Limb Dystonia

Focal limb dystonia (LD) is associated with dystonic spasms of arm or leg muscles. These spasms are accompanied by repetitive, twisting movements or abnormal positions or postures of the affected limb. Limb dystonia may be segmental, i.e., affecting muscle groups of an arm as well as the neck, and is also present in those with hemidystonia or generalized dystonia.

Upper limb dystonias often appear only when performing specific tasks. Thus, these dystonias are often referred to as task-specific dystonias. The most common task-specific limb dystonia of the arm occurs with writing and is therefore known as writer's cramp.

Writer's cramp (WC) typically affects the person's dominant side, meaning the "writing hand." It is often characterized by an abnormally pronounced, forced grip on the writing instrument. This may occur immediately upon grasping the pen or pencil or shortly after beginning to write. Less commonly, there may be excessive extension of the fingers that causes the writing instrument to drop from the hand. Additional findings may include exaggerated flexion or extension of the affected wrist, forcing the palm of the hand downward or upward. In some patients, dystonic spasms may also extend to involve certain muscles of the arm and shoulder, potentially resulting in elevation of the elbow and outward extension of the shoulder. Writing may be labored and shaky with discomfort or pain in the forearm. Some individuals are not able to write–even after just a few words. Touching or stabilizing the affected hand with the other hand may help to alleviate symptoms.

In approximately one-third of patients with writer's cramp, dystonic spasms may eventually occur with tasks other than writing. In about 25% who attempt to write with the uninvolved hand, writer's cramp may extend to the previously unaffected hand (bilateral WC).

In some patients, dystonic spasms may eventually affect adjacent or other body regions. In addition, writer's cramp is often associated with hand tremor that may occur with writing (action tremor) or while holding the hand in a fixed position against gravity (postural tremor).

Other focal task-specific limb dystonias have also been described that may affect...

• Musicians. Characteristic task-specific dystonias (TSDs) have been reported among pianists, guitarists, and clarinetists. TSDs may affect musicians using almost any type of instrument.
• Participants in certain sports. For example, TSDs have been described in golfers (a TSD known as the "yips"), tennis players, and dart throwers.
• Workers in certain occupations, such as seamstresses, shoemakers, or milkers.

Generally, activities that may provoke certain TSDs include those requiring highly specialized, precise actions or extremely repetitive movements. Although most TSDs affect the upper limbs, they have rarely been described in the lower limbs, such as among dancers, or cyclists.

Lower limb dystonia is a focal dystonia that may primarily affect the ankle and foot, often resulting in inward turning of the heel with upward bending of the sole of the foot. The dystonic spasms initially occur only with walking (action dystonia). However, the dystonia may gradually be present at rest and eventually lead to sustained, fixed postures. Lower LD that appears during childhood is usually associated with the onset of generalized dystonia. However, lower LD that initially becomes evident during adulthood is rare. In such cases, experts indicate that diagnostic evaluations should be conducted to determine whether lower limb dystonia is present secondary to Parkinson's disease, parkinsonism syndromes, or other underlying causes.

	Other Focal Dystonias