Overview and classification of myoclonus.

This article is introductory to the special articles devoted to various aspects of myoclonus that appear in this issue and that cover both clinical and basic aspects. The definition and the classification of myoclonus are provided. Myoclonus can be classified in various ways depending on which aspect is focused upon, but classification based on the pathophysiological mechanisms proposed in this article might be of practical use in-terms of both diagnosis and treatment. The physiological mechanisms underlying generation of spontaneous cortical or cortical reflex myoclonus have been partially elucidated through various electrophysiological techniques, although the mechanism of pathologically exaggerated excitability of the sensorimotor cortex remains to be clarified. The mechanisms of subcortical myoclonus of various kinds are still unknown. Elucidation of the pathophysiology of each kind of myoclonus will lead to its most appropriate treatment.