy.