Myoclonus: current concepts and recent advances.

Myoclonus presents as a sudden brief jerk caused by involuntary muscle activity. An organisational framework is crucial for determining the medical significance of the myoclonus as well as for its treatment. Clinical presentations of myoclonus are divided into physiological, essential, epileptic, and symptomatic. Most causes of myoclonus are symptomatic and include posthypoxia, toxic-metabolic disorders, reactions to drugs, storage disease, and neurodegenerative disorders. The assessment of myoclonus includes an initial screening for those causes that are common or easily corrected. If needed, further testing may include clinical neurophysiological techniques, enzyme activities, tissue biopsy, and genetic testing. The motor cortex is the most commonly shown myoclonus source, but origins from subcortical areas, brainstem, spinal, and peripheral nervous system also occur. If treatment of the underlying disorder is not possible, treatment of symptoms is worthwhile, although limited by side-effects and a lack of controlled evidence.