Focal dystonia and repetitive motion disorders.

It commonly is observed that focal hand dystonias, such as writer's cramp or musician's cramp, are associated with repetitive movements, although definitive proof of a causal relationship is lacking. These focal dystonias are often task specific, with involuntary muscle contractions occurring only when patients perform specific acts such as writing or playing a musical instrument. Physiologic studies show deficiencies in spinal reciprocal inhibition and abnormalities of central sensory processing and motor output that may be related to reduced cortical inhibition. Recent studies in primates support the notion that repetitive motions can induce plasticity changes in the sensory cortex leading to degradation of topographic representations of the hand, and raise the possibility that sensory training may be beneficial. Current treatment options for focal dystonia include botulinum toxin injections, anticholinergics, baclofen, benzodiazepines, and occupational therapy.