Dystonia is defined as a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. (Sanger et. al., Pediatrics 111(1):e89-e97, January 2003 [pdf]).
The child's perception of dystonia may be that an attempt to move produces the wrong pattern of muscle activity and results in a movement different from the intended one. This emphasizes the fact that dystonia usually occurs only during voluntary movement or with voluntary maintenance of a posture of the limbs or body. For example, attempted flexion of the fingers to hold a pen may lead to flexion of additional fingers, extension of the wrist, or movements of the opposite hand or the neck.
Characteristic postures that are frequently seen in dystonia include...
It is important to realize that, despite its name, there is often no abnormal muscle tone in children with dystonia. This means that, upon examination, a dystonic limb may or may not have increased resistance to movement so that it may be either stiff or floppy, or change with time.
Dystonia is described according to the part or parts of the body that are affected. If only one body part is involved, such as a hand, foot, or the neck, then this form is termed a "focal dystonia." If two contiguous parts are involved, such as the face and neck, then it is termed a "segmental dystonia." If two noncontiguous parts of the body are involved, such as the face and one leg, it is termed a "multifocal dystonia." If one half of the body is involved, it is "hemidystonia," and if both legs, as well as one additional body part are involved, then it is termed "generalized dystonia." A focal dystonia that progresses to become generalized or generalized dystonia itself are the most common patterns observed in children.
Dystonia may occur at rest or with action. A feature of dystonia that distinguishes it from most other movement disorders is that a dystonic movement of one limb may be triggered by an attempted movement of a different limb. For example, a dystonic posture of the right hand may occur while the left hand is performing a rapid movement, or a dystonic posture of the foot may occur during walking. The triggering movements may be very specific; for example, walking forward may be a trigger, while walking backward may not be a trigger. In adult focal, task-specific dystonias, the trigger may be as specific as writing or playing a musical instrument; this type of task-specific dystonia occurs only rarely in children.
When dystonia is due to another identified disease, then it is called "secondary dystonia." When dystonia is not due to another disease, it is termed "primary dystonia." Primary dystonia includes the genetic dystonias and some adult-onset, focal dystonias. Secondary dystonia may be due to a wide variety of causes, including cerebral palsy, metabolic disease, head trauma, and others listed here.
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Section Author: Terence Sanger, MD PhD
Scientific Reviewers: Leon Dure, MD, Associate Professor of Pediatrics and Neurology, The University of Alabama at Birmingham; Marjorie A Garvey, MD, Pediatrics and Developmental Neuropsychiatry Branch, NIMH, Human Motor Control Section, NINDS; Jonathan W. Mink, MD PhD, Associate Professor of Neurology, Neurobiology & Anatomy, and Pediatrics Chief, Child Neurology, University of Rochester Medical Center, Rochester, New York
Editor: Joy B. Leffler, NASW, AMIA