Cortical myoclonus in Janz syndrome

Objective: To evaluate the characteristics of EEG paroxysms and the relatio nship between EEG spikes and ictal myoclonic jerks in patients with juvenil e myoclonic epilepsy (JME). Methods: Six patients with a typical form of JME entered the study and unde rwent computerized polygraphic recordings. In each patient, the inter-peak spike interval was measured on repeated EEG bursts, and jerk-locked back av eraging was performed on ictal epochs using a time window including the 100 ms before and the 100-200 ins after the point at which the jerk-related EM G potential diverged from baseline. Results: In all cases, the myoclonic jerks were associated with polyspike w aves (PSW) complexes. The frequency of repeated spikes within the PSW compl ex ranged from 16 to 27 Hz. Jerk-locked averaging revealed a positive-negat ive EEG transient with maximal amplitude on the frontal leads, which preced ed the myoclonic jerk by 10.25 +/- 0.96 ins. A delay of 9.50 +/- 1.73 ins w as measured between the jerk-locked positive peak detected on the frontal E EG leads of the two hemispheres; a comparable time lag was observed between the onset of myoclonic jerks in the two deltoid muscles. Conclusions: Our data suggest that the ultimate mechanism responsible for i ctal myoclonic jerks in JME is largely similar to that sustaining cortical myoclonus in more severe pathological conditions such as progressive myoclo nus epilepsies, despite the different pathogenic substrate and triggering m echanisms. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.