Clinical neurophysiology in movement disorders

Neurophysiological tools are very helpful in characterizing various movement disorders, consequently guiding etiological research and therapy. Movement disorders recordings are currently underutilized in neurological practice in adults and could also be extended to the pediatric population. Surface polymyography (EMG) combined with accelerometry is commonly used for the analysis of many types of hyperkinetic movement disorders, mainly myoclonus, tremor, dystonia, and sometimes tics and chorea. To study myoclonus, techniques exploring cortical excitability, namely conventional EEG, EEG-jerk-locked-back-averaging (JLBA), somatosensory evoked potentials (SEP) and C-reflex studies, should necessarily complete the EMG analysis. Premovement potential recording and measures of the stimulus induced jerks latencies may help to differentiate psychogenic jerks from myoclonus. The field of clinical usefulness of movement disorders recordings is large. Main issues are: (1) to differentiate tremor from myoclonus, (2) to demonstrate and locate dystonic features, either isolated or associated to tremor and myoclonus, (3) to define the nature of a tremor, (4) to assess the psychogenic nature of a tremor or jerks, and (5) to define the neurophysiological generator of myoclonus in the central nervous system. Neurophysiological data allow us to clearly classify myoclonus as cortical, cortico-thalamic, and subcortical-resulting from lesions or dysfunctions of basal ganglia/reticular system-or spinal.