A study on pahtophysiology and non-invasive treatment of dystonia

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Dystonia is a syndrome of sustained muscle contractions frequently causing repetitive or twisting movement or abnormal posture. It is a common disorder with its incidence being approximately one fifth of that of Parkinson's disease. Writer's cramp is a focal dystonia, affecting only writing in its onset. This task-specificity provides a unique opportunity of investigating the mechanism of normal motor control for performing a specific task. It is also known notorious because of the resistance to treatment. We tried to treat these patients with writer's cramp by decreasing the excitability of the premotor cortex, which is known to be hyperactive in previous PET studies. For this, we used subthreshold low-frequency repetitive transcranial magnetic stimulation (rTMS), which inhibits the cortex. Using a computerized system for evaluating handwriting, we demonstrated significant improvement in handwriting and normalization of the abnormal cortical silent periods. Therefore the premotor cortex, one of the major output receptive areas from the basal ganglia, was shown hyperactive in dystonia, and its correction by rTMS may provide a useful method for treating these patients.We on the other hand had a chance to examine the immunohistochemichal findings in 7 autopsied patients with X-linked recessive dystonia-parkinsonism. We found the early loss of striosomal neurons in the neostriatum is the pathological hallmark of the dystonic phase of this disease. Striosomal cells are inhibiting the nigrastriatal dopaminergic projections from substantia nigra pars compacta, and their loss should lead to uncontrolled release of dopamine. Dystonia may therefore be caused by excess dopamine, which disinhibits premotor and other cortical areas.