Dystonia is a disorder of movement characterized by sustained involuntary muscle contractions induced by co-contraction of antagonistic muscles and the overflow of activation to extraneous muscles. Dystonia may affect the body in many different areas, or may be confined to isolated muscle districts, or to single or few specialised movements. In these mildest forms of dystonia, recent advances in basic and clinical neuroscience show that sensory and motor systems function abnormally, and their interaction to produce voluntary movements is altered. As a consequence, the motor system is disinhibited, the sensorimotor cortical representations are disorganised, and the mechanisms controlling neural plasticity in these cortical areas are faulty. Accumulating evidence underlines the research usefulness of repetitive transcranial magnetic stimulation (rTMS) in patients with dystonia. rTMS has widened our understanding of cortical excitability in dystonia, and clarified some of the mechanisms underlying normal and deranged neural plasticity. From a therapeutic viewpoint, low frequency rTMS applied over the premotor cortex elicits neurophysiological and clinical effects on motor and sensory symptoms, although the effect lasts longer than the stimulation period. Whether these lasting rTMS-induced changes in motor cortical excitability can be combined with other treatment strategies to improve dystonia remains an exciting question for future research.
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