Neurophysiology of myoclonus and progressive myoclonus epilepsies.

The high temporal resolution of neurophysiological recordings makes them particularly suited to faithfully describing the time course of rapid events such as myoclonus and to precisely measure its time relationship with other related activities. In progressive myoclonus epilepsies (PMEs) polygraphy with simultaneous EMG-EEG recordings is a crucial tool for defining the characteristic of myoclonic jerks their topography over different muscles (namely antagonists), their time course and relationship with vigilance muscle activation and stimulations. Moreover on polygraphic recordings it is possible to detect EEG activities associated to myoclonic jerks and define their time relationship with myoclonus thus differentiating cortical types of myoclonus from subcorticallly generated ones. Tanks to the back averaging technique non obvious time-locked EEG potentials can be detected on polygraphy , furthermore in stimulus sensitive myoclonus the analysis can include the potential evoked by the somatosensory stimulus (SEP). The polygraphic recording also gives information on muscle activity suppression occurring after jerk or as pure negative myoclonus. Besides the time domain analysis, techniques based on frequency analysis have been developed to evaluate EEG-EMG coherence. The neurophysiological techniques provide investigators and clinicians with an invaluable information to define the type of myoclonus and its generating circuitry thus substantially contributing in the diagnosis and management of PMEs.