Epileptic negative myoclonus in a case of atypical benign partial epilepsy of childhood: a detailed video-polygraphic study

Abstract

Purpose: To describe the clinical and electroencephalographic features of a child diagnosed as having atypical benign partial epilepsy (ABPE) who suffered from frequent lapses of postural tone in the right lower limb that were considered to represent a focal epileptic negative myoclonus (ENM). Material and methods: Electrophysiological evaluation included four serial waking and two sleep EEGs. Moreover, the investigation included a polygraphic recording with simultaneous video-EEG monitoring performed in rest, during hyperventilation, and while standing up with the aim of capturing patient’s typical seizures. Results: During awake the EEG showed frequent bilateral centrotemporal discharges maximal over the left central area. Moreover, we recorded short generalised paroxysms of spike-and-wave discharges accompanied by a clear transient cognitive impairment that were in keeping with absences. We also captured several episodes of sudden and unexpected loss of postural tone in the right lower limb. These focal inhibitory seizures were associated with brief diffuse but asymmetrical paroxysms of irregular spike-and-wave discharges maximal over the left side. EMG flattening of the right quadriceps muscle was time-locked to the midline of the slow-wave component of the diffuse spike-and-wave discharges. Conclusions: ENM leading to focal lapses of postural tone in lower extremities may be a predominant type of seizures in ABPE. A polygraphic recording with video-EEG monitoring is essential to confirm the diagnosis, and to detect other concomitant seizures, such as atypical absences. In our case, ENM could be more likely due to a transient disruption of cortical function.