A Functional MRI Study On Writer's Cramp Before And After Treatment With Botulinum Toxin

Background: Writer's cramp is the most common task-specific idiopathic focal dystonia with incompletely understood pathophysiology. It is characterized by excessive cocontractions of agonist and antagonist hand and forearm muscles during writing .In previous study ,the patients of writer's cramp showed greater activation of contra lateral basal ganglion (esp. putamen), ipsilateral cerebellar hemisphere, and contralateral sensorimotor, supplementary motor , premoter, primary sensory cortex in the task of writing with pencils than normal controls. But it is unclear which areas are directly related to the pathogenesis of writer's cramp.Objective: Using functional magnetic resonance imaging (fMRI), to observe the changes of brain areas activities of writer's cramp before and after treatment with botulinum toxin.Method: A fMRI block design was used. Four right-handed patients with unilateral writer's cramp were scanned at 1.5 Tesla magneticresonance imaging scanner while they were performing the visually instructive task writing with pencil with MR Vision 2000 ,before and after they received the treatment with botulinum toxin injection. After image dates were co-registered to correct head motion, spatial normalized , deconverlution ,we got the average functional activated maps using AFNI software. The maps of "pre- minus post- treatment" were also gotten with general linear analyzed. Finally, we got the interesting area by observing the match of stimulating and area activated.Result: We found after the treatment with botulinum toxin, the patients showed significant impaird activation of contralateral primary moter cortex, premotor cortex , sensory cortex;enhanced activation of contralateral frontal association cortex;moderate impaird activation of ipsilateral cerebellar hemisphere and contralateral thalamus;while the mild change of contralateral basal ganglion and no change of putamen.Conclusion: These results indicates that the dysfunction of basal ganglion and subcortical-cortical loop are likely to play the role of the pathophysiology of writer's cramp. And the changes of motor cortex, sensory cortex , cerebellar and thalamus may be secondary.