Functional magnetic resonance imaging study of writer's cramp.

BACKGROUND: Writer's cramp is a type of task specific idiopathic focal dystonia and has an incompletely understood pathophysiology. The present study utilized functional magnetic resonance imaging (fMRI) to investigate what type of brain activity correlates with writer's cramp and its physiological mechanism.

METHODS: Ten patients with writer's cramp were age and gender matched with ten healthy control subjects in a block design. Subjects were scanned by fMRI while performing three consecutive, visually instructive, tasks with MR Vision 2000: (1) suppositional writing, (2) writing with finger and (3) writing with a pencil. Data was analysed using AFNI software for groups of patients and controls.

RESULTS: The patients with writer's cramp showed significant activations of contralateral basal ganglion (especially the putamen), motor cortex (primary sensorimotor cortex, supplementary motor cortex, premotor cortex) and ipsilateral cerebellar hemisphere in writing with a pencil compared with controls; whereas there was no obvious difference between patients and controls during writing with finger. Furthermore, these differences exist in the subtractive activated maps for "writing with a pencil" minus "writing with finger" of patients, when the activation of subcortical area and insula in controls disappeared.

CONCLUSIONS: Abnormal activations of contralateral basal ganglion, motor cortex and ipsilateral cerebellar hemisphere of the patients with writer's cramp suggest dysfunction of basal ganglion and subcortical-cortical loop might play a pathophysiological role in writer's cramp.