Differentiation of myoclonic seizures in epileptic syndromes: A video-polygraphic study of 26 patients

Objective:   We conducted a video-polygraphic study of myoclonic seizures (MS) in different epileptic syndromes to clarify semiologic and electroencephalography (EEG) differences among them.
Subjects and methods:   The subjects were 26 children with MS, including benign myoclonic epilepsy in infants (BME) in 10, severe myoclonic epilepsy in infants (SME) in 6, idiopathic epilepsy with myoclonic-astatic seizures (IEMAS) in 4, and juvenile myoclonic epilepsy (JME) in 6. We reviewed the video-polygraphs of MS, including the predominant area of muscle involvement (neck, trunk, and proximal or distal upper extremities), postural changes including astatic falling, and mode of appearance. We also analyzed the frequency of a corresponding generalized spike-and-wave complex (GSW) and the duration of myoclonic electromyography (EMG) activity.
Results:   A total of 550 MS were documented in the 26 cases. MS manifested with proximal predominance/forward flexion/single occurrence in BME, proximal predominance/forward astatic flexion/single occurrence in IEMAS, proximal predominance/extension/succession in SME, and distal predominance/extension/succession in JME. The median frequency of GSW was 1.5, 1.3, 3.2, and 3.1 Hz, respectively, and the median duration of the myoclonic EMG activity was 387, 587, 81, and 65 ms, respectively.
Conclusion:   MS in the four different epileptic syndromes show significant semiologic and EEG differences, as well as similarities. Although our study has the limitations of the small number of patients and retrospective methodology, these results should be considered in the classification and differential diagnosis of myoclonic epileptic syndromes.