Movement disorders in children.

Introduction Supreme Court Justice Potter Stewart, in 1964, while trying to define “obscenity,” articulated the now well-known “I shall not today attempt to define the kinds of material I understand to be embraced . . . [b]ut I know it when I see it . . . .” In some respects, a similar comment can be made about movement disorders. A movement disorder typically is defined as dysfunction in the implementation of appropriate targeting and velocity of intended movements, dysfunction of posture, the presence of abnormal involuntary movements, or the performance of normal-appearing movements at inappropriate or unintended times. The movement abnormalities are not due to weakness or abnormal muscle tone, but may be accompanied by weakness or abnormal tone. By convention, movement disorders are divided into two major categories. The first is hyperkinetic movement disorders, sometimes referred to as dyskinesias. This term refers to abnormal, repetitive involuntary movements and encompasses most of the childhood movement disorders, including tics, chorea/ballismus, dystonia, myoclonus, stereotypies, and tremor. The second category is hypokinetic movement disorders, sometimes referred to as akinetic/rigid disorders. The primary movement disorder in this category is parkinsonism, manifested primarily in adulthood as Parkinson disease or one of many forms of secondary parkinsonism. Hypokinetic disorders are relatively uncommon in children. Although ataxia, weakness, and spasticity are characterized by motor dysfunction, by common convention these entities are not included among “movement disorders.” This review focuses on dyskinesias because they represent the bulk of movement disorders in children. The components of the central nervous system typically implicated in disorders of movement are the basal ganglia (caudate, putamen, globus pallidus, subthalamic nucleus, substantia nigra) and frontal cortex. The accomplishment of smooth, coordinated movement requires a multifaceted network of brain regions, including basal ganglia and frontal cortex, but also thalamus, cerebellum, spinal cord, peripheral