Jerking during absences: video-EEG and polygraphy of epileptic myoclonus associated with two paediatric epilepsy syndromes.

Epileptic myoclonus (EM) is reported in many paediatric epilepsies from neonatal period to adolescence. Myoclonus can be the only seizure type or may occur among others, independently or in combination as a single ictal event. We report two children presenting with absences associated with myoclonus, predominating on one side, in a setting of two different types of absence seizures and two different electro-clinical syndromes. Patients were explored with long-duration video-EEG coupled to surface EMG polygraphy. EEG was visually analysed and complemented by jerk-locked back-averaging. Two types of seizure, encompassing myoclonus and absence, were identified: myoclonic absences in the context of epilepsy with myoclonic absences and atypical absences with atonic component (negative myoclonus) in the context of encephalopathy related to status epilepticus during slow sleep (ESES). In the latter case, rhythmic upper limb jerking, mimicking positive myoclonus, corresponded to recovery of muscular tone after each negative myoclonus. Due to the rhythmic recovery of muscle tone, subsequent rhythmic negative myoclonus may exhibit a similar clinical picture to that of rhythmic positive myoclonus. Video-EEG recording coupled to EMG polygraphy is essential in order to precisely characterize motor manifestations during seizures with myoclonus [Published with video sequences].