[EMG for study of involuntary movements]

Involuntary movements caused by disorders in the central nervous system are peculiar, purposeless movements whose characteristics have been elaborately described in the literature of clinical neurology, although their neural mechanism has not yet been fully clarified. As involuntary movement is the result of abnormal contraction of the skeletal muscles, simultaneous recording from many muscles or muscle groups with different functions furnishes information on characteristic patterns of involuntary movements based on physiological features and provides us with a tool for differential diagnosis and for evaluation of the degree of disorder. For these purposes concurrent examination of muscle tone and of voluntary contraction is desirable. In this article, quantitation of movement and strength by EMG recorded with surface electrodes, characteristic patterns of EMG in various involuntary movements including tremor, chorea, ballism and dystonia were described.